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Home My WebLink AboutGeoTech Report for BLD2006-01971 - BLD Engineering / Geo-tech Reports - 12/7/2006 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton, Washington 98584 H. DATE: December 7, 2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Kel McAboy/ Planning PARCEL # 32236-51-00027 FROM: Patricia Carroll, PW BUILDING PERMT NUMBER: BLD2006-01971 SUBJECT: Geotechnical Report NAME: Jeff Brady —Bob Drohman Hi Kel; The Geotechnical Report that was prepared for the proposed single-family residence at 9991 East State Route 106, Union was received and reviewed by the Mason County Public Works. The use of a building setback of 25 feet from the face of the northern slope is necessary. The building setback may be measured from the bottom of the footing to the face of the steep slope in accordance with the IBC (International Building Code) (1805.3.1). The use of conventional spread footing may be utilized at the site for support of the structure. A vapor barrier is recommended for all slabs-on-grade. All areas to be excavated should be cleared of deleterious matter including any existing structures, debris, duff, and vegetation. Removal of natural vegetation should be minimized and limited to the active construction areas. Yard landscaping around the home and on the slopes should be encouraged as much as possible as a deterrent to erosion. Materials that cannot be used for landscaping or erosion control should be removed from the project site. They recommend that trees be removed with the roots, unless located on slopes. A member of their staff should evaluate the exposed subgrade conditions after vegetation removal and topsoil stripping is completed. Compaction of all structural fills should be placed horizontal lifts and compacted to 95% according to ASTM D-1557. The engineer states that 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 for the life of the project. They recommend that earthwork be undertaken during favorable weather conditions. Retaining walls may be utilized on the sloping portion of the site to retain fill material and should be designed for a lateral pressure. The lateral pressures acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. Is also dependent upon the presence or absence of hydrostatic pressure. If Jeff Btady/Bob Drohman BLD2006-01971 Page 1 of 2 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). See recommendations of the engineer. 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 appropriate drainage facilities or to the base of the northern slope. Roof drains and footing drains shall be installed and should not be connected. The drain invert should be below the bottom of the footing and be directed to the appropriate drainage facilities by tight-line or the base of the northern slope. Follow Drainage plan Figure 3. All requirement/recommendations contained in the assessment should be incorporated into the site's development and made conditions for permit issuance. Our agency cannot be responsible for unforeseen and widespread geologic events (such as earthquakes, large-scale faulting, and mass wasting). Please feel free to contact me at ext. 619 or John Sliva ext. 724 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, C" s� Patricia Carroll/Public Works Jeff Btady/Bob Drohman BLD2006-01971 Page 2 of 2 RECEIVED NOV 0 12006 MASON COUNTY GEOTECHNICAL REPORT -9991 EAST STATE HIGHWAY 106 LOT 1 UNION, WASHINGTON PREPARED FOR BOB DROHMAN BY GEOTECHNICAL TESTING LABORATORY OLYMPIA, WASHINGTON MAY 8, 2006 RECEIVED OCT 16 2006 FOSTER&WILuAMS ARCHITECTS GEO'i ECHNICAL TESTING LABORATORY I CONTACT INFORMATION PREPARER INFORMATION GTL PROTECT NUMBER: 06-2489-04 ADDRESS: 10011 BLOMBERG STREET SOUTHWEST OLYMPIA,WASHINGTON 98512 TELEPHONE: (360)754-4612 IFACSIMILE: (360) 754-4848 IEMAIL ADDRESS: GEOTESTLAB@COMCAST.NET ' CLIENT INFORMATION CLIENT: BOB DROHMAN CELLULAR: (360) 789-6514 I MAILING ADDRESS: 4326 LEGACY DRIVE OLYMPIA,WA 98516 ' SITE ADDRESS: LOT 1 ^9991 EAST STATE ROUTE 106 UNION,WA 98592 PARCEL NUMBER: 322365100027 GPS LOCATION: N470 21.496' W1230 00.785' I I I10011 Blomberg Street SW,Olympia, WA 98512 2 Phone#: (360)754-4612 Fax#: (360) 754-4848 I GEOTECHNICAL TESTING LABORATORY SCOPE OF UNDERSTANDING BOB DROHMAN 4326 LEGACY