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Home My WebLink AboutSPI2005-00263 GeoTech Report - SPI Inspections - 4/12/2006 SON.STAT MASON COUNTY A o PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEEPO ° S NU o T Z Shelton, Washington 98584 0 r N Y O Z 00 � 1884 iO DATE: April 12, 2006 4j INTER-DEPARTMENTAL COMMUNICATIONS ` TO: Allan Borden PARCEL # 32234-51-00041 FROM: Alan Berbisco, Project Engineer-PW BUILDING PERMIT NUMBER: SPI 2005-00263 SUBJECT: Geotechnical Report NAME: Frank Isaac Allan, The geotechnical report prepared for the proposed single family residence located at 540 East Olympic Vista Drive Union,has been received and reviewed by Public Works. The report satisfactorily meets the County's requirements for geotechnical reporting. The site has a steepest slope of more than 100%and the author recommended a building setback of 25 feet. During site investigation,the author did not find any evidence of deep-seated landslide activity or significant erosion onsite. The author concluded that, the proposed development of property is stable and will not cause stability problems for the subject property or neighboring properties. For the foundation elements that are located near the slope between 5 and 30%, the footing should be located a minimum of 2 times the footing width from the slope or properly prepared structural fill. Removal of natural vegetation should be minimized and limited to the active construction areas. Only hazard trees located on steep slopes may be removed only if the stumps remain to deter erosion. Surface water and roof runoff should be controlled and tight-lined to infiltration area. I recommend accepting the report as satisfying the county's requirement(s)for stability investigation and geotechnical reporting. 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. Please feel free to contact me at 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, +Aan brbi�sco�� Project Engineer RECI E N 0 5 202J MCCD - PLANNING Geotechnical Report 540 East Olympic Vista Drive Union, WA Prepared for: Frank Isaac Victoria, TX by Geotechnical Testing Laboratory Olympia, Washington September 26, 2005 GEOTECHNICAL TESTING LABORATORY FRANK ISAAC 512 WEST COLORADO STREET VICTORIA,TX 77901 RE: GEOTECHNICAL REPORT 540 EAST OLYMPIC VISTA DRIVE UNION,WASHINGTON 98592 PARCEL 322345100041 N470 20.774',W 1230 03.300' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence. The site is located along the north-facing hillside, approximately 2 miles east of Union, Washington. The location of the site is shown relative to the surrounding area on the Vicinity Map, Figure 1. it lk �" .. ,• yam, - i� s Our understanding of the project is based on our discussions with you and our explorations and review of the site. We understand that the one-acre site is to be developed with a single-family residence and septic drainfield. A conventional foundation is proposed. The site is accessed from East Olympic Vista Drive. In general, grading will consist of the excavation of the foundation and footings. The approximate layout of the site is shown on the Site Plan,Figure 2. The site slopes toward the north and northwest from the proposed building location. The steepest slope measured onsite was in excess of 22 percent. Offsite slopes to the north are in excess of 40 percent. 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 1 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 and surrounding vicinity. 3. Investigate shallow subsurface conditions at the site by observing the exposed soil and reviewing published well logs. 4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations. 