HomeMy WebLinkAboutGeotechnical RecommendationsDuane Miller Associates LLC
5821 Arctic Boulevard, Suite A
Anchorage, AK 99518-1654
(907) 644-3200 Fax 644-0507
August 17, 2009
CTA Architects Engineers
306 West Railroad Avenue, Suite 104
Missoula, MT 59802
Attention: Nick Salmon, Project Manager
Subject: Geotechnical Recommendations
Tok Biomass Boiler Building
Tok, Alaska
DMAJob No.: 4276.001
Arctic & Geotechnical Engineering
www.alaskagElO.com
This report presents Duane Miller Associates LLC (DMA) recommendations for
the proposed Biomass Boiler Building in Tok, Alaska. DMA' s scope of services was to
complete a site geotechnical exploration, conduct geotechnical laboratory testing on
select soil samples, and develop geotechnical engineering recommendations for the
proposed structure. Our services were completed in general accordance with our
proposal to CTAArchitects Engineers (CTA) dated May 4, 2009.
We have coordinated with Mr. Nick Salmon of CTA for this project and Mr. Paul
Weisner of CE2 Engineers (CE2) during our work for this project. It is our
understanding that the Biomass Boiler Structure will be a 48 by 88-foot pre-engineered
steel structure. The proposed facility will be a single story with a concrete slab-on-
grade floor and reinforced concrete spread foundations. A 16 by 48-foot section of the
building will have a fuel storage (wood chip) basement extending approximately 12 feet
below finish grade. The remainder of the structure will be a slab-on-grade.
Regional Geology and Climate
Tok, Alaska is located within the Tanana Lowland physiographic province of
Interior Alaska. The Tanana Lowland province is situated on a wide northward sloping
alluvial fan composed of sand and gravel. The sand and gravel is moderately well-
stratified, unconsolidated, and generally poorly-graded. Cobbles and boulders are
Biomass Boiler Building
August 17, 2009
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Duane Miller Associates LLC
present with in the granular soils. The granular soils are covered with a layer of fine silt
(loess) of variable areal extent and thickness, but is generally less than two feet thick. A
relatively thin organic mat covers the fan supporting trees, brush, and grasses.
Relatively warm permafrost is present throughout the Tanana Lowland province,
but is generally absent in developed areas or where the surface vegetation has been
removed. Frozen ground (permafrost) is not expected in the project footprint. Seasonal
frost may extend to a depth of eight feet or deeper below grade along roadways and
other developed and windswept areas. Groundwater is expected at approximately 40
feet below existing grade in the project area.
Tok is considered a continental climate zone with cold winters and warm
summers. The mean annual air temperature is approximately 25" F. The average low
and high temperatures are -32 and 72" F. Extreme temperatures have been measured
from -71 to 99" F. Average annual precipitation is 11 inches including 33 inches of snow.
DMA has reviewed regional climatic data throughout Alaska from 1980 to the
present. Our analysis has determined that both average and design mean air
temperature, thawing, and freezing indices have increased relative to the 20 to 30 year
period prior to 1980. Long-term warming trends are expected to continue. However,
short-term variations to the expected longer-term warming trends should be
anticipated.
Geotechnical Exploration
A site exploration program was conducted by Miss Heather Brooks, E.I.T. of DMA
on May 12, 2009. A total of three test pits were completed with a CAT Excavator owned
and operated by Burnham Construction. Two of the test pits (TP-1 and TP-2) were
completed at the preferred location for the structure. These test pits were completed in
an area previously cleared and graded. One test pit (TP-·3) was completed at an
alternative building location. While test pits TP-1 and TP-2 were advanced in a recently
re-vegetated area, test pit TP-3 was advanced in a cleared, gravel area with sparse
surface grass cover. All test pits were completed to 14.5 feet below ground surface.
Disturbed but representative soil samples were collected from the excavator bucket and
Biomass Boiler Building
August 17,2009
Page 3
Duane Miller Associates LLC
visually classifed in the field. Representative portions of select soil samples from each
test pit were double-sealed in polyethylene bags to preserve natural moisture content
and shipped to the DMA laboratory in Anchorage for further analysis.
Subsurface conditions at test pits TP-1 and TP-2 consisted of six inches of organic
mat and organic silt. Underlying the silt in both test pits is a sandy gravel with
subrounded cobbles to the depth explored. Test pit TP-3 is located in the shoulder of an
existing roadway and no surface organics were observed. The uppermost five feet of
test pit TP-3 is a sandy gravel fill overlying the in-situ sandy gravel with cobbles to the
depth explored. Particle size differences were used delineate granular fill from in-situ
sand and gravel in test pit TP-3.
Layers of frozen soil were encountered in test pit TP-·1 from four to five feet below
grade. This frozen soil is considered seasonal frost. Frozen soil was not encountered in
test pit TP-2. In test pit TP-3, frozen soil was encountered from four to at least 14.5 feet
below grade, the limit of the excavation equipment. Though not confirmed, the
observed frozen soil encountered in test pit TP-3 is considered seasonal frost. The
deeper seasonal frost penetration encountered in test pit TP-3 can result from the
removed surface organic mat, a relatively thick layer of low moisture content granular
soil, and the area being cleared of snow and other surface insulation during the winter.
