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Home My WebLink AboutBLD2004-01862 - BLD Engineering / Geo-tech Reports - 12/23/2004MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton, Washington 98584 DATE: December 23`d, 2004 INTER -DEPARTMENTAL COMMUNICATIONS TO: Charles Mead McCoy III, DCD - Planner FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO# PLG -04 SUBJ: Geo -Tech Assessment Review NAME: Ramsfield (&, 240 Rock Way BLD2004-01862 Charles, The geotechnical assessment prepared for the proposed Ben Ramsfield Single Family Residence to be constructed at 240 Rock Way, Shelton, has been received and reviewed by Public Works. The report appears to satisfactorily fulfill County requirements for geotechnical assessment reporting. The assessment's author indicates that, in his opinion, the completed development of the property will not cause stability problems for either the subject property or neighboring properties, and that a more detailed investigation (report) is not warranted. From the contents of the assessment, I recommend accepting the report as satisfying the County's requirement(s) for stability investigation and geotechnical reporting. Recommendations contained in the assessment should be incorporated into the site's development and made conditions for permit issuance. Adequate Erosion and Sediment (E&S) control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. In summary, the geotechnical assessment prepared for the proposed residence appears acceptable, and stability issues may be considered to have been adequately investigated and addressed. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, Allen A. Tahja File: H:\WP\GEO\Assessments\Ramsfield.doc WORK ORDER - PUBLIC WORKS DEPT. (A) Date: /2/Z,3701/ PERMIT #: 'pLz)zz:254/ -O/F62- Requested by: C-44,arle5 44 - /14cCo Authorized by: Type of Work: Ger, - fts5e5547 / CHARGE TO: NAME AGENCY/COMPANY BILLING ADDRESS PHONE (B) Pub. Works Person in Charpe: (c) Project Time Une: (from to dat) Project Start date: Z-7/1/11 Approximate hours: / COST ESTIMATE Work Order Number: 1 Date: TO Estimated Finish Date: ESTIMATED TOTAL IS: 2113F (D) Pik Employee ispit Hours Subtotal' Films % TOTAL 17-A3/ /a11(4 3F zz__ EQUIPMENT USED: MATERIAL USED: (F) Actual Cost DATE EmPeoYea WORKED Name EQUIPMENT USED: MATERIAL USED: (G) BILLED DATE UNIT „ ' ..................................... BARS: PROJ Hours 2.M1112114 Rime % Pate Mnit TOTAL $'S B_Att TOTAL S'S TOTAL ALL INV/ PAID DATE REC.% CKN TOTAL $ gu-F00(4 - 0 18(07, Geotechnical Assessment 240 Rock Way Shelton, WA 3ie,6s 7.6 5coiLl Prepared for Ben Ramsfield by Geotechnical Testing Laboratory Olympia, Washington Dec. 20, 2004 RECEIVED DEC Z32004 >26 W. CEDAR S GEOTECHNICAL TESTING LABORATORY BEN RAMSFIELD 1664 CAMILLA LANE SW, #302 TUMWATER, WA 98512 RE: GEOLOGICAL ASSESSMENT 240 Roca WAY SHELTON, WA PARCEL 320087690014 N47°14.422' W123°05.419' PURPOSE The objective of the geological assessment is to assess the surface and subsurface conditions prevalent at the subject site according to Mason County Ordinance 17.01.100.E4. The parcel will be developed as a single-family residence with a septic drainfield and well. A geotechnical report from the adjoining parcel is included in the appendix following this report. SITE CONDITIONS The subject site is a lot located approximately 1.5 miles northeast of Shelton, Washington (see attached vicinity map). The site is accessed from Rock Way along the northern property line. The subject site (1.16 acres) is located in an area of moderate residential development. The site slopes toward the north. The steepest portion of the site contains slopes approaching 5 percent. Minimal grading is expected at the proposed building location due to the previous clearing. The lot is vegetated mostly with Scot's broom. Rapid stream incision was not identified at the site. Slope instability was not discerned onsite or on adjoining parcels. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 1 1 1 1 1 1 1 1 GEOTECHNICAL TESTING LABORATORY GEOLOGIC CONDITIONS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as a Shelton gravelly sandy loam, 15-30 percent slopes (Sg). The Shelton soils typically formed from gravelly glacial till mixed with considerable basaltic rock of local origin and with local drift from the Olympic Mountains. The substratum is cemented till. They are described as having good natural drainage. Typically, there is no occurrence of a high water table. Internal drainage is described as medium. Root penetration is limited by cemented till at depths of 30 to 36 inches. The Shelton soil is described as having a slight erosion hazard. 