5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria (including hillside grading), temporary and permanent cut and fill slopes, drainage and erosion control measures. SITE CONDITIONS SURFACE CONDITIONS The site is located in an area of moderate residential development in the Puget Sound glacial upland south of the Hood Canal. The site has mostly northwestern exposure. We conducted a reconnaissance of the site area on September 16,2005. Site elevations range from approximately 286 to over 344 feet. The proposed building location has vegetation common to the Northwest. The vegetation includes fir, cedar, hemlock,pine, and madrone trees as well as bracken fern, sword fern, salal,huckleberry,manzanita,and grasses. At the time of the site visit, we observed no evidence of active surface erosion at the potential building location. No evidence of deep-seated slope instability was observed. Sloughing and sliding was not observed onsite. Surface water flow was not observed onsite. The general topography of the site area indicates that drainage flows toward the north and northwest from the potential building location. '�: • '�i y• .ems,. ti h, SITE GEOLOGY The site is generally situated within the 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 (stage) of the Fraser glaciation that occurred between about 8,000 and 11,000 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, the soils are composed of Vashon glacial material. 10011 Blomberg Street SW,Olympia, WA 98512 2 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SITE SOILS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as an j Alderwood gravelly sandy loam, 30 to 45 percent slopes(Ad),at the site. The report reads: j The Alderwood soils typically formed from gravelly glacial 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. An erosion hazard may exist if the vegetation is removed. ,, _ r �• _.� _ " �tit. 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: Till— 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. The Geologic Map of Southeastern Mason County, Washington, USGS Water-Supply Bulletin 29 by Noble and Molenaar(1970)describes the site as till. The till(Qvt) is described as: Cobbles and coarse gravel in matrix of fine sand, silt, and clay. Generally a compact, unsorted mixture. Extensively underlies drift plains in thicknesses of a few feet to more than 50 feet. Poorly pervious, but has sand and gravel streaks that may yield small quantities of perched groundwater. Serves as confining aquiclude to artesian groundwater at some localities near sea level. The Geologic Map of the Shelton 7.5-minute Quadrangle, Mason and Thurston Counties, Washington by Schasse, Logan,Polenz,and Walsh(2003)describes the site as Vashon till(Qgt)and is described as: Vashon till—Unsorted and generally highly compacted mixture of clay, silt, sand, and gravel deposited directly by glacier ice; gray where fresh and light yellowish brown where oxidized; 10011 Blomberg Street SW, Olympia, WA 98512 3 Phone#: (360)754-4612 Fax#: (360)754-4848 i I I __ GEOTECHNICAL TESTING LABORATORY generally of very low permeability; most commonly matrix-supported but may be clast- supported; matrix generally feels more gritty than outwash sands when rubbed between fingers, due to being more angular than water-worked sediments; cobbles and boulders commonly faceted and(or) striated; ranges in thickness from wispy, discontinuous layers less than 1 in. to more than 30 ft thick; thicknesses of 2 to ]Oft are most common; mapped till commonly includes outwash clay, silt, sand, gravel, or ablation till that is too thin to substantially mask the underlying, rolling till plain; y g, n, erratic boulders are commonly associated with till plains g P y p but may also occur as la deposits where the underlying g p y g deposits have been modified by meltwater; typically, weakly developed modern soil has formed on the cap of loose gravel, but the underlying till is unweathered; local textural features in thick till exposed along Hammersley Inlet in the adjacent Squaxin Island quadrangle (Logan and others, 2003a) include flow banding and apophyses commonly extending 10 to 15 ft downward into underlying sand and gravel and that are oriented transverse to ice flow direction. d►- t SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed building site soils as well as reviewing available well logs. Depth to groundwater is unknown but presumed deep. Depth to competent soil is approximately 14 inches throughout the potential building location. SUBSURFACE CONDITIONS 3 In general, dense Alderwood gravelly sandy loam _ was observed in the undisturbed portions of the site. Glacial till material was observed below the w t Alderwood material. Groundwater was not t observed or encountered. Groundwater seepage was not observed onsite. Based on the site topography and the nature of the near surface soil, seasonally perched groundwater conditions are not expected at the proposed building location during periods of extended wet weather. 