A hand slotted l-inch PVC standpipe was installed in each test pit to
approximately 14.5 feet below grade for measuring the groundwater level. Prior to
backfilling test pits TP-1 and TP-3, some minor seepage was observed above the frozen
soil. A day after installation water levels were measured with no measurable water
observed in the standpipes.
A Dynamic Cone Penetrometer (DCP) field test was conducted at a depth of five
feet below grade in test pit TP-2. The DCP measured the number of blows required to
advance a conical tipped rod into undisturbed soil using a 16.2-pound hammer falling
22.6 inches. The DCP procedure relates penetration energy (blows) to rod penetration
length, converted to a California Bearing Ration (CBR). In general, the greater the
penetration energy I depth ratio, the stiffer I denser the subgrade soil. At test pit TP-2, 24
blows for 3 inch rod penetration was recorded. This field ratio converts to a
Biomass Boiler Building
August 17, 2009
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Duane Miller Associates LLC
comparative CBR of 80. For reference, a CBR of 100 is defined as well compacted,
crushed rock aggregate. The CBR of 80 is larger than expected for the observed soil and
may be the result of the cone lodging against cobbles or coarse gravels.
Laboratory Testing
Soil samples were re-examined in the laboratory to confirm visual field
classifications. Select representative samples were tested for natural moisture content
and grain-size distribution. Soils were classified according to the Unified Soil
Classification System (USCS). The results of laboratory testing are presented on the test
pit logs (Plates 2 to 4) and the Summary of Samples, Plate 6. DMA' s soil classification
key is presented on Plate 5. Particle size distributions are summarized on Plate 7.
Recommendations
Based on our understanding of the structural design and building layout,
continuous and isolated reinforced concrete spread foundations with a concrete floor
slab are considered appropriate for the proposed structure. The 12 foot vertical
subgrade wall at the fuel storage basement will incur additional lateral load from
trucks I trailers delivering wood chips to the facility. DMA has developed the following
geotechnical recommendations for site grading, the reinforced concrete foundation, and
the concrete slab-on-grade floor.
Site Grading
Site grading appears necessary for the structure. Based on site development plans,
the organic soil, debris, unclassified fill, and inorganic silt must be removed within the
proposed building footprint. Any fill within the foundation footprint without reliable
placement and compaction records should also be removed to in··situ soil. Over-
excavation of unsuitable material at the project site should extend at least five feet
laterally from the exterior of the proposed foundation footprint. The perimeter and
interior building foundations must extend beneath the silt and be founded on a
minimum of six inches of compacted non-frost susceptible (NFS) fill placed on the in-
situ granular soil. If the over-excavation of unsuitable material extends below the
Biomass Boiler Building
August 17,2009
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----------
Duane Miller Associates LLC
design grade for foundation support, NFS fill should be used to achieve the appropriate
grade.
Exposed subgrade soil must be fully thawed, scarified, and moisture-conditioned
to facilitate compaction using vibratory compaction equipment. The soil exposed at the
foundation over-excavation grade should be proof-compacted to at least 95% of the
maximum dry density as determined by the modified Proctor test method, ASTM
D-1557. If soft or yielding soil is encountered during proof compacting, these areas
should be over-excavated and replaced with compacted NFS fill. If wet spots are
present that "pump" during compaction, the wet material should be over-excavated,
replaced with NFS fill, and compacted as recommended above.
The NFS fill should consist of a fully thawed, cohesionless, well graded sand and
gravel mixture with low fine content conforming to Alaska Department of
Transportation and Public Facilities (ADOT&PF) Subbase" A" specification. The NFS
fill should be placed in a fully thawed state in nominal12-inch lifts. Each lift should be
compacted to at least 95% of modified Proctor maximum dry density using heavy
vibratory roller compaction equipment prior to placement of subsequent lifts. Nominal
6-inch lifts are recommended if using hand operated vibratory compaction equipment.
At least one field density test per fill lift should be conducted under load bearing areas.
Foundation Design
The building loads can be supported on continuous perimeter and isolated interior
square foundations that bear on properly compacted NFS fill placed on the proof-
compacted in-situ granular soil. Based on the reviewed site geotechnical data,
continuous perimeter foundations should be founded at least 42 inches below the
exterior finish grade in heated structures. Isolated interior foundations not exposed to
temperatures below 32°F should be founded at least 12 inches below the base of the
concrete slab. Continuous strip foundations should be at least 18 inches wide and
isolated square foundations should be at least 24 inches wide. Foundations installed as
recommended above can be designed for an allowable bearing pressure of 4,000 pounds
per square foot (psf) for dead plus sustained live loads. This allowable bearing pressure
Biomass Boiler Building
August 17, 2009
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--------------------
Duane Miller Associates LLC
can be increased by one third (1/3) to accommodate short term transient loading
conditions.
We have assumed the structure will be heated throughout its design life. Normal
heat loss through the slab-on-grade floor and fuel storage basement should prevent the
soils from freezing beneath the building foundations. The perimeter foundation walls
should be insulated along their entire exterior faces with 2 inches of 40-pound per
square inch (psi) compressive strength extruded or expanded polystyrene insulation.
