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AUG 1 6 19131
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
TASK 6 -DESIGN DEVELOPMENT
SUBTASK 6.02 -CLOSEOUT REPORT
INVESTIGATE TUNNEL ALTERNATIVE
JUNE 1981
ACRES AMERICAN INCORPORATED
1000 Liberty Bank Building
Main at Court
Buffalo, New York 14202
Telephone (716) 853-7525
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no. 33S
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
TASK 6 -DESIGN DEVELOPMENT
SUBTASK 6.02 -CLOSEOUT REPORT
INVESTIGATE TUNNEL ALTERNATIVE
TABLE OF CONTENTS
Page
LIST OF TABLES . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i i i
LIST OF FIGURES . . . . • . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . ... . i v
LIST OF PLATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
1 -INTRODUCTION
1. 1 -Over vi ew . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
1. 2 -Dev i 1 Canyon Dam and Tunne 1 Schemes . . . . . . . . . . . . . . . . . . . . 1-1
1.3-Report Contents ...............•........................ 1-2
2 -SUMMARY
2.1 -Scope of Work .. ... . . . . . .. .. . . .. .. .. . . •. . . . . . . ... . .. .. . . . 2-1
2.2 -Conceptual Tunnel Schemes ....................... ~...... 2-1
2.3-Tunnel Design and Construction Considerations .......... 2-1
2.4-Screening of Conceptual Tunnel Schemes ................. 2-2
2.5-Preferred Tunnel Scheme ................................ 2-3
2.6-Comparison with Devil Canyon Dam Scheme ................ 2-3
2.7 -Conclusions and Recommendations ... .. ... . .. . .. . .. .. . . .. . 2-3
3 -SCOPE OF WORK
3.1-Study Objectives ....................................... 3-1
3.2 -Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . 3-1
4 -CONCEPTUAL TUNNEL SCHEMES
4.1 -Economics of Tunnel Schemes within the Susitna
Bas in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
4.2-Conceptual Devil Canyon Tunnel Schemes ................. 4-1
4. 3 -Scheme 1 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-~2
4. 4 -Scheme 2 . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . • . . . . . . . . . . . . . 4-3
4.5 -Scheme J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
4.6 -Scheme 4 . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4--3
4.7-Historical Precedence .......................•.......... 4-3
5 -TUNNEL DESIGN AND CONSTRUCTION CONSIDERATIONS
5.1 -Geologic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.2-Geotechnical Design Aspects ............................ 5-2
5.3-Seismic Considerations ........................•........ 5-3
5.4-Design Considerations ...•.............................. 5-4
5.5-Construction Methods ..........................•........ 5-5
i
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
TASK 6 -DESIGN DEVELOPMENT
SUBTASK 6.02 -tLOSEOUT REPORT
INVESTIGATE TUNNEL ALTERNATIVE
TABLE OF CONTENTS (Cont'd)
6 -SCREENING OF CONCEPTUAL TUNNEL SCHEMES
6.1 -Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.2 -Tunnel Scheme Costs .. . .. .. . .. . . . . . .. .. . . . .. .. . .. .. . .. .. 6-1
6. 3 -Power and Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.4-Environmental Considerations ........................... 6-2
6.5-Geotechnical Considerations ............................ 6-3
6.6-Preferred Tunnel Scheme ................................ 6-4
7 -PREFERRED TUNNEL SCHEME
7.1-Introduction ........................................... 7-1
7.2-Design and Operational Assumptions ..................... 7-1
7.3-Project Description .. .. .. .. .. .. .. ...... ... . . .. .. ... .. .. 7-2
7.4-Cost Estimate and Construction Schedule ··~············· 7-2
7. 5 -Power and Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
7.6-Environmental Impact Assessment ........................ 7-3
8 -COMPARISON WITH DEVIL CANYON DAM SCHEME
8.1-Economic Comparison .................................... 8-1
8.2-Environmental Comparison ............................... 8-2
8.3 -Comparison of Construction Schedules . . . . . . . . . . . . . . . . . . . 8~2
8.4-Summary................................................ 8-2
9 -CONCLUSIONS AND RECOMMENDATIONS
9.1 -Conclusions . .. .. . . . .. .. . . ... .. .. . . . . . . .. ... .. .. .. . . . . . . 9-1
9.2 -Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1
BIBLIOGRAPHY
PLATES
APPENDIX A -ROCK UNIT DESCRIPTIONS (40)
LIST OF TABLES
Number
4.1
4.2
4.3
5.1
5.2
5.3
5.4
6.1
6.2
6.3
7.1
7.2
7.3
7.4
7.5
8.1
8.2
Title Page
Assumptions for Tunnel Site Comparison Index ....•........ 4-5
Information on the Devil Canyon Dam and Tunnel Schemes . . . 4-6
Historical Tunneling Precedence 4-7
Geologic Structure of Region Between the Devil Canyon
and Watana Dam Sites . . . • . . . . . . . . . . . . • . . . . . . . • . . . . . . . . . . . . 5-8
Effects of Seismic Loading on Tunnels {11) . . . . . . . . . . . . . . . 5-9
Tunnel Cover Experience oo•o••o········o•o••···o·········· 5-10
Regional Geology Map Units •o•ooo•••ooo•oooo•o······oo•o•• 5-11
Assumed Tunnel Support ooo•o••oo•··o•o··o·····o••••o······ 6-5
Devil Canyon Tunnel Schemes -Costs, Power Output and
Average Annual Energy ••o••·•••o•oo•o··o•••ooo•···•o•o•••o 6-6
Lithology of Tunnel Routes 6-7
Drilling Results at Watana and Devil Canyon Dam Sites .oo• 7-6
Optimization of Tunnel Diameter ..................... 0 .... 7-7
Cost Estimate for Devi 1 Canyon Tunnel Scheme (Two 30-
Foot Diameter Tunnels) o ••• o o •• o o •••• o •• o o •••• o •••••••• o.. 7-8
Cost Estimate for De vi 1 Canyon Tunne 1 Scheme (One 40-
Foot Diameter Tunne 1 ) • o • o o o 0 o o ••••• o ••• o ••••••• o •••••• o • • 7-9
Power and Energy Production from Tunnel Scheme .. o o....... 7-10
Summary of Economic Evaluations (Million Dollars) ........ 8-4
Summary of Economic Sensitivity Evaluations (Mi 11 ion
Dollars) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5
iii
LIST OF FIGURES
Number
1.1
4.1
4.2
5.1
5.2
5.3
5.4
5.5
5.6
6.1
7.1
8.1
Title Page
Tunnel Alternative Vicinity Map ......................... 1-3
Economic Potentia 1 of Tunne 1 Schemes . . . . . . . . . . . . . . . . . . . . 4-8
Schematic Representation of Conceptual Tunnel Schemes ... 4-9
Plate Tectonic Map {Reproduced from Reference 43) ....... 5-12
Regional Geology with Tunnel Routes (Reproduced from
Reference 43) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
Boundary Fault and Significant Feature Map for the
Site Region (Reproduced from Reference 43) . . . . . . . . . . . . . . 5-14
Devil Canyon Area Significant Feature Map (reproduced
from Reference 43) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15
Devil Canyon Site Significant Feature Map (reproduced
from Reference 43) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16
Watana Site Significant Feature Map (Reproduced from
Reference 43) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17
Typical Daily Power Production for March
Construction Schedule Preferred Scheme 3
Construction Schedule Comparison ....................... .
iv
6-8
7-11
8-6
LIST OF PLATES
Number
1
2
3
Title
Conceptual Tunnel Schemes -Plan & Sections
Preferred Tunnel Scheme 3 -Plan Views
Preferred Tunnel Scheme 3 -Sections
1 -INTRODUCTION
1.1 -Overview
Subtask 6.02 of Task 6 Design Development studies for the Susitna Hydroelectric
Project is entitled 1'Investigate Tunnel Alternative 11 • The scope of this subtask
as originally defined in the Acres flmerican Inc. POS dated February 1980, was
expanded in the revisions to the POS issued in September 1980. The objective of
the Subtask 6.02 study is to undertake a preliminary assessment of the feasibil-
ity of using a major tunnel to develop hydroelectric power on the Susitna River
between the proposed Watana and Devil Canyon dam sites (see Figure 1.1).
The scope of work involves essentially a desk study utilizing available data.
The limited specific geologic or geotechnical information available along the
tunnel route will allow no more than a conceptual assessment of the feasibility
of excavation of tunnels in the geologic structures adjacent to t~e Susitna
River in the region considered. Thus the assessment of the structural design
requirements and the determination of feasible size and cost of such tunnels has
necessarily been based on Acres engineering judgement and experience at this
time. It is considered unlikely that goetechnical conditions would be so poor
that tunnels could not be excavated by some means in the region under considera-
tion. Nevertheless it is important to note that the worse the conditions, the
higher the cost will be. Estimates based substantially on judgement and experi-
ence, however good, will be subject to the uncertainties of the basic assump-
tions used.
To establish the technical and economic feasibility of a tunnel alt~rnative,. a
substantial amount of field geotechnical investigation, design, and construction
cost estimating and scheduling work would be required. Notwithstanding the
foregoing constraints, the study has been directed towards assessing whether or
not there are sufficient grounds to consider the tunnel option in more detail as
a potentially economic, technically feasible and environmentally sound alterna-
tive to the Devil Canyon development. This report presents the results and con-
clusions of this study.
1.2 -Devil Canyon Dam and Tunnel Schemes
The Watana-Devi 1 Canyon dam scheme is comprised of two major dams, Watana and
Devil Canyon (Figure 1.1). As currently envisaged, Watana is a 840-foot high
gravel and rockfi ll structure with a crest elevation at 2225 feet and an 800 MW
underground powerhouse. The full pool surface area of Watana reservoir is
43,000 acres and full pool storage volume is 10 million acre-feet. The large
storage val ume allows regulation of river flows on both a seasonal and yearly
basis. The Devil Canyon dam is a 625-foot high concrete arch structure with a
crest elevation of 1464 feet and a 400 MW underground powerhouse. The Devil
Canyon dam has a full pool storage volume of 1 million acre-feet and the reser-
voir surface area is 7600 acres.
A 1 arge power tunnel caul d be utili zed to develop the head be low Watana instead
of the Devil Canyon dam. Conceptually, this Devil Canyon tunnel scheme could be
used to develop either the total head of both dams or just that portion develop-
ed by the Devi 1 Canyon dam. This could be achieved by locating the intake works
either in the Watana reservoir or at some point downstream from the Watana dam.
Based on initial conceptual design considerations, a typical tunnel scheme would
comprise the following major components:
1-1
-Power tunnel intake works.
-Are-regulation dam if the intake works are located downstream from Watana~
with a small hydroelectric development to utilize the available head and
flow.
One or two power tunnels of up to forty feet in diameter and up to thirty
miles in length.
-An underground powerhouse with a capacity of up to 1200 MW located in the
vicinity of the Devil Canyon dam site.
1.3 -Report Contents
Section 2 of this report is a summary of the work undertaken and conclusions and
recommendations. Section 3 is an outline of the scope of work. The four basic
conceptual tunnel schemes considered are described in Section 4 and the screen-
ing process used to select the preferred scheme is outlined in Section 6. An
overview of the site geology and geotechnical design considerations are dealt
with in Section 5. The preferred tunnel scheme is described and analyzed in
more detail in Section 7 and compared to the Watana-Devil Canyon dam scheme in
Section 8. Conclusions and Recommendations are presented in Section 9.
1-2
I w
LEGEND
A DAM SITES
0
SCALE IN MILES
10
TUNNEL ALTERNATIVE VICINITY MAP
FIGURE 1.1
2 -SUMMARY
2.1 -Scope of Work
The scope of work for Subtask 6.02 consisted of a preliminary assessment of the
feasibility of using a major tunnel to develop hydroelectric power on the
Susitna River between the proposed Wdtana and Devn Canyon dam sites (See Figure
1.1). Utilizing available geologic and geotechnical data along the proposed
tunnel route, four basic conceptual tunnel schemes were proposed as alternatives
for developing the head between the Watana and Devil Canyon sties. Each of the
four tunnel schemes was investigated further with regard to cost, energy yields,
and environmental impact and, based on this information, one scheme was selected
for additional study. The selected tunnel scheme was compared with the Devil
Canyon dam alternative by considering technical, economic, environmental, and
construction schedule factors, and a number of conclusions and recommendations
were developed.
2.2 -Conceptual Tunnel Schemes
Four basic tunnel schemes were selected for study. They involved utilizing
either the full head represented by both the Watana and Dev i1 Canyon dams, or
just the head represented by the Devil Canyon dam and two basic operating modes
(peaking and base load power generation). The installed capacities for the
schemes were all based on a total Susitna Basin development plant factor of
between 50 and 55 percent. The schemes are:
-Scheme 1: This scheme involves the development of head between the Devil
Canyon dam site and Watana, and incorporates peaking operation of the tunnel
powerhouse.
-Scheme 2: Similar to Scheme 1, except that the full head (including that
available at the Watana dam) is utilized.
-Scheme 3: This scheme involves the development of head between the Devil
Canyon dam site and Watana, and incorporates base load operaton of the tunnel
powerhouse.
-Scheme 4: Similar to Scheme 3, except that the full head (·including that
available at the Watana dam) is utilized.
These schemes involve tunnel lengths of up to 30 miles and diameters up to 40
feet. A review of world wide experience indicates that, although there is
little precedent for power tunnels of this size and length, similarly sized
tunnels have been built for other purposes. The proposed tunnel schemes are
therefore within the current state-of-the-art.
2.3 -Tunnel Design and Construction Considerations
Geotechnical design (and hence the cost and construction schedule) for a tunnel
is heavily dependent upon evaluation of the geology along the potential routes.
Major tunne 1 ing prob 1 ems are usually created by fault and shear zones, joint
2-1
sets, lithologic contacts, water and gas. These factors, along with seismic
considerations, rock quality, and construction methods must be explored in more
detail before any final decision can be rendered concerning the relative merits
of a tunnel scheme versus the two dam scheme.
