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HomeMy WebLinkAboutSoils Report - GEO General - 4/13/1993 S O=L S S NVE S T=GAT=ON REPORT F O R THE NEW FAC =L=TY P E N I N S ULA C OMMUN I TY C RE D=C T UNION B E L FA=R � WAS H I NGT ON Bradley-Noble Geotechnical Company 2401 Bristol Court S.W. • P.O. Box 10267 • Olympia, WA 98502 • Phone (206) 357-7883 Bradley-Noble Geotechnical Company Soils Engineers and Geologists Testing and Inspecting Services SOILS INVESTIGATION REPORT FOR THE NEW FACILITY PENINSULA COMMUNITY CREDIT UNION BELFAIR, WASHINGTON This report presents the results of our subsurface investigation for the new Peninsula Community Credit Union site in Belfair, Washington. Our purposes in exploring the subsurface soil conditions were to evaluate bearing capacity of the site soils , to present recommendations for foundation design, and to address other geotechnical considerations for this project. We understand that the building will be a single-story structure, probably using wood framing and having a footprint of about 2500 square feet. We expect that a vault will be included in the design, either a cast-in-place vault or one of modular construction. We also expect that exterior wall loads will be carried on continuous perimeter footings, column loads on isolated footings, and that strip footings will be used for carrying interior bearing wall loads . Parking areas and driveways will occupy the most of Lot 2 not under the structure. Work was authorized on behalf of the owner by Mr. Mike Phifer, Principal of Phifer Design. A preliminary report was issued on 1 May 1993 which included the site sketch showing boring locations and the boring logs . The project was placed on hold until various concerns of the credit union could be resolved about this site. We recently received authorization to complete the work and prepare a final geotechnical report for this project. SITE CONDITIONS Surface Conditions The property fronts on State Highway 3 in Belfair and is located east of this highway. It slopes from east to west; the slope is gentle in the eastern half and moderate in the western half . A steep transition of about 4 to 5 feet is found at the west property line adjacent to State Highway 3 . Parcel 2 , where the construction is proposed, appeared 93040503 Page 1 of 8 2401 Bristol Court S.W. • P.O. Box 10267 9 Olympia, WA 98502 • Phone (206) 357-7883 93040503 Page 2 of 8 to have been recently cleared. The surface is disturbed only by low weeds in patches . There is a debris pile in the southwest corner of the site . We found the surface to be rutted in the western half of the lot, with water standing in the ruts on the lower western side. At the time of our site exploration, we observed indications that high seasonal water tables may be encountered at this site. There is a wetland area to the east of the east property line. Parcel 1 to the north had vegetation indicative of year around wet soil conditions . There was slowly flowing water on the surface. Flows of surface and ground water from these parcels was flowing into the catch basin on the east side of the frontage to Highway 3 . Volumes of water were estimated to be about 5 to 10 gallons per minute. Subsurface Conditions On 16 April 1993, we explored the subsurface conditions by two test borings at locations indicated on the enclosed site plan. These explorations were made using a continuous-flight, hollow-stem auger to advance the borings and to provide borehole support between sampling intervals . Samples were obtained at standard intervals using a two-inch outside diameter, split-spoon sampler driven by a pin-guided, 140-pound weight free falling 30 inches . The blows per six-inch interval were recorded. The first six-inch drive interval is allowed for seating the sampler. The blow counts for two six-inch intervals, when combined, yield the Standard Penetration Resistance (N-value) of the soils encountered in the sample interval . The number of blows required to drive the sampler the last 12 inches provides a measure of the relative density of granular soils or the consistency of cohesive soils . The results obtained from the Standard Penetration Test, along with other tests and engineering judgments, were used to develop the recommendations of this report . In general, we found the upper 3 to 4 .5 feet of soil to be a loose, organic-rich, black, silty sand with small scattered gravels . Underlying this topsoil 93040503 Page 3 of 8 unit, we found dense silty sands, silty sandy gravels, and sands . In Exploration Two, in the lower, western portion of the property, the exploration extended through the soils associated with the Vashon recessional outwash deposits and terminated in what we interpret as silts probably deposited into a shallow freshwater lake which had formed on the Vashon recessional outwash plain and was subsequently covered with additional deposition outwash sands and gravels . High ground water levels were encountered in both explorations . We expect that during the dry season the apparent ground water level may fall . The piezometric surface was 3 . 