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Home My WebLink AboutGeoTech Report for BLD2006-02096 - BLD Engineering / Geo-tech Reports - 12/1/2006 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton, Washington 98584 p DATE: January 25, 2007 INTER-DEPARTMENTAL COMMUNICATIONS TO: Kell McAboy PARCEL # 32235-52-01007 FROM: John Sliva, Programs Engineer-PW BUILDING PERMIT NUMBER: BLD2006-02096 SUBJECT: Geotechnical Report NAME: Correa Roy Kell, The Geotechnical Report prepared for the proposed foundation replacement and addition to the existing residence at 31 East Merrimount Lane at Union has been received and reviewed by Public Works. The Geological Assessment was upgraded to a Geotechnical Report due to the proposed construction taking place 240+/-feet from the toe of a 70+/- percent slope, which rises in elevation from approximately 80 feet to 480+ feet. The geotechnical report notes that the lot slopes to the northwest from the proposed building location. The report notes that the remodel includes a proposed daylight basement. The steepest slope on site is approximately 35 percent. Slope stability was modeled in both static and dynamic conditions. The author's opinion notes 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 development. The proposed development will not undermine adjacent slopes. If their analysis and recommendations are followed, they do not anticipate any on site or off site impact from the construction. The report appears to satisfactorily address County requirements for Geotechnical Reporting. Recommendations contained in the report should be incorporated into the site development plans and made conditions for permit issuance Adequate erosion and sediment 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 724 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sirfc re , ohn Sliva rograms Engineer GEOTECHNICAL REPORT 31 EAST MERRIMOUNT ROAD UNION, WASHINGTON PREPARED FOR DOGWOOD CONSTRUCTION, INC. BY GEOTECHNICAL TESTING LABORATORY OLYMPIA, WASHINGTON JANUARY 10, 2007 OCEVED brauf JAN ► 4ASON COUNTY GEOTECHNicAL TESTING LABORATORY CONTACT INFORMATION PREPARER INFORMATION GTL PROJECT NUMBER: 06-2971-11 CONTACT: LANCE LEVINE ADDRESS: 10011 BLOMBERG STREET SOUTHWEST OLYMPIA,WASHINGTON 98512 TELEPHONE: (360)754-4612 FACSIMILE: (360)754-4848 EMAIL ADDRESS: GEOTESTLAB@COMCAST.NET CLIENT INFORMATION CLIENT: DOGWOOD CONSTRUCTION,INC. CONTACT: ROB MCGUIRE TELEPHONE: (360)898-6100 FACSIMILE: (360)898-6102 MAILING ADDRESS: 90 EAST TOWER LANE UNION,WASHINGTON 98592 SITE ADDRESS: 31 EAST MERRIMOUNT ROAD UNION,WASHINGTON 98592 PARCEL NUMBER: 322355201007 GPS LOCATION: N47°21.286' W 123°01.010' 10011 Blomberg Street SW,Olympia,WA 98512 2 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHWAL TESTING LABORATORY SCOPE OF UNDERSTANDING DOGWOOD CONSTRUCTION,INC. 90 EAST TOWER LANE UNION,WASHINGTON 98592 RE: GEOTECHNICAL REPORT 31 EAST MERRIMOUNT ROAD UNION,WASHINGTON 98592 PARCEL 322355201007 N47o 21.2861 W 123°01.0101 Mr. McGuire: 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. Soil samples were submitted for laboratory testing from the project site. The 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. We are also a full service laboratory that can meet all your building, testing (compaction, asphalt, concrete), and inspection needs. 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 o{ WaSh;�� GEOTECHNICAL TESTING LABORATORY Harold Parks,L.G., L.E.G. Engineering Geolo,'at/ !� 827 X, Senior Engineering Geologist oe*sed G eo\0 HAROLD PARKS EkI. 7-31 —o 7 10011 Blomberg Street SW,Olympia, WA 98512 3 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY TABLE OF CONTENTS CONTACTINFORMATION.....................................................................................................................................2 SCOPE OF UNDERSTANDING ...............................................................................................................................3 TABLEOF CONTENTS............................................................................................................................................4 INTRODUCTION.......................................................................................................................................................5 SITECONDITIONS...................................................................................................................................................6 SurfaceConditions..................................................................................................................................................6 