10011 Blomberg Street SW,Olympia,WA 98512 4 Phone#: (360)7544612 Fax#: (360)754-4848 i GEOTECHNICAL TESTING LABORATORY SLOPE STABILITY Slopes in excess of 100 percent were observed onsite. 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. The near-surface soils are in a dense to very dense condition except at the ground surface. The surficial soils are generally in a medium dense condition. In general,the undisturbed native soils of the site consist of a mixture of variable amounts of sand, silt,and gravel. These soil materials are in a 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 was observed onsite 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. Raveling, sloughing,and sliding were not observed along the sloping portions of the site. 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 discouraging runoff from the steep slopes. Erosion control recommendations for the sloping areas are provided in the"Erosion Control"section of this report. 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 project. The proposed project will not undermine adjacent slopes. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope stability. The hazards of the landslide area can be overcome in such a manner as to prevent harm to property and public health and safety,and the project will cause no significant environmental impact. In general, the Alderwood soils observed at the site may be suitable for use as structural fill material. Saturated soil conditions are not 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 structure with conventional 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 single-family residence are presented below. 10011 Blomberg Street SW,Olympia,WA 98512 5 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Y ,ter ,, •// f;i;.�i ,A - � ilk Ak it { �� r 'i ♦ ! ��r -:.� � i �. 1_ y��rr I� i.a'7►. '1i' ' •r. J .4� -Iot kll J/ i e4 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 northern slope 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. 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 ("Hh') d. Kitsap silt loam ("Kc') The soils at the site are mapped as Alderwood gravelly sandy loam(Ad). This site does meet the technical criteria of an erosion hazard area. '• jt�'�'� ^vH r i t• +�rf _ ,�.�t ! �JR:�(�ir_ , �'""'��h,►,�.; tws � ,` ♦`1 1� 16 .-L�-e.1w. .•tip_.�Xl� .�`.r.� _ ' '�!. tea: —-_ � � F . 10011 Blomberg Street SW,Olympia, WA 98512 6 Phone#: (360)754-4612 Fax#:(360)754-4848 GEOTECHNICAL TESTING LABORATORY SLOPE STABILITY The Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977) describes the site area as Class 2. Class 2 is expressed as: Areas believed to be stable under normal conditions, but may become unstable if disturbed by man's activities, if slope is oversteepened by erosion, or if subjected to strong seismic shaking. Slopes generally steeper than 15 percent, but may be less in some areas of weak geologic materials. Includes areas underlain by. well-drained sand and gravel, mostly on valley sides that lack known slope failures;glacial till with steep slopes;and bedrock. Based on our field observations, explorations and our experience with the soil types encountered on the property, we conclude that although portions of the slopes on the lot exceed 22 percent and offsite slopes exceed 40 percent, the proposed building location is generally stable relative to deep-seated failure in their present configuration. Excavation and backfilling 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. BUILDING SETBACK A building setback from landslide hazard areas is required unless evaluated and Peak Shear Stress vs. Normal Stress reduced by an engineering geologist or a Gravelly Sandy Loam licensed professional engineer. Based on 300° 41 our geotechnical evaluation of the site and our experience in the area, a building 2500 setback will be needed for this lot. The building setback may be measured from the 2000 Ir bottom of the footing to the face of the a steep slope in accordance with the International Building Code (1805.3.1). 