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HomeMy WebLinkAboutSubsurface Soils Investigation - BLD Engineering / Geo-tech Reports - 12/7/2000 Subsurface Soils Investigation 9421 SR 106 Mason County, WA Prepared for David Vandervort Architects by Geotechnical Testing Lab Olympia, WA Dec. 7, 2000 INSPECTION&TESTING SERVICES SPEARS GEOTECHNICAL ENGINEERING CONSTRUCTION MATERIALS ENGINEERING ENGINEERING & CONSTRUCTION/PROJECT MANAGEMENT SPECIAUZING IN ROADS&BRIDGES TECHNICAL I-MP://WWW.SPEAIZS-ENGINEERING.COM SERVICES GEOTECHNICAL TESTING LABORATORY 10011 Blomberg Street SW Olympia, WA 98512 ATTN: MR. HAROId PARKS RE: FOUNdATION ANd SODS ANAtySIS PROjECT: 942 1 SR 106, MAsoN CouNTy DATE: 1 2/06/00 Gentlemen; As per your request, SETS senior engineer has reviewed the above referenced report prepared by your firm. The exploration and analysis of the project site reported therein are considered sufficient in detail and scope to form a reasonable basis for the recommendations as put forth in the report. The soils engineer warrants that our review of the findings, recommendations, specifications, or professional advice contained therein, have been promulgated after being prepared according to generally accepted professional engineering practice in the fields of foundation engineering, soil mechanics and engineering geology. No other warranties are implied or expressed. Any revision in the plans for the proposed structure from those enumerated in the report should be brought to the attention of the soils geologist and/or soils engineer so that they may determine if changes in the recommendations made in the report are required. If deviations from the noted subsurface conditions are encountered,they should also be brought to their attention. If you have any questions concerning the above items,the procedures used,or if SETS can be of any further assistance please call on us at(253)833-7967. Respectfully Submitted, SPEARS E GINEERING &TECHNICAL SERVICES NK Sp� _ � F WASH_ �P J. Frank Spears,P.E. President cFn t 27595 j FtPfRF.S P.O.Box 1007 PHONE: (253) 833-7967 Report#96007-029 AUBURN,WASHINGTON 98071-1007 FAX: (253)735-2867 Page 1 of 1 G EOTECIINICAL TESTING LABORATORY DAVID VANDERVORT ARCHITECTS 5135 BALLARD AVE. NW SEATTLE, WA 98107 Attn: Mr. Mark Wierenga Re: Report-Soils and foundation investigation 9421 SR 106 Mason County,WA Gentlemen: This letter presents the results of our soils and foundation investigation at the above referenced site. The existing site is located on a lot on the south side of Hood Canal in Mason County,Washington. Authorization to proceed in accordance with our proposal to you was received in November,2000. We understand that the proposed structure will be a garage of wood frame construction with an apartment above. It is anticipated that the second floor will be expanded,thereby increasing its square footage. SUBSURFACE EXPLORATION PROGRAM The subsurface exploration program consisted of excavating and logging four test pits through the building and garage areas, making a reconnaissance of the site and adjacent areas,and reviewing information from our files. The test pits ranged in depth from four to six feet. All test pit locations were selected by our engineering geologist in consultation with our senior engineer. The soils exposed in the test pits were logged by an engineering geologist from our office who examined the soils exposed and evaluated the difficulty of excavating the soil as an indication of its relative density. The soil strata shown on the test pit logs were observed at spot locations across the site. Actual subsoil conditions between test pit locations and exposed in excavations may vary from those shown on the test pit logs. The test pit logs are presented in the Appendix. Test pit locations are shown on the Site Plan in the Appendix. SURFACE AND SUBSURFACE SOIL CONDITIONS The lot has a gentle relief but very minimal building space from SR 106 to the shoreline. It has been previously graded and used as a garage and yard area with a bulkhead and rockery constructed along the shoreline. The fill material imported for backfill behind the bulkhead is similar to the native soil. The existing home was built on pile supported on concrete pads. Little is known of the original site topography. It appears that the area was possibly filled with material from the south side of SR 106 when the highway was originally built. Test pit information indicates that there is localized fill of up to about five ft. in thickness. All fill appears to be composed of native material, i.e. brown gravely sand ranging from medium dense to dense.Beneath the native brown colored soils,the materials are light brown sandy gravels to sand and gravel in a dense to very dense condition. All soils encountered in the test pits below three feet were found to be in a moist condition. No groundwater was observed in any of the excavations but could be expected when high tide occurs. 