SiteGeology............................................................................................................................................................7 SiteSoils.................................................................................................................................................................8 SubsurfaceExplorations..........................................................................................................................................8 SubsurfaceConditions............................................................................................................................................9 SlopeStability.........................................................................................................................................................9 CONCLUSIONS AND RECOMMENDATIONS.................................................................................................... 11 General.................................................................................................................................................................. 11 LANDSLIDE—EROSION HAZARD AREA........................................................................................................... 12 Classification ........................................................................................................................................................ 12 SlopeStability....................................................................................................................................................... 12 BuildingSetback................................................................................................................................................... 13 Seismic—Liquefaction Hazard............................................................................................................................. 15 ErosionControl..................................................................................................................................................... 16 EARTHWORK......................................................................................................................................................... 16 SitePreparation..................................................................................................................................................... 16 StructuralFill........................................................................................................................................................ 17 Suitability of Onsite Soils as Fill.......................................................................................................................... 17 Cutand Fill Slopes................................................................................................................................................ 18 FoundationSupport............................................................................................................................................... 18 FloorSlab Support................................................................................................................................................ 19 RetainingWalls..................................................................................................................................................... 19 RetainingWall Alternatives..................................................................................................................................20 SiteDrainage.........................................................................................................................................................20 SepticImpact.........................................................................................................................................................21 LIMITATIONS.........................................................................................................................................................21 Figure1 Vicinity Map...........................................................................................................................................22 10011 Blomberg Street SW, Olympia, WA 98512 4 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICA L 'VESTING LABORATORY INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed remodel and building raise of the existing single-family residence. A daylight basement is proposed. The site is located