1500 The following figure represents a shear y angle for the gravelly sandy loam. Shear o 100 angle and cohesion are variables used to a model the site. I 500 I t i!4 ton fl2ton 0 1 ton 0 500 1000 1500 2(= 2500 MM Normal Stress(pan 10011 Blomberg Street SW, Olympia, WA 98512 7 Phone#: (360)754-4612 Fax#:(360)754-4848 GEOTECHNICAL TESTING LABORATORY Slope stability was modeled using the GEO-SLOPE/W program(version 5.20) in both static and extreme dynamic conditions (Ca = 0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price methods. The site was modeled using a monolithic layer of Alderwood gravelly sandy loam. The material was determined to have a unit weight of 139 pcf, cohesion of 200 psf, and a shear angle of 41°. Under static conditions, the slopes remained stable to deep- seated and shallow failure. Under dynamic loading, the 3,328 computations demonstrated that the slope is not susceptible to surficial raveling and large deep-seated failure. The following figure illustrates the moment factor of safety for slope "A" under the existing conditions. The figure is the solution of greatest concern and exhibits the need for a building Setback setback of 25 feet from the crest of the northern slope. All foundation elements shall be constructed on native material or engineered fill material. Isaac Site -- Slope A • • • • • • Analysis Method: Morgenstern-Price . b• • • • • • Direction of Slip Movement: Left to Right • . • • • • • Slip Surface Option: Grid and Radius . . n• • • • • • • Seismic Coefficient: Horizontal and Vertical • • • • • • • • 1.50 . . . . . . . . . . co . . . . . . . . . • 330 320 310 c: 300 Alderwood Gravelly Sandy Loam }► 290 Unit Weight: 139 > 280 Cohesion: 200 W 270 Phi: 41 260 250 0 25 50 75 100 125 150 175 200 225 250 Distance (ft) 10011 Blomberg Street SW, Olympia, WA 98512 g Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are natural processes that affect slope areas. Surficial raveling or sloughing was not observed onsite. 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 sloped areas. 2. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill. 3. Trees may be removed on sloped areas as long as the stumps remain. SEISMIC—LIQUEFACTION HAZARD According to the Seismic Zone Map of the United States contained in the 2003 International Building Code(IBC), the project site is located where the maximum spectral response acceleration is 45 percent of gravity(g). The Liquefaction Susceptibility Map of Mason County, Washington by Palmer, Magsino, Poelstra, Bilderback, Folger,and Niggemann(September 2004)maps the site area as having a very low liquefaction potential. The Site Class Map of Mason County, Washington by Palmer, Magsino, Bilderback, Poelstra, Folger, and Niggemann(September 2004)maps the site area as site class C. Site class C is a very stiff soil. Based on the subsurface conditions observed at the site,we interpret the site conditions to correspond to a seismic Soil Profile Type D, for Stiff Soil, as defined by Table 1615.1.1 (IBC). 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 only mildly susceptible to jliquefaction. The near-surface soils are generally in a dense condition and the static water table is located well j below the surface. Shaking of the already dense soil is not apt to produce a denser configuration and subsequently j excess pore water pressures are not likely to be produced. k µ• tl 10011 Blomberg Street SW,Olympia, WA 98512 9 Phone#: (360)7544612 Fax#: (360)754-4848 I GEOTECHNICAL TESTING LABORATORY EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development. Removal of natural vegetation should be minimized and limited to the active construction areas. Yard landscaping around the home is permissible, but understory growth on the slopes should be encouraged as much as possible as a deterrent to erosion. Hazard trees located on steep slopes may be removed only if the stumps remain to deter erosion. Temporary and permanent erosion control measures should be implemented and maintained during construction and/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 will create a need for erosion control measures as listed above. „� � .