8 feet below ground level in Exploration One at completion of the drilling and at -2 . 2 feet in Exploration Two at completion. This high ground water level and the clearing work had loosened and saturated the soils, and we had to extract the drill truck by winching from the site of Exploration Two. DISCUSSION AND RECOMMENDATIONS The high apparent ground water level at this site will affect site development work. We expect that the site will be graded to create a building pad that will minimize transition grades from Highway 3 onto the site. The ground water flowing downslope from the east will need to be intercepted and controlled. In our 1 May letter we recommend that a curtain drain be constructed as soon as possible to intercept this water and allow the site to dry. Once dry, it may be graded with standard construction equipment, and the soils exposed will be protected from loosening as a result of construction activity and soils that may be saturated or under hydraulic pressures . The upper topsoil unit offers poor support for foundations or paving sections . In our opinion, this material is not suitable for structural fill . It may be used as general fill outside of paving areas and for landscape use. The underlying soils are granular and are firm to dense. When protected from saturation, the firm to dense soils offer excellent support for standard spread footings and paving 93040503 Page 4 of 8 sections . We expect that site grading will expose these soils . If not, the upper layer of organic soil should be removed and replaced with compacted structural fill conforming to the Earthwork Criteria section of this report. After the soils have been uniformly densified by proof rolling to the minimum requirement of the Earthwork Criteria section, they may be used for support of footings and paving sections . Footings placed on the re-densified native soils exposed in the building pad may be designed using a bearing value of 2500 pounds per square foot. A one-third increase in this bearing capacity is allowable for short-term wind or seismic loadings . We recommend that the footing supporting the vault be isolated from the structure's footings to minimize differential settlements and reactions between the two units . Exterior footings should be founded a minimum of 18 inches below planned finish grade for frost protection and confinement. We recommend that continuous and strip footings have a minimum width of 16 inches . Isolated footings supporting column loads should have a minimum dimension of 3 . 0 by 3 . 0 feet square. Settlement of structures designed to the recommended bearing values and placed on soils prepared according to the recommendations of this report should not be significant. Generally, we expect that both differential and total settlements of 25 millimeters or less will occur, mostly during construction and immediately after the loads are imposed. There should be little long-term settlement. Floor Slabs A vapor barrier and capillary break should be installed between soil and the concrete slab to ensure dry slabs . For a capillary break, we recommend a minimum thickness of six inches of clean free draining sandy gravel or four inches of pea gravel or one-inch minus coarse concrete aggregate. The vapor barrier is to be installed between the capillary break and the concrete slab-on-grade. It should be a minimum of 8 mil PVC with all seams and penetrations sealed. Care should be taken during the casting of the slab to protect the vapor barrier from damage. 93040503 Page 5 of 8 Provisions should be included in the design to ensure the drainage of the capillary break section. Where mechanical penetrations extend through the vapor barrier, they should be sealed to maintain the integrity of the membrane. Paving Section Paving sections placed on the densified native soils below the topsoil unit may be designed to a CBR value of 20 . This design value requires that a uniform minimum density of 95% of ASTM D698 be achieved on the subgrade. Lateral Soil Pressures It is our understanding that no retaining walls or foundation walls restraining earth over four feet high are to be incorporated in the design. If walls meeting these criteria are to be built, we should be consulted for design information. Lateral loads may be resisted either by passive soil pressures or friction between the footings and earth. For passive soil pressures for footings cast and backfilled according to the Earthwork Criteria, a design value of 300 pounds per cubic foot may be used. A coefficient of friction of 0 . 