The perimeter foundation wall insulation should be continuous with the above-grade
building insulation. The above grade portion of the polystyrene insulation should be
protected from ultraviolet light and damage. We have assumed waterproofing along
subgrade foundation wall will be addressed by the civil design team.
If unheated foundations such as isolated, exterior coiumn supports are expected,
specialized cold foundations be warranted to reduce seasonal frost impacts. A variety
of cold foundation options may be suitable for this site, including driven pile, insulated
shallow foundation, and helical anchor (screw pile). We should be contacted if cold
foundations are anticipated for this project.
------··---·
Duane Miller Associates LLC Arctic & Geotechnical Engineering
~~--~~--~~~~--------------· 5821 Arctic Boulevard, Suite A www.alaskageo.com
Anchorage, AK 99518-1654
(907) 644-3200 Fax 644-0507
August 17,2009
CTA Architects Engineers
306 West Railroad Avenue, Suite 104
Missoula, MT 59802
Attention: Nick Salmon, Project Manager
Subject: Geotechnical Recommendations
Tok Biomass Boiler Building
Tok, Alaska
DMA Job No.: 4276.001
This report presents Duane Miller Associates LLC (DMA) recommendations for
the proposed Biomass Boiler Building in Tok, Alaska. DMA' s scope of services was to
complete a site geotechnical exploration, conduct geotechnical laboratory testing on
select soil samples, and develop geotechnical engineering recommendations for the
proposed structure. Our services were completed in general accordance with our
proposal to CTAArchitects Engineers (CTA) dated May 4, 2009.
We have coordinated with Mr. Nick Salmon of CTA for this project and Mr. Paul
Weisner of CE2 Engineers (CE2) during our work for this project. It is our
understanding that the Biomass Boiler Structure will be a 48 by 88-foot pre-engineered
steel structure. The proposed facility will be a single story with a concrete slab-on-
grade floor and reinforced concrete spread foundations. A 16 by ,~:8-.foot section of the
building will have a fuel storage (wood chip) basement extending approximately 12 feet
below finish grade. The remainder of the structure will be a slab-on-grade.
Regional Geology and Climate
Tok, Alaska is located within the Tanana Lowland physiographic province of
Interior Alaska. The Tanana Lowland province is situated on a wide northward sloping
alluvial fan composed of sand and gravel. The sand and gravel is moderately well-
stratified, unconsolidated, and generally poorly-graded. Cobbles and boulders are
Biomass Boiler Building
August 17,2009
Page2
----------------
Duane Miller Associates LLC
present with in the granular soils. The granular soils are covered with a layer of fine silt
(loess) of variable areal extent and thickness, but is generally less than two feet thick. A
relatively thin organic mat covers the fan supporting trees, brush, and grasses.
Relatively warm permafrost is present throughout tl1e Tanana Lowland province,
but is generally absent in developed areas or where the surface vegetation has been
removed. Frozen ground (permafrost) is not expected in the proJiect footprint. Seasonal
frost may extend to a depth of eight feet or deeper below grade along roadways and
other developed and windswept areas. Groundwater is expected at approximately 40
feet below existing grade in the project area.
Tok is considered a continental climate zone with cold winters and warm
summers. The mean annual air temperature is approximately 25° F. The average low
and high temperatures are -32 and 72° F. Extreme temperatures have been measured
from -71 to 99° F. Average annual precipitation is 11 inches including 33 inches of snow.
DMA has reviewed regional climatic data throughout Alaska from 1980 to the
present. Our analysis has determined that both average and design mean air
temperature, thawing, and freezing indices have increased relative to the 20 to 30 year
period prior to 1980. Long-term warming trends are expected to continue. However,
short-term variations to the expected longer-term warming trends should be
anticipated.
Geotechnical Exploration
A site exploration program was conducted by Miss Heather Brooks, E.I.T. of DMA
on May 12, 2009. A total of three test pits were completed with a CAT Excavator owned
and operated by Burnham Construction. Two of the test pits (TP-1 and TP-2) were
completed at the preferred location for the structure. These test pits were completed in
an area previously cleared and graded. One test pit (TP-3) was completed at an
alternative building location. While test pits TP-1 and TP-2 were advanced in a recently
re-vegetated area, test pit TP-3 was advanced in a cleared, gravel area with sparse
surface grass cover. All test pits were completed to 14.5 feet below ground surface.
Disturbed but representative soil samples were collected from the excavator bucket and
Biomass Boiler Building
August 17, 2009
Page 3
-----------·-------------------------
Duane Miller Associates LLC
visually classifed in the field. Representative portions of select soil samples from each
test pit were double-sealed in polyethylene bags to preserve natural moisture content
and shipped to the DMA laboratory in Anchorage for further analysis.
Subsurface conditions at test pits TP-1 and TP-2 consisted of six inches of organic
mat and organic silt. Underlying the silt in both test pits is a sandy gravel with
subrounded cobbles to the depth explored. Test pit TP-3 is located in the shoulder of an
existing roadway and no surface organics were observed. The uppermost five feet of
test pit TP-3 is a sandy gravel fill overlying the in-situ sandy gravel with cobbles to the
depth explored. Particle size differences were used delineate granular fill from in-situ
sand and gravel in test pit TP-3.