along the northwest-facing hillside overlooking the Hood Canal in Mason County. The site is approximately 4 miles east of Union, Washington. The location of the site is shown relative to the surrounding area on the Vicinity Map,Figure 1. A a DEP -_ ram• c- ,�� 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 re-developed by raising the existing single-family residence to create a lower level. The site will be accessed by the existing driveway from Merrimount Road. In general, grading will consist of the excavation of the foundation. The approximate layout of the site is shown on the Site Plan, Figure 2. The site slopes toward the northwest from the proposed building location. The steepest slope measured onsite was approximately 35 percent. Because a slope exceeding 40% is within 300 feet of the building site, 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 GEOTECIINICAL TESTING LABORATORY r • Y _ - a• r � 'h•`! i'.',a•.1,��i'1' ` ail , ram' SITE CONDITIONS SURFACE 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 northwestern exposure. We conducted a reconnaissance of the site area on November 27,2006 and January 8,2007. Site elevations range from approximately 20 to 74 feet. The building area of the site has vegetation common to the Northwest. The vegetation includes hemlock, cedar, maple, alder, and fir trees as well as salal, Oregon grape, sword ferns, blackberry, huckleberry, bracken ferns, rhododendron,and grasses. At the time of the site visit, we observed no evidence of active surface erosion. No evidence of deep-seated slope instability was observed. Minor raveling and sloughing was not observed onsite. Surface water flow was observed along the SR-106 in an established ditch. The general topography of the site area indicates that drainage flows toward the northwest from the proposed building location. iW ' _ ,�•_ _ t 10011 Blomberg Street SW,Olympia,WA 98512 6 Phone#: (360)754-4612 Fax#: (360)754-4848 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 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 PP non glacial P lacial 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. jo. .ai The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by w Logan (2003) describes the site as glacial advance outwash (Qga). The glacial advance outwash is described as: I � Advance outwash, late Wisconsinan (Pleistocene)— '' Glaciofluvial sand and gravel and lacustrine clay, silt, and sand t deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained, with interlayered coarser M: sand, gravel, and cobbles and silt rip-up lag deposits at their base; may contain nonglacial sediments; generally overlain by till. The Geologic Map of Southeastern Mason County, Washington, USGS Water-Supply Bulletin 29 by Noble and Molenaar(1970)describes the site 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. 10011 Blomberg Street SW,Olympia, WA 98512 7 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNicAL TESTING ILABoRATORY � �� - ; • ; lam. _�. i — ;�� .s+� r,� '.♦ 'fir• '' /� R. ♦♦ 1� + ` '��`! +, �� i SITE SOILS � a The Soil Survey of Mason County, Washington, USDA Soil Conservation = s r Service(1960)has mapped the site soils as an Alderwood gravelly sandy "�` :•7 loam,30 to 45 percent slopes(Ad),at the site. The report reads: t- j Y1, Jts 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. SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed building site soil and reviewing available well logs. Groundwater was not encountered at the proposed building location and is beyond the scope of this report. Depth to competent soil is approximately 8 inches throughout the proposed building location. L� a% Af •'3/' e � "�ek.yT.r. fy. 10011 Blomberg Street SW,Olympia, WA 98512 8 Phone#: (360) 754-4612 Fax#: (360)754-4848 C EOTECHNICAL TESTING UmRATORY d IFIVIV, t A Y •u. -'3 - .. Ili SUBSURFACE CONDITIONS In general, dense Alderwood gravelly sandy loam was observed in the undisturbed portions of the site. Vashon Stade glacial material was observed below the Alderwood material. Groundwater was not 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 during periods of extended wet weather. a • R r , - R• i L • t A. tip! .r � �{ ,�� i,�if„�• '-. } � « r SLOPE STABILITY 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 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. 