DRIVE OLYMPIA,WA 98516 RE: GEOTECHNICAL REPORT LOT 1 —9991 EAST STATE ROUTE 106 UNION,WA 98592 PARCEL 322365100027 N470 21.496' W 1230 00.785' As per your request, we have conducted a soils exploration, foundation evaluation, and slope stability analysis for the above-mentioned parcel. The results of this investigation,together with our recommendations, are to be found in the following report. We have provided three copies for your review and distribution. Data has been carefully analyzed to determine soils bearing capacities, footing embedment depths, and setback distances. The results of the exploration and analysis indicate that conventional spread and continuous wall footings appear to be the most suitable type of foundation for the support of the proposed structure. Some variability was encountered in comparing the soil profiles of the site. Net allowable soil pressures, embedment depth,and total expected settlements have been presented for the site later in the report. Often, because of design and construction details that occur on a project, questions arise concerning soil conditions. We would be pleased .to continue our role as geotechnical consultants during the project implementation. We appreciate this opportunity to be of service to you and we look forward to working with you in the future. If you have any questions concerning the above items, the procedures used, or if we can be of any further assistance please call us at the phone number listed below. Respectfully Submitted, ♦��e��Wash�� fO GEOTECHNICAL TESTING LkLABORATORV 00 //a',L� Harold Parks,L.G.,L.E.G. nolrowft Geologist � Senior Engineering Geologist 827 ed G eo\0 HAROLD PARKS x C, � 10011 Blomberg Street SW,Olympia, WA 98512 3 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHN1CAL TESTING LABORATORY 1 TABLE OF CONTENTS CONTACTINFORMATION......................................................................................................................2 SCOPEOF UNDERSTANDING................................................................................................................ 3 TABLEOF CONTENTS............................................................................................................................. 4 INTRODUCTION........................................................................................................................................ 5 SITECONDITIONS.................................................................................................................................... 6 SurfaceConditions................................................................................................................................... 6 SiteGeology............................................................................................................................................. 7 SiteSoils................................................................................................................................................... 7 SubsurfaceExplorations........................................................................................................................... 8 SubsurfaceConditions.............................................................................................................................. 8 SlopeStability .......................................................................................................................................... 8 CONCLUSIONS AND RECOMMENDATIONS..................................................................................... 10 General ................................................................................................................................................... 10 LANDSLIDE—EROSION HAZARD AREA........................................................................................... 10 Classification.......................................................................................................................................... 10 SlopeStability........................................................................................................................................ 11 BuildingSetback .................................................................................................................................... 