• ,ice EARTHWORK SITE PREPARATION All areas to be excavated should be cleared of deleterious matter including any existing structures, debris, duff, and vegetation. Based on our observations, we estimate that stripping on the order of 6 to 12 inches will be necessary to remove the root zone and surficial soils containing organics. Areas with deeper, unsuitable organics should be expected in the vicinity of depressions or heavy vegetation. Stripping depths of up to 2 feet may occur in these areas. These materials may be stockpiled and later used for erosion control and landscaping. Materials that cannot be used for landscaping or erosion control should be removed from the project site. 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. We recommend that trees be removed with the roots, unless located on a slope. 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. If structural fill is needed, we recommend that a member of our staff evaluate the exposed subgrade conditions after removal of vegetation and topsoil stripping is completed. g P PP g P eted. Any soft, loose or otherwise unsuitable areas delineated during foundation preparation or probing should be compacted, if practical, or over-excavated and replaced with structural fill, based on the recommendations of our report. 10011 Blomberg Street SW,Olympia, WA 98512 10 Phone#: (360)754-4612 Fax#:(360) 754-4848 GEOTECHNICAL TESTING LABORATORY 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 the 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 ma terial should be adjusted as necessary for proper compaction. SUITABILITY OF ONSITE SOILS AS FILL Onsite soils may be considered for use as structural fill. In general,the native soils(sand, loam,and minor gravel) encountered on the site must have less than 10 percent fines (material passing the US No. 200 Sieve) to be suitable for use as structural fill. CUT AND FILL SLOPES All job site safety issues and precautions are the responsibility of the contractor providing services and/or work. The following cut/fill slope guidelines are provided for planning purposes. Temporary cut slopes will likely be necessaryduring grading operations. Asa general guide temporary slopes of 1.5 to 1 (horizontal to vertical) or flatter may be used for temporary cuts in the upper 3 to 4 feet of the glacially P g Y consolidated soils that are weathered to a loose/medium-dense condition. Temporary p rary slopes of 1 to 1 or flatter may be used in the unweathered dense to very dense sands and gravel. These guidelines assume that all surface loads are kept at a minimum distance of at least one-half the depth of the cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slopes will be necessary where significant raveling or seepage occurs. Surface drainage should be directed away from all slope faces. All slopes should be seeded as soon as practical to facilitate the development of a protectiv evegetative cover or otherwise protected. i 10011 Blomberg Street SW,Olympia,WA 98512 11 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY FOUNDATION SUPPORT Where foundation elements are located near slopes between 5 and 30 percent, the footings should be located a minimum of 2 times the footing width from the slope face(horizontally), and founded in medium dense or denser native soils or properly prepared structural fill. We recommend a minimum width for isolated and continuous wall footings to meet IBC 2003. Footings founded as described above can be designed using an allowable soil bearing capacity of 2,000 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. 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 0.40 be used to calculate friction between the concrete and the underlying soil. Active pressure may be determined using an allowable equivalent fluid density of 150 pcf(pounds per cubic foot). We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions, with differential settlements between comparably loaded footings of'/2 inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation subgrade 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 5 percent fines (by weight). The drainage material should be placed and compacted to an unyielding condition. A synthetic vapor barrier may 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. RETAINING WALLS Retaining walls may be utilized on the sloping portion of the site to retain fill material. The lateral pressures acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space is backfilled with clean granular, well-drained soil (washed rock), the design active pressure may be determined using an active pressure coefficient equal to 0.25 (Ka= 0.25). This design value assumes a level backslope and drained conditions as described below. Retaining walls located on or near the toe of a slope that extends up behind the wall should be designed for a lateral pressure, which includes the surcharge effects of the steep slope in proximity to the wall. Although not expected at this site,the following data is provided for planning purposes. 