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lation Cover Sheet PROJECT No. f''5}oo. 0'
DEPARTMENT ___ ~C
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( ALCULATIONS FOR:
ORIGJ NAL BY /.... • i>u NCA¥V
CHECKED BY
REV No. BY DATE
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ORIGINAL COPIES PLACED IN MAIN FILE ON Cl.DSURE OF PROJECT
BY""" L~
FILE No.f S?ot> ·/lf, ~ o6 .. O'i
SERIAL No. 00 t. S ·
UAII:. ~ t~l PI
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DATE I I
CHECKED DATE
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APPROVED BY
PROFESSIONAL ENGINEERS
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DATE ?::.IC..tJ I!J3
TOTAL. No. OF SHEETS _fl; lJ ~('p~
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Calculaiion Criteria, Data
and References
WATANA -TOP 0~ ROCK CRITERIA
Project No. _r_6700. 06
File No. P5700.) 4 .• 06.09
Ser~al No. 00 e£
L. Duncan 9/2/Rl ~ 1 of 2
. l ,.._ ""'>. -·
41 Or~er of quality of data:
1) drill holes;
2) mapped outcrops;
3) seismic lines;
4) inferred geologic features;
5) topographic expressions!
w&..S The above data applied to the topography of the base ma~lnterpretations were
made, where data could be extrapolated,to construct top-of-rock contours.
Using borehole plots and outcrops, segments were constructPd to show general
100 ]00 ft contours. Using seismic line data, extensions were then made. Final
connection of contours was made by comparing the inferred geology (shear zones,
sound rock areas) with local topography at nearby known locations. The results
were contours drawn from known bedrock locations to adjacent spots, assuming:
1) vjrtually all outcrops have been located;
2) areas of no observed outcrop have deeper overburden;
3) shear zones will ha~e deeper erosion, hence deeper overburden;
4) toprgraphic "swales" and "gt.ii:s" except where bedrock is exposed have deeper
overburden that adjacent "knobs" and 11 ridges".
Application of these Rssumptions was modified in four cases:
1) Left abutment, upstream of axis, gut that passes south through DH-25.
2)
Because of the depth of glaciofluvial or till material enco~ntered in the
hole and because of observed deep alluvial and boulder deposits at the
break in slope, the topographic feature was inferred to be an infilled gully.
e Left abutment downstream of dam, vicinity of plungspool area. Due to
observed deep talus material, the topographic basin was inferred to be an
eroded .~lly l~ter !ill~d with talus and till. This interpretation is
~~~~o~able ~fn addition t,;c~use a set of significant shear zones (North
~ ~--r-tA• ... South and 300° sets) intersect in the area and would probably have been
A much more readily eroded.
••
~ -,.. .... ,....._;.;...·· ---.. :-----------------------r----------------.
3)
CalcJ,Jiation Critt.~ria, Data
and References
WATANA -TOP OF ROCK CRITERIA
Project No. P5700. 06
File No. P5700. 14. 06. 09
Seria( No. C>c -z.5" _,.
L. Dunca~ 2 of 2
I
SW-2, north abutment. t?ecause BH-r encountered rock at the intersection of
SvJ-2 and SL-80-2 at about 19 ft in depth, the 6030 fps zone on S~J-2 was
inferred to be rock at all points.
4) The river seismic lines run off the ice in the spring of 1981 did not provide
good top-of-rock interpretation. The 12,000 and 14,000 fps zones in SL-81-4
and SL-81-5 are probably rock, but to be conservative the assumption is being
made at this time that they are talus or frozen alluvium. The resultant
bedrock elevati.on of 1355-1370 ft do1es compare moderately well with the
downstream dril1hole elevation of 1380-1400 ft for top of rock. However,
Line SL-81-6 does not compare comparably so this line was thrown out and
1360 was taken as assumed bedrock low in the channel. This may very well
be some 20 ft on the conservative side but avoids the unjustified assumption
that the four boreholes to rock did indeed hit the deepest bedrock elevations .
The first two and fourth deviations mentioned above represent conservative .
assumptions to preclude introducing major changes in arrangement configuration
at a later date should these features be proven to exist. The third case
represents a reasonable correction of the seismic line information based on
numerous outcrops and the borehole BH-1.
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WATANA -TOP OF ROCK CRITERIA
Order of quality of data:
1) drill holes;
2) mapped outcrops;
3) seismic lines;
4) inferred geologic features;
5) topographic expressions.