10011 Blomberg Street SW,Olympia, WA 98512 9 Phone#: (360)754-4612 Fax#: (360)754-4848 GE,OTECHNICAL TESTING LABORATORY The Coastal Zone Atlas, Volume 9, Mason County 23, (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 J runoff potential is low. Infiltration is moderate on - natural slopes and high on cut slopes. Springs at the s bases of slopes are common. The slope stability is described as"intermediate." n Slopes approximately 35 percent were observed onsite. Since slopes of 40 percent or greater with 10 S feet or more of vertical relief occur near the site, r Mason County requires that a geologic hazards f` S report be completed according to the Critical Areas Ordinance. s S 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 s condition. -----_-- S.1d 1 '3.000 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 0 = 11 condition except where they have been disturbed by weathering activity. These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or significant erosion was observed 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 sloughing were not observed onsite. 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. K r R 1 " r , 10011 Blomberg Street SW,Olympia, WA 98512 10 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on the results of our site reconnaissance, subsurface observations, and our experience in the area, it is our opinion that the site is suitable for the proposed project. The slope is stable relative to deep-seated instability and will not be affected by the proposed development. The proposed development 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. J i Aw, 10011 Blomberg Street SW,Olympia, WA 98512 11 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 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 approximately 35 percent with the vertical relief in excess of 10 feet. Offsite to the south(75 feet) is an area where the slope is 90 percent. 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 ("HY) 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. SLOPE STABILITY Based on our field observations, explorations and our experience with the soil types encountered on the property, we conclude that although slopes are approximately 35 percent, they are generally stable relative to deep-seated failure in their present configuration. Excavation and back-filling will occur based on appropriate engineering and earthwork recommendations found in the following"Earthwork" section. Grading in the building portion of the site should be conducted in accordance with geotechnical recommendations provided herein. 10011 Blomberg Street SW,Olympia, WA 98512 12 Phone#: (360)754-4612 Fax#: (360)754-4848 GE®TECHNICAL TESTING LABORATORY 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 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 Setback 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 3 2500 _ - —. — -- Shear = 39° i 2000 a I " I y in 500 r i Y W d a 1000 f 1/4 ton 500 - - - - - - - - 1'2 ton Cohesion = +1 ton 200 psf 0 0 500 1000 1500 2000 2500 3000 Normal Stress(psf) 1001 1 Blomberg Street SW,Olympia, WA 98512 Phone#: (360)754-4612 Fax#: (360)754-4848 I I GEOTECHNICAL 'VESTING LABORATORY lSlope stability was modeled using the GeoStudio 2004 program(version 6.17) in both static and extreme dynamic conditions (Ca = 0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price I methods. The site was modeled using a monolithic layer of gravelly sandy loam. The gravelly sandy loam was determined to have a unit weight of 131 pcf, cohesion of 200 psf, and a shear angle (�) of 39°. Under static conditions, the onsite slopes remained stable to deep-seated and shallow failure. Under dynamic loading, the 3328 computations demonstrated that the onsite slope is not susceptible to surficial raveling or large deep-seated failure. Offsite to the south, the slope is susceptible to surficial raveling. The following figure illustrates the moment factor of safety for slope"A"under the existing conditions. The figure is the solution of greatest concern I and exhibits the need for a building setback of 5-feet from the crest of the northern slope. All foundation elements shall be constructed on native material or engineered fill material. Dogwood Construction Site -- Slope A • . . . . �// ��i• 160 ✓/ f•/�� I 140 120 100 � Proposed Ia 80 Description: Graveily Sandy Loam Building w 60 Wt: 131 Location Cohesion: 200 40 Phi: 39 - 20 o 0 50 100 150 200 250 300 350 400 450 500 55n Ono Distance (ft) 10011 Blomberg Street SW, Olympia, WA 98512 14 Phone#: (360) 754-4612 Fax#: (360) 754-4848 I C EOTECHNICAL TESTING ]LABORATORY � y +0011 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. 