The tunnel schemes are located in a complex geologic region incorporating
Argillite-Graywacke, Biotite-Granodiorite and Schist-Migmatite-Granite litho-
logic units. Although there is very limited geologic or geotechnical informa-
tion along the proposed tunnel routes, the results of exploratory drilling at
the Devil Canyon and Watana dam sites are available. These data indicate that
one can expect the rock quality to generally vary from good to excellent, but
zones of fair to poor rock could also be encountered. These conditions can
generally be termed as favorable for tunnel construction.
Due to the lack of specific geologic knowledge, conservative and relatively
flexible methods of tunnel construction and tunnel support have been assumed for
purposes of estimating capital costs in this study. These assumptions include a
modified horseshoe shape cross section and drill and blast construction methods.
One third of the tunnel length is assumed to require structural concrete lining
and rockbolt support, one third shotcrete lining and rockbolt support, and the
remaining one third is assumed to require no lining (but occasional rockbolts
for support) and a concrete-lined invert.
2.4 -Screening of Conceptual Tunnel Schemes
A screening analysis was performed to compare the four conceptual tunnel schemes
and to determine the best tunnel scheme for further study. Costs, power and
energy, geology, and environmental aspects were used as screening criteria.
Due to a lack of detailed geologic information, total project cost estimates are
tentative at this time; however, total project costs are relevant for a valid
economic comparison between conceptual tunnel schemes. Scheme 3 has the lowest
comparative cost, followed by Schemes 4, 1, and 2, respectively (See Table
6. 2) .
Energy values for the tunnel schemes were determined from an annual flow dura-
tion curve developed from the simulated monthly outflow from the Watana reser-
voir (35). This curve was adjusted to allow for a 1000 cfs minimum discharge in
the river, and allowance was made for tunnel friction and minor losses. As
shown in Table 6.2, Scheme 3 yields the largest increase in energy production
with 2180 Gwh of added annual energy. Scheme 1 would provide for a 2050 Gwh
increase, Scheme 2 a 1900 Gwh increase, and Scheme 4 a 890 Gwh increase.
From a geotechnical perspective, the northern and the alternative direct align-
ments for Schemes 1, 2, and 4 are similar (See Plate 1); therefore, they were
compared as a group while Scheme 3 was considered separately. Using the infor-
mation presently available, Scheme 3 appears to be preferable geotechnically.
However, further explorations are required to confirm this point.
A preliminary assessment of the environmental aspects associated with the four
tunnel schemes was carried out for comparison and screening of the tunnel
2-2
schemes only, and impacts common to all schemes were not addressed. Based on
the avail able data, Scheme 3 would incur the least overall environmental
impact.
2.5 -Preferred Tunnel Scheme
Scheme 3 was chosen for further study. The aim of the more detailed study was
to further refine engineering concepts, improve the accuracy of the cost
estimate, and evaluate the power and energy potential in more detail.
Scheme 3 is composed of are-regulation dam, power tunnel, and powerhouse at
Devil Canyon. The re-regul at ion dam is located approximately 16 mi 1 es down-
stream from the Watana site. Site selection was based on regional geologic
mapping, and air photo and topographic interpretations. The 245 foot high dam
is assumed to be a rockfill dam with an impervious core. A spillway is located
on the north abutment, and a relatively small 30 MW powerhouse is located on the
south side of the river.
Power tunnel intakes are lcoated on the south side of the river approximately
2000 feet upstream from the re-regulation dam. The optimum power tunnel
diameter is 30 feet for each of the two tunnels.
The underground Devil Canyon powerhouse has an installed capacity of 300 MW,
with an assumed four generating units. Overland acces to the powerhouse access
adit area runs parallel to Cheechako Creek. A surge tank for each power tunnel
is located just upstream of the powerhouse. Small cellular cofferdams are
required along the south bank of the Susitna to allow construction of the tail-
race. As part of this scheme, the installed capacity at the Watana dam is
increased by 50 MW to reduce the overall system plant factor once the base load
tunnel generating plant comes on line.
2.6 -Comparison with Devil Canyon Dam Scheme
The comparison of the tunnel scheme with the Devil Canyon dam scheme indicates
that the dam would yield approximately 36 percent more energy at a 49 to 54 per-
cent lower energy cost. Environmentally, the tunnel scheme has advantages; how-
ever, these do n9t appear to outweigh the economic benefits of the dam scheme.
From a construction schedule point of view there is little difference between
the schemes.
2.7-Conclusions and Recommendations
A base load tunnel scheme incorporating are-regulation dam downstream from
Watana dam and developing the potential head of the Devi 1 Canyon Dam is the most
economic tunnel scheme. There is no evidence that this scheme is not techni-
cally feasible. However, a substantial amount of field data would be required
to firmly establish feasibility.
A comparison of the tunnel scheme with the Devil Canyon Dam scheme indicates
that the tunnel scheme yields less (26 percent) and more costly (93 to 120
percent) energy. The tunnel scheme exhibits less environmental impact than the
dam, but this reduced impact is insufficient to outweigh economic advantages of
the dam scheme.
2-3
In order to confirm the economic comparisons with the dam scheme, the preferred
tunnel scheme should be incorporated with the Susitna Basin development selec-
tion studies. These will involve a system wide generation planning model, which
wi 11 allow a more realistic assessment of the economics of the tunnel scheme to
be carried out.
Based on the data evaluated, it is recommended that additional field or office
studies of the tunnel sch~me not be undertaken at this stage.
2-4
3 -SCOPE OF WORK
3.1 -Study Objective
The objectives of this study are to investigate the feasibility of replacing the
currently proposed Devil Canyon dam project with a tunnel-supplied power plant
fed from the Watana dam site.
3.2 -Approach
To satisfy the study objectives, the work was organized and carried out in the
following manner:
-Four basic conceptual tunnel schemes were developed to investigate alterna-
tives for utilizing the available head between the Watana and Devil Canyon
dam sites.
-The available information on tunnels of similar size previously constructed
elsewhere in the world was reviewed and summarized.
- A general evaluation of the topography, geology, and seismicity of the area
was undertaken on the basis of the available information.
-Preliminary assessments were made of geotechnical and structural design
assumptions and criteria for use in evaluation and comparison of alterna-
tives.
A preliminary assessment of costs, energy yields, and environmental impact
associated with the conceptual tunnel schemes was undertaken.
Based on the information developed above~ a single scheme was selected as a
tentative optimum for further study. This, more detailed study~ included:
Development of preliminary engineering layouts.
More detailed assessment of capital costs and development of construction
schedules.
Monthly simulation of power and energy yields utilizing a computer model.
-Preliminary environmental impact assessment.
-The selected tunnel scheme was compared with the Devil Canyon dam alternative
on the basis of technical~ economic, environmental and construction schedule
considerations.
The study was completed with the development of conclusions on the viability
of the tunnel scheme and recommendations for further consideration of the
scheme as an alternative for inclusion in Susitna Basin development planning
studies.
4 -CONCEPTUAL TUNNEL SCHEMES
4.1 -Economics of Tunnel Schemes Within
the Susitna Basin
In order to put the Devil Canyon tunnel scheme into perspective, a brief study
was undertaken to assess the relative economics of tunnel schemes located in
various portions of the basin. An essential part of a tunnel scheme is an
upstream reservoir for seasonal and yearly flow regulation. Initially, the
Watana and Vee dam sites (see Figure 1.1) were se 1 ected as potentia 1 upstream
reservoir sites at which tunnel intakes would be located. An appropriate index
for initial comparison of alternatives was derived on the basis of the estimated
energy yield in kWh per cubic yard of tunnel excavation for each alternative.
The basic assumptions used in this analysis are shown in Table 4.1. The energy
yield was evaluated using the average annual discharge less 500 cfs compensating
flow, and the net head allowing for friction losses. Studies indicated that
minimum cost of energy occurred at maximum flow velocities ranging from about
5.9 to about 9.9 feet per second at rated tunnel discharges, as shown in Table
7.2. For preliminary study purposes a constant annual average velocity of 6
feet per second was adopted. Estimates of kWh/yd3 for the alternatives
considered are illustrated in Figure 4.1, from which it is evident that the
first 12 miles of a tunnel starting at Watana has lower economic potential than
the lower portion from Devil Creek downstream to Portage Creek.
The curves also indicated that the economic potential of a tunnel scheme down-
stream from the Vee dam site is much lower than that between Devil and Portage
Creeks.
The third curve on Figure 4.1 indicates the economic potential of a tunnel
starting from are-regulation dam located downstream from Watana and just
upstream from Devil Creek. As outlined in the following section, this
re-regulation dam was ultimately chosen as the site for the ·intake in one of the
tunnel schemes.
4.2 -Conceptual Devil Canyon Tunnel Schemes
All tunnel schemes considered assume that Watana (maximum water surface eleva-
tion 2200 feet) with an installed capacity of 800MW is the project•s first stage
of development and that a minimum of 1000 cfs compensation flow is required in
the·Susitna River downstream from Watana at all times.
Four basic tunnel schemes were selected for study. These involve utilizing
either the full head represented by both the Watana and Devil Canyon dams or
just the head represented by the Devil Canyon dam and two basic operating modes,
i.e. peaking and base load power generation. The installed capacities for the
schemes are all based on a total Susitna Basin development plant factor of
between 50 and 55 percent. These schemes are depicted in Figure 4. 2 and are as
follows:
4-1
(a) Scheme 1
This scheme involves the development of head between the Devil Canyon dam
site and Watana and incorporates peaking operation of the tunnel power-
house.
(b) Scheme 2
As for Scheme 1 except that the full head, including that available at the
Watana dam, is utilized.
(c) Scheme 3
This scheme involves the development of head between the Devil Canyon dam
site and Watana and incorporates base load operation.
(d) Scheme 4
As for Scheme 3 except that full head, inc 1 ud ing that avail ab 1 e at Watana
dam, is ut i1 i zed.
Schemes 1 and 3 require a secondary dam downstream of Watana to re-regulate
Watana releases and to control the water level at the tunnel intakes.
For Scheme 1 this re-regulation dam requires relatively little storage as the
two powerhouses operate essentially in series, i.e. they both peak
simultaneously. This can be provided by a small re-regulation dam located some
2 miles downstream from Watana.
Re-regulation storage requirements for Scheme 3 are much greater. To allow
peaking operations from the Watana reservoir and base load operation of the
tunnels requires a substantially larger volume. A brief economic study revealed
that this could best be provided by a re-regulation dam located some 15.8 miles
downstream from Watana. This site appears to be suitable for dam construction
and is located immediately upstream from the reach from Devil Canyon to Portage
Creek with higher economic tunnel potential, as discussed in Section 4.1. The
savings in tunnel cost at this site more than compensate for the increased
height of the re-regulation dam located this far downstream from Watana.
A more detailed discussion, of the tunnel schemes is presented in the following
sections. Table 4.2 summarizes pertinent information on each of the schemes
which are illustrated on Plate 1.
4.3 -Scheme 1 (Devil Canyon Head,
Peaking Operation)
Scheme 1 consists of the Watana dam with an 800 MW powerhouse and a re-regula-
tion dam approximately 75 feet in height located two miles downstream. The
tunnel intake works are located just upstream from the re-regulation dam and a
550 MW powerhouse is located in the vicinity of Devil Canyon. Tunnel length is
about 27 miles. A minimum compensation flow of 1000 cfs is provided between
Watana and Devil Canyon. The re-regulation dam•s storage capacity is that
4-2
required for the powerhouses to operate in series. For preliminary study
purposes it has been assumed that sufficient storage to absorb approximately one
hour of peak power discharge from Watana .will be necessary. This requires 1,600
acre-feet of storage. Peaking operations will create daily water level fluctua-
tions downstream from the Devil Canyon powerhouse, which will probably require
regulation.
4.4 -Scheme 2 (Full Head, Peaking Operation)
Scheme 2 consists of the Watana dam and power tunnel intake works located
upstream of the dam. Two tunnels, 29 miles long will discharge at a 1150 MW
powerhouse at Devil Canyon. Upon completion of the tunnel stage of the overall
project, the Watana powerhouse capacity will be reduced from 800 MW to 70 MW,
just sufficient to release the required minimum compensation flow. Base load
and peak power demands will be generated at the Devil Canyon powerhouse. Water
level fluctuations downstream of Devil Canyon are similar to those of Scheme 1.
4.5 -Scheme 3 (Devil Canyon Head, Base Load Operation)
Scheme 3 consists of the Watana dam with an 850 MW powerhouse and are-regula-
tion dam approximately 245 feet in height located 15.8 miles downstream from
Watana. The tunnel intake works are upstream of the re-regulation dam with a
300 MW powerhouse in the vicinity of Devil Canyon. The re-regulation dam has a
storage capacity of approximately 350,000 acre-feet. A maximum water level
fluctuation of four feet is sufficient to store the daily peak discharge from
Watana and release a constant discharge into the power tunnels. Watana•s 800 MW
powerhouse will be operated as a peaking hydro facility discharging into the
re-regulation reservoir. Devil Canyon•s 300 MW powerhouse will be operated as a
base load facility, and thus, no significant daily water level fluctuation will
occur downstre~n.
A relatively small powerhouse with a capacity of 30 MW w·ill be constructed at
there-regulation dam. A minimum flow of 1000 cfs will be passed through the
re-regul at ion dam powerhouse to supply the required downstream compensation
flow.
4.6 -Scheme 4 (Full Head, Base Load Operation)
The general layout of Scheme 4 is similar to Scheme 2 with the following opera-
tional changes. The Watana powerhouse will remain at 800 MW and meet peaking
requirements. During off ·peak periods a constant base load of 35 MW will be
generated at Watana while satisfying compensation flow requirements between
Watana and Devil Canyon. The Devil Canyon 365 MW powerhouse and tunnel wi 11 be
operated as a base load facility. The full head potential for the entire flow
is not developed in Scheme 4, and thus annual energy production is less than the
other schemes. Daily water level fluctuations downstream of Devil Canyon are
similar to Schemes 1 and 2, and large water level fluctuations between Watana
and Devil Canyon will occur.