1 1 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 2 i 1 1 GEOTECHNICAL TESTING LABORATORY The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site as Till, late Wisconsinan (Pleistocene). The glacial till (Qgt) is described as: Unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel, and boulders deposited by glacial ice of the Puget lobe; gray; may contain interbedded stratified sand, silt, and gravel; sand -size fraction is very angular and contains abundant polycrystalline quartz, which distinguishes this unit from alpine till; cobbles and boulders are commonly striated and (or) faceted; although unweathered almost everywhere, may contain cobbles or small boulders of deeply weathered granitic rock The Geologic Map of Washington — Northwest Quadrant (2002) has mapped the site geology as glacial till deposits (Qgt) of continental glacial origin. The report reads: Til — Unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel, and boulders deposited by glacial ice; may contain interbedded stratified sand, silt, and gravel. Includes part of the Vashon Drift undivided. GROUNDWATER CONDITIONS Groundwater seepage was not observed at or near the proposed building location. No wetland vegetation was observed at or near the proposed building location. Depth to static groundwater is unknown, but is assumed to be beyond the scope of the project. Ilb DEPTH TO COMPETENT SOIL Typically, dense gravelly sandy loam is found throughout the site. Competent soil can be expected approximately 14 inches below the ground surface. PAST SLOPE INSTABILITY Near the proposed building location, trees were found straight and verticaL No indication of past instability was discerned at the proposed building location or throughout the site. Adjoining parcels display similar signs of stability as the subject site. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 3 1 1 1 1 1 1 1 1 1 1 1 1 GEOTECHNICAL TESTING LABORATORY HISTORY OF LANDSLIDE ACTIVITY No historical landsliding was observed during our site investigation onsite or near the subject parceL At the proposed building location, the slopes are dense, compact, and low in slope angle. Neighboring trees are straight and vertical. POTENTIAL FOR LANDSLIDE ACTIVITY This site has a very low potential for landslide activity. The building location is proposed where slopes are approximately 5 percent. Even though the parcel borders another parcel with a landslide hazard area, the potential for landslide activity is not a concern. RECOMMENDATIONS There is no evidence of soil erosion or deposition onsite to suggest that the site should be included in the Erosion Hazard Area designation. Site conditions for the proposed development do not warrant a more comprehensive Geotechnical Report. We recommend no further action is needed unless areas of concern are unearthed during construction. If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. I HAROLD PARKS I E1/0, 7 -3/ — oSi Respectfully, GEOTECHNICAL TESTING LABORATORY ii4)4ao ifszA Harold Parks, L.G., L.E.G. Senior Engineering Geologist 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 4 • 1 1 1 GEOTECHNICAL TESTING LABORATORY VICINITY MAP 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 r 1 Tt i� IQ „ `` gy tt'- /r ZON Q•a ! --� �• l 1 '•em •c'ma I ••� III • i –' 0 •y x Grpv•gl . •• r f%,% _ ' ` . ' b5-V£TS ,44 C 1044 • I • II 1.---/-./ "4-'14 . I i” i •. -,,,,,....,7r • it y :" er u • ''. • Land Lake : 1•' . ' � a •o- a `Gravel 5 `gtgek.I 4— b J. nd Lake 69 3..:. —., ..i --`, i • 1 q gfi 5 IS /Ii / �� ,,,,-,7M RAsrIELD :la fid: H SITE s -- ;-- -_---%�_,_ (I � J / , _s._---+ ;�_ ; r r J �— — _. kr - ' r/ , f . .• .. W. es I_ SReittvn Spriprji. it,. `: -1 , --•--- -'i.4-- - -/ paid -1-_-t ' r - �,f 1/ ----N I 7 > _ Ti:',;.1' . • , • a.A. ••>I - a. I "PO . 1 ; —= .. ~ I ,. ,.a rA7 . 1 SII u1 1 i enl 1 'i.--- 'ate 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 Geotechnical Report 601 East Eagle Ridge Drive Parcel #320087690022 Shelton, WA Prepared for Toby Lane by Geotechnical Testing Laboratory Olympia, Washington March 16, 2004 RECEIVED DEC 23 2004 426 W: CEDAR STI GEOTECHNICAL TESTING LABORATORY TOBY LANE 1904 WASHINGTON STREET SHELTON, WA 98584 Re: Geotechnical Report 601 East Eagle Ridge Drive Shelton, WA 98584 Parcel No. 320087690022 N47°14.336' W123°05.421' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence to be located at 601 East Eagle Ridge Drive, approximately 1.5 miles northeast of Shelton, Washington. The location of the site is shown relative to the surrounding area on the Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with you and our explorations and review of the site. We understand that the proposed single-family residence is to be constructed on a flat area, essentially a topographic high point. The general layout of the site is shown on the Site Map, Figure 2. We further understand that minor grading may be required at the site to reach design lig grade. In general, grading will consist of the excavation of the foundation material, which either becomes fill or excess spoils to be disposed offsite. We understand that a private well serves the site with water. A septic system and drainfield is located onsite. 1 1.0 The steepest slope measured onsite was near 40 percent, sloping toward the north. Therefore, Mason County requires that a geotechnical report be prepared in accordance with the Critical Areas Ordinance. The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing geotechnical recommendations and design criteria for the project, and to satisfy the requirements of the Mason County Critical Areas Ordinance. Geotechnical Testing Laboratory is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY 1. Review the available geologic, hydrogeologic, and geotechnical data for the site area. 2. Conduct a geologic reconnaissance of the site area. 3. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations. 4. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria (including hillside grading), suitability of on-site soils for use as structural fill, temporary and permanent cut and fill slopes, drainage and erosion control measures. 5. Provide recommendations and design criteria for the structural foundation and floor slab support, including allowable bearing capacity, subgrade modulus, lateral resistance values and estimates of settlement. SITE CONDITIONS SURFACE CONDITIONS The site is located in an area of sparse development in the Puget Sound glacial upland area located northeast of Shelton. The proposed layout of the site is shown on the Site Plan, Figure 2. We conducted a reconnaissance of the site area March 11, 2004, and observed the soil exposed onsite. Elevations for the proposed building location range from approximately 234 to 292 feet. The general topography of the site area indicates that drainage flows toward the north and south. No evidence of surface water flow was observed in the site area at the time of our reconnaissance. We observed no evidence of erosion. No evidence of deep-seated slope instability was observed on the site slope or areas adjacent to this site at the time of our investigation. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SITE GEOLOGY The site is generally situated within the lower Puget Sound glacial upland. The existing topography, as well as the surficial and shallow subsurface soils in the area, are the result of the most recent Vashon stade of the Fraser glaciation that occurred between about 10,000 and 12,000 years ago, and weathering and erosion that has occurred since. A description of the surficial soils is included in the "Site Soils" section of this report. In general, Vashon glacial till is represented by the soils of the site. The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site as Till, late Wisconsinan (Pleistocene). The glacial till (Qgt) is described as: Unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel, and boulders deposited by glacial ice of the Puget lobe; gray; may contain interbedded stratified sand, silt, and gravel; sand -size fraction is very angular and contains abundant polycrystalline quartz, which distinguishes this unit from alpine till; cobbles and boulders are commonly striated and (or) faceted; although unweathered almost everywhere, may contain cobbles or small boulders of deeply weathered granitic rock. SITE SOILS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as a Shelton gravelly sandy loam, 15-30 percent slopes (Sg). The Shelton soils typically formed from gravelly glacial till mixed with considerable basaltic rock of local origin and with local drift from the Olympic Mountains. The substratum is cemented till. They are described as having good natural drainage. Typically, there is no occurrence of a high water table. Internal drainage is described as medium. Root penetration is limited by cemented till at depths of 30 to 36 inches. The Shelton soil is described as having a slight erosion hazard. The project site is beyond the scope of The Coastal Zone Atlas, Volume 9, Mason County. 10011 Blomberg Street SW, Olympia, WA 98512 3 Phone #: (360) 754-4612 Fax #: (360) 754-4848 1 1 t GEOTECHNICAL TESTING LABORATORY SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing exposed construction site and hillside soils in addition to reviewing available well logs. Sandy gravel with cobbles was found to approximately 22 feet below the ground surface. The well log for a nearby site follows this report. SUBSURFACE CONDITIONS IPP In general, undisturbed dense gravelly sandy loam was observed throughout the site. Groundwater was not observed or encountered. No instances of seeps of groundwater were seen on the slopes on or adjacent to the parcel. Based on the site topography and the nature of the near surface soil, seasonally perched groundwater conditions are not expected during periods of extended wet weather. We observed no active erosion or slope disturbance in the site area during our reconnaissance. c SLOPE STABILITY Slopes in excess of 40 percent were observed on the site. Since slopes of 40 percent or greater with 10 feet or more of vertical relief occur on portions of the site, Mason County requires that a geologic hazards report be completed according to the Critical Areas Ordinance. In general, the undisturbed native soils of the site consist of a mixture of variable amounts of sand and gravel. These soil materials are in a dense to very dense condition except where they have been disturbed by weathering activity. These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or significant erosion was observed at the site at the time of our investigation. Weathering, erosion, and the resultant sloughing and shallow landsliding are natural processes that can affect steep slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone, which has been disturbed and has a lower strength. Evidence of minor surficial erosion, raveling and sloughing was not observed in the site area at the time of our investigative visit. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles, and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced by encouraging vegetation and keeping runoff from the steep slope, or controlling the flow from top to bottom by a drainpipe. Erosion control recommendations for the sloping areas are provided in the "Building Setback" and "Erosion Control" sections of this report. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on the results of our site reconnaissance, subsurface observations, and our experience in the area, it is our opinion that the site is suitable for the proposed project. The slope is stable relative to deep-seated instability and will not be affected by the proposed home. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope stability. In general, the sandy gravelly loam observed at the site is suitable for use as structural fill material. The soils that occur on the site are moderately moisture -sensitive and moderately susceptible to disturbance when wet. Saturated soil conditions may be associated with these soils during or following extended periods of rainfall. However, to reduce grading time and construction costs, we recommend that earthwork be undertaken during favorable weather conditions. Conventional construction equipment may be utilized for work at the site. Conventional spread footings may be utilized at the site for support of the structure. We do recommend that roof and footing drains be installed for the home with normal spread footings. A vapor barrier is recommended for all slab -on -grades. Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed home are presented below. LANDSLIDE — EROSION HAZARD AREAS CLASSIFICATION The Mason County Critical Areas Ordinance (17.01.100) defines a landslide hazard area as one containing slopes equal to or greater than 40 percent with more than a 10 -foot vertical relief. The slope (north of the proposed structure) is in excess of 40 percent and the vertical relief is in excess of 10 feet. Based on this, this site does meet the technical criteria of a landslide hazard area. The Mason County Critical Areas Ordinance (17.01.104) defines an erosion hazard area as: Areas in Mason County underlain by soils which are subject to severe erosion when disturbed. Such soils include, but are not limited to, those for which potential for erosion is identified in the Soil Survey of Mason County, USDA Soil Conservation Service, 1960, or any subsequent revisions or additions to this source. These soils include, but are not limited to, any occurrence of River Wash ("Ra") or Coastal Beaches ("Cg") and the following when they occur on slopes 15% or steeper: a. Alderwood gravelly sandy loam ("Ac" and "Ad") b. Cloquallum silt loam ("Cd') c. Harstine gravelly sandy loam ("Hb') d. Kitsap silt loam ("Kc") The soils at the site are mapped as Shelton gravelly sandy loam (Sg) in the building portions of the site. These soils do not meet the technical criteria of an erosion hazard. No construction is expected to take place on the slopes. There is no evidence of soil erosion anywhere on the site to suggest that the site should be included in the Erosion Hazard Area designation. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SLOPE STABILITY Based on our field observations, explorations and our 1144 i11h the soil types encountered on the property, we conclude that although portions of the slopes on the lot equal 40 percent, they are generally stable relative to deep- seated failure in their present configuration. 2500 - 2000 co 3 cn 1500 a► N 1000 d 500 0 D 500 1000 1500 2000 Normal Stress (psT) Peak Shear Stress vs. Normal Stress A ■ • 29° 2500 1t4 ton —�-1f2 ton —A-1 ton For a proper foundation, uncompacted fill material and any underlying vegetation shall be removed in order to construct the foundation. Excavation and back -filling will occur based on appropriate engineering and earthwork recommendations found in the following "Earthwork" section. Grading in the building portion of the site should be conducted in accordance with geotechnical recommendations provided herein. As previously discussed, weathering, erosion, and the resultant surficial sloughing and landsliding are natural processes that affect slope areas. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles and freeze/thaw cycles. Over excavation may be necessary to ensure the removal of deleterious material. These processes can be managed and the risk reduced through proper construction of the residence. Erosion control recommendations in the slope and buffer areas are provided in the "Building Setback" and "Erosion Control" sections of this report. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 6 1 GEOTECHNICAL TESTING LABORATORY BUILDING SETBACK Slope stability was modeled using the GEO-SLOPE/W .. gram (version 5.13) in both static and extreme dynamic conditions (ce = 0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern -Price methods. Previously, the gravelly sandy loam was determined to have a unit weight of 128 pcf, cohesion of 300 psf, and a shear angle (4)) of 29°. Under static conditions, the slopes remained stable to deep-seated and shallow failure. Under dynamic loading, the 4096 computations demonstrated that the slope is not susceptible to surficial raveling. Large deep-seated failure was not demonstrated by our model. The following figure illustrates a moment F.S. of 1.28, the lowest value derived from modeling the proposed building location. t 1 1 1 1 1 1 1 Lane Site - Slope A Analysis Method: Morgenstern -Price • Direction of Slip Movement: Left to Right Slip Surface Option: Grid and Radius • Seismic Coefficient: Horizontal and Verticif , , 330 320 310 330 290 260 270 260 250 240 230 220 210 200 Shelton Gravely Sandy Loam Soil Model: Mohr -Coulomb Unit Weight 128 Cohesion: 300 Phi: 29 60 100 120 140 160 160 200 220 240 260 Distance (ft) Ihp A building setback from landslide hazard areas is required unless evaluated and reduced by an engineering geologist or a licensed professional engineer. Based on our geotechnical evaluation of the site and our experience in the area, a building setback will be needed for this lot. We recommend a building setback of 10 feet from the intercept of the slope and the edge of the footing. The building setback may be measured from the bottom of the footing to the face of the slope, in accordance with the Unified Building Code. 10011 Blomberg Street SW, Olympia, WA 98512 7 Phone #: (360) 754-4612 Fax #: (360) 754-4848 t 1 1 GEOTECHNICAL TESTING LABORATORY As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are natural processes that affect slope areas. No surficial raveling or sloughing from the past was observed in the sloping portions of the site. To manage and reduce the potential for these natural processes, we recommend the following: 1. No drainage of concentrated surface water or significant sheet flow onto the slope area. 2. Trees on slopes may be trimmed or removed if the root mass remains. 3. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill. SEISMIC — LIQUEFACTION HAZARD According to the Seismic Zone Map of the United States contained in Figure 16-2 of the 1997 UBC (Uniform Building Code), the project site is located within Seismic Risk Zone 3. Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic Soil Profile Type Sc, for Very Dense Soil, as defined by Table 1 6-J (UBC). This is based on the range of SPT (Standard Penetration Test) blow counts and/or probing with a '/2 -inch diameter steel probe rod. The shallow soil conditions were assumed to be representative for the site conditions beyond the depths explored. Based on our review of the subsurface conditions, we conclude that the site soils are not susceptible to liquefaction. The near -surface soils are generally in a dense condition and the static water table is located well below the surface (82 feet). Shaking of the already dense soil is not apt to produce a denser configuration and subsequently excess pore water pressures are not likely to be produced. EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed single-family residence. Removal of natural vegetation should be minimized and limited to the active construction areas. Temporary and permanent erosion control measures should be installed and maintained during construction or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include, but not be limited to, silt fences, berms and swales with ground cover/protection in exposed areas. A typical silt fence detail is included on Figure 2. Any re -contouring of the site for a level area for the house will create a need for erosion control measures listed above. EARTHWORK SITE PREPARATION All areas to be excavated should be cleared of deleterious matter including any existing structures, existing utilities, debris, duff, and vegetation. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 r 1 t 1 1 1 GEOTECHNICAL TESTING LABORATORY Where placement of fill material is required, the exposed subgrade areas should be proof -rolled to a firm and unyielding surface prior to placement of any fill. Excavations for tree stump removal in any building area should be backfilled with structural fill compacted to the density requirements described in the "Structural Fill" section of this report. Any soft, loose or otherwise unsuitable areas delineated during construction or probing should be compacted, if practical, or over -excavated and replaced with structural fill, based on the recommendations of our site representative. STRUCTURAL FILL All fill material should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least 90 percent of MDD (maximum dry density) as determined in accordance with ASTM D-1557 to within 2 feet of subgrade and 95 percent MDD in the upper 2 feet. The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend use of well -graded sand and gravel with less than 5 percent (by weight) passing the