10011 Blombere Street SW.Olvmoia.WA 98512 G E0TECBMCAL TESTING LABORATORY RECOMMENDATIONS GENERAL Based on our knowledge of the site conditions and observations made during our field work,we believe that the site can be satisfactorily developed as planned. The major earthwork considerations will be the placement of pin pile to support the foundation. SITE,GRADING AND PREPARATION Pavement, fill and building areas should be stripped of unsuitable existing fill,debris,or organic materials. Stripping to depths of a foot or less should be satisfactory for most of the site. Stripped soils should be wasted or used in landscape areas. Following the stripping and excavation of the site,the exposed subgrade should be thoroughly compacted so as to achieve a minimum of 95%of the maximum dry density as determined by ASTM D-1557 for a depth of at least 12 inches. Areas which are to be filled to bring the grades up to the desired elevation should then be filled with compacted granular material free from roots,trash,or other deleterious materials. If grading is necessary during wet weather,we recommend that free draining sand and gravel with not more than 5.0%fines(material passing a U.S.No.200 sieve)be imported for use as fill. All structural fill(fill below the building or paved areas)should be placed in layers approximately 12 inches in thickness, conditioned to a moisture content suitable for compaction,and compacted to 95%of the maximum dry density as determined by ASTM D-1557. Fill other than structural fill should be placed in layers of appropriate thickness,conditioned to the proper moisture content for compaction,and compacted to a minimum of 90%of the maximum dry density. To preclude the possible build-up of groundwater or storm runoff in the soils adjacent to the buildings, it is recommended that a four inch diameter perforated pipe be placed,perforations down,around the outside of the garage foundation at the footing subgrade elevation. All of the drainage system should be bedded in pea gravel and designed to carry any accumulated water away to the storm drainage system. Roof drainage should not be connected to the footing drains,but may use the same tight-line outfall away from the building. FOUNDATION DESIGN For the existing home we recommend that a periferal footing be installed,placed on pin pile. Over the past several years,Shannan &Wilson,Inc. has developed a system for underpinning or supporting relatively light structures such as residences and/or one to two-story apartment or office buildings where access is restricted and a competent bearing layer is located at relatively shallow . depth. This system consists of installing 2-inch diameter pipe piles with a jackhammer to transfer building loads to the bearing stratum. Structures which have been underpinned or supported with this system are currently performing satisfactorily. The 2-inch diameter pipe pile support system is particularly adaptable to conditions where access is restricted but it requires that structure loads are such that the load per pile does not exceed about 2 tons and that a suitable bearing layer exists at relatively shallow depth. Installation of the 2-inch pipes requires a jack hammer,air hose,and air compressor. This equipment is compact and mobile, allowing economic installation of the pile. For example,the air compressor can be parked in a driveway or on the street and a length of air hose selected so that a jack hammer can be used where required for installing footing underpinning for support. A design load of 2 tons per pile may be used for designing footing underpinning for support. Load tests performed during past installations demonstrate that this design load is achieved when the pipes are driven to a resistance of one inch or less of penetration for one minute of continuous driving. 10011 Blombere Street SW.Olvmoia_WA 98512 • GEOTECHNICAL TESTING LABORATORY The pipe under pinning piles are generally considered as end bearing since they normally penetrate soft or loose soils overlying the bearing stratum. The pipe piles should be driven with an 80 to 90 pound jack hammer to a depth of 15 feet or to reach the specified driving resistance (one inch or less of penetration for one minute of continuous driving.) Standard threaded couplings are used to connect pipe sections. The pipe sections should be butted together about the center of the coupling to avoid stripping the threads during driving. If hard driving is anticipated,the ends of the pipe sections can be machined square to provide more surface area for stress transfer during driving. The footing for the house should be poured over the pile ends followed by a stem wall. The house weight can then be transferred to the stem wall. This will place the home on a conventional foundation that should not be impacted by liquefaction potential. For the garage foundation we recommend that individual columns and load bearing walls be supported on spread or continuous footings,respectively,bearing on the medium dense to very dense in situ native soils or properly placed and compacted structural fill. The bearing surface should be firm and free of sloughed or water-softened soil. Recommended allowable soil bearing pressures are shown below. However,continuous footings should not be less than 16 inches wide,and isolated footings should not be less than 24 inches in their smallest dimension,regardless of the resulting bearing pressure. Soil Type Recommended Allowable Soil Bearing Capacity,psf Topsoil Unsuitable Existing soft or loose fill, backfill or in situ native soils Unsuitable Structural fill 2000 Medium dense to dense in situ native soils 2000 Dense to very dense in situ native soils 3500 All footings