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 2 to 8 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 3 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. No foundation elements shall be constructed on fill material unless it is an engineered fill. 10011 Blomberg Street SW,Olympia, WA 98512 16 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Where placement of fill material is required, the exposed subgrade areas should be proof-rolled to a firm and unyielding surface prior to placement of any fill. 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. 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. j. J 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 if industry standards are satisfied. In general, the native soils (sand, silt, 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. 10011 Blomberg Street SW, Olympia, WA 98512 17 Phone#: (360)7544612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Aft 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 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. 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 200 pcf(pounds per cubic foot). 10011 Blomberg Street SW,Olympia, WA 98512 18 Phone#: (360)7544612 Fax#: (360)754-4.848 GEOTECH IGAL TESTING ]LABORATORY We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions, witli differential settlements between comparably loaded footings of '/z 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. l �J 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 19 Phone#: (360)754-4612 Fax#: (360)754-4848 GEO TECHNICAL 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 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 can,with time,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 into the appropriate drainage facilities. 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. 10011 Blomberg Street SW,Olympia,WA 98512 20 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTEcHNicAL TESTING LABORATORY We recommend that the collected stormwater runoff be directed into the appropriate drainage facilities 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 existing septic drainfield is beyond the building location. Since the proposed development will not impact the existing septic drainfield,the slope stability of the site will not be adversely impacted. LIMITATIONS We have prepared this report for the use of Dogwood Construction, Inc. and members of their 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. Recent changes in the Mason County Code require our firm to revisit the site (after six months)to ensure the conditions are in agreement with our original report. 10011 Blomberg Street SW,Olympia, WA 98512 21 Phone#: (360)754-4612 Fax#: (360)754-4848 1 � 0 \�:..,,■. � y'� ��, �1�� f ��arS��^'' � 1, i - •✓��riil�-l„�r�1s_ J r J/7IL.��!♦tfir_'1Ml•L!Rl-/IAIIII��tlII/1�'�f�dlCtl.��Y/it\I�I �t�� )/y' FILTER FABRIC MATERIAL ST WIDE ROLLS / ABRIC TO ORE RING TOATTACHSE RE Geotechnical O / FABRIC TO WIRE 14 GAUGE FABRIC OR EQUIVALENT LENT Testing ea U FACE /A�\ Laboratory J 7d a MAX /; ✓O i 7%T WOOD POSTS,STANDARD OR ,B,IUq�RBAI IN B'X171 EQUALBETTER OR TRENCH S EL FENCEPOSTSLTERWATE. P / FILTER FABRIC S' FABRIC GAUGE WIRE 2J FABRIC OR EQUIVALENT GROUND SURFACE sd PRO OE 314.1 1?WASHED IN / GRAVEL B BOTH IULSIDES IN TRENCH B MI 12 i / AND ON BOTH SIDES OF FILTER i' \ 1 , j FENCE FABRIC ON THE SURFACE 7X4'WVOD STS ALT STEEL FENCE POSTS A �l ,' ;' PO Tl Geotechnical services FLIER FABRIC FENCE NOTES: --- 2f QA/QC Services 'OLS/ 1 l j I 1.FILTER FABRIC SHALL BE PURCHASED M A CONTINUOUS ROLL CUT TO THE LENGTH OF THE BARRIER TO AVOID USE OF JOINTS.WHEN JOINTS Testing Services ARE NECESSARY,FILTER CLOTH SHALL BE SPLICED TOGETHER ONLY AT A SUPPORT POST WRH A MINIMUM&INCH OVERLAP AND SECURELY FASTENED AT BOTH ENDS TO THE POST. 2.POSTS SHALL BE SPACED A MAXIMUM OF S FEET APART AND DRIVEN SECURELY INTO THE GROUND MINIMUM OF 30INCHES). ----_-- �� O 1 1 I 3.ATRENCHS HALL BE EXCAVATED APPROXIMATELY 8 INCHES WIDE AND/2 10011 Blomberg St.SW VVV ; 1 INCHES DEEP ALONG THE LINE OF POSTS AND UPSLOPE FROM THE BARRIER. 