The above data was applied to the topography of the base maps. Interpre-
tations were made, where data could be extrapolated, to construct top-of-
rock contours. Using borehole plots and outcrops, segments were con-
structed to show general 100 ft contours.. Using seismic line data,
extensions were then made. Fi na 1 connection of contours was made ',<;'
comparin~ the inferred geology (shear zones, sound rock areas) with .ocal
topography at nearby known locations. The results were cc~tours drawn
from known bedrock locations to adjacent spots assuming:
1) virtually all outcrops have been located;
2) areas of no observed outcrop have deeper oyerburden;
3) shear zones will have deeper erosion, hence, deeper overburden;
4) topographic 11 swales" and 11 guts 1' except where bedrock is expcsed have
deeper overburden that adjacent 11 knobs" and 11 ridges 11 •
Application of these assumptions was modified in four cases:
1) Left abutment, upstream of axis, gut that passes south through DH-25.
Because of the depth of glaciofluvial or till material encountered in
the hole and because of observed deep alluvial and boulder deposits at
the break in slope, the topographic feature was inferred to be an
infi11ed gul1y.
2) Lef:; abutment downstream of dam, vicinity of plunge pool area. Due to
obs•.:rved df;ap ta 1 us materia 1, the topographic basin was inferred to be
an eroded gully late~ fi11ed with talus and till. This interpretation
is supported by the fact that a set of significant shear zones (north
south and 300° sets) intersect in the area and the area would probably
have been much more readily eroded.
3) SW-2, north ab~tment. Because BH-1 encountered rock at the inter-
section of SW-2 and SL-80-2 at about 19 ft in depth, the 6030 fps zone
on SW-2 was inferred to be rock at all points.
4) The river seismic lines run··off the ice in the spring of 1981 did not
provide good top-of-rock interpretation. The 12,000 and 14,000 fps
zones i~ SL-81-4 and SL-81-5 are probably rock, but to be conservative,
the assumption is being made at this time that they are talus or
frozen a11uvium. The resultant bedrock elevation of 1355-1370 ft does
.. .
• ,i'f'
compare moderately well with ·~he downstream dri11hole elevation of
1380-1400 ft for top of rock.. However, Line SL-81-6 does not compare
comparable so this line was thrown out and 1360 was taken as assumed
bedrock 'low in the channel. This may very well be some 20 ft on the
conservative side but avoids the unjusti.fied assumption that the four
boreholes to rock did indeed hit the deepest bedrock elevations.
The first two and fourth deviations mentioned above represent conservative
assumptions to preclude introducing major changes in arrangement con-
figuration at a later date should these features be proven to exist. The
third case represents a reasonable correction of the seismic line
information based on numerous outcrops and the Borehole BH-1 •
!•' • ,.
R.K. Ibbotson
::;:> N. Bond .
Sus·ltna Hyd'roe1ectr1c Projeet
Watana Dam Foundat1on-Eicavation
September 21, 19R1
P5700.14.06.09
This memo sets out the depth of excavation to be used for estimating
purposes.
The depths have been largely based on borehole logs {suntnary llttached)
with additional information from seismic lines, rock outcropst photographs,
and field observations by geologists.
An appendix is attached g1v1ng further criteria used to estimate the
elevation of the top of rock 1n certain areas of the site.
Overburden
The foundation can be divided into two areas:
a) Riverbl!d
Depth eo bedrock in four boreho 1 es in ·the river ranged from 44 ft to
78 ft. The information available is limited, and for estimating
purpost.s, the average thickness of overburden should be taken as
78 ft, the maximum observed in the boreholes ..
b) Abutments
The depths to rock in 12 boreholes ranged from 3.5 ft to .~ ft,
averaging 9 ft. However, considering the results of the seismic
surveys and the distribution of the borehlles, 15 ft is a more
reasonable estimate.
The weighted average over the ~ole foundation area 1s 20 ft.
For estimating purposes, it is understood that th9 volume of overburden
material to be removed will be calculated from the "Preliminary Top of
Rock Contour Map 11 September J, 1981, and topographic maps.
Foundation For Core and Filters
The core and ff1ters shall be founded on sound, competent, u~~eathered
rock. A11 rock which has weathered to the extent that the rock mass
······, ' .
. •'
•
;
R .. K. Ibbotson September 21, 1981
-2
permeability and compressfbi11ty have bean adversely affected shall be
excavated.
Closely spaced jointing wf11 not itself be a criteria for excavation. If
the joints are tight and fresh, then excavation will not be required.
Joints which are only stained will not be considered as weathered.
Information from 15 boreholes indicates an average depth of weathered rock
of 30 ft with depths ranging from zero to 9 ft (see attached borehole
data).
A':'.d1t1ona 1 excavation of sound rock may be required to fonn a t'egular
·foundation surface on which the core may be we 11 compacted., There 1 s
insufficient information at present to assess the degree of irregularity
of the foundation. Observations of rock outcrops suggests the foundation
surface will be rugged and trimming will be required.