12 Seismic—Liquefaction Hazard............................................................................................................... 14 ErosionControl ...................................................................................................................................... 14 EARTHWORK.......................................................................................................................................... 15 SitePreparation...................................................................................................................................... 15 StructuralFill.......................................................................................................................................... 16 Suitability of Onsite Soils as Fill............................................................................................................ 16 Cutand Fill Slopes................................................................................................................................. 16 FoundationSupport................................................................................................................................ 17 FloorSlab Support.................................................................................................................................. 18 RetainingWalls...................................................................................................................................... 18 Slope Inclination: Equivalent Fluid Pressure......................................................................................... 19 SiteDrainage.......................................................................................................................................... 19 SepticImpact.......................................................................................................................................... 20 LIMITATIONS .......................................................................................................................................... 20 FIGURE1 VICINITY MAP....................................................................................................................... 21 10011 Blomberg Street SW, Olympia, WA 98512 4 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence to be located along the north-facing hillside,approximately 4 miles east of Union,Washington. The site overlooks The Narrows along the southern shore of the Hood Canal. The location of the site is shown relative to the surrounding area on the Vicinity Map,Figure 1. :. caw •~"r ? ram. ' .. �tb_ Our understanding of the project is based on our discussions with you and our explorations and review of the site. We understand that the parcel is to be developed with a single-family residence. The site will be accessed by an existing access road. 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 predominantly slopes toward the north from the proposed building location. The steepest slope measured onsite was in excess of 100 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: 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. 10011 Blomberg Street SW,Olympia,WA 98512 5 Phone#: (360)754-4612 Fax#: (360)754-4848 CEOTECHNICAL TESTING LABORATORY y r c' I I SITE CONDITIONS ISURFACE CONDITIONS The proposed building site is located in an area of moderate residential development in the Puget Sound glacial upland overlooking the Hood Canal. The site has a northern exposure. We conducted a reconnaissance of the site Iarea on April 19,2006. Site elevations range from approximately 8 to 68 feet. The building area of the site has vegetation common to the Northwest. The vegetation includes fir, alder, I madrone, and cedar trees as well as huckleberry, salal, Oregon grape, bracken fern, sword fern, mullien, blackberry,and grasses. I At the time of the site visit, active erosion was not observed at the proposed building location or throughout the site. No evidence of deep-seated instability was observed at the proposed building location or throughout the site. I Surface water flow was not observed onsite. Seepage was not observed throughout the site. The general topography of the site area indicates that drainage