4.7 -Historical Precedence
In order to obtain a perspective of the tunnel scheme in terms of world wide
historical experience, a brief review of other tunnel schemes was undertaken.
The results of this review are summarized in this section.
4-3
Table 4.3 compares on a greately abbreviated basis, the Susitna tunnel
alternative with several other projects.
It is clearly evident that the proposed tunnel concept at Susitna is unique.
However, it is important to note that tunnels of similar size, length, purpose,
and located in similar geology have been successfully completed. The Susitna
tunnel alternative is definitely within the state of the art. Larger and longer
tunnels have been driven in more complex geologic settings.
4-4
TABLE 4.1: ASSUMPTIONS FOR TUNNEL SITE COMPARISON INDEX
(1) The tunnel powerhouse operates as a base load facility.
(2) Straight line tunnel alignments between the dam site and the tunnel tail
race.
(3) Tunnel discharge is the average annual discharge less 500 cfs compensation
flow.
(4) Tunnel diameter is sized for an annual average flow velocity. of six feet
per second and one power tunnel.
(5) Annual energy is based on annual average head discharge and head loss.
(6) Average head loss is based on a flow velocity of six feet per second and a
manning n of 0.026.
4-5
TABLE 4.2: INFORMATION ON THE DEVIL CANYON DAM AND TUNNEL SCHEMES
Devil Canyon Tunnel Scheme
Dam
Reservoir Area
(Acres) 7,500 320 0 3,900 0
River Miles
Flooded 31.6 2.0 0 15.8 0
Tunnel Length
(Miles) 0 27 29 13.5 29
Tun9e1 Volume
(Yd ) 0 11,976,000 12,863,000 3,732,000 5,131 '000
Compensating Flow
Release from
5oo1 Watana (cfs) 0 1,000 1,000 1,000
Downstream2
Reservoir Volume
(Acre-feet) 1,100,000 9,500 350,000
Downstream D~
Height (feet) 625 75 245
Typical Daily
Range of Discharge
From Devil Canyon 5,750 4,000 4,000 8,300 3,900
Powerhouse to to to to to
(cfs) 8,400 14,000 14,000 8,900 4,200
Approximate
Maximum Daily
Fluctuations in
Downstream
Reservoir (feet) 2 15 4
~ 1,000 cfs compensating flow release from there-regulation dam.
Downstream from Watana.
3 Estimated, above existing rock elevation.
4-6
TABLE 4.3: HISTORICAL TUNNELING PRECEDENCE
Project Length Excavati~n Maximum Static
Name Location ~ (miles) Shape Diameter Rock Method Depth Head Lining
TARP Chicago Sewer Approx. Circular 18 ft-35 ft Dolomite TBM Approx. Partially concrete
140 300 ft lined
Kemano British Power 10.1 Modified 25 ft Igneous and D&B 2200 ft 2585 ft Approx. 1/3 unlined,
Columbia Horseshoe metamorphi.cs 1/3 concrete lined
and 1/3 lined with
rock bolts and shot-
crete
Snettisham Alaska Power 1.9 Modified 13.5 ft Quar tz-dor it e, D&B 1200 ft Approx. 87 percent unlined,
Horseshoe Gneiss, Biotite, 900 ft supported with rock
Schist bolts, 13 percent
supported with rock
bolts and concrete
Bersi.mis 1 Quebec Power 7.6 Modified 31.0 ft Gneisic and D&B 800 ft 875 ft Concrete lined,
Horseshoe Granitic entire length
Bersimis 2 Quebec Power 0.5 Circular 38 ft Gneisic and D&B N 387 ft Concrete lined
_p. Granitic
I
'-I Chute-des-Quebec Power 5.8 Modified 34.3 ft Gneisic and D&B N 640 ft Concrete lined
Passes Horseshoe Granitic
Chute-des-Quebec Tail 1.7 Modified 48 ft Gneisic and D&B 250 ft N Unlined
Passes Horseshoe Granitic
Paijanne Sweden Water 72 Horseshoe 26.4 ft Granite. Gneiss D&B N N Unlined
Supply
Oahe South Power 2.6 Circular 24 ft Clay-Shale TBM N 210 ft, Concrete lined
D.akota (2 tunnels) 2.8 Circular 24 ft Clay-Shale TBM 272 ft
Eklutna Alaska Power 4.5 Circular 9 ft Argillite, N N 74 ft Concrete lined
Graywacke
Bath Co. Virginia Power Approx. Horseshoe 32 ft Shale, Sandstone D&B N N Concrete lined
4
Susitna Alaska Power 13.5 or Modified 25 ft-40 ft Argillite, Gray-D&B Approx. 600 ft Suggest same as
(Tent a-29 Horseshoe wacke, Granite, 2000 ft to 1300 Kemano for study
tive) Granodiorite ft purposes
1 ABBREVIATIONS:
TBM -Tunnel Boring Machine
D&B -Drill and Blast
N -Not Known
X
LJ.l
0
~
0.6
0.5
0.4
<i
i= z
UJ 5 KWH0.3
~ vo3
0
i
0
8
LLI
0.2
0.1
15
TUNNEL LENGTH (MILES)
LEGEND
TUNNEL INTAKE WORKS AT:
RE-REGULATION DAM SITE LOCATED JUST
UPSTREAM FROM DEVIL CREEK
---WATANA DAM SITE
---VEE DAM SITE
lll: w
LLI a:
(,)
z
~
0
c(
LLI
0
ECONOMIC POTENTIAL OF TUNNEL SCHEMES
FIGURE 4.1
ll-8
2200 FT. WATANA
2 TUNNELS
38 FT. DIAMETER
800 MW-70 MW
38 FT. DIAMETER
800 MW-850 MW
15.8 Ml'-I ~-~~-1475 FT.
DAM
DEVIL CANYON
550 MW
----RE-REGULATION DAM
30 MW
30 FT. DIAMETER
BOO MW
2 TUNNELS 365 MW
24 FT. DIAMETER
SCHEMATIC REPRESENTATION
OF CONCEPTUAL TUNNEL SCHEMES
TUNNEL
SCHEME
#
t.
2.
3.
4.
FIGURE 4.2
d-9
5 -TUNNEL DESIGN AND CONSTRUCTION CONSIDERATIONS
5.1 -Geologic Setting
Determining the geology along the tunnel alignment is critical in predicting
tunneling conditions, methods, and costs. The information acquired to date
includes several regional geology reports, site specific geology for the Devil
Canyon and Watana dam sites, and the findings of the Woodward-ClYde Consultants 1
(WCC) 1980 Seismicity Study (43).
The Susitna project is located in a tectonically active and geologically complex
region. Subduction of the Pacific plate under the North American plate (Figure
5.1) has resulted in forces which have folded, faulted, thrusted, sheared,
differentially uplifted, metamorphosed and intruded the area. The most common
geologic structures encountered include folds, faults, shear zones, joints, flow
foliation, stocks, dikes, and plutons.
(a) Lithology
As shown on Figure 5.2, three main lithologic units are crossed by the
tunnel alignments: Argillite-Graywacke; Biotite-Granodiorite; and Schist,
Migmatite, and Granite.
The Argillite-Graywacke Unit (Kag) has undergone complex folding with a
well developed axial plane cleavage and numerous quartz stringers. The
argi 11 ite is dark gray to b 1 ack and in some areas has metamorphosed to a
slate or fine-grained phyllite. Tests performed by the USBR for samples
taken at the Devil Canyon site indicate its unconfined compressive strength
ranges from 12,900 to 16,850 psi, Young 1 s modulus averages 9 X 106 psi,
and Poissons 1 ratio averages 0.17.
The Graywacke is dark to medium-gray, fine to medium grained, and is inter-
calated with the argillite in graded beds ranging in thickness up to 16
feet. It comprises between 30 percent and 40 percent of the Argillite-
Graywacke Unit. Tests performed by the USBR indicate its unconfined com-
pressive strength ranges between 28,540 and 36,570 psi, Youn.g 1 s modulus
averages 9.8 x 1Q6 psi and Poissons 1 ratio ranges between 0.15 and 0.25.
The Biotite-Granodiorite Unit {Tbgd) is described as light to medium-gray",
medium to coarse grained intrusive rock with a granitic texture. Biotite
is the chief mafic mineral, but hornblende is occasionally present.
Although no test data is available, the average static properties for this
type of rock are generally believed to be an unconfined compressive
strength between 20,000 and 30,000 psi, Young 1 s modulus about 8 X 106 and
a Poissons• ratio of 0.2.
The Schist, Migmatite and Granite Unit (Tsmg) can be described as undiffer-
entiated terrain of relatively high grade pelitic schist, migmatite and
small granitic plutons occurring in approximately equal proportions with
gradational contacts.
5-l
Again, no static properties are known for this unit, but the granite and
migmatite properties are probably similar to the granodiorite. The
schistose rock properties will vary with the direction they are loaded and
will probably demonstrate a wide range of values. It is important to
determine the properties of this unit and the percentage of tunnel through
it. A poor quality schistose rock may present major problems to tunneling
operations.
A complete description of these units is included as Appendix A (40).
(b) Structure
As mentioned earlier, the geologic structure in this region is complex. The
major structural trends are NE-SW and NW-SE and major faults trend NE-SW.
Results of outcrop mapping between Devil Canyon and Watana are shown in
Tab 1 e 5.1.
(c) Topography
The topography is generally rugged along the tunnel alignments, and the
geologic structure exerts some topographic control. Elevations vary
between 1300 and 3500 feet. Topographic lows, such as the locations of
streams and creeks, are areas of concern. They may represent zones of
poorer rock quality and may require that tunnels be structurally lined to
meet stability and cover requirements.
(d) Lineaments
As part of the wee study, several lineaments were mapped which cross the
tunnel routes. These are shown on Figures 5.3 to 5.6. These lineaments
are considered significant for further investigations due to their charac-
teristics and possible problems in tunneling through them. Other linea-
ments may exist along the tunnel routes which were not identified due to
their distances from the dam sites. A more detailed investigation is
required if the tunnel alternative studies are continued as a preferred
scheme.
5.2 -Geotechnical Design Aspects
Potential geotechnical problems and their impact on the tunnel schemes are
reviewed in this section.
Geotechnical design and hence the cost and construction schedule for a tunnel is
heavily dependent on evaluation of the geology along the potential routes. The
major tunneling problems are created by fault and shear zones, joint sets, lith-
ologic contacts, water and gas. It is normally not economically feasible to
undertake a comprehensive exploration program for the entire route. Therefore,
reconnaissance, mapping, and exploratory work must be directed towards locating
all potential problem areas and these must be evaluated in detail.
Fault and shear zones may create severe problems. Special tunneling techniques
and heavy supports may be required and decreased production rates during con-
struction can be expected in these areas. If the lineaments identified by wee
prove to be fault and/or shear zones, the tunnel alignments will probably have
5-2
to be adjusted to avoid or m1 n 1m1 ze the impact of these features. The shortest
route across these zones is preferred.
Topographic lows such as Devil Creek~ Tsusena Creek and other creeks and streams
may indicate weak zones. Drilling and seismic refraction survey techniques will
be required to determine the properties of the lineaments and topographic lows.
A limited amount of outcrop geologic mapping has been used to align the routes
at this time. Tunnel al igr.tments have been oriented to cross the joints to
decrease support requirements and to help control overbreak.
Lithologic contacts may also present several problems. If the contact is sharp
and fresh, no structural problem may exist~ but production rates may change and
tunneling methods will have to be adjusted for the new rock. Problems will also
be encountered if the contact is sheared or brecciated. Special designs are
required if these contacts contain unconsolidated material and these contacts
may also be a source of water which can create serious difficulties. Many
joints in the Watana and Devil Canyon drill cores are tight and healed. Down-
hole permeabilities vary but average less than lo-5 em/sec below the
weathered zone. If this remains true along the tunnel alignments~ water should
not be a problem.
Gas can create both health and safety problems, i.e. asphyxiation and/or explo-
sion. Gas is not usually a problem in the lithologies present and good ventila-
tion will probably eliminate any potential problems.
5.3 -Seismic Considerations
There are several ways an earthquake may adversely effect a tunnel. Three
conmon sources of damage are displacement, shaking, and ground failure.
Displacement is usually associated with serious damage and is considered the
most severe problem. Small movements along discontinuities are generally not
critical and only minor damage may result. However, displacements of several
feet can lead to serious damage.
Shaking may cause cracking, rockfalls, or possibly collapse. Dynamic stress
concentrations occur which increase static loadings and may result in damage.
Ground failure includes liquefaction and landsliding. These types of failures
may not damage the tunnel itself, but may seriously damage portal areas, and
thus, effect the tunnel use.
Dowding and Rozen (11) studied the effects of seismic loading on tunnels.· Based
on 71 tunnels throughout Japan, Alaska, and California, they developed a corre-
lation between peak motion, particle velocity and observed damage. Table 5.2
summarizes their findings.
· They concluded that earthquakes expected to cause heavy damage to surface struc-
tures cause only minor damage to tunnels. Peak motions for earthquakes usually
occur in the 0.4 to 10 Hz range. These low frequencies are several orders of
magnitude lower than the natural frequencies of tunnels and not 1 ikely to create
differential acceleration and damage to tunnels. Lined and grouted tunnels are
less subject to damage than unlined ones. Under similar seismic loadings an
5-3
unlined tunnel may experience rockfalls while a lined and grouted tunnel may
experience only minor cracking.
Seismic design considerations for tunnels usually include:
-Avoiding faults which may experience large displacements during an earthquake.
-Supporting~ lining~ and grouting areas of poor rock quality.
-Adequately designing portals for seismic loadings.
The preliminary indications from the WCC studies indicate that the Benioff Zone
may produce the controlling or design earthquake in the vicinity of the Watana
and Devil Canyon dam sites. The design earthquake would~ thus, be as high as
8.5 magnitude event (Richter Scale) and produce mean peak horizontal accelera-
tions in the order of of 0.4 g. Therefore, minor rockfalls and some cracking of
concrete may occur but no major tunnel stability problems are anticipated.