10011 Blomberg Street SW,Olympia,WA 98512 12 Phone#: (360)754-4612 Fax#:(360)754-4848 GEOTECHNICAL TESTING LABORATORY For an irregular or composite slope, the equivalent slope angle may be determined by extending a line upward from the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical)to a point where the line intersects the ground surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by the percentage given in the following table: SLOPE INCLINATION: EQUIVALENT FLUID PRESSURE Slope Angle Percent Increase Equivalent Fluid Pressure Horizontal 0% 35 pcf 3H:1 V 25% 44 pcf 2H:1 V 50% 53 pcf 1 H:1 V 75% 61 pcf If the walls are greater than 6 feet in height, exclusive of the footing, additional design considerations should be applied. Positive drainage,which controls the development of hydrostatic pressure,can be accomplished by placing a zone of coarse sand and gravel behind the walls. The granular drainage material should contain less than 5 percent fines. The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should also extend from the base of the wall to within 1 foot of the top of the wall. The drainage zone should be compacted to approximately 90 percent of the MDD. Over-compaction should be avoided as this can lead to excessive lateral pressures. A perforated PVC pipe with a minimum diameter of 4 inches should be placed in the drainage zone along the base of the wall to direct accumulated water to an appropriate discharge location. We recommend that a non-woven geotextile filter fabric be placed between the drainage material and the remaining wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the drainage zone,with time,can reduce the permeability of the granular material. The filter fabric should be placed in such a way that it fully separates the drainage material and the backfill, and should be extended over the top of the drainage zone. Lateral loads may be resisted by friction on the bases of footings and as passive pressure on the sides of footings and the buried portions of the wall. We recommend that an allowable coefficient of friction of 0.40 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined by using a passive pressure coefficient equal to 4(Kp=4). Factors of safety have been applied to these values. RIM ., M_ , •,r' III ' +rr +.f '-"� _ . .Y j� � � .✓" +d /� 10011 Blomberg Street SW,Olympia, WA 98512 ; Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY RETAINING WALL ALTERNATIVES Typically, block wall systems are more cost effective for long-term walls than the other options. Specific design criteria for these options can be provided at your request by the block manufacturers. SITE DRAINAGE All ground surfaces, pavements and sidewalks should be sloped away from the residence and associated structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch basins and tight-lined to the proposed infiltration location in the western portion of the parcel. We recommend that conventional roof drains be installed. Footing drains shall be installed for the single-family residence. The roof drain should not be connected to the footing drain. For footing drains, the drain invert should be below the bottom of the footing. We recommend that the collected stormwater runoff be directed to the potential infiltration location by tight-line. Drainage control measures are included on Figure 3. Onsite irrigation to lawn areas should be closely monitored. We do not expect any adverse affects on the recharge condition of the groundwater system. SEPTIC IMPACT The proposed septic drainfield will be located in the western portion of the parcel. The location is over 50 feet from the northern slope and will not affect the overall slope stability of the site. Jt s LIIVIITATIONS We have prepared this report for the use of Frank Isaac and members of his design team to use in the design of a P P P 1� � 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. This report is quantified as a micro-stud and not a macro-study. Geotechnical Testing Laboratory P q Y Y g and its personnel cannot be responsible for unforeseen and widespread geologic events (such as earthquakes, ` large-scale faulting,and mass wasting)beyond the scope of this project. 