flows toward the north. I10011 Blomberg Street SW,Olympia, WA 98512 6 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 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 9,000 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. The Geologic Map of Washington—Northwest Quadrant(2002)has mapped the site geology as advance outwash deposits(Qga)of continental glacial origin. The report reads: Advance outwash — Glaciofluvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained, with interlayered coarser sand, gravel, and cobbles; locally contains nonglacial sediments and deposits mapped as transitional between glacial and nonglacial. Includes the Colvos and Esperance Sand Members of the Vashon Drift and 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 area as advance outwash. The advance outwash(Qva)is described as: Gravel and sand, with some silt and clay at base. Unconsolidated and generally is in discontinuous strata. Underlies till in most of area and up to 200 feet thick. Yields moderate to large quantities (20-800 gp.m) of water where gravel and coarser sand facies below water table. The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site as glacial advance outwash(Qga). The glacial advance outwash is described as: Advance outwash, late Wisconsinan (Pleistocene)--Glaciojluvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained, with interlayered coarser sand, gravel, and cobbles and silt rip-up lag deposits at their base;may contain nonglacial sediments;generally overlain by till. SITE SOILS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as an Alderwood gravelly sandy loam, 15 to 30 percent slopes(Ac). The survey reads: This soil varies more in depth, but otherwise it is similar to Alderwood gravelly sandy loams, 5 to 15 percent slopes. It occurs in close association with and adjacent to that soil. It is on moderately steep ridges, along drainageways, and on elongated irregular slopes. Small areas with slopes of more than 30 percent are mapped with this soil. Surface drainage is more rapid than on the more gentle slopes. Runoff and erosion on the logged and semicleared areas are controlled by the dense growth of plants. Erosion would damage the soil if it were cleared for crops. 10011 Blomberg Street SW,Olympia, WA 98512 7 Phone#: (360)7544612 Fax#: (360)754-4848 GEOTECHNICAL 'TESTING LABORATORY y � t 40; SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed building site soil, reviewing available well logs, and observing the northern slope. The northern slope is exposed due to previous grading. Static groundwater was not encountered,presumed deep,and is beyond the scope of this report. Depth to competent soil is approximately 8 inches throughout the proposed building location. SUBSURFACE CONDITIONS In general, undisturbed dense Alderwood gravelly sandy loam was observed in the undisturbed portions of the site. At the proposed building location, glacial till was observed below the surficial soils. Based on the site topography and the nature of the near-surface soil, seasonally perched groundwater conditions may be expected during periods of extended wet weather. 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. The Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977) describes the site area as Class 2. Class 2 is described as: Areas believed to be stable under normal conditions, but may become unstable if disturbed by man's activities, if O �- slope is oversteepened by erosion, or if subjected to strong seismic shaking. Slopes generally steeper than 15 percent, 6" 36 , but may be less in some areas of weak geologic materials. U Includes areas underlain by: well-drained sand and gravel, mostly on valley sides that lack known slope failures; ------_____ S..k _•.O glacial till with steep slopes; and bedrock 10011 Blomberg Street SW,Olympia, WA 98512 8 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY The Coastal Zone Atlas, Volume 9, Mason County(MA-9)maps the site as Vashon Advance Outwash(Qva). The chance of flooding is less than one percent. Permeability is described as high, while runoff potential is low. Infiltration is moderate on natural slopes and high on cut slopes. Springs at the bases of slopes are common (springs or seeps were not observed during the site reconnaissance). The slope stability is described as "intermediate." 