5.4 -Design Considerations
The following preliminary design considerations were adopted for purposes of
estimating costs of the conceptual tunnel schemes outlined in Section 4.
(a) Tunnel Size
The power tunnels were sized to max1m1ze the net benefit. This required
cross-sectional areas of between 700 and 2000 ft2. The geologic
information to date indicates that tunnels in the 700 to 1000 ft2 range
could be constructed without major problems. Although it may be difficult
to economically construct very large tunnels through poor rock, no
adjustments to the economically sized tunnels was made during this study as
the amount of geologic information available was not sufficient for this
adjustment.
(b) Tunnel Shape
Tunnel shape is generally a function of hydraulics, stability and ease of
construction. In good quality, high strength rock, stability is not a
problem and the other factors govern the shape. As rock quality and
strength decrease or the rock is overstressed, shapes tend to be more
circular.
For purposes of this study, a modified horseshoe shape was tentatively
selected based on the assumptions that:
-The majority of the tunnel is in good to excellent rock requiring little
support.
-It is the easiest shape to drill and blast.
(c) Tunnel Alignment
The objective of aligning the tunnels is to have the shortest tunnel
through the best rock. Avoiding zones of poor quality and topographic
5-4
lows, crossing adverse geologic structures (not paralleling them),
attaining the minimum cover over the tunnel, and keeping the stresses
compressive around the tunnel are major considerations.
(d) Tunnel Grade
Tunnel grade or depth is selected so as to locate the tunnel in a competent
strata and meet cover requirements. These cover requirements vary greatly
and Table 5.3 summarizes the cover used in several projects. It indicates
that values of between 15 percent and 50 percent of the total hydraulic
design head have been used.
For purposes of these studies, rock cover equal to the static head was
used. When the rock cover is less than this, a lining is assumed neces-
sary.
It has been assumed that slopes within the tunnels will be inclined
slightly (approximately 0.5 percent) to ease construction and haulage.
Access adits are located so as to minimize their lengths. Maximum grades
are 3 percent for rail haul age system and 10 percent for trucks.
(e) Tunnel Lining and Support
Dri 11 ing at Watana and Devi 1 Canyon indicate that the rock is tight and
impermeable at depth. For purposes of this study it has been assumed that
one third of the tunnel length will require structural concrete lining with
a combination of steel sets and rockbolting, one third shotcrete lining and
rockbolting, and the remaining one third will require no 1 ining or support,
except for the concrete-lined invert.
5.5 -Construction Methods
Initially, three tunnel"ing methods were considered for this study:
-Drill and Blast
-Tunnel Boring Machine (TBM)
-Road Header
Based on available knowledge, drill and blast appears to be the most viable for
Susitna and the tunnel estimates are currently based on this method. Each
method, however, has advantages and di sadv ant ages and is discus sed briefly
below.
{a) Drill and Blast
Drill and blast is the oldest form of rock tunneling. Each cycle involves:
-Dri 11 ing
-Loading
-Shooting
5-5
-Ventilating
-Supporting
-Mucking.
The two most common approaches involve heading and bench or full face
excavation. Heading and bench removes a small top heading at a higher unit
cost~ then removes the bench at a lower unit cost. The full face excava-
tion method excavates the entire face at once. In large tunnels~ heading
and bench may be more economical than full face excavation. Both methods
would be suitable for the proposed Susitna tunnel scheme.
There are several advantages to drilling and blasting:
-It is flexible and will accommodate most rock types~ tunnel shapes,
grades, and can be adapted to rapidly changing geologic conditions.
-The initial cost is generally lower.
-Lead and mobilization times are usually shorter.
-There are many experienced contractors.
Some of the disadvantages include:
-Running costs are higher.
-Ground disturbance is high and overbreak may be considerable.
-More extensive support and/or lining may be required.
-Production~ on the average, is lower than for mechanical excavators.
Considering the complex geology and the present lack of geologic informa-
tion along the tunnel routes, this method was selected. It is sufficiently
flexible to deal with any problems that may arise and yields a relatively
conservative construction cost estimate.
(b) Tunnel Boring Maching (TMB)
Machine tunneling has advanced greatly in the last 20 years. TBMs are
being designed to handle a variety of geologic conditions and by the time
the Devil Canyon tunnels are required machine tunneling may be an attrac-
tive option. Presently, this system seems too inflexible for the geologic
conditions anticipated.
The TBMs have several advantages:
-Low rock disturbance.
-Lower support requirements.
-Lower running cost.
5-6
-A lining may not be required.
-Higher production rates if the rock quality is good and the geology is
uniform.
Some major disadvantages are:
-They are inflexible, that is, grades and operating radii are limited and
only a circular shape is possible for large tunnels.
-High initial cost. These machines are uneconomical for tunnels less than
several miles in length.
-Longer lead time, probably one year.
-Longer setup time, probably six weeks.
-Problems tunneling through poor quality rock. TBMs work very well under
the conditions they were designed for, but do not adapt well to geologic
changes.
(c) Road Headers
A road header is an offshoot from the m1n1ng industry and involves a
mechanical tunneling system. It has the advantages of being more flexible
than a TBM, but presently cannot cut hard rocks efficiently. If these
machines had the capability of cutting hard rocks at reasonable production
rates, they would merit seriou£ consideration.
(d) Mucking
Mucking is the term used to describe remov a 1 of the excavated materia 1 from
the tunnel. Selecting a mucking system depends on tunnel grade, length,
and equipment the contractor has available. Within the tunnel, two haulage
systems are commonly used, rail and truck.
Rail systems are favored for long tunnels since they can usually haul large
quantities economically. Their maximllll grade is 3 percent, but they may be
winched on steeper grades. Trucks are favored in tunnels less than about
4000 feet. Their maximum grade is 10 percent.
Considering the volume of material and haul distance to the access way, a
rail system has been assumed for the Susitna tunnel schemes.
5-7
TABLE 5.1: GEOLOGIC STRUCTURE OF REGION BETWEEN THE
DEVIL CANYON AND WATANA DAM SITES
A. GENERAL AREA
Orientation
Feature Average Range
Major Joint Set 335"' 82° sw 320"-355°, 63"-90" sw
Major Joint Set 325", 77" NE 300°-355", 62"-90" NE
Major Joint Set 48°' 79" SE 40"-60", 65"-90" SE
B. ARGILLITE-GRAYWACKE AND UNIT IN THE IMMEDIATE VICINITY Of THE
DEVIL CANYON DAM SITE (Based on Geologic Mapping)
Feature
Bedding •••••••••••••.•••
Major Joint Set .•.••••••
Major Joint Set ••••••••.
Minor Joint Set .••••••••
Orientation
53"-70", 50"-80" SE
320"-350", 82" NE (average)
70"-105", 15"5 (average)
70"-105", 65" NW (average)
5-8
Spacing
6 in to 2 ft
6 in to 3 ft
6 in to 1.5 ft
TABLE 5.2: EFFECTS OF SEISMIC LOADING ON TUNNELS (11)
Horizontal
Accelerat~on(g)
( ft/sec )
< 0.19
0.19-0.25
0.25 -0.52
Velocity
(In/sec)
< 8
8.16
16-32
Damage
None
Few instances of minor
cracking, some rock falls
in unlined tunnels
One partial collapse in
a m~sonry lined tunnel
associated with a landslide
TABLE 5.3: TUNNEL COVER EXPERIENCE
Ratio of
Rock Cover to
Project Hydraulic Head*
Abjors 0.4
Bersimis 2 0.5
Gonda 0.2
Handek I 0.16
Handek I I 0. 1 8
Innertkirchen 0.14
Kemano 0.4
Montpezat 0. 26
South Holston 0. 5
Bersjmis 1 0.5
Calancasa 0.33
Olute des Passes 0.5
Spray 0.24
*Hydraulic head includes both static and dynamic head.
5-lO
0
..-l
0
N
0 c:
Ql u
0 .....
0
N
0
(/]
Ql :::::
0 .....
0
N
0
Ql
.-t
C1l
Q..
TABLE 5.4: REGIONAL GEOLOGY MAP UNITS
Qs
Tsu
Tv
Tbgd/Thgd
Tsmg/Tkgr
Kag
Jt r/ Jgd/ Jgdm
Jam
TRv
TRvs
Psv/Pls
Undi fferent iate d Surficial Deposits
Undifferentiated Sedimentary Rocks
Undifferentiated Volcanic Rocks
Biotite &: Biotite-Hornblende Granodiorite
Granites and Schists
Argillite and Graywacke
Quarts Diorites & Granodiorites
Amphibolites
Basaltic Metavolcanic Rocks
Metabasalt and Slate
Basaltic to Andesitic Metavolcanogenic Rocks
with Interbedded Limestone
Modified after Csejtey and others, 1978.
5-11
...
I
I
j
01
I
N
PLATE
l -N-
~
1
1. Base map from Tarr (19741.
2. After Packer and others (19751, Beikman (1978),
Cormier (19751, Reed and Lamphere (19741,
Plafker, and others (1978).
PACIFIC
1
AMERICAN
PLATE
LEGEND
:;:;:;:;:;:;:;:;:;:;:Wrangell Block ••••• 'Ill ••••
PLATE
• Relative Pacific Plate Motion
----Plate Boundary, dashed where interred
A 4 4 Shelf Edge Structure with Oblique Slip
---Intraplate Transform or Strike-Slip Fault
1
Pl-ATE TECTONIC MAP
FIGURE 5.1
T 32N
T 31 N
T
32
N
T
31
N
·~ •
R 2 E
11\/"l'
1'. t.
z
ct
9 a:: w ::z
0
~~7\~\.r7\A7~~~~~~J\A7\A7\A7\A~r.i~*'~"r?~~~~~~r-~~--~~~~
T
30
N
w
VI
>-a::
ct
,:;) z ::::>
0
ID
J:
1-a::
~~H+Hf~~--~+HL-----~----~~~~~~-+---------------~~
Modified from Cse,tey ,et ol, 1978
• • •
....
CENOZOIC
QUATERNARY ;----;
Ff'"--... ,
I + + 4
Lo.._-.-....J
r·--. ,....,. -,
I 1
L.----1
MESOZOIC
CRETACEOUS
:=:====~~===~ 1.-~-----_-.J
,'URASSIC
flJiflfiO
REGIONAL
lEGEND
Ul\lDIFFERENTIATED SURFICIAL DEPOSITS
UNDIFFERENTIATED VOLCANICS 8 SHALLOW
INTRUSIVES
GRANODIORITE,
BIOTITE· HORNBLENDE GRANODIORITE,
BIOTITE GRANODIORITE
SCHIST, MIGMATITE, GRANITIC ~OCKS
UNDIVIDED GRANITIC ROCKS
rl\7i r"f':J ~/\ ~ " r-. ,... _T __ _
TRIAtSIC r-z;;.....,. ;-;;~
'(' .J..>,., > "' -....;._ __ _.
f-'ALEOZutC
~~
i
THRUST fAULT --... --~-~· :
. .
•
.C.MPHIBOLITES, GR£ ENSCHIST, FOLIATED DIORITE
BASALTIC METAVOLCANIC ROCKS, METABASALT
f,ND SLATE
BASALTIC TO ANDESITIC METAVOLCANIC$ LOCALLY
INTERBEDDED WITH MARBLE
TEETH ON UPTHROWN SIDE, DASHED WHERE I
JOTTED WHERE CONCEALED
tAAFIC INTF;USIVES INTENSE ~HEtl'<iNG ::.OSSIBLE THRUST FAULT, TE.[ln ON lJPTHROWN
• • • \l• • " • \1 • • • Sl DE
PROPOSED DAM SITES
ARGILLITE AND LITHIC GRAYWACKE 6 e
SCALE IN MILt.S . .
GRANODIORITE, QUARTZ DIORITE, TRONDHJEMiTE I ! lll GEOLOGY WITH TUNNEL ROUTES FIGURE 5.2
LEGEND
BOUNDARY FAULTS
Faults with recent displacement
SIGNIFICANT FEATURES
----Indeterminate A foature
• -·-·-Indeterminate B feature
0
BOUNDARY FAULT AND SIGNIFICANT
FEATURE MAP FOR THE SITE REGION
10 20 30 40 50 Miles g;; t;;q t FA I 3
0 10 20 30 40 50 Kilometers
FIGURE 5.3
---·-Indeterminate· A feature
---·-Indeterminate · 8 feature
• • • • • • · • · · • • Indeterminate · BL feature
5
I--t E3 F-IJ-3 I
5 10
lndetenninate • A feature
-• -lndetenninate -B feature
• • • · • • • • Indeterminate • B feature . L
DEVIL CANYON SITE
SIGNIFICANT FEATURE MAP
0~~~~=~1~~~~~2 Miles
0 1 2 3 Kilometers
FIGURE 5.5
1 ;
)',
17 / ;Y
j
-~
W90DWARD-CLYDE CONSULTANTS 14658A December 1900 5.17
"' .. \ 1.
'-{ 2
,.:.·:··
i ./
/----..___-;_:..' ·: ·-·-·
22 . ··.
'·-i
l, (
I: c.. ,
.,..-· •. ? ;: ..... i: /.
LEGEND
Indeterminate .• A feature
-• -.-Indeterminate • B feature
•• , • • • • • • • • • • Indeterminate • BL fe•ture
, -~ ~~
21
/' ' .,~
' : _j:. 63050'
FIGURE 5.6
6 -SCREENING OF CONCEPTUAL TUNNEL SCHEMES
6.1 -Introduction
The screening analysis was performed to compare the four conceptual tunnel
schemes and·determine the best tunnel scheme for further study. Costs, power
and energy, geology, and environmental aspects are used as screening criteria.
6.2 -Tunnel Scheme Costs
All costs are based on 1980 dollars. Unit prices were applied to estimated
quantities for the various components in each tunnel scheme. The total project
cost for each tunnel scheme includes the total construction cost plus a 20
percent contingency and a 12 percent allowance for engineering and administra-
tion.