Layers of frozen soil were encountered in test pit TP-1 from four to five feet below
grade. This frozen soil is considered seasonal frost. Frozen soil was not encountered in
test pit TP-2. In test pit TP-3, frozen soil was encountered from four to at least 14.5 feet
below grade, the limit of the excavation equipment. Though not confirmed, the
observed frozen soil encountered in test pit TP-3 is considered seasonal frost. The
deeper seasonal frost penetration encountered in test pit TP-3 can result from the
removed surface organic mat, a relatively thick layer of low moisture content granular
soil, and the area being cleared of snow and other surface insulation during the winter.
A hand slotted l-inch PVC standpipe was installed in each test pit to
approximately 14.5 feet below grade for measuring the groundwater level. Prior to
backfilling test pits TP-1 and TP-3, some minor seepage was observed above the frozen
soil. A day after installation water levels were measured with no measurable water
observed in the standpipes.
A Dynamic Cone Penetrometer (DCP) field test was conducted at a depth of five
feet below grade in test pit TP-2. The DCP measured the number of blows required to
advance a conical tipped rod into undisturbed soil using a 16.2-pound hammer falling
22.6 inches. The DCP procedure relates penetration energy (blows) to rod penetration
length, converted to a California Bearing Ration (CBR). In general, the greater the
penetration energy I depth ratio, the stiffer I denser the subgrade soil. At test pit TP-2, 24
blows for 3 inch rod penetration was recorded. This field ratio converts to a
Biomass Boiler Building
August 17, 2009
Page4
~-~-~-----------·----
Duane Miller Associates LLC
comparative CBR of 80. For reference, a CBR of 100 is defined as well compacted,
crushed rock aggregate. The CBR of 80 is larger than expected for the observed soil and
may be the result of the cone lodging against cobbles or coarse gravels.
Laboratory Testing
Soil samples were re-examined in the laboratory to confirm visual field
classifications. Select representative samples were tested for natural moisture content
and grain-size distribution. Soils were classified according to the Unified Soil
Classification System (USCS). The results of laboratory testing are presented on the test
pit logs (Plates 2 to 4) and the Summary of Samples, Plate 6. DMA' s soil classification
key is presented on Plate 5. Particle size distributions are summarized on Plate 7.
Recommendations
Based on our understanding of the structural design and building layout,
continuous and isolated reinforced concrete spread foundations with a concrete floor
slab are considered appropriate for the proposed structure. The 12 foot vertical
subgrade wall at the fuel storage basement will incur additional lateral load from
trucks I trailers delivering wood chips to the facility. DMA has developed the following
geotechnical recommendations for site grading, the reinforced concrete foundation, and
the concrete slab-on-grade floor.
Site Grading
Site grading appears necessary for the structure. Based on site development plans,
the organic soil, debris, unclassified fill, and inorganic silt must be removed within the
proposed building footprint. Any fill within the foundation footprint without reliable
placement and compaction records should also be removed to in-situ soil. Over-
excavation of unsuitable material at the project site should extend at least five feet
laterally from the exterior of the proposed foundation footprint. The perimeter and
interior building foundations must extend beneath the silt and be founded on a
minimum of six inches of compacted non-frost susceptible (NFS) fill placed on the in-
situ granular soil. If the over-excavation of unsuitable material extends below the
Biomass Boiler Building
August 17, 2009
PageS
-------------
Duane Miller Associates LLC
design grade for foundation support, NFS fill should be used to achieve the appropriate
grade.
Exposed sub grade soil must be fully thawed, scarified, and moisture-conditioned
to facilitate compaction using vibratory compaction equipment. The soil exposed at the
foundation over-excavation grade should be proof-compacted to at least 95% of the
maximum dry density as determined by the modified Proctor test method, ASTM
D-1557. If soft or yielding soil is encountered during proof compacting, these areas
should be over-excavated and replaced with compacted NFS fill. If wet spots are
present that "pump" during compaction, the wet material should be over-excavated,
replaced with NFS fill, and compacted as recommended above.
The NFS fill should consist of a fully thawed, cohesionless, well graded sand and
gravel mixture with low fine content conforming to Alaska Department of
Transportation and Public Facilities (ADOT&PF) Subbase" A" specification. The NFS
fill should be placed in a fully thawed state in nominal 12-inch lifts. Each lift should be
compacted to at least 95% of modified Proctor maximum dry density using heavy
vibratory roller compaction equipment prior to placement of subsequent lifts. Nominal
6-inch lifts are recommended if using hand operated vibratory compaction equipment.
At least one field density test per fill lift should be conducted under load bearing areas.
Foundation Design
The building loads can be supported on continuous perimeter and isolated interior
square foundations that bear on properly compacted NFS fill placed on the proof-
compacted in-situ granular soil. Based on the reviewed site geotechnical data,
continuous perimeter foundations should be founded at least 42 inches below the
exterior finish grade in heated structures. Isolated interior foundations not exposed to
temperatures below 32°F should be founded at least 12 inches below the base of the
concrete slab. Continuous strip foundations should be at least 18 inches wide and
isolated square foundations should be at least 24 inches wide. Foundations installed as
recommended above can be designed for an allowable bearing pressure of 4,000 pounds
per square foot (psf) for dead plus sustained live loads. This allowable bearing pressure
Biomass Boiler Building
August 17, 2009
Page6
Duane Miller Associates LLC
can be increased by one third (1 I 3) to accommodate short term transient loading
conditions.