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. Deep-seated landslide activity was not 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 and minor sloughing were observed along the northern cut slope. 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. Y ii e17. ,4 a'Y`. _ ate`' a"'...• Ida 1 � 10011 Blomberg Street SW,Olympia,WA 98512 9 Phone#: (360)754-4612 Fax#: (360)7544848 GEOTECNNICAL 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 northern slope will not be affected by the proposed structure. The proposed structure 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 for the life of the project. In general, the Alderwood gravelly sandy loam 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 slabS-on-grade. Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed single-family residence are presented below. LANDSLIDE - EROSION HAZARD AREA 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 100 percent and the vertical relief is in excess of 10 feet. Based on the preceding, 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("Hb') d. Kitsap silt loam ("Kc') The soils at the site are mapped as Alderwood gravelly sandy loam(Ac). This site does meet the technical criteria of an erosion hazard area. 10011 Blomberg Street SW,Olympia, WA 98512 10 Phone#: (360)7544612 Fax#: (360)7544848 -7 GEOTECHNICAL TESTING LABORATORY - s - .n �-C Yr�"/�G.. �wMW ... -tea.. -. /. "... •F... ...� w SLOPE STABILITY 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 100 percent, the proposed building location is generally stable relative to deep-seated failure at the 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. iy U . ♦Y a+w Y.: 10011 Blomberg Street SW, Olympia, WA 98512 11 Phone#: (360) 754-4612 Fax#: (360)7544848 CEOTECRNICAL TESTING LABORATORY BUILDING SETBACK 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. The building setback may be measured from the bottom of the footing to the face of the steep slope in accordance with the International Building Code (1805.3.1). The following figure represents a shear angle for the gravelly sandy loam. Shear angle and cohesion are variables used to model the site. Peak Shear Stress vs. Normal Stress 3000 � She=38' 2500 - ff • c 2000 I N a UI d i 1500 d t 1000 �-1 tton t m ton 500 t 1 ton Cohesion = � 200 psf 0 0 500 1000 1500 2000 2500 3000 Normal Stress(psf) I Setback I I 10011 Blomberg Street SW,Olympia, WA 98512 12 Phone#: (360) 754-4612 Fax#: (360)754-4848 I GEOTECHNICAL TESTING LABORATORY 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 building site area as having a very low to low liquefaction potential. The Site Class Map of Mason County, Washington by Palmer, Magsino, Bilderback, Poelstra, Folger, and Niggemann (September 2004) maps the building site area as site class C to D. Site class C is a very stiff soil or soft rock and site class D is a 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 probing with a '/z-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 liquefaction. The near-surface soils are generally in a dense condition and the static water table is located well below the surface. 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. zz 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 and growth on the slopes should be encouraged as much as possible as a deterrent to erosion. 10011 Blomberg Street SW,Olympia, WA 98512 14 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEO'TECHNICAL TES'TtNG LABORATORY 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. TJ •.y'. 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 vegetation removal and topsoil stripping are completed. 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 15 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 9 percent(by weight)passing the No. 200 sieve based on that fraction passing the 3/4-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 ONSITE SOILS AS FILL Onsite soils may be considered for use as structural fill. In general, the native soils (sand, loam, and 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. 