Wherever possible unit prices were developed and/or compared with cost informa-
tion on recent projects in Alaska. Unit prices developed from projects outside
of Alaska were adjusted to Alaska using the Handy Whitman price indices. In
general, costs are based on the same unit prices as those used for the Susitna
Basin dam alternatives outlined in the Subtask 6.05 report on 11 0evelopment
Selection ...
Tunnel costs are based on the conservative assumption that excavation will be
done by conventional drill and blast operations. Knowing very little about the
rock mass quality along the route, support requirements are difficult to
predict. Therefore, the lining and support assumptions were based largely on
experience at the Kemano Project which is similar in concept, and the results of
drilling at Devil Canyon and Watana, as outlined on Table 6.1.
As mentioned previously, due to the lack of geologic information and the fact
that the tunnel is a major cost item, total project cost estimates must be
regarded as tentative at this time. In any event, total project costs are
relevant for a valid economic comparison between conceptual tunnel schemes.
Tunnel scheme total project costs are given in Table 6.2 for each of the four
tunnel schemes.
6.3 -Power and Energy
Energy values for the tunnel schemes were determined from an annual flow·
duration curve developed from the simulated monthly outflow from the Hatana
reservoir {35). This curve was adjusted to allow for a 1000 cfs minimum
discharge in the river. Allowance was made for tunnel friction and entrance
losses. Installed capacities were calculated to yield an overall plant factor
of between 50 and 55 percent for the total Watana dam-tunnel system. For the
tunnel generating portions of the total development plant factors of about 50
percent were used for peaking tunnels and about 80 percent for base load
tunnels.
The resultant installed capacities and average annual energy yields are shown in
Table 6.2. Figure 6.1 illustrates in the form of simplified power duration
curves the operating modes of the various powerhouses in the tunnel schemes.
6-1
Of primary importance in the assessment of the tunnel schemes' potential is the
increase in energy production over the single Watana development. As shown on
Table 6.2, Scheme 3 yields the largest increase in energy production with 2180
Gwh of added average annual energy. Schemes 1 and 2 would provide for an
increase in average annual energy of 2050 Gwh and 1900 Gwh, respectively. Scheme
4 would have the smallest increase of only 890 Gwh.
6.4 -Environmental Considerations
A preliminary assessment of the environmental aspects associated with the four
tunnel schemes has been made (33). This preliminary assessment was done for
comparison and screening of the tunnel schemes only~ and impacts common to all
schemes were not addressed. The results of this assessment are as follows:
(a) Scheme 1
The environmental impacts associated with this tunnel scheme are likely to
be greater than those of at least one of the other tunnel schemes evaluated
(i.e. Scheme 3). The main criterion for this assessment is the adverse
effects~ particularly on fisheries and recreation of the variable down-
stream flows (4000-14000 cfs daily) created by the Devil Canyon powerhouse
peaking operation. Other negative impacts would result from construction
of both there-regulation dam and a relatively long tunnel. Tunnel impacts
are similar to those of Schemes 2 and 4 and include disturbance of Susitna
tributaries as a result of tunnel access and the potential problems
associated with disposal of a relatively large volume of tunnel muck.
(b) Scheme 2
As for Scheme 1, this scheme involves adverse environmental impacts
associated with variable downstream flows caused by peaking operation at
the Devil Canyon powerhouse (4000-14000 cfs). Without there-regulation
dam~ however, less land would be inundated and the impacts associated with
construction of this relatively small dam would be avoided. As for Scheme
1, the long tunnel proposed will also have negative consequences 9 including
disturbance of tributaries for tunnel access and the potential problems
connected with tunnel muck disposal.
(c) Scheme 3
The overall environmental impact of this scheme is considered less than
that related to each of the two previous schemes, and also less than that
related to the fourth scheme. The relatively constant discharge (about
8300-8900 cfs) from the Devil Canyon powerhouse is desirable for maintain-
ing downstream fish habitat and recreational potential. A general reduc-
tion in river flows through Devil Canyon in this alternative may allow
anadromous fish access to a previously inaccessible 15 mile stretch of the
Susitna River, and an opportunity for enhancement of the fisheries
resource.
With a compensation flow sufficient to allow minimum discharge of 1000 cfs
through Devil Canyon, the riverine character of the reach should be main-
tained.
6-2
As with all of the tunnel schemes, the wildlife habitat in the stretch of
river bypassed by the tunnel might improve temporarily because of an
increase in riparian zone vegetation. With Scheme 3, however, this stretch
of river is shorter than with the other tunnel schemes so a smaller area
would benefit. The wildlife habitat downstream of Devil Canyon powerhouse
may well benefit from the flow from the hydroelectric project regardless of
the scheme chosen. With the constant flows allowed in Scheme 3, the
improvements to that habitat may be somewhat greater than with the variable
flows resulting from peaking in the other tunnel schemes.
One environmental disadvantage of this scheme compared to the others is the
larger area to be inundated by there-regulation reservoir. This area
includes known archeological sites in addition to wildlife habitat. Never-
theless, this disadvantage is offset by the more positive environmental
factors associated with constant discharge from the Devil Canyon power-
house.
(d) Scheme 4
Scheme 4 involves peaking operation at Watana with baseload operation in
the tunnel. Since the net daily fluctuations in flow below Devil Canyon
would be considerable (4000-13000 cfs), Scheme 4 is judged to be less
desirable than Scheme 3 from an environmental standpoint. Although Scheme
4 would avoid the impacts associated with the lower dam and its impoundment
(as planned under Scheme 3), the adverse impacts that would result from
fluctuating downstream flows are considered to be an overriding factor.
Another, although less significant, disadvantage of Scheme 4 compared to
Scheme 3 is the longer tunnel length planned for the former, and perhaps
the proposed location of the tunnel on the north side of the river.
6.5 -Geotechnical Considerations
From a geotechnical perspective, the northern and the alternative direct align-
ments for Schemes 1, 2 and 4 are similar (see Plate 1). Therefore, they will be
discussed together while Scheme 3 will be discussed separately. Table 6.3 shows
estimates of tunnel length proportions within the various lithologic units.
The results of drilling at Devil Canyon and Watana show that rock quality
improves with depth. Therefore, the rock at tunnel grade for all three align-
ments should be good since the minimum rock cover is several hundreds of feet.
The geology along the northern and direct routes seems more complex. These
routes cross at least four lithologic contacts, three different rock units, two
major lineaments, and several minor ones. One lineament is the Susitna Feature.
Although it is not currently considered likely, if this feature were found to be
a fault zone, it could create a very difficult tunneling environment. The topo-
graphic low at Devil Creek may also be a prob-lem zone. Tunneling through the
schistose portions of the schist, migmatite and granite unit may also be diffi-
cult.
Scheme 3 has several advantages. It is about half as long, crosses only one
known lithologic contact, is 90 percent in the Biotite-Granodiorite unit, and
crosses one known major lineament and several minor ones. Being 90 percent in
one unit, machine tunneling may be possible.
6-3
Various lineaments cross the alignments. None have been classified as active
faults and most were in the doubtful category as being faults (43). None of
these features ap~ear to present extreme tunneling problems, but all will
require exploration to determine their characteristics. If they are faults,
strengthened linings will have to be designed and tunneling techniques may have
to be-modified.
All tunnel alignments were laid out so that they crossed the known joint sets.
The northern alignment (for Schemes 1, 2 and 4) was suggested because as it
increases available cover. The tunnel length crossing topographic lows at
Tsusena and Devil Creeks is minimized, but is about two miles longer than the
direct route. The direct route has been proposed because it is the shortest.
However, the tunnel lengths crossing the topographic lows at Devil and Tsusena
Creeks are longer and the cost of lining these areas may make this alignment
less attractive. Also, if these lows are zones of poor rock quality, tunneling
through them may be more costly than minimizing these lengths by avoiding them.
Scheme 3 was aligned to maintain the minimum cover over the entire route. The
tunnel was diverted around topographic lows. Future alignment adjustments may
decrease the tunnel length, but not significantly.
Presently, the Scheme 3 alignment appears to be preferable from a geotechnical
viewpoint. However, explorations are required on all three alignments to firm
up this judgement.
6.6 -Preferred Tunnel Scheme
It is evident from the above discussion that of the four conceptual tunnel
schemes, Scheme 3 is preferred. The economic aspects, environmental aspects,
and geological conditions of Scheme 3 are considered superior to the other
tunnel schemes at this time. Scheme 3 produces additional energy at by far the
lowest cost as is shown in Table 6.2. Scheme 3 was, therefore, selected for
further, more detailed study.
6-4
Rock Quality
(RQD)
> 90
50-90
25-50
< 25
TABLE 6.1: ASSUMED TUNNEL SUPPORT
Percent of
Tunnel
34
33
25
8
6-5
Support and Lining
None to occasional rockbolts
Rockbolts, shotcrete,
welded wire fabric
Rockbolts, shotcrete,
welded wire fabric,
concrete
Steel sets, shotcrete,
concrete
en
I
en
TABLE 6.2: DEVIL CANYON TUNNEL SCHEMES
COSTS, POWER OUTPUT AND AVERAGE ANNUAL ENERGY
Installed Increase1 in
Cal!acit~ (MW)
Watana Devil Canyon
Installed Capacity
(MW)
STAGE 1:
Watana Dam 800
STAGE 2:
Tunnel:
-Scheme 1 800 550 550
-Scheme 2 70 1;150 420
-Scheme 32 850 330 380
-Scheme 4 800 365 365
Increase over single Watana, 800 MW development, 3250 Gwh/yr
2 Includes power and energy produced at re-regulation dam
Devil Canyon
Average Annual
Energy
(Gwh)
2,050
4,750
2,240
2,490
3 Energy cost is based on an economic analysis (i.e. using 3 percent interest rate)
as discussed in Section 7.6.
Increase 1 in Tunnel Scheme
Average Total Project
Annual Energy Costs
(Gwh) ($ x 1 o3 )
2;050 1,979,000
1 t 900 2,317,000
2,180 1,221,000
890 1,494,000
3 Cost of
Additionyl
Energy
(mills/kWh)
42.6
52.'9
24.9
73.6
TABLE 6.3: LITHOLOGY OF TUNNEL ROUTES
Percent Tunnel Route in Each Lithologic Unit**
Scheme(s) Alignment Lithologi:
Rag Tbgd Tsmg Qs*
1 '2, 4 Northern 31 11 10 48
1, 2,4 Direct 13 29 31 27
3 10 90 0 0
NOTES:
* The rock units below the Quaternary soils along the alignments are most
likely Tsmg and Tbgd.
** These percentages are based on surficial rock unit distributions. The actual
length of tunnel in each unit is unknown.
6-7
-1200
3: 1000 ~ 800 0::
UJ 600 ~ 400 a..
200
0
-1200
~ 1000
0: 800
IJJ ~ 600
a.. 400
WATANA
. POWER HOUSE
200
at======
1200r
~ 1000
800 0::
~ 6001-
~ 400f-
200
0~
-1200f ~ 1000
i" 800 w ~ soar-
a.. 400
200
0,___
0 24
HOURS
DEVIL CANYON
POWER HOUSE
J L,
0 24
HOURS
TOTAL
SUSITNA BASIN
DEVELOPMENT
HOURS
TYPICAL DAILY POWER PRODUCTION FOR MARCH
6-8
FIGURE 6.1
TUNNEL
SCHEME
#
).
2.
3.
4.
7 -PREFERRED TUNNEL SCHEME
7.1 -Introduction
As outlined in Section 6, tunnel Scheme 3 was selected for more detailed study.
The aim of the more detailed study is to further refine the engineering con-
cepts, to improve the accuracy of the cost estimate, and to evaluate the power
and energy potential in more detail. This information is used for comparison of
the tunnel scheme with the Devil Canyon dam scheme in Section 8.
7.2 -Design and Operational Assumptions
(a) Design Assumptions
The design assumptions used in the more detailed study are essentially as
previously outlined in Section 5.4 and the construction technique as in
Section 5.5.
The proposed alignment crosses the known joint sets to m1n1m1ze support and
overbreak problems. Adequate cover is maintained along the entire route
and the minimum tunnel depth of 250 feet is believed to be conservative.
The lining requirements for the tunnel are as outlined in Section 5.4.
Table 7.1 summarizes the rock quality observed in the drill holes at the
Watana and Devil Canyon dam sites. If these rock qualities remain true
along the Scheme 3 alignment, up to 50 percent to 80 percent of the tunnel
could be unlined and 1 ightly supported, 20 percent to 40 percent may
require rock bolts and shotcrete, and 10 percent to 20 percent may require
rock bolts, shotcrete and a cast in place concrete lining. In view of
these results, the lining and support requirements suggested in Table 6.1
are conservative and were retained.
As before, the tunnel size was selected on the basis of an economic
analysis. The optimal tunnel size was determined such that the sum of the
amortized tunnel cost and the value of energy lost due to friction is mini-
mized. The value of energy was based on a thermal coal-fired plant in the
year 2000. Table 7.2 summarizes the results of the analyses and also
indicates that tunnel sizes would not be significantly different for lower
energy values or if the cost of energy produced by the tunnel had been
minimized.
The single tunnel diameter was taken to be 40 feet, which is relatively
large. In view of the sparsity of geotechnical data, two smaller, parallel
tunnels of similar total capacity were conservatively selected for study
purposes. Such a concept also has security advantages, the optimum sizes
of these tunnels being 30 foot diameter.
For this study it has been assumed that the powerhouse is located at the
downstream end of the tunnel. This does not necessarily imply that a
powerhouse located at the upstream end would not be studied, with the
tunnels being used for tailrace discharges. Further study would be
required to determine the optimum location.
7-1
(b) Operational Aspects
Minimum discharge of not less than 500 cfs from Watana and 1000 cfs from
there-regulation dam were specified. No daily maximum limit on the dis-
charge from Watana was specified because of the downstream re-regulation
dam. Constant daily discharges from the re-regulation dam and the Devil
Canyon powerhouse were specified.
