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92-101282I SOUTH KING COUNTY MULTI —SERVICE CENTER WAREHOUSE 1200 SOUTH 336TH STREET FEDERAL WAY, WASHINGTON JOB NO. 9101-18G I 1 j J TABLE OF CONTENTS Introduction Page 1 Site Description Page 2 Subsurface Conditions Page 2 Conclusions and Recommendations Page 3 I Foundation Placement Page 4 Slab -on -Grade Floor Page 4 I Grading Page 5 Pavement Design Page 6 General Page 6 Appendix A Test Pit Location Map Appendix B Test Pit Logs Appendix C Unified Soils Classification System -it J I I j J CASCADE GEOTECHNICAL, INC. 12911 N.E. 126TH PLACE (206) 821-5080 KIRKLAND, WASHINGTON 98034 FAX: (206) 823-2203 February 14, 1991 Job No. 9101-18G South King County Multi -Service Center c/o Gleason and Associates 551 First Avenue South Seattle, Washington 98104 Attention: Sharon Atkin Reference: South King County Multi -Service Center Warehouse 1200 South 336th Street Federal Way, Washington Dear Ms. Atkin: As requested By Roger Tucker of Gleason and Associates, Architects, we have completed a soils investigation for the proposed addition at 1200 South 336th Street in Federal Way, Washington. The following report contains our findings, conclusions and recommendations. INTRODUCTION The scope of our work was to investigate the subsurface conditions at the site by excavating backhoe test pits and to prepare a soils report for the site. The purpose of our study was to determine the subsurface soil and ground water conditions at the site and to offer conclusions and recommendations for foundation design, drainage, grading and pavement design. We understand that the project is to consist of a 3300 square foot, single -story, metal framed warehouse with a slab -on -grade floor and associated parking areas. We reviewed Sheets A-1, A-2, A-3 and C-1 of the provided plans prepared by Gleason and Associates dated September and November 1990. We also understand that a soils CASCADE GEOTECHNICAL February 14, 1991 South King County Multi -Service Center Job No. 9101-18G Page 2 report conforming to the 1988 Uniform Building Code Chapter 29 specifications is required. SITE DESCRIPTION The site, approximately 900 sq. ft., is located on the north side of South 336th in Federal Way, Washington approximately 170 feet north of South 336th Street. At the time of our visit, the site f was being used as a parking lot for the multi -service center employees and was covered wOith gravel. Existing single -story buildings were noted to the west, east and south of the site. An asphalt paved roadway was found along the north side of the site. The overall topography of the site was relatively flat. The site i sloped five (5) feet down to the south at a gentle grade on the southern side of the site. On the eastern side, the site sloped two (2) feet down to the east also at a relatively gentle grade. A four (4) foot cut was observed on the northern side of the existing asphalt roadway, north of the proposed building area. _1 There was no vegetation on the site at the time of our ` investigation. A deciduous tree was noted on the eastern side of the site. Grass covered the slopes on the southern and eastern sides of the site. i SUBSURFACE CONDITIONS The site subsurface conditions were investigated by excavating four (4) backhoe test pits on January 28, 1991. The test pit locations determined by our geologist and located by pacing relative to the property lines and existing building are shown on the site plan presented in Appendix A. Detailed test pit logs and soil descriptions are presented in Appendix B. The soils were CASCADE GEOTECHNICAL February 14, 1991 South King County Multi -Service Center Job No. 9101-18G Page 3 classified using the Unified Soils Classification System presented in Appendix C. The depths referred to in this report are relative to the ground surface at the time of our investigation. The test pits were terminated at depths of between five (5) and seven and one-half (7 1/2) feet due to very dense soils. We observed from two and one-half (2 1/2) to six (6) feet of loose lto dense, rusty -brown to brown, gravelly sand with minor to some 1 cobbles in Test Pits 1, 3 and 4. Below the gravelly sand in these test pits, we found dense to very dense, gray silty sand with some gravel (till) to the test