We have assumed the structure will be heated throughout its design life. Normal
heat loss through the slab-on-grade floor and fuel storage basement should prevent the
soils from freezing beneath the building foundations. The perimeter foundation walls
should be insulated along their entire exterior faces with 2 inches of 40-pound per
square inch (psi) compressive strength extruded or expanded polystyrene insulation.
The perimeter foundation wall insulation should be continuous with the above-grade
building insulation. The above grade portion of the polystyrene insulation should be
protected from ultraviolet light and damage. We have assumed waterproofing along
subgrade foundation wall will be addressed by the civil design team.
If unheated foundations such as isolated, exterior column supports are expected,
specialized cold foundations be warranted to reduce seasonal frost impacts. A variety
of cold foundation options may be suitable for this site, including driven pile, insulated
shallow foundation, and helical anchor (screw pile). We should be contacted if cold
foundations are anticipated for this project.
Exterior backfill along perimeter foundation walls should be NFS fill compacted to
95% of maximum dry density as determined by ASTM D-1557, modified Proctor. Along
the slab-on-grade areas, the foundation wall backfill should be placed and compacted in
a balanced manner along the interior and exterior portion of the foundation wall. The
fuel storage basement walls will require unbalanced backfill and should be designed to
permit vibratory compaction to achieve the recommended 95% of maximum dry
density compaction. This compaction level is recommended along the fuel storage
basement walls to accommodate truck/ trailer access.
If the foundations are constructed as recommended above, estimated total
settlement will be less than one inch. The majority of the settlement will occur as the
loads are applied (elastic settlement). Post-construction differential settlements are
expected to be less than 0.5 inch. Subsurface utilities or appurtenances attached to the
building should be designed to allow for the differential movement.
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August 17,2009
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Duane Miller Associates LLC
Lateral loading along subgrade walls is related to two loading conditions; active
soil pressures from subgrade wall backfill and shorter-term surcharge loading from fuel
(wood chip) truck/ trailer delivery.
Lateral loads can be resisted by friction on the base of the foundations and by
passive pressures against the faces of the foundations and foundation walls under the
slab-on-grade sections. The frictional resistance can be calculated as 0.35 times the
vertical dead load on the foundation. The active pressure per unit length of the
foundation wall can be calculated as a triangular distribution (method of equivalent
fluid pressure) of 30xH psf, where His the depth below the finish grade in feet The
passive pressure per unit width of the foundation wall can be calculated as a triangular
distribution of 300xH psf. The uppermost 12 inches of soil should be ignored in
calculating H for the passive case. Factors of safety have not been applied to these
equivalent fluid pressures. The above earth pressures assume a flexible subgrade wall
that will permit mobilization of the soil section to develop the active and passive state
pressures. Also, these earth pressures do not include surcharge loading.
Surcharge loading is expected along the wood chip storage area subgrade walls.
Three axle loading conditions were considered to determine the active lateral pressures
acting on the wood chip storage area subgrade walls resulting from surcharge loads:
~ Single axle, 16,000 pound axle load
~ Tandem axle, 23,000-pound axle load (expected maximum wood chip load)
~ Tandem axle, 32,000-pound axle load
For all three loading conditions, the axle load is modeled as a line load as the axle
load divided by an assumed wheel-to-wheel length of seven feet. For the tandem axle
configurations, the surcharge load is modeled as a single line load bisecting the tandem
axles. For the single axle configuration, the line load is assumed to act three feet from
the building wall. For the tandem axle configuration, the line load is assumed to act
five feet from the building wall.
We have assumed the subgrade wall for the wood chip fuel storage area is 12 feet
below finish exterior grade. The additional active pressures for the three loading
conditions are summarized in the following plot. The lateral loads developed by the
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August 17, 2009
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Duane Miller Associates LLC
surcharge should be combined with the equivalent fluid pressures to determine with
full lateral loading on the subgrade walls in the fuel storage area. As with the
equivalent fluid active pressure case, the surcharge derived lateral loads are unfactored.
Surcharge Lateral Loads
(due to the wood chip fuel truck/ trailer)
Lateral Load (psf)
0 50 100 150 200 250 300 350 400 450
0+·~--~~::~~-~~--~,
2
-X-Single Axle, 16,000-lb Load
12 -o-Tandem Axle, 23,000-lb Wood Chip Load
-+-Tandem Axle, 32,000-lb Load
14
Based on the site exploration completed in May 2009, groundwater should be
below the foundation bearing and over-excavation depths. If shallow groundwater is
encountered during foundation construction, dewatering may be necessary and
foundation drainage systems may be necessary. We should review our foundation
recommendations if shallow groundwater is encountered during construction.