The Devil Canyon powerhouse is assumed to be operated as a base load power
facility. No daily discharge fluctuations are allowed at the Devil Canyon
powerhouse and daily peaking power demands are supplied by the Watana
powerhouse. Daily peak discharges from Watana are regulated at the
re-regulation dam with a maximum fluctuation in there-regulation reservoir
of less than four feet. A relatively small powerhouse at there-regulation
dam operates as a base load power facility and supplies the required down-
stre~n compensation flow.
7.3-Project Description
Scheme 3 is composed of are-regulation dam, power tunnel, and powerhouse at
Devil Canyon. Plates 2 and 3 illustrate the details.
There-regulation dam is located approximately 15.8 miles downstream from the
Watana darn site. Site selection was based on regional geologic mapping and air-
photo and topographic interpretations. The 245 foot high dam is assumed to be a
rock fill dam with an impervious core. A spillway is located on the north abut-
ment, and a relatively small powerhouse with a capacity of 30 MW on the south
side of the river.-The maximum normal operating reservoir level is 1475 feet.
Power tunnel intakes are located on the south side of the river approximately
2000 feet upstream from the re-regulation dam. The optimal power tunnel dia-
meter is 30 feet for each of the two power tunnels.
The underground Devil Canyon powerhouse has an installed capacity of 300 MW,
with an assumed four generating units. Overland access to the powerhouse access
adit area runs parallel to Cheechako Creek. A surge tank for each power tunnel
is located just upstream of the powerhouse. Small cellular cofferdams are
required along the south bank of the Susitna to allow construction of the tail-
race.
As part of this tunnel scheme, the installed capacity at the Watana dam is
increased by a small amount to reduce the overall system plant factor once the
base load tunnel generating plant comes on line. A provision for an additional
50 MW has been made in this study.
7.4 -Cost Estimate and Construction Schedule
(a) Cost Estimate
The cost estimating methodology described in Section 6.2 was employed to
develop cost estimates for the preferred scheme. However, as more detailed
engineering layout drawings were available, it was possible to undertake a
more detailed cost estimate than for the study described in Section 6.
7-2
Total project costs were re-estimated for both the two 30 foot diameter and
the one 40 foot diameter schemes. These costs amounted to $1.50 billion
and $1.34 billion, respectively. It should be noted that they are somewhat
higher than the estimates associated with the conceptual tunnel schemes due
to the higher level of detail involved. Summary cost estimates for the two
schemes are shown in Tab 1 es 7. 3 and 7. 4.
(b) Construction Schedule
As shown in Figure 7.1, five yearswill be needed to complete construction
of the Scheme 3 facilities. For the purposes of this study, the schedule
is based on an assumption that access will be available from a previously
constructed road from the Parks Highway to the Watana site. Underground
work is assumed to be possible throughout the entire year, and rock
placement only throughout the six months of summer. The exact timing and
sequencing of the various 11 noncriticaP activities will be dependent upon
resource and seasonal limitations and other factors.
Initial work will be to construct several access roads of up to six miles
in length to connect the Watana-Parks Highway to the re-regulation dam,
Devil Canyon and intermediate access sites. It is expected that the
construction of the Devi 1 Canyon powerhouse can start shortly thereafter
with the power on line date approximately 52 months after work commences.
Access to the main power tunnels will be through inclined access tunnels at
two intermediate points. Additional tunneling will occur at both the power
intake portal and at the main powerhouse. This will enable the tunnels to
be driven from as many as six faces, resulting in an estimated maximum
tunnel length of approximately five miles.
The complete re-regulation dam wili take approximately three and one half
years to construct with an estimated placement rate of approximately
640,000 cubic yards/month during the two year placement period.
As shown in Figure 7.1, the power on line date is approximately the s~1e
for both the re-regul ation dam and the Devi 1 Canyon powerhouses.
7.5 -Power and Energy
Power and energy have been evaluated by a demand driven computer simulation
model. The model is based on monthly average demands and 30 years of historical
monthly inflows. Scheme 3 incorporated with the Watana dam has been simulated
to accurately represent operation of the entire development. Powerhouses were
sized to achieve an overall capacity factor of 53 percent which is within the
desired plant factor range of the Watana-Devi 1 Canyon dam scheme.
Power and energy production from a Susitna basin development composed of Watana
and Tunnel Scheme 3 is summarized in Table 7.5.
7.6 -Environmental Impact Assessment
A more detailed assessment of the environmental aspects associ a ted with Scheme 3
has been made (33). A comparative environmental analysis on the location of the
Devi 1 Canyon powerhouse was also performed to determine the preferred powerhouse
location.
7-3
(a) Location of Devil Canyon Powerhouse
Alternative locations for the Devil Canyon powerhouse have been proposed.
Two alternative locations have been determined by the ease of access to the
tailrace and powerhouse access area. The two sites are an upstream loca-
tion about 0.3 miles above the Devil Canyon dam site and a downstream loca-
tion about 1.5 miles below Portage Creek. The major environmental consid-
eration is that a powerhouse upstream of Devil Canyon would preserve much
of the aesthetic value of the canyon. In addition, the shorter tunnel
would confine construction activities to a smaller area and may result in
slightly less ground disturbance~ particularly if there are fewer access
points as well as a smaller muck disposal problem. It is for these reasons
that this powerhouse location is preferred.
A downstrean powerhouse location, on the other hand, might create a mitiga-
tion opportunity by opening up a longer stretch of river that perhaps could
be managed to create salmon spawning habitat due to the lower flows through
the rapids. However, there is currently no data to confirm this and at
this stage the downstream powerhouse location is considered less flexible.
(b) Environmental Impacts
The major adverse environmental impacts associated with the tunnel scheme
are the inundation of 3900 acres by there-regulation reservoir, disruption
during construction, disposal of tunnel muck, and bypassing the major por-
tion of river flows through the tunnel. The area to be inundated by the
re-regulation reservoir includes known archeological sites in addition to
wildlife habitat.
The major beneficial environmental impact is the ability to regulate peak
discharges from the Watana Dam. There-regulation dam would store the
daily peak discharges from Watana and release a constant downstream flow.
The re-regul at ion dam would eliminate the effects of Watana peaking opera-
tions on the Susitna River. This would allow Watana to produce the maximum
amount of peak energy possible with no adverse impacts downstream.
The compensation flow in the bypassed section of the Susitna River is
totally controllable and could be varied seasonally. The controlability of
the compensation flow could be an asset to the fisheries and wildlife in
the stretch of the river bypassed by the tunnel.
(c) Disposal of Tunnel Muck
It is important to note that cost estimates for tunne 1 schemes are current-
ly based on minimal requirements for transportation and disposal of excava-
ted materials by whatever means are finally selected. If a costly disposal
method is selected, total project costs could increase as much as 1
percent. The total volume of excavated material from the two 30 foot
diameter tunnels anounts to 3.7 million cubic yards. Allowing for a
bulking factor of 1.5 this would amount to approximately 5.6 million cubic
yards of muck.
7-4
There are a number of options which may to be considered for environmen-
tally acceptable disposal of the rock removed in excavating the tunnel.
All of these will probably involve a small additional transportation and/or
disposal cost, and include: stockpiling the material for use in access
road repair, construction of there-regulation dam (total volume= 7.7
million cubic yards), or stabilization of the reservoir shoreline; disposal
irr Watana reservoir; dike construction; disposal in a borrow pit created in
dam constructions; sculpture, cover, and seed the pile; and disposal in a
ravine or other coRvenient location. It is unlikely that the most environ-
mentally acceptable option will also be the most economical. Because many
unknown factors now exist, a firm recommendation cannot be made without
further evaluation. It is quite likely, however, that a combination of
disposal methods will be the best solution.
Stockpiling at least some of the material for access road repairs is
believed to be environmentally acceptable provided a suitable location is
selected for the stockpile. The material could possibly be utilized for
construction of any of the access road spurs or temporary roads that are
not already completed at the time the tunnel is excavated.
Another acceptable solution might be to stockpile the material for use in
construction of the re-regulation dam. This rock could also be a potential
source of material for stabilization of reservoir shorelines if required.
As with the previous option, an environmentally acceptable stockpile loca-
tion would be required. Material disposal in Watana Reservoir might also
be environmentally acceptable. A small amount of tunnel muck could
possibly also be used for stream habitat development. With any of these
options, the possible toxicity of minerals exposed to the water should be
first determined by assay, if there is any reason to suspect the occurrence
of such materials and minerals.
Two environmental problems might be solved by disposing of the material in
a borrow pit created in dam construction.
To sculpture, cover, and seed the material is worthy of further considera-
tion, and would require proper planning. For example, borrow areas used in
dam construction could, perhaps, be restored to original contour by this
method. The source of soil for cover is a major consideration as earth
should only be taken from an area slated for future disturbance or inunda-
tion.
The most economical solution might be to fill a ravine with the material or
to dispose of it in another convenient location. Unless the chosen dispos-
al site will eventually t:>e inundated, however, such an arrangement is
environmentally unacceptable, especially since better options are obviously
av ai 1 ab 1 e.
7-5
TABLE 7.1: DRILLING RESULTS AT WATANA AND DEVIL CANYON DAM SITES
Percent of Core
Drill Hole Depth ( ft) RQ0580 :50<: R 00 <: 8lJ Raooo
BH-4 486 76 16 8
BH-2 653 89 8 3
BH-1 738.4 87 9 4
BH-2 391 46 28 26
BH-6 732.4 78 19 3
BH-8 736.7 70 21 9
7-6
TABLE 7.2 -OPTIMIZATION Of TUNNEL DIAMETER
Installed Ca~acit~
Devile-regulation Maximum Maximum Tunnel Alternative Tunnel Alternative Cost of Energy
Diameter Watana Canyon Dam Head Loss Velocit~1} Annual Net Benefif 2 ) Annual Net Benefi f3) Produced
( ft) __111!'!2_ ~ (MW) ( ft) ( f~s) ($ X 10 6 ) ($ X 10 6 ) (mills/kwh)
Two Tunnels
20 850 115 100 97.5 5.6 1. 0 (17 .3) 45.2
25 850 220 50 88.0 6.8 29.9 1.5)* 30.8*
30 850 300 30 45.6 5.9 34. 7* ( 1. 7) 30.8*
35 BOO 400 30 30.5 5.6 29.4 ( 9.0) 34.0
One Tunnel
30 875 190 50 86.0 8.1 31.9 3.1 28.2
---1 35 880 310 30 94.0 9.9 44.7* 9.3* 25.5*
I
---1 40 800 300 30 33.4 6.5 44.7* 7.1 26.8
45 900 375 30 19.9 6.3 42.9 3.4 28.5
50 900 380 30 9.8 5.0 35.8 ( 3.9) 31.7
Notes: -n)
(2)
Velocity in unlined tunnel section.
Based on an
(3)
energy value of 47 mills/kwh, (i.e. the thermal system cost in the year 2000). This value used in this study.
Based on an energy value of 30 mills/kwh, (the average Watana-Devil Canyon Dam hydrosystem cost in the year 2000).
( )Denotes a loss in annual net benefit.
* Optimum tunnel diameter.
TABLE 7.3: COST EST!MATE FOR DEVIL CANYON TUNNEL SCHEME
(TWO 30-FOOT DIAMETER TUNNELS)
1980 PRICE LEVELS
Item
Land and Damages ••.•.•••.•••..••••.••.••.••.
Reservoir Clearing .••••.••••••••••.••...•••.
Re-Regul at ion Dam ••••••.•.•••••.••...••••.••
Spill way ••.••••••.•••••••.•••..•••..••••••••
Diversion Works ....•••.••••.••..•••.•.••••••
Intake War ks -Main •••.•••••••••.••••••••.•.
Power Tunnels ••••.•••••.••••..••••...•....•.
Powerhouse -Main •.•••••••••..••••••.••.••••
Tailrace-Main ••••••.••••.•••••••..•••...••
Switchyard •••••••••••••••••••••.••••••.••.••
Transmission Lines •••..••••••••••.•.•..••.••
Roads and Bridges •••.•••••.•.••••.•••.•••..•
Recreational Facilities ••••.•••••..•••.••.••
Building and Grounds .••.••••..•••...••..••.•
Permanent Operating Equipment ••••.•..••••••.
Secondary Power Station ••.•••••••••.••••.•••
Subtotal •••....•••.•...•••...•..•••••..••..•
Camp Facilities and Support ..••••••••.••..••
Mobilization ••.••..••....••.•.••••••••.••.••
TOTAL CONSTRUCTION COST .................... .
Engineering, Construction, Management and
Owner's Costs •.••••••••..•••...•••.•••••••••
Contingencies •••••••.•••••••••.••••.••••••.•
TOTAL PROJECT COST .•.••••.•••••.•.••••.•••••
7-8
Cost
($1,000)
$ 1 o, 200
3,300
101,900
41 '700
34,800
26,000
556,600
80,300
13,000
3,500
15,000
42,000
1,000
4,000
3,000
21,400
$ 957,700
130,700
47,000
$1 '136,300
136,400
227,300
$1,500,000
TABLE 7.4: COST ESTIMATE FOR DEVIL CANYON TUNNEL SCHEME
(ONE 40-FOOT DIAMETER TUNNEL)
1980 PRICE LEVELS
Item
Land and Damages • • • • • • . • . • . • • • • • . . • • • • • . . . • • . $
Reservoir Clearing ••••.••••••••••.•••••••.•••
Re-regulat ion Dam ••••••••.••••.•.••••••••••••
Spillway ••.•••••••••••.••••••••••••••••••••••
Diversion Works •••.•••••••••••••••••••••••.••
Intake Works -Main ••••••••••••••••.•.•••••••
Power Tunnel ••••••.•.•••••••••••••••.•••••.••
Powerhouse -Main •••••••••••••••••.•••••.••••
Tailrace -Main ••.•.•••••••••••••••••••••••••
Switchyard •••••••••••••••••••••••••••••••.•••
Transmission Lines •••••••••••••••.•••••••••••
Roads and Bridges .•••••.•••••.•••••••••••••••
Recreational Facilities •••••••••••••••..••• , •
Building and Grounds ••.••••••• , •• , •••.•••••••
Permanent Operating Equipment ••••••••.•••••.•
Secondary Power Station ••••••••••••••••••••••
Cost
($1 ,DOD)
10,200
3,300
101,900.