10011 Blomberg Street SW,Olympia,WA 98512 14 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY 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. 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. Respectfully submitted, �e o{ Wash�� GEOTECHNICAL TESTING LABORATORY P,"U po,,� Harold Parks,L.G.,L.E.G. Engineering Geologist Senior Engineering Geologist 827 Geo�o HAROLD PARKS 10011 Blomberg Street SW, Olympia, WA 98512 15 Phone#: (360)754-4612 Fax#:(360)754-4848 G EOTECHNICAL TESTING LABORATORY FIGURE I VICINITY MAP �, `aT• G �f.. •,y d i -0� _ - �l'-�/��• ..K• 4' _''.51f1'" `r�rr��N /�/~\ � !^--�'. ••✓: e:'fl '/�r'r �/�, ~J\ram �4J% N47•-2: , C , N47.2t5' S IN zy Scale -^� T� \�f `ram "`• J/// � --_ � 't I � � i � ` r��, .ii� }I '�s, I !� i, / '/ : •I/ -.�"SI�/i'• , lye,`� -_- G r yT,�'� / ! �,.#I'4J • ....':.r f/ `i/ •. �/r /4 -~� .. /. f�'1. �'Ir{; �, t ! Sy/ ',/!r r+ � r , L._ tom_ .i—'Y j 1'\ i '.'•: t :,� I ,� r i / ��` 1 n 1 f� n ° // } 1 - I. i/ 49 10011 Blomberg Street SW, Olympia, WA 98512 16 Phone#: (360) 754-4612 Fax#: (360) 754-4848 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH M'IV144�M MINIMUM,6 INCH SUGGESTED i_'�."Y :a.N`�v� ,.j.:_ ^. •'.:\..`f�';,mil-.'-_ s4: _; '•..tea t._.: .l�~�:1:•. T.... .�.:'�i'MSS f.:�`;, �. ��.�;��4�i� ..7 �,a.;•�!8�1'�<`wi�L�T••�+sa -X.%ry`,'��y��!.t..w:a'...._ tiy-Y;�.`:..�`Y,', _.,$+; .�:..:,ty,.:..�h.♦ �.:�.-��,;�_i.-f....ti - .::�i:ems:=•:•"..�.-r.::;::',' _•:;t.•�,�>w`�.. - `•. *,y�•�:.w. tit ..�' �:ti:•: `.�.: TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL ` OR ENERGY DISPERSION DEVICE "`'`<" -v `._ - �.• 's ': ;,_i..s:>_.t`,_, t -• "�:�. ..�_.�... aid•` •tti_ GRASS—LINED SWALE SHOULD BE A MINIMUM ONE FOOT WIDE AT THE BOTTOM AND ONE FOOT DEEP WITH A MAXIMUM SLOPE OF 5 PERCENT. MINIMUM 4 FEET LEVEL SECTION GEOTEXTILE FABRIC Geotechnical Testing Laboratory Geotechnical Services +oon 8bmb- sc sw 12 FIGURE 3 QA/QC Services Ph �1°wn sss" P" ( 0)75"8 DRAINAGE DETAILS Testing Services Fes:(3so>�s+aase Not to scale FILTER FABRIC MATERAL 60-WIDE ROLLS USE STAPLES OR WIRE RING TO ATTACH FABRIC TO WIRE • F �Q�°EWIIRE Geotechnical e / 2 iti1 Testing 5� SURFACE �\I E ij Laboratory - / 1 me WOOD POSTS,STANDARD OR BURY BOTTOM OF FILTER BETTER EQUAL ALTERNATE: MATERIAL IN 6'X17 TRENCH R� \? STEEL FENCE POSTS FILTER FABRIC 6' ZXT X14GAUGE WIRE (� FABRIC OR EQUIVALENT GROUND SURFACE Z 5'-0' •l•- PROVIDE SIP-1 1/7 WASHED GRAVEL BACKFILL IN TRENCH 17 AND ON BOTH SIDES OF FILTER miry OTE TIAL � FENCE FABRIC ON THE SURFACE 8'MIN � ,y0♦ IN FI n LEED\ POSTS ON AT STEEL FENCE \ FILTER FABRIC FBNCI NOTES: Geotechnical Services I.FILTER FABRIC SHALL BE PURCHASED IN A CONTINUOUS ROLL CUT TO A/^C Services THE LENGTH OF THE BARRIER TO AVOID USE OF JOINTS.MEN JOINTS ARE NECESSARY,FILTER CLOTH SHALL BE SPLICED TOGETHER ONLY AT ASTENED AT BOTH ITH END MIN OT HE 184NCH OVERLAP AND SECURELY Testing Services FASTENED AT BOTH ENDS TO THE POST. YJ� �lO 2 SECURELLY INTO THE GROUND(MINIMUM OF F EET APART AND DRIVEN WINCHES) tS f- S.A TRENCH SHALL BE EXCAVATED APPROXIMATELY 81CNE8 WOE AND 12 ,y INCHES DEEP ALONG THE LINE OF POSTS AND UPSLOPE FROM THE BARRIER. 30 ?�, 10011 Blomberg St.SW 4.WHEN STANDARD STRENGTH FILTER FABRIC IS USED,A WIRE MESH SUPPORT FENCE SHALL BE FASTENED SECURELY TO THE RSLOPE SIDE Olympia,WA 98512 Try / b OF THE POSTS USING HEAVY43UTV WARE STAPLES AT LEAST I INCH L LONG,TIEVARESOR HOG RINGS.THE AIRE SHALL EXTEND INTO THE Phone:(360)754-4612 h O , IN ECH A MINIMUM OF 41NCHES AND SHALL NOT EXTEND MORE THAN 36 31 O NCHESABOVE THE ORIGINAL GROUND SURFACE. Fax:(360)754-4848 ♦ 5.THE STANDARD STRENGTH FILTER FABRIC SHALL BE STAPLED OR VARIED _(1 TO THE FENCE AND 201CHES OF FABRIC SHALL BE EXTENDED INTO THE TRENCH.THE FABRIC SMALL NOT EXTEND MORE THAN36 Date: 09/22/2005 O D 3 INCHES ABOVE THE ORIGINAL GROUND SURFACE.FILTER FABRIC SHALL N