45 is permissible between footings and native soils and slabs placed on select granular fill sections . Seismic Site Period The project area is in Seismic Zone 3 as shown by Figure 23-2 , Seismic Zone Map of the United States, in the 1991 edition of the Uniform Building Code . Actual ground motion during a seismic event is influenced by the distance from the epicenter, the depth to bedrock under the site, and the condition (degree of consolidation and saturation) of the soils supporting the structure. We do not believe that the underlying soils are prone to spontaneous liquefaction under seismic loadings . Available geologic information, as presented in Thickness of Unconsolidated Sediments, Puget Lowland, Washington by Hall and Othberg, 1974 , shows a sediment thickness of about 1800 feet under the project area. We believe that these soils are 93040503 Page 6 of 8 predominantly granular and are well consolidated as a result of loading by the Vashon glacial ice mass . We recommend that a soil coefficient type S2 be used for seismic design. Earthwork Criteria In areas under structures, paving sections, and sidewalks, strip all topsoil and organic material. For struct _111 in areas under footings and slabs-on-grade, we recommend that all soils be compacted to a minimum density of 90 percent of ASTM D-1557 . This includes proofrolling native soils exposed in the bottom of the excavation before placing fill . Materials under the paving section should also be compacted to the minimum density by proofrolling before placing the paving section. This includes proofrolling in-place soils, soils that have been disturbed during construction, and all structural fill materials . For imported structural fill, we recommend that a clean, six-inch minus, well graded gravel or gravelly sand (classifying as GW or SW as determined by ANSI/ASTM test method D-2487 ) , conforming to APWA specification 9-03 . 14 for gravel borrow, be used. We also recommend that no more than 7% by weight pass the number 200 screen as tested by ANSI/ASTM D-1140 test procedure. Other material may be used with the prior written approval of the soils engineer or engineering geologist. All fill should be placed in uniform horizontal lifts of six- to eight- inch- loose thickness . Each lift should be conditioned ed to the optimum moisture content and compacted to the specified minimum density before placing the next lift. We further recommend that all utility trench backfill be compacted as specified above. Earthwork should be performed under the continuous supervision and testing of Bradley-Noble_ Ge echnical Company to ensure compliance with the compaction requirements . Placement of fill sections on slopes greater that 4 : 1 (horizontal to vertical) will be benched as directed into the native soils . Height and width of the bench 93040503 Page 7 of 8 will be determined in the field by the soils engineer or engineering geologist. Unrestricted slopes shall not exceed 2 : 1 (horizontal to vertical) for fill embankments and cuts that expose native soils . All fill slopes will be rolled. The project's civil engineer is responsible for the protection of the constructed fill slopes from uncollected runoff . We recommend that all cut-and-fill slopes be seeded as soon as possible after construction, so that vegetation can protect the slopes from sheet washing. No fill is to be placed during periods of unfavorable weather or while the fill is frozen or thawing. When work is stopped by rain, placement of fill will not resume until the soils engineer or engineering geologist determines that the moisture content is suitable for compactive effort and that the previously placed fill has not been loosened. The contractor will take appropriate measures during unfavorable weather to protect the fill already placed. Measures that may be required include limiting wheeled traffic and grading to provide temporary drainage of the fill . At the direction of the soils engineer or engineering geologist, the contractor will be responsible for the removal and reworking of fill that has softened or has less than the required compaction. LIMITS OF LIABILITY BRADLEY-NOBLE GEOTECHNICAL COMPANY is responsible for the opinions and conclusions contained in this report. These are based on the data relating only to the specific project and locations discussed herein. This report was prepared within the standard and accepted practices of our industry. In the event conclusions and