41 '700
34,800
26,000
453,100
80,300
13,000
3,500
15,000
42,200
1,000
4,000
3,000
21;400
Subtotal • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • . • • • • $ 854,400
Camp Facilities and Support ••••••••.••••.•••• 117,000
Mobilization .•••.••••••••••••• , ••..••••.••••• __ 4_2_,_,_7_0_0
TOTAL CONSTRUCTION COST •••••••••••••••••••••• $1,014,100
Engineering, Construction, Management and
Owner's Cost ................................ .
Cant ingencies ••••.••••••••••••..••••••••.••.•
121,700
202,800
TOTAL PROJECT COST ........................... $1,338,600
7-9
TABLE 7. 5: POWER AND ENERGY PRODUCTION FROM TUNNEL SCHEME
Oeser ipt ion
Installed Capacity:
Watana Dam ••••••••.•••••••••••
Devil Canyon ••••••••••••••••••
Re-regulation Dam •••••••••••••
TOTAL •••••••••••••••••••••••••
Average Annual Energy:
Watana Dam •••••••••••••••••••
Devil Canyon •••••••••••••••••
Re-regulation Dam ••••••••••••
TOTAL ••••••••••••••••••••• , ••
Annual Firm Energy:
Watana Dam •••••••••••••••••••
Devil Canyon •••••••••••••••••
Re-regulat ion Dam ••••••••••••
TOTAL ••••••••••••••••••••••••
1-40 Ft Diameter
Tunnels
850 MW
300 MW
30 MW
1,180 MW
3,194 Gwh
2,064 Gwh
195 Gwh
5,453 Gl'k1
2,810 Gwh
1,927 Gwh
127 Gwh
4,864 Gwh
7-10
2-30 Ft Diameter
Tunnels
850 MW
300 MW
30 MW
1,180 MW
3,192 Gwh
2,053 Gwh
188 Gwh
5,433 Gwh
2,833 Gwh
1,925 Gwh
127 Gwh
4,885 Gwh
_,
YEAR I -2 3 4 5 6 7
I I I l I I I I -I i I I I I L I
ACCESS 1111111 ..
DIVERSION TUNNELS .-: IIIIF....-...-
--
COFFERDAMS ................... -
RE-REGULATION OM4 .::' -~----
POWER TUNNELS .. J
I
INTAKE STRUCTURE J
I
.
MAIN POWER PLANT:
POWER/SURGE CHAMBER _,.j
I
POWERHOUSE 1111111111111111111111111111 111111111111111111111111111 IIIII-
-DRAFT TUBE I
I
TAILRACE I -I
TRANSFORMER GALLERY I
I
TUBINE I GENERATOR '1111111111111111111 IIIIIIIIIIIIIIIIIRIIIIIIIII llllUUIIIII ...
IMPOUNDMENT -
UNIT I ON-LINE i TEST AND COMMISSION HH
-
tUNIT 2 ON-LINE
SECONDARY POWER P~ANT WI': --....,.~~~~ ...... ~ .,...,.. ..... .., ....................... ..................... JWT ........... I .
CRITICAL ACTIVITIES EARLIEST START OF ACTIVITY
11111111111111 MAl N POWER PLANT I I EARLIEST FINISH OF ACTIVIH
., .................... SECONDARY POWER PLANT LATEST FINISH
TOTAL ~OF ACTIVITY -
-FLOAT
CONSTRUCTION SCHEDULE PREFERRED TUNNEL SCHEME 3 [ii]
FIGURE 7.1
7-11
8 -COMPARISON WITH DEVIL CANYON DAM SCHEME
This section outlines a brief comparison of the preferred tunnel scheme with the
Devil Canyon dam scheme. The schemes are compared from economic, environmental,
and scheduling points of view . .
8.1 -Economic Comparison
Table 8.1 summarizes the results of the comparative economics of the two
versions of the tunnel scheme involving either one or two tunnels and the Devil
Canyon dam scheme~ The economic parameters use<i are as follows:
Interest rate = 3%.
Escalation rate = 0%.
Economic life = 50 years.
-Annual cost factor = (3.00 interest
+0.89 -sinking fund
+0.10 -insurance)
= 3.99
Operation and maintenance= $11/kW/year.
-Allowance for funds during construction was based on an assumed S-shaped dis-
tribution of cash flow throughout the construction period.
The average annual energy yields in Table 8.1 represent the net increases over
the first stage Watana dam in each case. It wi 11 be noted that the one and two
tunnel schemes can deliver energy at a cost of $29 or $33 per 1000 kWh, respec-
tively. The equivalent cost associated with the Devil Canyon dam is $15 per
1000 kWh. The tunnel scheme represents a 93 or 120 percent increase in cost.
It should also be noted that the tunnel schemes annually yield between 770 and
790 Gwh less energy than the Devil Canyon dam scheme. This represents about 26
percent.
A further factor that should be taken into consideration in the economic compar-
ison of the tunnel and dam schemes is the lower reliability associated with the
capital cost estimate of the tunnel scheme. Because of the uncertainty associ-
ated with the geologic conditions as well as the probable availability of more
sophisticated tunnel construction methods in the next decade, it is conceivable
that the tunnel costs estimates could vary widely. For purposes of this study,
sensitivities have been checked by assuming that tunnel costs could be doubled
or halved. Allowing for this potential range in tunnel construction costs and
still incorporating a 20 percent general contingency the economic analyses shown
in Table 8.1 were repeated and the results are summarized on Table 8.2.
Table 8.2 clearly indicates that even allowing for the uncertainty associated
with the costs of the tunnel scheme, the Devil Canyon dam scheme is still
economically superior.
8-1
8.2 -Environmental Comparison
At present, many gaps exist in the available environmental data. Additional
information, combined with environmental field investigations would permit a
much more detailed comparison of these two development alternatives. Neverthe-
less, from what is presently understood about Scheme 3, it is believed that it
is environmentally superior to the Watana-Devil Canyon dam scheme. By virtue of
size alone, construction of the smaller re-regulation dam (245ft) would have
less environmental impact than the Devil Canyon dam. The river miles flooded
and the reservoir area created by the Scheme 3 re-regulation dam would be about
half those of the Devil Canyon dam, thereby reducing negative consequences such
as loss of wildlife habitat and possible archeological sites. In addition, the
adverse effects upon the aesthetic value of Devil Canyon would be substantially
lessened with Scheme 3, particularly with the powerhouse location upstream of
the Devil Canyon dam site. Furthermore, Scheme 3 may possibly present a rare
mitigation opportunity by creating new salmon spawning habitat that could be
actively managed. With the increase in riparian zone vegetation allowed by
Scheme 3 the wildlife habitat in the stretch of river bypassed by the tunnel
might be temporarily improved. It is believed that the impacts associated with
tunnel access and disposal of tunnel muck would be offset by the plan's advan-
tages.
8.3 -Comparison of Construction Schedules
As shown in Figure 8.1, the construction duration of the tunnel scheme is
approximately one year shorter than the dam scheme. Construction startup to
power on line for the dam scheme is approximately 66 months while the tunnel
scheme is 52 months. The dam scheme's critical path is controlled by dam con-
struction and the tunnel scheme is controlled by powerhouse construction. There
is about a 6 month float period in the construction associated with the tunnel
and this could accommodate some of the potential construction delays which are
more likely with the tunnel than the dam scheme given the limited geologic
information.
The construction schedule for the tunnel alternative is based on the assumption
that an access road from the Parks Highway to Watana is avail able. Should this
not be the case, access by a new route from Watana, presumably via the Denali
Highway, will be required. The same is clearly true for construction of the
Devil Canyon. However, additional costs will arise due to a considerably longer
haul distance for equipment and materials from Anchorage and/or Fairbanks.
8.4 -Summary
The comparison of the tunnel schemes with the Devil Canyon dam scheme indicate
that the dam would yield approximately 36 percent more energy at a 49 to 54
percent lower energy cost. From an environmental viewpoint, the tunnel scheme
has advantages, however, these do not appear to outweight the economic benefits
of the dam schemes. From a construction schedule point of view there is little
difference between the schemes.
It should be borne in mind that the reduced environmental impact outlined in
Section 8.2 would have to be traded off ag~inst the higher cost and lower
energy production of the tunnel scheme. This can be quantified in two ways as
outlined below.
8-2
(a) Environment a 1-Capita 1 Cost Tradeoff
The total increase in capital cost between the Devi 1 Canyon Dam Scheme and
the more expensive tunnel scheme amounts to $500 to $700 mi 11 ion. These
figures are derived by assuming a base fixed cost of 30 percent and
prorating the remaining 70 percent of the Devil Canyon dam costs downwards
by the ratio of the average annual energy yield of the tunnel schemes to
that of the dam scheme. (This hypothetically results in a Devil Canyon Dam
capable of producing energy equal to the tunnel scheme for a capital cost
of $0.80 bill ion.) The environmental benefits to be gained in terms of
about 16 miles of Susitna River and Devil Canyon which would not be
inundated~ would not appear to be justified by this additional cost.
(b) Environmental-Energy Tradeoff
The tunnel schemes yield approximately 770 Gwh less energy on an annual
basis than does the dam scheme. In the long term this implied that an
additional generating facility would have to be provided to generate this
energy when required and this would create an additional source of
environment a 1 impact and cost which has not been factored into the
comparison at this time.
8-3
TABLE 8.1: SUMMARY OF ECONOMIC EVALUATIONS
Total Investment Cost:
.Total Project Cost
Construction Period (years)
Allowance for Funds During Construction
( i = 3%, e = 0%)*
Annual Cost:
Amortized Cost ( i = 3%, 50-year economic
life)
Operation and Maintenance Cost (® $11/kV)
Cost Per kWh!
Increase in Average Annual Energy (Gwh)**
Cost of Additional Energy ($/1000 kWh)
Relative Cost of Power (Devil Canyon
Dam = 100%)
* i = interest rate, e = escalation rate
Scheme 3
2-30 Foot Tunnels
$
$
$
$
1,500
5
121
1,621
65
6
71
2,183
32.5
217
(Million Dollars)
Scheme 3
1-40 Foot Tunnel
$
$
$
$
1,339
5
108
1,447
58
6
64
2,203
29.1
194
** Increase over single Watana dam, 800 MW developed with an average annual
production of 3250 Gwh
8-4
Devil Canyon
$
$
$
$
Dam
903
6
81
984
39
6
45
2,997
15.0
100
TABLE 8.2: SUMMARY OF ECONOMIC SENSITIVITY EVALUATIONS (Million Dollars)
Total Investment Cost
Including AFDC
-maximum*
-minimum**
Cost per kWh
($ per 1000 kWh)
-maximum
-minimun
Relative Cost of Power
(Devil Canyon Dam = 100%)
-maximum
-minimun
*Based on doubled tunnel costs.
**Based on halving tunnel costs.
Scheme 3
2-30 Foot Tunnels
$ 2,563
$ 1 '150
8-5
48.7
22.9
341
160
Scheme 3
1-40 Foot Tunnel
$ 2,213
$ 1,063
41.9
21.1
293
148
YEAR I 2 3 4 5 6 7
I I I I I I I I I I I I I I I I I I I I I
PREFERRED TUNNEL SCHEME 3 I 52 MONTHS .. I r-
ACCESS
COFFERDAMS AND DIVERSION
RE-REGULATION DAM ~-.::
POWER TUNNELS
MAIN POWERPLANT
IMPOUNDMENT ..
UNIT I ON-LINE
TEST AND COMMISSION
·-
UNIT ON-LINE
SECONDARY POWERPLANT
' . I I DEVIL CANYON DAM I 66 MONTHS -1
ACCESS
COFFERDAMS AND DIVERSION
I
SPILLWAYS
DAMS
I
POWER PLANT
IMPOUNDMENT -
TEST AND COMMISSION
UNIT I ON-LINE+
CONSTRUCTION SCHEDULE COMPARISON • FIGURE 8.1
8-6
9 -CONCLUSIONS AND RECOMMENDATIONS
9.1 -Conclusions
The conclusions of this study are:
- A base load tunnel scheme incorporating a re-regul at ion dam downstream from
the Watana dam site and developing the head that could be developed by the
Devil Canyon dam is the most economic type of tunnel scheme.
-There is no evidence that the tunnel scheme is not technically feasible. How-
ever, a substantial amount of additional field data would be required to
firmly establish feasibility.
-The estimated capital cost (excluding AFDC) for the selected tunnel schemes
varies from $1.34 to $1.50 billion depending on whether one or two tunnels are
required. The range of capital costs associated with a tunnel scheme could be
as high as $2.37 billion or as low as $0.98 billion, i.e. from $1.06 to $2.37
billion or from $0.98 to $2.05 billion for the two and one tunnel schemes,
respectively.
-The total average energy yield from the tunnel scheme is approximately 22QO
Gwh over and above that obtained from the Watana dam.
-A comparison of the tunnel scheme with the Devil Canyon dam scheme indicates
that it yields less (26 percent) and more costly (93 percent to 120 percent)
energy. The potential environmental impact associated with the tunnel scheme
is less than that of the dam scheme, but it is believed that this reduced
impact is not sufficient to outweigh the economic advantages enjoyed by the
dam scheme.
9.2 -Recommendations
The recommendations resulting from this study are:
-In order to confirm the economic comparisons with the dam scheme the preferred
tunnel scheme should be incorporated in the Susitna Basin development selec-
tion studies. These studies incorporate a systemwide generation planning
model which will allow a more realistic assessment of the economics of the
tunne 1 scheme to be made.
-Additional field or office studies of the tunnel scheme should nbt be under-
taken at this stage.
9-1
BIBLIOGRAPHY
1. ASCE, Rock Engineering for Foundations and Slopes, Volumes 1 and 2, August,
1976.
2. ASCE, Symposium on Underground Rock Chambers, Phoenix, Arizona, January,
1971.
3. Bleifuss, D.J., 11 Theory for the Design of Underground Pressure Conduits .. ,
Power division, ASCE, V. 81, July, 1955.