Biomass Boiler Building
August 17, 2009
Page 9
Slab-on-Grade Floor
Duane Miller Associates LLC
The site grading work discussed previously for the building footprint area will be
suitable support for a concrete slab-on-grade floor. All organics and silt should be
removed and the excavation extended to at least six inches below the base of the slab
area, backfilled with NFS fill and compacted as discussed above for the building
foundations. The surface of the in-situ granular soil under the slab fill should be proof-
compacted with vibratory compaction equipment to detect soft or yielding areas. Soft
or yielding areas should be removed and backfilled with NFS fill as discussed
previously.
Seismic Design Criteria
Based on the observed and expected site soils, the seismic site class is considered
Site Class "D", relatively dense soils with an average "N" value greater than 15 and less
than 50 in the upper 100 feet, per IBC 2006, Section 1615.1.1. The site seismic design
criteria are based on a mapped spectral response acceleration for short period (Ss) of
0.63g and a mapped spectral response acceleration for a 1 second period (51) of 0.49g
for Site Class D.
Site coefficient factors Fa and Fv of 1.45 and 1.87, respectively, are considered
appropriate for this project. Based on these values, the design spectral response
acceleration for short period and a 1-second period can be determined using the
following equations:
Sos = 2/3FaSs and Sm = 2/3FvSl
Sos = 0.42g and S m = 0.33g
Liquefaction of saturated fine-grained soil may occur during seismic events. The
local groundwater level at the proposed site was not encountered and is expected to be
40 feet below grade at the site. The density of the sand and_ gravels with depth is
assumed to be medium dense to dense. Based on the expected sand and gravel and the
groundwater depth, liquefaction potential is considered low for this site.
Biomass Boiler Building
August 17,2009
Page 10
Shallow Frost Protected Foundation Option
Duane Miller Associates LLC
Within the areas of the continuously heated building footprint where a slab on
grade floor is proposed, a frost protected thickened slab foundation can be utilized in
lieu of a continuous spread foundation, provided additional subgrade insulation is
used. A frost protected foundation should not be used along the wood chip storage
area.
The Revised Builder's Guide to Frost Protected Shaliow Foundations provides a
recommended heated building system for seasonal frost areas, such as Tok. The
Builder's Guide has been developed in accordance with the American Society of Civil
Engineers (ASCE) Chapter 32 and is referenced in the 2006 IBC. The recommended
foundation system relies on both vertical and horizontal subgrade foundation
insulation. The vertical section of subgrade insulation should be similar to our
recommendation for subgrade walls, but possibly thicker. The horizontal insulation
section extends outward from the base of the vertical insulation forcing the frost line
away from the perimeter foundation. If requested, DMA can provide recommendations
for frost protected shallow foundations for the proposed development for consideration
by the design team and the owner.
Review and Field Quality Control
The plans and specifications should be reviewed by DMA to verify they are in
accordance with the intent of our recommendations. The over-excavation of subgrade
soil, the placement and compaction of NFS fill, and the construction of the foundations
should be observed and tested by an experienced engineer or materials technician. In
particular, the exposed base of the excavation should be carefully inspected for
unsuitable materials before new NFS fill is placed.
Based on limited grain size distribution analyses, the in-situ sand and gravel near
the foundation elevation is considered NFS material per the U.S. Army Corps of
Engineers Frost Design Soil Classification System. The NFS classification is based on
assumption that 50% (by mass) of the material passing the U.S. No. 200 sieve size will
pass the 0.02-mm grain-size. The open excavation should not be allowed to freeze
Biomass Boiler Building
August 17, 2009
Page 11
Duane Miller Associates LLC
within the building footprint and earthwork construction should be scheduled
accordingly. If necessary, temporary heat may be necessary to prevent freezing of the
soil beneath foundations and slabs until reliable permanent building heat is operational.
The compaction of the in-situ soil and fill should be tested and recorded as part of
the construction as-built record. Field quality control will permit the detection of
unanticipated conditions and allow verification that the work was completed in
accordance with the intent of our recommendations.
If you have any questions regarding our geotechnical engineering
recommendations, please feel free to contact us.