It is proposed, therefore, that a further 10 ft of rock excavation be
allowed to cover this requirement and as a further contingency because of
the limited data available.
The total rock excavation depth in the core area should, therefore, be
taken as 40 ft for present estimating purposes •
It must be emphasized that this is an average figure, and the actual
excavation may vary from 5 ft to 65 ft or more.
Weathered joints and shears may extend under the foundation to considerable
depths. In such cases where it is impracticable and/or uneconomic to
excavate all weathered and sheared material, these zones will be locally
excavaeed to a shallow depth backfilled with concrete and. if necessary,
grouted~
It is expected that after excavation of the weathered rock, the exposed
rock foundation will contain jointing which w111 require consolidation
grouting. Provision has been made for consolidation grouting to a depth
of 30 ft over the area of the core and filter/rock contact ..
Rock Excavation Under the Rockfill Shells
The r·ockfill shells shall be founded on competent rock. This will require
the removal of overburden and rippable rock.
Heavily jointed and fractured rock need not be excavated unless there fs
a substantial amount of joint in-fill material which could be washed out
and cause the rock to became unstable or ~1ve rise to settlement of the
rock sur:face.
••
•
•
R.K. Ibbotson September 21, 1981
Steep slopes will be required to be trimmed and a regular rock surface
formed for placement ff the rockfill.
This excavation under the rockf111 shells 1s expected to total 10 ft
average depth over the whole shell foundation area •
N. Bond
NB:ccv
cc: D. Meilhede
Geotech file copy cird: l. Duncan
K. ~fhite
R. Gorny
N. Bond
File
.... -,
0
•
~JP.TANfl. -TOP OF ROC!( CRITERIA
Order of quality of data:
1) drill holes~
2) · sapped outcrops;
3) seismic lines;
4) inferred geoloqic features;
5) topographic expressions.
The.above data was applied to the topography of the base maps. Interpre-
tatlons were made, where data could be extrapolated, to construct top-of-
rock contours. Using borehole plots and outcrops~ segments were con-
structed to show general 100 ft contours. Using seismic line data,
extensions were then made. Final connection of contours was made by
comparing the inferred geology (shear zonesy sound rock areas) with local
topography at nearby kno\'m 1 ocati ons. The resu 1 ts we1"e contours drawn
from knovm bedrock locations to adjacent spots assuming:
1)
2)
3)
4)
virtually all outcrops have been located;
areas of no observed outcrop have deeper overburden;
shear zones will have deeper erosion, hence, deeper overburden;
topographic ~~~wales" and 11 guts 11 except where bedrocl~ is exposed have
deeper overburden that adjacent 11 knobs" and 11 ri dges I!.
Application of these assumptions was modified in four cases:
1) Left abutment, upstream of axis~ gut that passes south through DH-25.
Because of the denth of alaciof1uvia1 or till Material encountered in
the hole and beca~se of ~bserved deep a11uvial and boulder deoosits at
the break in slope, the topographic feature was inferred to be an
infilled gully.
2) Left abutment dovmstream of dam:: vicinity of plunge pool area. Due to
obset~ved deep talus material, the topographic basin was inferred to be
an eroded gully later filled with talus and till. This interpretation
is supported by the fact that a set of significant shear zones {north,
south and 300° sets) intersect in the area and the area would probably
have been much more readily eroded.
3) SH-2, north abutment. Because BH-1 encountered rock at the inter-
section of SW-2 and SL-80-2 at about 19 ft in depth, the 6030 fps zone
on SW-2 was inferred to be rock at all points.
4) The river seismic lines run off the ice in the spring of 1981 did not
prov~de good top-of-rock interpretation. The 12,.900 and 14,000 fps
zones in SL-81-4 and SL-81-5 are probably rock, but to be conservative,
the assumption is being made at this time that they are talus or
frozen alluvium. The resultant bedrock elevation of 1355-1370 ft tioes
•
•
compare moderately well with the downstream drillho1e elevation of
1380 .. 1400 ft for top of rock. However~ Line SL-81-6 does not compare
comparable so this line was throvm out and 1360 \'-tas taken as assumed
bedrock low in the channela This may very well besom~ 20ft on llhe
conservative side but avoids the unjustified assumption that the four
borehilles to rock did indeed hit the deepest bedrock elevations.
The first two and fourth deviations mentioned above represent conservative
assumptions to preclude introducing major changes in arrangement con-
figuration at a later date should these aeatures be proven to exist. The
third case represents a reasonable correction of the seismic line
information based on numerous outcrops and the Bbuieole BH-1.
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