4. Brown, Hydroelectric Engineering Practice, Vol. 1, Blackie and Son,
Limited, 1958.
5. Colebrook, 11 The Flow of Water in Unlined, Lined, and Partly Lined Rock
Tunnels 11 , 1958.
6. Cooke, J.B., Libby, J.W., and Madill, J.T., 11 Kemano Tunnel Operation and
Maintenance", The Engineering Journal, August, 1962.
7. Cording, E.J., Mathews, A.A., and Peck, R.B., 11 0esign Criteria for
Permanent Structural Linings for Station Excavations in Rock, Washington
Metropolitan Area Transit Authoritj•, Prepared for Deleuw, Cather and Co.,
July, 1976.
8. Cummins, A.B., and Given, LA., SME Mining Engineering Handbook, The
American Institute-of Mining, Metallurgical and Petroleum Engineers, Inc.,
Volumes 1 and 2, 1973.
9. Davis and Sorensen, Handbook of Applied Hydraulics, McGraw-Hill, 1969.
10. Deere, D.U., et al, 11 Design of Tunnel Liners and Support Systems 11
, Univer-
sity of Illinois, 1969.
11. Dowding, C. H., and Rozen, A., 11 Damage to Rock Tunnels from Earthquake
Shaking 11
, Journal of the Geotechnical Engineering Division, ASCE, February,
1978.
12. Eckenfelder, G.V., "Spray Hydroelectric Power Development .. , The Engineering
Journal, April, 1952.
13. Hamel, L. and Nixon, D., 11 Excavation of World•s Largest Underground
Powerhouse 11 , Journal of the Construction Division, ASCE, September, 1978.
14. Hampton, D. and McCusker, T.G., 11 Economic Potential of Tunnel Standardiza-
tion11, Journal of the Construction Division, ASCE, September, 1980.
15. Holda, J., 11 Tunnel-driving Techniques Until the Year 2000 11 , May, 1980.
16. Huber, W.G., 11 Kemano Penstocks 11 , The Engineering Journal, Nov. 1954.
BIBLIOGRAPHY (Cont 1 d)
17. Jaeger, C., "Present Trends in the Design of Pressure Tunnels and Shafts
for Underground Hydroelectric Power Stations", Proceedings of Inst. of
Civil Engineers, March, 1955.
18. Lawton, F.L., and Kendrick, J.S., 11 Nechako-Kemano-Kitimat Hydroelectric
Power Development and Aluminum-Reduction Plant 11
, The Engineering Journal,
September, 1952.
19. Maevis, A.C., and Hustrulid, W.A., Editors, Proceedings-1979 Rapid
Excavation and Tunneling Conference, Volumes 1 and 2, June, 1979.
20. McFeat-Smith, I., and Tarkoy, P.J., 11 Site Investigations for Machine
Tunneling Contracts", Tunnels and Tunnelling, Vol. 12, No. 2, March, 1980,
Pg. 36.
21. Moavenzadeh, F., and Markow, M.J., "Simulation Model for Tunnel
Construction Costs 11
, Journal for the Construction Division, ASCE, March,
1976.
22. Moye, D. G., 11 Rock Mechanics in the Investigation and Construction of T.l.
Underground Power Station, Snowy Mts., Australia11
, Engineering Geology Case
Histories, Number 3, Geological Society of America, Inc., 1964.
23. Munsey, T.E., 11 Unique Features of the Snettisham Hydroelectric Project".
24. Obert, L., and Duvall, W.I., Rock Mechanics and the Design of Structures in
Rock, John Wiley and Sons, 1967.
25. Parker, A.D., Planning and Estimating Underground Construction, McGraw-
Hill, 1970.
26. Patterson, F.W., Clinch, R.L. and McCaig, I.W., 11 Design at Large Pressure
Conduits in Rock 11
, Journal of the Power Division, ASCE Proc., Vol. 83.
27. Proctor, R.V., and White, T.L., Rock Tunneling with Steel Supports,
Commercial Shearing and Stamping Co., 1946.
28. Richardson, H.W. and Mayo, R.S., Practical Tunnel Driving, McGraw-Hill,
1941.
29. Rosenstrom, S., "Kafue Gorge Hydroelectric Power Project 11
, Water Power,
June-July, 1972.
30. Rousseau, F., 11 Bersimis-Lac Casse Hydroelectric Power Development 11
, The
Engineering Journal, April, 1956.
31. Stagg, K.G. and Sienkiewicz, O.C., Rock Mechanics in Engineering Practice,
John Wiley and Sons, 1968.
BIBLIOGRAPHY (Cont 1 d)
32.
33.
34.
35.
36.
37.
38.
39.
Tarkoy, P.J., "Predicting Raise and Tunnel Boring Machine Performance:
State of the Arts", 1979 RETC Proceedings, Vol. 1.
Terrestrial Environmental Specialists, Inc., "Preliminary Environmental
Assessment of Tunnel Alternatives", December, 1980.
U.S. Department of the Army, Corps of Engineers (Alaska District), Final
Environmental Impact Statement, Hydroelectric Power Development, Upper
Susitna River Basin, Southcentral Railbelt Area, Alaska, Anchorage, Alaska.
u.s. Department of the Army, Corps of Engineers (Alaska District),
Hydroelectric Power and Related Purposes: Southcentral Railbelt Area,
Alaska Upper Susitna River Basin - I nteri rn Fe as i bil ity Report, Anchorage,
Alaska, 1975.
u.s. Department of the Army, Corps of Engineers (Alaska District),
Hydroelectric Power and Related Purposes: Southcentral Railbelt Area,
Alaska Upper Susitna River Basin-Supplementary Feasibility Report ••• ,
1979.
U.S. Department of the Army, Corps of Engineers, Tunnels and Shafts in
Rock, EM 1110-2-2901, 1978.
U.s. Department of the Army, Corps of Engineers (Alaska District),
"Snettisham Hydroelectric Project".
u.s. Department of the Interior, Bureau of Reclamation (Alaska District),
Vee Can,xon Project, Susitna River, Alaska: Engineering Geology of Vee
Canyon Dam Site, Sacramento, Cal ~fornia, 1962.
40. u.s. Department of the Interior Geological Survey, Reconnaissance Geologic
Map and Geochronoloqy, Talkeetna Mountains Quadrangle, Northern Part of
Anchorage Quadrangle, and Southwest Corner of Heal,Y Quadrangle, Alaska,
1978.
41. Vasilescu, M.S., Benziger, C.P., and Kwiatkowski, R.W., "Design of Rock
Caverns for Hydraulic Projects", Underground Rock Chambers, ASCE, 1971.
42. Wheby, F.T. and Cikanek, E.M., 11 A Computer Program for Estimating Costs of
Tunneling", Report prepared for Federal Railroad Administration by Harza
Engineering Company, Chicago, Illinois, October, 1973.
43. Woodward-Clyde Consultants, 11 Interim Report on Seismic Studies for Susitna
Hydroelectric Project", January, 1981.
SCHEMES '2.4 4
10
~ALTERNATIVE. D!I<ECi" II.UGNMENT
--.c.~---~~1;.~ l,'lf4)
[ POWEia TUk .. '!.L.
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15
NORTI-IER.N ALIGNMENT (5C~E.ME.5 I, '2 4-4)
POWILR. T' JNWI!:L
UNOE.i02GROUNO
POWER.I-IOLI.SI!
~:
1.) TUNNEl. Al.IGNMEIIIT l"'!t SC:HI.ME S IS
':>WOWN 0111 DAAWING N* 5TOO-<;CO·II'2.
2.) ALL PL.A.NS t.ND PI<OFII.ES FOR
.::oNCE.PTUA.l. 5TU171' PURPOsES ONL'(.
T . .....,;L.. EL..e'7o' ~======~=======b==========~~==~==========~~J: L.
L-----±------------------------------ir-----------------------------.5-----------------------------.t------------------------------~~---------------------------l'J 1.5 ~ ·~
DISTANCE'. IN MILES
OII<.ECi ALIGNMENT (SCI-4E.ME.S VZ. 44)
DATE ....
ALASKA POWER AUTHORITY
SUSITNA HYDRO[LECTfttC PRO .. E~,.
CONCEPTUAL TUNNEL
SCHEMES
PLAN a SECTIONS
_,. MAY, 1981
,
1400
I :.CO
...,cP \
l
---......:_,900
SUSITNA
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....... ____ ··~
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APPENDIX A
ROCK UNIT DESCRIPTIONS (40)
ROCK UNIT DESCRIPTIONS (40)
Tbgd
Tsmg
BIOTITE GRANODIORITE (Paleocene, in part may be Eocene) --Biotite
granodiorite and adamellite in approximately equal proportions.
Biotite is the chief mafic mineral, hornblende is occasionally
present. Color is light to medium gray, grain size is from medium
to coarse, texture is granitic to seriate. Very faint flow struc-
tures have developed only locally. These rocks occur in shallow,
forcibly emplaced epizonal plutons in the northwestern Talkeetna
Mountains. Aplitic and pegmatitic dikes are common in all the
plutons. Just north of the map area, these plutonic rocks grade
into felsic volcanic rocks. Potassium-argon age determinations
(see Table 1} indicate that the biotite granodiorite and adamel-
1 ite of the present unit are essentially of the same age as the
biotite-hornblende granodiorite (unit Thgd). Thus, the rocks of
these two units, in view of their spatial proximity, probably are
the products of differentiation of the same parent magma, either
in situ or at some deeper levels in the Earth 1 s crust. The
biotite granodiorite intrusives are also considered to be the
plutonic equivalents of some of the felsic volcanic rocks in the
lower portion of the unit Tv.
SCHIST, MIGMATITE, AND GRANITE (Paleocene intrusive and metamor-
phic ages) --Undifferentiated terrane of andalusite and (or)
sillimanite-bearing pelitic schist, lit-par-lit type migmatite,
and small granitic bodies with moderately to well-developed flow
foliation. These rocks occur in approximately equal proportions,
and the contacts between them are generally gradational, as is the
contact between the schist and its unmetamorphosed pelitic rock
equivalents (unit Kag} outside the present map unit.
The pelitic schist is medium to dark gray, medium grained, has·
well-developed but wavy foliation, and contains lit-par-lit type
granitic injections in greatly varying amounts. Rock forming
mateials of the schist include biotite (pleochroism Nz =dark
reddish brown, Nx = pale brown), quartz, plagioclase, minor
K-feldspar, muscovite, garnet, and sillimanite which locally
coexists with and a 1 us i te.
The lit-par-lit type granitic injections within the schist are
medium gray, medium grained, and consist of feldspar, quartz, and
biotite.
The rocks of the small, granitic bodies range in composition from
biotite adamellite to biotite-hornblende granodiorite. They are
medium gray and medium grained, generally have granitic textures,
and, in addition to the flow foliation, locally display flow band-
ing of felsic and mafic minerals. These granitic bodies appear to
be the source of the lit-par-lit intrusions.
A-1
Tsmg
(Cant • d)
Kag
The proximity of the schist to the small granitic bodies, the
occurrence of the lit-par-lit injections, and the presence of
andalusite in the schist indicate that the schist is the result of
contact metamorphism. Perhaps this metamorphism took place in the
roof zone of a large pluton, the cupolas of which may be the small
granitic bodies.
ARGILLITE AND LITHIC GRAYWACKE (Lower Cretaceous) These rocks
occur in a monotonous, intensely deformed flyschlike turbidity
sequence, probably several thousand meters thick~ in the northwest
part of the mapped area, north of the Ta·r keetna thrust fault. The
whole sequence has been compressed into tight and isoclinal folds
and probably has been complexly faulted as well. The rocks are
highly indurated, and many are sheared and pervasively cleaved as
a result of low-grade dynamometamorphism, the intensity of which
is only locally as high as the lowermost portion of the
greenschist metamorphic facies of Turner (1968). Most of the
cleavage is probably axial plane cleavage. Neither the base nor
the top of the sequence is exposed and, because of the intense
deformation, even its minimal thickness is only an estimate.
The argillite is dark gray or black. Commonly it contains small
grains of detrital mica as much as 1 mm in diameter. Because of
the dynamometamorphism, in 1 arge areas the argillite is actually a
slate or fine-grained phyllite. This sections show that some the
argillites are derived from very fine grained siltstone and that
they contain considerable carbonaceous material.
The typical lithic graywacke is dark to medium gray, fine to
medium grained, and occurs intercalated with the argillite in
graded beds ranging in thickness from laminae to about 1.5 m. The
individual graywacke beds are not uniformly distributed throughout
the whole sequence, of which they comrpise about 30 to 40 percent
by volume, but tend to be clustered in zones 1 to 5 m thick. Thin
sections of graywacke samples show them to be composed of angular
of subrounded detrital grains of lithic fragments, quartz,
moderately fresh plagioclase, and some, generally altered, mica in
a very fine grained matrix; euhedral opaque grains, probably
authigenic pyrite, are present in most thin sections. The 1 ithic
fragments consist in various proportions of little altered,
fine-grained to aphanitic volcanic rocks of mafic to intermediate
composition; fine-grained, weakly foliated low-grade metamorphic
rocks; chert; and some fine-grained unmetamorphosed sedimentary
rocks possibly of intraformational origin. No carbonate grains
were seen. The matrix constitutes about 20 to 30 percent of the
rock by volume, generally contains some secondary sericite and
chlorite, and, in the more metamorphosed rocks, biotite and
possibly some amphibole.
A-2
Kag
(Cont'd)
Analyses of paleocurrent features, such as small-scale cross-
stratification, found in several exposures near the western edge
of the mapped area, suggest that depositional currents came from
the east or northeast (A.T. Ovenshine, oral commun., 1974).
Because fossils are extremely sparse, the exact age of the
argillite and lithic graywacke sequence is imperfectly known. A
poor specimen of Inoceramus sp. of Cretaceous age was found just
west of the map area between the Chulitna and Susitna Rivers, and
a block of Buchia-bearing limestone of Valanginian age was found
in float near Caribou Pass in the Healy quadrangle north of the
mapped area (D.L. Jones, oral commun., 1978).
A-3