Respectfully submitted,
Duane Miller Associates LLC
Attachments:
Plate 1: Site Map
Plates 2 to 4: Test Pit Logs
Plate 5: DMA Soil and Ice Classification Key
Plate 6: Summary of Samples
Plate 7: Particle Size Data
Plate 8: Representative Site Photographs
LEGEND ~ TEST PIT LOCATiON NOTES: 1. Adapted from aerial photograph from Google Earth. 2. Test pit locations are approximate Duane Miller Associates LLC Job No.: 4276.001 Date: August 2009 SITE MAP Biomass Boiler Building Tok, Alaska Plate 1
DUANE MILLER ASSOCIATES LLC
Project: Tok Biomass Project
DMA Job No.: 4276.001
Logged By: Heather M. Brooks
Moisture Content% (e),
PL & LL (H),Salinity (.6)
and Sampling Blows/It (0)
0 20 40 60 >80 P200
'
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: '
•
••
Other
Tests
Duane Miller Associates LLC
Job No.: 4276.001
Date: August 2009
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Log of HOLE: TP-1
Date Drilled: May 12,2009
Contractor.: Burnham Construction
Equipment: CAT Turbo Excavator
GPS Coord.:N 63°19'42.26" W 142°58'48.17" (WGS84)
Description
PEAT (Pt) Dark brown fibrous organics
SANDY GRAVEL (GP) 60-35-5 Brown subrounded
to rounded gravel and cobbles to 6 inches with
medium to coarse sand
slight seepage observed into excavation above
frost
Test pit completed to 14.5 feet on 5/12/09. Hand
slotted 1-inch PVC was inserted to 12.7 feet for
groundwater monitorin!l
LOG OF TEST PIT TP-1
Tok Biomass Site
Plate
2 Tok, Alaska
DUANE MILLER ASSOCIATES LLC
Project: Tok Biomass Project
DMAJob No.: 4276.001
Logged By: Heather M. Brooks
Moisture Content% (e),
PL & LL (H),Salinity (6)
and Sampling Blows/fl (0) Other
o 20 40 60 >80 P200 Tests
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!; .••..•..•.•.•••.•.•..•.•..•••..•• , .••..••..•.. Job No.: 4276.001
Date: August 2009
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Log of HOLE: TP-2
Date Drilled: May 12, 2009
Contractor.: Burnham Construction
Equipment: CAT Turbo Excavator
GPS Coord.: N 63°19'41.96" W 142°58'43.75" (WGS84)
SANDY GRAVEL (GP) 70-25-5 Brown, moist,
subrounded to rounded gravel and cobbles to 6
inches with medium to coarse sand
decreased moisture content, gray color at 4 feet
Dynamic Cone Penetrometer Test at 5 feet 24
blows per 3 inches results in CBR of 80
larger cobbles observed to 8 inches
Test pit completed to 14.5 feet on 5/12/09. Hand
sloUed 1-inch PVC installed to 14.4 feet for
groundwater monitorin9.
LOG OF TEST PIT TIP-2 Plate Tok Biomass Site 3 Tok, Alaska
DUANE MILLER ASSOCIATES LLC
Project: Tok Biomass Project
DMA Job No.: 4276.001
Logged By: Heather M. Brooks
Moisture Content% (e),
PL & LL (H),Salinity (6)
and Sampling Blows/ft (0)
0 20 40 60 >80 P200
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Other
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t--~:-2~ Duane Miller Associates LLC
Job No.: 4276.001
.................. ~
Date: August 2009
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Log of HOLE: TP-3
Date Drilled: May 12,2009
Contractor.: Burnham Construction
Equipment: CAr Turbo Excavator
GPS Coord.: N 63°19'40.96" W 142°59'1.39" (WGS84)
Description
SANDY GRAVEL (GP) FILL 55-40-5 Brown, moist,
medium to coarse sand with subrounded to
rounded wavel to 4 inches
SANDY GRAVEL (GP) 70-30-0 Gray, moist,
subrounded to rounded gravel and cobbles to 6
inches with medium to coarse sand
standing water observed at base of test pit
Test pit completed to 14.5 feet on 5/12/09. Hand
slotted 1-inch PVC inserted to 14.5 feet for ground
water monitoring.
LOG OF TEST PIT 'TP-3
Tok Biomass Site Plate
4 Tok, Alaska
MAJOR DIVISIONS SYMBOL TYPICAL NAMES
E GW ":·•·! Well graded gravE1Is,
E GRAVELS Clean gravels with ,;:·,:·: sandy gravel
l{) little or no fines I'-~:,::: Poorly graded 0 More than half of the GP en· ·:·•·! gravels, sandy gravel _.o_ coarse fraction is -w larger than #4 sieve l Silty gravels, silt sand C> GM fn.!!? size,> 4.75 mm. Gravels with more gravel mixtures U)
Co than 12% fines ~ Clayey gravels, clay wo
ZC\1 GC sand gravel mixtures -"*' ~~ --
CJ~ Clean sands sw ~-.:.:.: :·.: Well graded sand,
ww SANDS with little or no :.:=~!:.:: gravelly sand
tne' ........ Poorly graded a:.!ll More than half of the fines SP );(:.: CCw coarse fraction is sands, gravelly sand co smaller than #4 si1eve Silty sand, silt gravel (,)E SM 0 size,< 4.75 mm. Sands with more sand mixtures
-;!!_ than 12% fines h/ --
0 sc Clayey sand, clay 0
l{) gravel sand mixtures . .
ML I Inorganic silt and very
SILTS and CLAYS fine sand, rock flour
0~ Liquid limit less ~ Inorganic clay, gravelly and ....1.!!1 CL -oo flaslicill£ Cba[l than 50 sandy clay, silty clay Co 0o Organic silts and clay of QC\1 X 4Q OL I I
w"*' Q) CH I I low plasticity z~ "0 ---..c: .s / cc-~ CL MH Inorganic silt a:Q; :S2 20 / CJ.§ U5 ~I ~ MH Liquid limit greater W-:!!_ 0:: ;:::::=::=7 CH Inorganic clay, fat clay z~ ML than 50
ii:l{) 0 :I 1\ 0 50 OH I Organic silt and clay of
Liquid Limit I high plasticity
HIGHLY ORGANIC SOILS Pt ~ Peat and other highly
~ organic soil
UNIFIED SOIL CLASSIFICATION SYSTEM_
GROUP ICE VISIBILITY DESCRIPTION
Segregated ice not
Poorly bonded or friable
N visible by eye I No excess ice
Well bonded I Excess microscopic ice
Segregated ice is Individual ice crystals or inclusions
visible by eye and Ice coatings on particles v is one inch or less
in thickness Random or irregularly oriented ice
Stratified or distinctly oriented ice
Uniformly distributed ice
Ice greater than one Ice with soil inclusions
ICE inch in thickness
Ice without soil inclusions
ICE CLASSIFICATION SYSTEI\4.