10011 Blomberg Street SW,Olympia, WA 98512 16 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Temporary cut slopes will likely be necessary during grading operations. As a 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 consolidated soils that are weathered to a loose/medium-dense condition. Temporary 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 protective vegetative cover or otherwise protected. .�, „ Y.. tt Y£ 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% 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. 10011 Blomberg Street SW,Olympia, WA 98512 17 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY 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. } a,, 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. 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: 10011 Blomberg Street SW,Olympia, WA 98512 18 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHl ICAL TESTING LABORATORY SLOPE INCLINATION: EQUIVALENT FLUID PRESSURE Slope Angle Percent Increase Equivalent Fluid Pressure Horizontal 0% 35 pcf 3H:1V 25% 44 pcf 2H:1 V 50% 53 pcf 1H:1V 75% 61 pcf If the walls are greater than 4 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. 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 appropriate drainage facilities or to the base of the northern slope. 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 appropriate drainage facilities by tight-line or to the base of the northern slope. Drainage control measures are included on Figure 3. 10011 Blomberg Street SW,Olympia, WA 98512 19 Phone#: (360)754-4612 Fax#: (360)7544848 GEOTECHNICAL TESTING LABORATORY 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 location of the proposed septic drainfield will be offsite to the southeast. Since the location is in an area where the slope is approximately 15 percent,the slope stability will not be compromised. 77 ' L AT 4,i r LIMITATIONS We have prepared this report for Bob Drohman and members of his design team to 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. This report is quantified as a micro-study and not a macro-study. Geotechnical Testing Laboratory 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. 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. 10011 Blomberg Street SW,Olympia,WA 98512 20 Phone#: (360)754-4612 Fax#: (360)754-4848 r � � 1 r - / s•" 11�N�z Jy�7l' � '�Flri VI m� 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE � :..• CORRUGATED TIGHTLINE 4 INCH r= C� / �N7M MINIMUM,6 INCH SUGGESTED }taati .•—a•.f 1"• j.l']: a-`y.:y.�.N-i":.� r�\isi•: �''•^>'•:.`t•.-ywAe; 1 ):..'.•_ih'�_r.V.r Z � Tip..-= ?;"`•`: '�L S ~..tat.- .•:"�� 'S'::•.4:��`w•!.� tz-r•.•�'\'i..4;:r • . .:�r-� �!-+;e. '-use,-t - TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL OR ENERGY ,:-�•-•..'` ?:: .::. r.t..�_�.. DISPERSION DEVICE w�aa.. 'yf, ••J.. .ifv. ..a.-::..;_ ; ,..::�-_.:. ram':..:. .::a"",.' ► .`•I'.r.'..'.'.. 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 10011 Blomberg s,.sw QA/QC services Olympia,,of�,2 FIGURE 3 Testing Services F-:(rio)754-4 a Not to scale DRAINAGE DETAILS FILTER FABRIC MATERIAL W WIDE ROLLS USE ICSTAPLES 0R WIRE RING TOATTACH Geotechnical FABRIC TO RE 27(27l14OAlX)E WIFE FABRIC OR EQUIVALENT T-V Testing s� Laboratory 7d S MAX TXP WOOD POSTS,STANDARD OR BURY BOTTOM OF FILTER BETTER OR EQUAL ALTERNATE: MATERIAL RA S'X1 T TRENCH STEEL FENCE POSTS FILTER FABRIC S• ZXZ'X14GAUGE WIRE FABRIC OR EQUIVALENT 7d GROUND SURFACE 6JT PROVIDE 3V'-1 1?'WASHED GRAVEL BACITILL IN TRENCH 1T AND E BORN SIDES OF FILTER FENCE BOTH IDES OF FILTER 8'MI TXP WIIOOD POSTS ALT.STEEL FENCE POSTS Geotechnical Services FLIER FABRIC FENCE NOTES: ^/ 1.FILTER FABRIC SWILL BE PURCHASED IN A CONTINUOUS ROLL CUTTO Qom/QC Services THE LENGTH OF THE BARRIER TO AVOID USE OF JOINTS.WHEN JOINTS ARE NECESSARY,FILTER CLOTH SHALL BE SPLICED TOGETHER ONLY AT Testing Services ASUPPORTPOSTNAMINIMUM OVERLAP AND SECURELY FASTENED AT BOTHH E ENDS TO THE POST. T£NTTAL //// // 2.POSTS$HALL BE SPACED A MAXIMUM OF S FEET APART AND DRIVEN •i' IN TRATION //, / / / / SECURELY INTO THE GROUND(MINIMUM OF 301NCHES). LOCA oN/ , 10011 Blomberg St.SW 3.INCHES DEEP N THELI LINE FAPPROXIMATELY UPSL INCHES NATHEBAR2 INCHES DEEP ALONG THE LINE OF POSTS AND UP$LOPE FROIA THE BARRIER. ESH Olympia,WA 98512 4 SUPPORT FENCE SHAWHEN STANDARD LL BETFASTENED SECURELY TO THE U SH FILTER FABRIC IS USED,A WIRE L10PE SIDE Phone:(360)754-4612 LONG, G,TIE WIRES USING HEAVY-DUTY