4j A L Olympia,WA 98512 / O ' V 1.WHEN RT FENCE STRENGTHS TER FABRIC IS USED,A WIRE MESH SUPPORT FENCE SHALL A FASTENED SECURELY TO THE T I INCH SIDE Phone:(360)754-4612 O , ) LONG, THE POSTS USING HOG RINGS WIRE STAPLES AT LEAST 1 INCH I j LONG TIE WIRES OR HOG RINGS.THE WIRE SHALL EXTEND INTO THE Fax:(360)7544848 TRENCH A MINIMUM OF/INCHES AND SHALL NOT EXTEND MORE THAN M INCHES ABOVE THE ORIGINAL GROUND SURFACE. S.THE STANDARD STRENGTH OF FABRIC SHALL BE STAPLED OR WIRED Date: 01/11/2007 J , � TO THE FENCE AND 201NCHES ES OF FABRIC SHALL BE EXTENDED / INTO THE TRENCH.THE FABRIC SHALL NOT EXTEND MORE THAN 38 `- _ '� / i / �1 � � � �, INCHES ABOVE THE ORIGINAL GROUND SURFACE,FILTER FABRIC SHALL Designed by: LL O / , / / / NOT BE STAPLED TO THE EXISTING TREES. Drawn by: LL S.WEN E%TRASTRENGTH FILTER FABRIC AND CLOSER POST SPACING IS Checked by: LL -- USED,THE WIRE MESH SUPPORT FENCE MAP BE ELIMINATED.IN SUCH ----- j i _ --- ACAM.THE FILTERFABRIC IS STAPLED OR HARED DIRECTLY TO THE Dyyg#:01 11-07-005 ' POSTS WITH ALL OTHER PROVISIONS OR ABOVE NOTES APPLYING. ------------ 7.FILTER FABRIC FENCES SHALL NOT BE REMOVED BEFORE THE UPSLOPE i AREA HAS BEEN PERMANENTLY STABILIZED. B.FILTER FABRIC FENCES SHALL BE INSPECTED IMMEDIATELY AFTER EACH i i ND AST RAINFALL REPAIRS SHALL DAILY MADE URING IMMEDIATELY RAINFALL.ANY REQUIRED REPAIRS SMALL BE MADE IMMEDIATELY. ------ -- - - - ,,- 5 - GENERAL EROSION CONTROL NOTES: -- -- ---------- 1. EROSION CONTROL MEASURES SHALL BE IN PLACE PRIOR CE TO THE-� SHALLBEGINNINGINSPECT OF CONSTRUCTION.THE PROJECT ENGINEER AND THE COUNTY i SHALL IN CONTAND APPROVE THE INSTALLATION OF i ____ EROSION CONTROL MEASURES PRIOR TO BEGINNING CONSTRUCTION. - -_- ------- - 2.EROSION CONTROL MEASURES ARE NOT LIMITED TO THE ITEMS ____-____ ONTHISPLAN.THECONTRACTORIS RESPONSIBLE FOR THE PROJECT NAME: _ INSTALLATION AND MAINTAINANCE OF ALL EROSION CONTROL MEASURES. -- NO SILTATION OF EXISTING OR PRO POSED DRAINAGEFACILITES DOGWOOD CONSTRUCTION SHALL BE ALLOWED.CARE SHALL BE TAKEN TO PREVENT MIGRATION ` - OF SILTS TO OFF SITE PROPERTIES. _--- -- 3.THE CONTRACTOR SHALLMAIO:DAILY SURVEILLANCE OF ALL EROSION CORREA SITE - ----� - CONTROL MEASURES AND MAKE ANY NECESSARY REPAIRS OR ADDITIONS p ' TO THE ERONAL S ION CONTROL MEASURES THE CONTRACTOR SHALL PROVIDE 31 EAST MERRIMOUNT ROAD ADDITf ' 1 �O// _ BYTH COUNT INSPECTOR FAILURE UNION,WASHINGTON M BY THE COUNTY INSPECTOR ANDOMI THE PROJECT ENGINEER.FAILURE TO COMPLY WITH ALL LOCAL AND STATE EROSION CONTROL - f %/i '1 / ; ^ I •\ '- ----------` REQUIREMENTS MAY RESULT INCMLPENALTES BEING LEVIED PARCEL 322355201007 - AGAINST THE CONTRACTOR ANWOR PROJECT OWNER. / lI I I I J I i I / 1tOO-- �` 4.DURING THE WET SEASON(NOVEMBER TO MARCH)ALL DISTURBED SOILS _ SHALL BE STABILIZED WATHIN 48 HOURS AFTER STOP OF WORK.EROSION e�/I�W� S. CONTROL MEASURES SHALL INCLUDE,BUT NOT BE LIMITED TO, RGIIJNI I COVERING THE EFFECTED AREA INCLUDING SPOIL PILES VATH ___ PLASTIC SHEETING,STRAW MATING,JUTE MATTING,STRAW MULCH , VO --� ``� \` OR WOOD CHIPS.SEEDING OF THE DISTURBED AREAS SHALL TAKE `�� PUCE AS WEATHER PERMITS. NORTH �' / I I' i 1 I j I I 5 ALL SEEDED OR SODDED AREAS SHALL BE CHECKED REGULARLY ,f ! // I j I I I j `\ TO MAKE SURE VEGETATIVE COVERAGE IS COMLETE AREAS SHALL BE SCALE 1"=50 1 I I -'`�� \ � REPAIRED.RESEEDED.AND FERTILIZED AS REQUIRED. C.I.=5' DATUM ASSUMED TRACKING OF SOIL OFFSITE HALL NOT BE ALLOWED.IF ANY SOIL IS / 1 I I I I , 1 / \ TRACKED ONTO A COUNTY STREET,IT SHALL BE REMOVED BY THE END / i 1 I �\ % OF THAT WORKING DAY.ANY FURTHER TRACKING OF MUD WILL THEN THIS IS NOT ASURVEY i' i I I I j \\ ` \ BEPREVENTEDBV SWEEPING OR WASHING OF THE VEHICLES TIRES `` \\ BEFORE DRIVING ON A COUNTY STREET. 1 W M�AF� THAN\` \ / i 1 ' ` \% T.NO MORE THAN EOD LF OF TRENCH ON A WNNSLOPE OF MORE THAN 5 D 10 20 30 10 50 ; A i I , I i , \� i \\ ` PERCENT SMALLT BE OPENED AT ONE HE `` S.EXCAVATED MATERIAL SHALL BE PLACED ON THE UPHILL SIDE OF TRENCHES. S.TRENCH DEWATERING DEVICES SHALL BE DISCHARGED IN A MANNER THAT WILL NOT ADVERSELY AFFECT FL OWANG STREAMS.DRAINAGE SYSTEMS OR OFFSITE PROPERTIES. SCALE:finch=50 feet 10.ALL STORM SEWER INLETS RECEIVING RUNOFF FROM THE PROJECT WRING CONSTRUCTION SWILL BE PROTECTED SO THAT E E WATER WILL BE FILTERED BEFORE ENTERING THE CONVEYANCE SYSTEM . ALL OFFSRE CATCH BASINS I 1I. L ADJACENT TO THE SITE S4LTA SHALL BE PROTECTED FROM SILTATION. 12.ALL DISTURBED AREAS SHALL BE SEEDED OR SODDED UPON COMPLETION FIGURE 2 OF WORK.THE CONTRACTOR SHALL BE RESPONSIBLE TO ENSURE THAT COMPLETE COVERAGE OF THE DISTURBED AREAS IS PROVIDED S THAT GROWTH OF THE ALL TRAP SITE PLAN ON IS ESTABLISHED. 13.CATCH BASINS SHALL TRAP SEDIMENT OR FILTER FABRIC MUST BE / f '/BOO PLACED UNDER GRATE UNTIL VEGETATION IS ESTABLISHED. I 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH MINIMUM,6 INCH SUGGESTED 70 }z a " ti•A-1^' �Viz.]: ♦:, .. .>~••-'ti'": .?..�+s-�s: {•'%•;�.tom.••.. ..;:;';:. -e•.;• `ti�_c..::.••i'ya�•z.:.�•.:r:.':: TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL OR ENERGY DISPERSION DEVICE 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 sL SW QA/QC Services O1'°"'a•W"98512 FIGURE 3 PhoTesting Services Fax:� 'Z i°j Not to scale DRAINAGE DETAILS