KEY TO TEST
DATA
PP = Pocket Penetrometer
Dd = Dry Density (pcf)
LL = Liquid Limit
PL == Plastic Limit
PI == Plastic Index
NP =non Plastic
SpG = Specific Gravity
SA == Sieve Analysis
MA = Sieve and
Hydrometer Analysis
OLI = Organic Loss
RD = Relative Density
D1557 = modified Proctor
TS = Thaw Consolidation
Con = Consolidation
TXULJ =Unconsolidated
Undrained Triaxial
TXCU = Consolidated
Undrained Triaxial
TXCD = Consolidated
Drained Triaxial
Strength Data
XXX(YYY), where
XXX = ( CJ 1 -u3)/2
yyy = CJ3
KEY TO
SAMPLE TYPE
Gr= Grab sample
Ag =Auger grab
Ab =Auger bulk
Ac =Air chip
Sh = 2.5" ID split
barrel w/ 340 lb.
manual hammer
Sh* == 2.5" ID split
barrel w/140 lb.
manual hammer
Sha== 2S ID split
barrel w/ 340 lb.
automatic hammer
Tw = Shelby tube
Ss = 1.4" ID split
barrel w/140 lb.
manual hammer
Cc = 3.25" continuous
core barrel
SYMBOL
Nf
I Nbn Nb I Nbe
Vx
Vc
Vr
Vs
Vu
ICE + soil type
ICE
~""'!'!r..,.!"'' Duane Miller Associates LLC SOIL & ICE CLASSIFICATION DATA KEY
Tok Biomass Site
Plate
Job No.: 4276.001
Date: August 2009 Tok, Alaska 5
Sample Mlllype ~ampler ~ampHng !Vlmsture Passmg
Test Hole Depth (USCS) Thermal State Type Blows/ ft Content Salinity Gravel% Sand% #200
TP-2 3.0 ft. GP Unfrozen 2.8% 70% 29% 1.4%
TP-2 5.5 ft. GP Unfrozen 1.6% 53% 46% 0.7%
TP-2 10.0 ft. GP Unfrozen 1.2% 64% 36% 0.3%
TP-3 2.0 ft. GP Unfrozen 4.7%
TP-3 8.5 ft. GP Unfrozen 6.5%
Duane Miller Associates LLC Summary of Samples Plate
!i: •••. ,i•······~ ·····. Job No.: 4276.001 Tok Biomass Building 6 i Date: August 2009 Tok, Alaska
100
Boring=>
Depth=>
3" =>
1.5" =>
3/4" =>
3/8" =>
#4 =>
#10 =>
#20 =>
#40 =>
#60 =>
#100 =>
#200 =>
Analysis of Data
D10 size=>
D30 size=>
D50 size=>
D60 size=>
Coeff. of Uniformity, Cu =
Coeff. of Curvature, Cc =
Gravel (+#4) percentage=
Sand percentage =
Fines percentage =
Unified Soil Class Symbol =
10
-<>-TP-2@3.0ft.
Duane Miller Associates LLC
Job No.: 4276.001
......,_.....,.......,Date: August 2009
TP-2 TP-2 TP-2
3.0 ft. 5.5 ft. 10.0 ft.
100% 100% 100%
92% 100% 93%
61% 81% 60%
41% 62% 46%
30% 47% 36%
23% 36% 30%
20% 27% 23%
12% 10% 7%
6% 2% 1%
3% 1% 1%
1.4% 0.7% 0.3%
0.359 mm 0.429 mm 0.477 mm
4.655 mm 1.153 mm 1.901 mm
13.018 mm 5.453 mm 11.707 mm
18.313 mm 8.671 mm 18.800 mrn
50.95 20.19 39.39
3.29 0.36 0.40
70% 53% 64%
29% 46% 36%
1.4% 0.7% 0.3%
GP GP lit-'
0.1
Grain Size (mm)
-D-TP-2@5.5ft. --n-TP-2@ 1 O.Oft.
Particle Size Distribution
Tok Biomass Building
Tok, Alaska
100%
90%
80%
70% Dll c ·u;
60% (I) • 0.
IV
50% m
IU ...
40% {i
~
IV
30% 0.
20%
10%
0%
0.0"1
Plate
7
PHOTO 1: Typical upper soil profile in test pits 1 and 2.
PHOTO 2: Typical cobble size.
Duane Miller Associates LLC
Job No: 4276.001
Date: August 2009
SITE PHOTOGRAPHS
Tok Biomass Site
Tok, Alaska
Plate
8