recommendations based on these data are made by others, such conclusions and recommendations are not the responsibility of the soils engineer or engineering geologist unless he has been given an opportunity to review them and concurs in such conclusions or recommendations in writing. The analysis and recommendations submitted in this report are based upon the data obtained in the 93040503 Page 8 of 8 explorations at the locations indicated on the attached plan. This report does not reflect any variations that may occur between these explorations . The nature and extent of variations between explorations may not become evident until construction is underway. Bradley-Noble is to be given the opportunity to review the final plans and specifications for soils work. This is to verify that our geotechnical engineering recommendations have been correctly interpreted and implemented in the final design and specifications . We also recommend that we be retained to provide geotechnical services during the foundation construction and trenching. These services would include review of backfill operations, excavations, and other geotechnical considerations that may arise during construction. We would observe compliance with the design concept and project specifications . If the subsurface conditions differ from those anticipated in our explorations, we would also evaluate changes in construction specifications . BRADLEY-NOBLE GEOTECHNICAL COMPANY Report prepared by: Reviewe c a d by: WA18 in David C. S rong J. Vi EjjAt � fd, D. , P.E. Engineering Geologist MC Squ ONA L 30 August 1993 Ex�g 1171 1 9 9s FROM PHIFER ASSOCIATE_ 05. 14. 19 C.S 7P ' PO4ZsVof r r ��1�Q Pavkt� ,• .�li �tfiCs �--- �i f e .�Ua�u�-{�t� 'f • !� •� j�►�Pc► ,i��wP �h o '4a f Q) BRADLEY-NOBLE GEOTECHNICAL, INC. JOB: FENNINSULA C,IVI WNITY G.U. 2401 BRISTOL COURT SW #C-5 JOB #: 55024--5 OLYMPIA, WA 98502 DATE: PHONE: (206) 957-7889 TESTING BY: DC5 / I •E-1 f'ROf=05ED BUILDING ®-•I`XPLORATION LOCATIONS L --- - - I SITE PLAN TtT S Bradley-Noble Geotechnical Company Soils Engineers and Geologists Testing and Inspecting Services GENERAL NOTES FOR SOIL INVESTIGATIONS CONDUCTED BY AUGERED BORINGS SAMPLE IDENTIFICATION All sample classifcations are reviewed by a soils engineer in accordance with the Unified Soil Classification System ASTM D-2487 . Field soil classifications are in accordance with ASTM D-2488 . SOIL PROPERTY SYMBOLS Dd: Dry density, pcf LL: Liquid limit PL: Plastic limit W : Moisture content qp: Penetrometer value, tsf qs : Vane-shear strength, tsf qu: Unconfined compressive strength, PI : Plasticity index tsf N: Penetration resistance per foot or fraction thereof, of standard 2-inch O.D. , 1 . 3-inch I .D. , split-spoon sampler driven with a 140-pound weight free falling 30 inches, in accordance with Standard Penetration Test Specifications ASTM D-1586 Apparent ground water level at the time noted after completion SOIL STRENGTH CHARACTERISTICS COHESIVE SOILS Unconfined Compressive Comparative Consistency Blows/Foot Strength (tsf) Very soft 0 - 2 0 - 0 . 25 Soft 2 - 4 0 . 25 - 0 . 50 Medium 4 - 8 0 . 50 - 1 . 00 Stiff 8 - 15 1 . 00 - 2 . 00 Very stiff 15 - 30 2 . 00 - 4 . 00 Hard 30+ 4 . 00+ NON-COHESIVE (GRANULAR) SOILS Relative Density Blows/Foot (N-Value) Very loose 0 - 4 Loose 4 - 10 Firm 10 - 30 Dense 30 - 50 Very dense 50+ DRILLING AND SAMPLING SYMBOLS SS: Split spoon DB: Diamond bit core AU: Auger sample CB: Carbide bit core WS: Washed sample RL: Ring-lined sampler TC: Tri-core drilling ST: Shelby tube - 3" O.D. (except where noted otherwise) 2401 Bristol Court S.W. • P.O. Box 10267 • Olympia, WA 98502 • Phone (206) 357-7883 BRADLEY-NOBLE GEOTECHNICAL, INC. JOB: PENNINSULA COMMUNITY C.U. 2401 BRISTOL COURT S1/ #C-5 JOB #:_S3.04-01 OLYMPIA, WA 88502 DATE: PHONE: (206) 357-7883 TESTING BY: DCS EXPLORATION NO. 1 0' _ EXISTING SURFACE ELEVATION BLOWS PER b" DRIVE USWCs A 2.0 INCH O.D. SPLIT SPOON SAMPLER -35' TO -45' OF LOOSE SLACK ORGANIC RICH SILTY, SMALL -3.8' v GRAVELLY SHAD -5. 21-5-20 FIRM SATURATED SILTY GRAVELLY SAND N■25 r0-13-18 DENSE SATURATED SILTY SANDY GRAVEL -10' N,31 S-I1-14 FIRM GREY COARSE WATER BEARING SANDS WITH SMALL -15' — N■25 3/8" - 1/2" MINUS GRAVELS BRADLEY-NOBLE GEOTECHNICAL, INC. JOB: PENNIN5LILA COMMUNITY CU. 2401. BRISTOL COURT SW #C-5 JOB #: 33.04-01 OLYMPIA., WA 98502 DATE: PHONE: (206) 357-7883 TESTING fiY: PCs EqXr."rLORATION NO. 2 0' _ EX15TING SUR=ACI= ELEVATION BLOWS PER fo" DRIVE USING A 2.0 INCH O.D. SPLIT SPOON SAMPLER -22 T- -2' TO -3' OF BLACK ORGANIC RICH SILTY 5AND WITH SMALL GRAVEL5 1-21-20 DENSE GREY SATURATED MEDIUM SAND -5' N-41 9-25-'1 DENSE GREY 5ATURATED SANDY GRAVELS OVER MEDIUM SAND N■32 4-3-4 L005E GREY PLASTIC SILT -15' NA7