HE WRE SHALL EXTEND INTO THE / LONG,TIE HARES OR HOG RINGS.THE WARE SHALL EXTEND THE Fax:(360)754-4848 TRENCH A MINIMUM OF 41NCHES AND SHALL NOT EXTEND MORE THAN 36 INCHES ABOVE THE ORIGINAL GROUND SURFACE. S.TO THE FENCE AND 20I TH ES OF FABRIC SHALL E E STAKED ED OR WIRED Date: 04/20/2006 TO THE FENCE AND THE FABRIC OF FABRIC SHALL N EXTENDED INTO THE TRENCH.THE FABRIC SHALL NOT EXTEND MORE THAN 38 INCHES ABOVE THE ORIGINAL GROUND SURFACE.FILTER FABRIC SHALL Designed by: LL NOT BE STAPLED TO THE EXISTING TREES. Drawn by: LL _I.. I S.WHEN EXTRA$TRENGTH FILTER FABRIC AND CLOSER POST SPACING IS Checked b LL / 1 I I POTENTIAL / I USED,THE WIRE MESH SUPPORT FENCE MAP BE ELIMINATED,IN SUCH y INIF ',,,IIIy ACASE,THE FI LTER FABRIC IS STAPLED OR WIRED DIRECTLY TO THE Dw9#:04-20-06-029 �L 770N / I POSTS MATH ALL OTHER PROVISIONS OR ABOVE NOTES APPLYING. 7.FILTER FABRIC FENCES SHALL NOT BE REMOVED BEFORE THE USLOPE AREA HAS BEEN PERMANENTLY STABILIZED. B,FILTER FABRIC FENCES SHALL BE INSPECTED IMMEDIATELY AFTER EACH RAINFALL AND AT LEAST DAILY DURING PROLONGED RAINFALL.ANY REQUIRED REPAIRS SHALL BE MADE IMMEDIATELY. GENERAL EROSION CONTROL NOTES: / ' ' /• � �'7—'� '/ / I 1. EROSION CONTROL MEASURES SHALL BE IN PLACE PRIOR TO THE / / / // BEGINNING OF CONSTRUCTION.THE PROJECT ENGINEER AND THE COUNTY / ///LL ,/ / / I BEGIN INSPECT AND APPROVE THE INSTALLATION OF /Bl�,(Ir DI / / l I EROSION CONTROL MEASURES PRIOR TO BEGINNING CONSTRUCTION. L/' �''/\//� T�/F�' / /' ' 2.EROSION CONTROL MEASURES ARE NOT LIMITED TO THE ITEMS /(' _A ! /J / / I ON THIS PLAN.THE CONTRACTOR IS RESPONSIBLE FOR THE PROJECT NAME: J\�V T!V INSTALLATION AND MAINTAIWINCE OF ALL EROSION CONTROL MEASURES. / / / NO SILTATION OF EXISTING OR PROPOSED DRAINAGE FACILITIES DROHMAN SITE ,` ___- $HALL BE ALLOWED.CARE SHALL BE TAKEN TO PREVENT MIGRATION OF SILTS TO OFF SITE PROPERTIES, 3.THE CONTRACTOR$HALL MAKE DAILY SURVEILLANCE OF ALLEROSION LOT 1 CONTROL MEASURES AND MAKE ANY NECESSARY REPAIRS OR ADDITIONS TO THE EROSION CONTROL MEASURES THE CONTRACTOR SHALL PROVIDE —9991 EAST STATE ROUTE 106 ADDITIONAL EROSION CONTROL MEASURES AS DETERMINED NECESSARY BY THE COUNTY INSPECTOR AND/OR THE PROJECT ENGINEER.FAILURE UNION,WASHINGTON TO COMPLY MATH All LOCAL AN O STATE EROSION CONTROL 41 REQUIREMENTS MAY RESULT IN CIVIL PENALTIES BEING LEVIED PARCEL 3223651OW30 AGAINST THECONTRACTOR AND/OR PROJECT OWNER. 4.DURING THE WET SEASON(NOVEMBER TO MARCH)ALL DISTURBED SOILS SHALL BE STABILIZED WATHIN M HOURS AFTER STOP OF WORK EROSION p��I/�HA CONTROL MEASURES SHALL INCLUDE,BUT NOT BE LIMITED TO, RevWo11S. COVERING THE EFFECTED AREA INCLUDING SPOIL PILES KITH PLASTIC SHEETING,STRAW MATTING,JUTE MATTING,STRAW MULCH, OR WOOD CHIPS.SEEDING OF THE DISTURBED AREAS SHALL TAKE / / \ PLACE AS WEATHER PERMITS. I /// 1 5.ALL SEEDED OR SODDED AREAS SMALL BE CHECKED REGULARLY NORTH / c TO MAKE SURE VEGETATIVE COVERAGE IS COMLETE AREAS SHALL BE SCALE 1'-40' I /'� REPAIRED.RESEEDED,AND FERTILIZED AS REOUIRED. C.I.•Y I G� S TRACKING OF SOIL OFFSITE WILL NOT B ALLOWED.IF ANY SOIL IS DATUM ASSUMED TRACKED ONTO COUNTY STREET,IT SHALL BE REMOVED BY THE END OF THAT WORKING GAY.ANY FURTHER TRACKING OF MUD WLL THEN THIS IS NOT A SURVEY lT. BE PREVENTED BY SWEEPING OR WASHING OF THE VEHICLES TIRES ` BEFORE DRIVING ON A COUNTY STREET. ].NO MORE THAN 500 LF OF TRENCH ON A DOWNSLOPE OF MORE THAN 5 D 10 ZO 30 40 PERCENT SHALL B OPENED AT ONE TIME. 8.EXCAVATED MATERIAL SMALL B PLACED ON THE UPHILL SIDE OF TRENCHES. B.TRENCH DEWATERING DEVICES SHALL BE DISCHARGED IN A MANNER THAT WILL NOT ADVERSELY AFFECT FLOWNG STREAMS.DRAINAGE SYSTEMS OR OFFSITE PROPERTIES. SCALE:1 Inch=40 feet 10 ALL STORM SEWER INLETS RECEIVING RUNOFF FROM THE PROJECT DURING CONSTRUCTION SHALL BE PROTECTED SO THAT SEDIMENT-LADEN WATER WILL BE FILTERED BEFORE ENTERING THE CONVEYANCE SYSTEM, 1 I.ALL OFFSITE CATCH BASINS IMMEDIATELY ADJACENT TO THE SITE SMALL BE PROTECTED FROM SILTATION. I /1 ^ ^ /� 12 ALL DISTURBED AREAS SHALL BE SEEDED S SODDED UPON COMPLETION /G K LE 2 OF WORK.THE CONTRACTOR SHALL BE RESPONSIBLE O ENSURE TTHAT HAT COMPLETE COVERAGE A THE DISTURBED AREAS IS PROVIDED S THAT GROWTH OF THE VEGETATION t5 ESTABLISHED. SITE PLAN 13.CATCH BASINS SHALL TRAP SEDIMENT OR FILTER FABRIC MUST BE PLACED UNDER GRATE UNTIL VEGETATION IS ESTABLISHED.