pit termination depths. In Test Pit 2, we noted two (2) feet of uncontrolled fill I consisting of brown gravelly sand with some cobbles overlying a six (6) inch layer of the old topsoil. The old topsoil consisted of black silty sand with some gravel and roots. Three and one-half (3 1/2) feet of medium dense to dense, rusty -brown to brown gravelly sand with some cobbles was observed beneath the old topsoil layer. At six (6) feet below the surface, we found very dense, gray silty i sand with some gravel (till). There was no ground water seepage noted in any of the test pits at the time of our investigation. ICONCLUSIONS AND RECOMMENDATIONS We conclude that the site is suitable for the proposed addition if our recommendations are carefully followed. The fill and the topsoil noted in Test Pit 2 is unsuitable for the support of a building foundation. If the topsoil and fill is not removed, some settlement can be anticipated within the building area. We recommend removing the topsoil material from the building area and replacing it with compacted, structural fill. j 1 CASCADE GEOTECHNICAL February 14, 1991 South King County Multi -Service Center Job No. 9101-18G Page 4 Foundation Placement The native, undisturbed medium dense to dense gravelly sand with _1 minor to some cobbles is suitable for the placement of a spread 1 footing foundation. The fill and topsoil noted in Test Pit 2 is unsuitable for the support of the proposed foundation and the proposed slab -on -grade floor. We recommend replacing the unsuitable material with structural fill meeting the recommendations stated in the Grading Section of this report. Spread footings placed on firm, undisturbed, horizontal surfaces of the recommended bearing soils may be designed to a maximum safe 1 bearing value of 2000 psf if the footing excavations are free of 1 organic material, water and loose or wet soil prior to the j placement of the concrete. We recommend that all footings be at 1 least eighteen (18) inches below the outside finished grade for frost protection. The minimum footing widths should conform to the local building codes. A maximum total settlement of one (1) inch and a differential settlement of three -fourths (3/4) inch can be anticipated over the l site if our recommendations are followed. ] Slab -on -Grade Floor We recommend placing the slab on structural fill placed directly on the native gravelly sand. Fill should meet the recommendations contained in the Grading Section of this report. We recommend placing a minimum of four (4) inches of free draining Jmaterial beneath the slab to act as a capillary break. The free draining material should consist of crushed rock or clean sand with a maximum of five (5) percent passing the #4 sieve. A vapor CASCADE GEOTECHNICAL February 14, 1991 South King County Multi -Service Center Job No. 9101-18G Page 5 barrier should be placed between the capillary break and the slab. If desired, two (2) inches of sand may be placed on top of the vapor barrier to aid in concrete curing. Grading I The on -site native gravelly sand and the fill consisting of gravelly sand is suitable for use as a structural fill material as long as the soil is free of organic material and the moisture is kept at or just below the optimum value as determined by the ASTM D-1557 moisture -density test. The topsoil noted in the test pit is unsuitable for the use as structural fill and should be removed from the building area. iIf imported fill is necessary, it should meet the following gradation: Sieve Size Percent Passin 4 inch 100 J#4 25 - 75 #200 10 maximum JIf a wet subg rade is encountered during fill placement, an all- weather fill having less than five (5) percent passing the #200 sieve based on the material passing the #4 sieve, may be necessary. We recommend using lifts not exceeding twelve (12) inches in loose thickness and compacting to at least 95 percent of the ASTM D-1557 maximum dry density value for the foundation and slab and 90 percent of the ASTM D-1557 maximum dry density value for the Jparking areas. J J "1 CASCADE GEOTECHNICAL February 14, 1991 South King County Multi -Service Center Job No. 9101-18G l Page 6 Draina e We recommend placing a four (4) inch diameter, rigid, perforated drain pipe, backfilled with at least twelve (12) inches of pea gravel, along the base of the exterior footings and tightlining it to the storm system. The roof drains should be directed into the storm system in a tightline separate from the footing drains. Pavement Design i We recommend a pavement section of four (4) inches of crushed rock with two (2) inches of Class B asphaltic concrete. This is suitable for the anticipated parking lot loading consisting of passenger cars, light trucks and up to two (2) heavy trucks per day. The subgrade should be dry and non -yielding before the pavement is placed. Any soft, wet or yielding areas should be removed and replaced with suitable fill as stated in the Grading Section of this report. General J We recommend that we be engaged to review the final building and grading plans for the site to confirm that our recommendations have been properly interpreted. We also recommend that we be engaged to confirm that suitable bearing soil has been reached, to observe that all the topsoil and uncontrolled fill has been removed from the building area, and to observe and test any fill that is placed. We expect the on -site conditions to reflect our findings; however, some variations may occur. Should soil conditions be encountered which cause concern and/or are not mentioned herein, Cascade Geotechnical should be contacted immediately to determine if additional or alternate recommendations are required. j I 1 1 I I I I CASCADE GEOTECHNICAL February 14, 1991 South King County Multi -Service Center Job No. 9101-18G Page 7 This report has been prepared for the exclusive use of Gleason and Associates, Architects, for specific application to the proposed construction at 1200 South 336th Street in Federal Way, Washington, in accordance with generally accepted soils and foundation engineering practices. No other warranty, expressed or implied, is made. Thank you for this opportunity to work with you. Should you have any questions, please feel free to contact us at any time. Sincerely, CASCADE EOTECHNIC. G r g e EQEngi Principa Bridget Krause Engineering Geologist I SOUTH KING COUNTY MULTI -SERVICE CENTER WAREHOUSE TEST PIT LOCATION MAP PROPOSED PARKING PROPOSED SIDEWALK T.P. T, EXISTING BLDG. ROPOSED WAREHOUSE EXS . OFFICE .2. r.p., 0 EXST. OFFICE FROM SITE PLAN BY GLEASON & ASSOCIATES, ARCHITECTS Job No. 9101-18G SCALE : ' 1" = 30' CASCADE GEOTECHNICAL, INC. 12919 N.E. 126TH PLACE (206) 821-5080 LOCATIONS ARE APPROXIMATE �! KIRKLAND, WASHINGTON 98034 FAX: (206) 823-2203 Date 1 /28/91 Dwn. By BK jEng - G._eooll U I UNIFIED SCAS CLASSIFICATIC d"'4 SYSTEM COARSE GRAINED SOILS FINE GRAINED SOILS MAJOR DIVISIONS CLEAN GRAVELS GRAVEL & GRAVELLY SOILS GRAVELS WITH FINES CLEAN SANDS SAND & SANDY SOILS SANDS WITH FINES SILTS & CLAYS Liquid Limit Less Than 50 SILTS & CLAYS Liquid Limit Greater Than 50 HIGHLY ORGANIC SOILS SYMBOL LETTER DESCRIPTION ° a Well -graded gravels or gravel -sand mixtures. aA Q-0oa GW little or no fines Poorly graded gravels or gravel -sand mixtures, .:�. C' P little or no fines • GM Silty gravels or gravel -sand-silt mixtures GC Clayey gravels or gravel -sand -clay mixtures Well -graded sands or gravelly sands, little or W no fines Poorly graded sands or gravelly sands, little SP or no fines $M Silty sands or sand -silt mixtures S C Clayey sands or sand -clay mixtures Inorganic silts & very fine sands, rock flour silty ML or clayey fine sands, or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, CL gravelly clays, sandy clays, silty clays or lean clays I l l l k i l Organic silts & organic silty clays of low 1111111 IIIIIII I I I OL plasticity Inorganic silts, micaceous or diatomaceous fine MH sandy or silty soils, elastic silts CH Inorganic clays of high plasticity, tat clays r • • • • � Organic clays of medium to high plasticity, ',',`•'r' OH organic silts r r r • � PT I Peat or other highly organic soils TOPSOIL .y" Humus & duff layer FILL Uncontrolled, with highly variable constituents Sol DATUM NOTE I2" O.D. Split Spoon Sampler Sample Interval Ring or Shelby Sampler Sample Interval PSampler Pushed Sample Interval * Other Sample Type Sample Interval BO L DATUM -7 NOTE SzWater Level Date Recorded Ts Torvane Reading qV Penetrometer Reading iWater Observation Well Tip Elevation I;(C1I CASCADE GEOTECHNICAL, INC. KEY CHART