should be designed to conform to UBC standards. It is recommended that all footing excavations be inspected,prior to placing concrete,to verify that the bearing surface has been properly cleaned and prepared. All foundation subgrade areas should be recompacted following excavation. Settlements for foundations designed and constructed as outlined above are estimated to be less than one inch. SLAB ON GRADE FLOORS Stab-on-grade floors may be satisfactorily supported on the medium dense to very dense in situ native soils or structural fill placed and compacted as recommended above. Existing fill or loose soils are suitable to provide adequate slab subgrade support but should be recompacted. Due to the high sand content of the anticipated slab subgrade soils, it is recommended that if work continues into the wet weather season,prior to slab placement,the slab subgrade should be over excavated a minimum of 6 inches and backfilled with compacted structural fill. 10011 Blombere Street SW.Olvmnia. WA 98512 GEOTECBMCAL TESTING LABORATORY A capillary break consisting of 4 to 6 inches of clean,coarse sand and gravel or concrete aggregate should be placed below the slab. The capillary break material should not contain more than 3.0%fines(material passing a U.S.No.200 sieve). A vapor barrier should be placed between the floor slab and capillary break. If a sand cushion is placed between the capillary break or vapor barrier and the slab, it should not contain free moisture when the slab is constructed. Excess moisture in the cushion could cause impervious floor coverings to bubble. LATERAL EARTH PRESSURES An active coefficient of 0.30 and a friction coefficient of 0.40 can be used for the on-site soils. GEOSEISMIC SETTING This project site is located within a"Zone 3 Area"as per the 2000 edition of the Uniform Building Code. All building structures on this project should be designed as per the U.B.C. requirement for such a seismic classification. The soil profile type is SD. LIQUEFACTION POTENTIAL The materials on site, under the home,are of a cohesionless nature,consisting of a mixture of silt and sand with gravel. Because of the wet conditions in the foundation area of the existing home,the potential for liquefaction is present. The placement of pile to support a normal foundation will mitigate this potential. Because of the end bearing characteristic of the pile,the home will became founded on a geologic material that is not as susceptible to liquefaction. GROUNDWATER CONTROL Groundwater may pose a problem during construction. Work should therefore be planned or timed to coincide with the driest conditions. REPORT LIMITATIONS The conclusions and recommendations in this report are based on our interpretation of site conditions as they presently exist, anticipated future construction activities,and the expectation that our exploratory efforts adequately define the subsurface conditions throughout the site. In the event that the scope or location of the project should change,or subsurface conditions different from those encountered during our study be observed or suspected,we should be advised. At that time a review of the changed conditions will be made and alternative or remedial recommendations given as requested. This report has been prepared for the exclusive use of David Vandervort Architects for specific application to the referenced project. Within limitations of scope,schedule,and budget for our work,we warrant that our work has been done in accordance with - generally accepted practices followed in this area at the time this report was prepared. No other warranty,expressed or implied,is made. Respectfully submitted, GEOTECHNICAL TESTING LAB //a,tvw I Harold Parks, Engineering Geologist 10011 Blombere Street SW.Olvmoia.WA 98512 GEOTECHNICAL TESTING LABORATORY SITE PLAN WITH BORING LOG LOCATIONS State Route 106 I shore line. House ara I� 9 #1 #2 oopppp bulkhead rockery 10011 Blomberg;Street SW, Olympia,WA 98512 Christensen Residence Date: Nov.24,00 File#: 2000-231 Boring Log#: 1 Client: Vandervort(Christianson) Boring Type: Hollow Stem Auger Depth Drilled: 5 feet Depth Field Change (in) Description in Soils %M N %3/4" %44 %4200 Comments 2.0 disturbed surface 4.0 6.0 silty sand with gravel 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 7.5% medium dense 26.0 28.0 30.0 32.0 34.0 36.0 7.11i6 34 100% 616 medium dense 38.0 40.0 42.0 44.0 46.0 Well Graded Sand 48.0 with Gravel 50.0 52.0 54.0 56.0 58.0 Well Graded Sand 60.0 with Gravel damp 38 Not enough sample recovered dense 62.0 and Boring Christensen Residence Date: Nov.24,00 File M 2000-231 Boring Log#: 2 Client: Vandervort(Christianson) Boring Type: Hollow Stem Auger Depth Drilled: 5 feet Depth Field Change (in) Description in Soils %M N %'/." %44 %4200 Comments 2.0 disturbed surface 4.0 6.0 silty sand with gravel 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 7.8% 28 medium dense 26.0 28.0 30.0 32.0 34.0 36.0 7.2% medium dose 38.0 40.0 42.0 44.0 46.0 Well Graded Sand 48.0 with Gravel 50.0 52.0 54.0 56.0 58.0 Well Graded Sand 60.0 with Gravel damp 31 dense 62.0 end Boring Water Side No. 5520 -8112"x11y. , + I • � i j i 1 I. , 1 7.I -�-' -�---- ' II i I � Locations of existing pile under the home 71 r r + x v JIM t i� / r � l ,,.�„�./" _„'+';a'- .... - � a� k v� tee' e •� .. - .� .'fit s�� _ •Z. e x } � 1