NOT BE STAPLED TO THE EXISTING TREES. Drawn by: B Winder N O lT r TBM = 321.14 6.MEN EXTRA-STRENGTH FILTER FABRIC AND CLOSER POST ACING IS Checked b SBG S �' USED,THE WARE MESH SUPPORT FENCE MAP BE ELIMINATED,IN SUCH y g M /s9 536 RR SPIKE ON SOUTH SIDE AAC E,THIWF„ER AERBRnONS STAPLED ABOVEC DIRECTLY TOTES3,THE Edited by: LL y� OF 8" DIA. DOUG FIR Dwg#:09-22-05-075 10 O C T'O g � 7.FILTER FABRIC FENCES SHALL T REMOVED BEFORE THE RSLOPE I T AREA HAS BEEN PERMANENTLY STABIBI LIZED. O `J O ^ NCf SIL Qh 6,FILTER FABRIC FENCES SHALL BE INSPECTED IMMEDIATELY AFTER EACH RAINFALL AND AT LEAST DAILY DURING PROLONGED RAINFALL.ANY \O a �1 1� REQUIRED REPAIRS SHALL BE MADE IMMEDIATELY. � E $ �♦\�6• G ;, 41 h 4 302 j //�''\�� GENERAL EROSION CONTROL NORB: JV \� I / 1. EROSION CONTROL MEASURES SHALL BE IN PUCE PRIOR TO THE L 1V- BEGIN I C Of AND THE E INSTALLATION PROJECT ENGINEER AND THE CWHTI' EROSION INSPECT AND APPROVE THE INSTO BEGINNING NJ a b EROSION CONTROL MEASURES PRIOR TO BEGINNING CONSTRUCTION. 2.EROSION CONTROL MEASURES ARE NOT LIMITED TO THE ITEMS T[� ON THIS PLAN.THE CONTRACTOR IS RESPONSIBLE FOR THE INSTALLATION ANDFE'STINGORPR OF ALL EROSION CONTROL MEASURES. POTENn '\e SHALNO L ATION BE ALLOWED. CARESHALLB TAKENSED OPRE FACILITIESPREVENT PROJECT NAME: TEN R SHALL BE ALLOWED.CARE SHALL BE TAKEN TO PREVENT MIGRATION INFI TION `F� h OF SILTS TO OFF SITE PROPERTIES. ISAAC SITE / CATION PRIVATE EASEMEN 3.THE CONTRACTOR SHALL MAKE DAILY SURVEILLANCE OF ALL EROSION r { TO THE EROSION AND MAKE MEASURES THSSARY E EPAIRS OR CONTRACTOR 540 EAST OLYMPIC VISTA DR. 4 1 TO THE EROSION CONTROL MEASURES.THE CONTRACTOR SHALL PROVIDE N ADDITIONAL EROSION CONTROL MEASURES AS DETERMINED NECESSARY UNION, WASHINGTON BY THE COUNTY INSPECTOR AND/OR THE PROJECT ENGINEER.FAILURE 4�.7' NCA b TO COMPLY WITH ALL LOCAL AND STATE EROSION CONTROL PARCEL 322345100041 N REQUIREMENTS MAY RESULT IN CIVIL PENALTIES BEING LEVIED Th p 4 ^ O AGAINST THE CONTRACTOR AND/OR PROJECT OWNER. Vj h O N 4.DURING THE WET SEASON(NOVEMBER TO MARCH)ALL DISTURBED SOILS N C SHALL BE STABILIZED WITHIN 48 CURS AFTER STOP OF WORK.EROSION CONTROL MEASURES SHALL INCLUDE,BUT NOT BE LIMITED TO, —��, ♦ ry ♦ ^� Z COVERING THE EFFECTED AREA INCLUDING SPOIL PILES WITH Revisions: J?B 7� 'yy y PLASTIC AR CHIPS.SHEETING,E D DING OF TH ISTURB D AREAS SHALL STRAW MATTING.JUTE MATTING,STRAW TAKE 1�.� 1�4.27 r (� PLACE AS WEATHER PEHU6TS. SB9'4934 E 2613.C81 BT�`��M 5.ALL SEEDED OR SODDED AREAS SHALL BE CHECKED REGULARLY TOMAKE SURE VEGETATIVE COVERAGE IS COMLETE.AREAS SHALL BE REPAIRED.RESEEDED,AND FERTILIZED AS REQUIRED. 6.TRACKING OF SOIL OFFSITE WILL NOT BE ALLOWED,IF ANY SOIL IS TRACKED ONTO A COUNTY STREET.IT SHALL BE REMOVED BY THE END OF THAT WORKING DAY.ANY FURTHER TRACKING OF MUD WILL THEN BE PREVENTED BY SWEEPING OR WASHING OF THE VEHICLES TIRES / BEFORE DRIVING ON A COUNTY STREET. 7.NO MORE THAN SOD LF OF TRENCH ON A DOWMSLOPE OF MORE THAN 5 PERCENT SHALL BE OPENED AT ONE TIME. 6.EXCAVATED MATERIAL SHALL BE PLACED ON THE UPHILL SIDE OF TRENCHES. A TRENCH DEWATERING DEVICES SHALL BE DISCHARGED IN A MANNER THAT W LL NOT ADVERSELY AFFECT FLOWING STREAMS.DRAINAGE SYSTEMS OR SCALE 1"=30' OFFSITE PROPERTIES SCALE:1 MICA=30 feet 10.ALL STORM SEWER INLETS RECEIVING RUNOFF FROM THE PROJECT DURING C.I.=2' CONSTRUCTION SHALL BE PROTECTED SO THAT SEDIMENT-LADEN WATER VALL BE FILTERED BEFORE ENTERING THE CONVEYANCE SYSTEM. DATUM ASSUMED II,ALL OFFSITE CATCH BASINS IMMEDIATELY ADJACENT TO THE SITE /� THIS IS NOT A SURVEY SHALL BE PROTECTED FROM SILTATION I2.ALL DISTURBED AREAS SHALL BE SEEDED OR SODDED UPON COMPLETION FIGUREL OF WORK.THE CONTRACTOR SHALL BE RESPONSIBLE TO ENSURE THAT COMPLETE COVERAGE OF THE DISTURBED AREAS IS PROVIDED 6 THAT O 10 ZO 30 GROWTH OF THE VEGETATION IS ESTABLISHED. SITE PLAN 13.CATCH BASINS SHALL TRAP SEDIMENT FILTER FABRIC MUST BE PLACED UNDER GRATE UNTIL VEGETATION N IS ESTABLISHED. ' �1'2/'�toy ( • WORK ORDSR *'PUBLIC WORKS DEPT• W. Do's PERMIT#1 - po26 N 'ty►pe of wnt otoe tos NAMED f� Sa�C-- AGENCY/OOMPANY eIwNo ADDRUS . PHONE AN—Pub.Waft P4rs& • ja Sam IIIUJED DATE TotAL AM ' tE'1 IktuM� �• • ' eAR,t: rRa!Nb ' ' • fanr� � l$isl HoYts i F� T�Tlll.i . • ��VIPMEtdt`UBEp: [?Ati !tA!! y � � ....,..,..,..�....INYrI<,,........,.,.. PAID-DATE...,.,....,,,,..,,