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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 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 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 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 Page 5 ---------- 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 Page 6 -------------------- 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. Biomass Boiler Building August 17,2009 Page 7 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 Biomass Boiler Building August 17, 2009 Page 8 ---~------··----~---- 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 ' i : ' • •• Other Tests Duane Miller Associates LLC Job No.: 4276.001 Date: August 2009 Q) El c. § ~ 0 (jj u D. s E 0 ell iii Cl) - - - - 5 - - - - - 10 - - - - - 15 - - - - - 20 - - - - - 25 - - - - - 30- - - - - 35 - - - - - 40 - :~::.;;:~ ~-···.·· .·~·.• ~:j::,: :.~::.;;:~ ~·· ··.··• .·~·.• . ··.··.·· ~.·:-·.-· :.~::.;;:~ ~:~:·• ~:j::,: :~::.;;:~ ~:~:·• ~::j::,: :~::.;;:~ ~:~:·• ~::j::,: :~::.;;:~ ~:~:·• 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 ' •• • 1.4% ~ • 0.7% jl j : ~~· i . 0.3% :1 .. j I i i ,, :! I .... , ... Duane Miller Associates LLC !; .••..•..•.•.•••.•.•..•.•..•••..•• , .••..••..•.. Job No.: 4276.001 Date: August 2009 QJ 2l Cl. § ~ 0 Q; u a. S: E 0 <ll Ci.i (f) Gr Gr Gr co :;=--£:: QJ QJ m-LL.f ~ O)(f.) () a.:§~ :.c QJ Cl. Cl. Cl. o E E <ll Dl <ll<ll ~ 0 (f) (f) (!l_j 0 -:~:;~,: -~:~:-• ~-·jlt·:,. I :~:;.;;;,: -~::~:·• 5 -~::j::,: I ......... ~ ~.:·~·:. -.··~·:• ~-·jlt·:,. -:~:;.;;;,: -~:~:-• ....... 10 ""'[ ~.·jlt·:,. :~:;.;;;,: -~:~:-• -~-·jlt·:,. -: .... :;.;;;,: -~:~:-• 15- - - - - 20 - - - - - 25 - - - - - 30 - - - - - 35 - - - - - 40- c: QJ N 2 lL 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 I :: I • I :: • : I . ! i : I !, •• i I I I : I 1: I I Other Tests t--~:-2~ Duane Miller Associates LLC Job No.: 4276.001 .................. ~ Date: August 2009 Cll .l!l 0. § ~ 0 (jj u (i ;;: E 0 <ll as (fJ Gr Gr 15- - - - - 20 - - - - - 25 - - - - - 30 - - - - - 35 - - - - - 40- 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