No. 200 sieve based on that fraction passing the %-inch sieve. If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a somewhat higher (up to 10 percent) fines content will be acceptable. Material placed for structural fill should be free of debris, organic matter, trash and cobbles greater than 6 inches in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction. SUITABILITY OF ON-SITE SOILS AS FILL On-site soils may be considered for use as structural fill. In general, the native soils (sand and gravel) encountered on the site have less than 10 percent fines (material passing the US No. 200 Sieve) and are suitable for use as structural fill. FOUNDATION SUPPORT We recommend a minimum width of 2 feet for isolated footings and at least 16 inches for continuous wall footings. Footings founded as described above can be designed using an allowable soils bearing capacity of 2000 psf (pounds per square foot) for combined dead and long-term live loads in areas of medium dense to dense soils. The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be increased by one-third for transient loads such as those induced by seismic events or wind loads. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY Lateral loads may be resisted by friction on the bases of footings and floor slabs and as passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.50 be used to calculate friction between the concrete and the underlying soil. We estimate that settlements of footings designed and constructed as recommended will be less than I inch for the anticipated load conditions, with differential settlements between comparably loaded footings of Y2 inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation sub - grade during construction could result in larger settlements than predicted. FLOOR SLAB SUPPORT Slabs -on -grade should be supported on medium dense or dense native soils or on structural fill prepared as described in the "Structural Fill" section of this report. We recommend that floor slabs be directly underlain by a minimum 6 - inch thickness of coarse sand and/or gravel containing less than 3 percent fines (by weight). The drainage material should be placed in one lift and compacted to an unyielding condition. A synthetic vapor barrier should be used for the control of moisture migration through the slab, particularly where adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier could result in wet spots on the slab, particularly in storage areas. SITE DRAINAGE Site drainage shall be directed away from all structures and steep slopes to the south of the proposed building location. We recommend that conventional roof drains be installed for the proposed garage. If footing drains are employed, they shall be placed with the invert below the bottom of the footing. The roof drain should not be connected to the footing drain. LIMITATIONS We have prepared this report for Toby Lane and members of his design team, for use in the design of a portion of this project. The data used in preparing this report, and this report, should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and our site reconnaissance, and should not be construed as a warranty of the subsurface conditions. Unforeseen catastrophic events are beyond the scope of this report. Variations in subsurface conditions are possible and may occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient consultation should be made with our firm during construction to confirm that the conditions encountered are consistent with those indicated by the recommendations and for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans. If our analysis and recommendations are followed, we do not anticipate any on site or off site impact from the construction. It is our conclusion that potential landslide hazards from the landslide area can be overcome so as not to cause harm to property, public health and safety, or the environment. 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 10 GEOTECHNICAL TESTING LABORATORY The scope of our services does not include services related to environmental remediation and construction safety precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures, except as specifically described in our report for consideration in design. If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. HAROLD PARKS Exp 7 Respectfully submitted, GEOTECHNICAL TESTING LABORATORY licwa Harold Parks, L.G., L.E.G. Senior Engineering Geologist 10011 Blomberg Street SW, Olympia, WA 98512 11 Phone #: (360) 754-4612 Fax #: (360) 754-4848 1 1 r f 1 1 1 GEOTECHNICAL TESTING LABORATORY VICINITY MAP Figure 1 10011 Blomberg Street SW, Olympia, WA 98512 Phone #: (360) 754-4612 Fax #: (360) 754-4848 47-H'-----=. F /; � 226l ! j' .-'1 ��I ( 1 41. ? • i ZON i.70r �► . • 6S-VEIS :�-C k . • i • j ,,, i k, ..-- i ....4,0•44". 44s. • ndo Lake , 11 V . 1 • ,,,/ -Gravel 5 410,vie`_ i I filitiiii. iii. : . • . -IL..- f 1 • 1 11 �%; aNE ITe ` 1 R 1 ( 1 , - ,•,\,, • 1 Ai . SO Spli 1 il' I I. r„ - , — - J 1 -1 \ piiii1 Aiti f i------ i J1I_ 1 fkik'. .ire . 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