Loading...
HomeMy WebLinkAboutBLD2006-00556 GEOTech Review - BLD Engineering / Geo-tech Reports - 11/18/2004 PLAN V w W Geotechnical Report Lot C-4 of SP#1233 Parcel #420252290234 Shelton, WA Prepared for: Ashby Homes Shelton, WA by Geotechnical Testing Laboratory Olympia, Washington November 18 2004 G EOTECHNICAL TESTING LABORATORY ASHBY HOMES P.O. Box 2192 SHELTON,WA 98584 ATTN: GALE ASHBY RE: GEOTECHNICAL REPORT LOT C-4 OF SP#1233 SHELTON,WASHINGTON PARCEL 420252290234 N47011.922'W123°08.398' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence to be located off West Shelton Valley Road,approximately 1.5 miles southwest of Shelton,Washington. The location of the site is shown relative to the surrounding area on the Vicinity Map,Figure 1. Our understanding of the project is based on our discussions with you and our explorations and review of the site. We understand that the parcel is to be developed as a single-family residence. The site will be accessed by a driveway from a gravel access road off West Shelton Valley Road. In general, grading will consist of the excavation of the foundation,possible daylight basement,footings,and driveway. E' i� View Looking East The site slopes toward the southeast and east. The steepest slope measured onsite was in excess of 10�percent. Therefore, Mason County requires that a geotechnical report be prepared in accordance with the Critical Areas Ordinance. The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing geotechnical recommendations and design criteria for the project and to satisfy the requirements of the Mason County Critical Areas Ordinance. Geotechnical Testing Laboratory is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: 10011 Blomberg Street SW,Olympia,WA 98512 1 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHWAL TESTING LABORATORY 1. Review the available geologic, hydrogeologic, and geotechnical data for the site area. 2. Conduct a geologic reconnaissance of the site area and surrounding vicinity. 3. Investigate shallow subsurface conditions at the site by observing the exposed soil and reviewing published well logs. 4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations. 5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria (including hillside grading), temporary and permanent cut and fill slopes, drainage and erosion control measures. SITE CONDITIONS SURFACE CONDITIONS The proposed building site is located in an area of sparse residential development in the Puget Sound glacial upland along the hillside west of Coffee Creek. The site has southeastern and eastern exposure. We conducted a reconnaissance of the site area several times in October 2004. Site elevations range from approximately 136 to approximately 202 feet. A septic system and well are proposed onsite. i. fl The building area of the site has a well-mixed variety of vegetation common to the Northwest. The vegetation includes fir, cedar, maple, and alder trees as well as bracken ferns, sword ferns, holly, Oregon grape, salal, Scot's broom, blackberry, and grasses. At the time of the site visit, we observed no evidence of active surface erosion at or around the proposed building location. Slope instability was not observed onsite at the time of our investigation. No active surficial erosion, exposed soil, sloughing, or raveling was observed. Surface water flow was not observed at the time of our reconnaissance. Groundwater was not encountered or observed onsite. The general topography of the site area indicates that drainage flows east towards Coffee Creek. 10011 Blomberg Street SW, Olympia, WA 98512 2 Phone#: (360)754-4612 Fax#:(360) 754-4848 i 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 10,000 and 12,000 years ago, and weathering and erosion that has occurred since. A description of the surficial soils is included in the "Site Soils" section of this report. In general, the soils are composed of glacial outwash material. SITE SOILS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as Cloquallum silt loam, 5-15 percent slopes(C j. The report reads: The Cloquallum series consists of moderately well-drained, brown upland soils. They occupy gently undulating to rolling areas where surface drainage is fairly well established. They have developed from silty sediments that washed from the southwestern terminal moraine and were deposited in glacial lakes formed when the Yashon glacier retreated. The glacial sediment contained considerable amounts of local basic material that gave the soil a reddish cast. Internal drainage is retarded by firm or slightly compact, slightly stratified silt and clay in the lower subsoil and substratum. low ' . f.. ;a i� The Geologic Map of Washington — Southwest Quadrant (1987) has mapped the site geology as deposits of continental glaciers(Qgo). The report reads: Undifferentiated outwash deposits — Recessional and proglacial stratified sand and gravel; locally contains silt and clay. Consists of part of the Yashon drift. 10011 Blomberg Street SW, Olympia, WA 98512 3 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site as Proglacial and recessional outwash(Qgo), late Wisconsian(Pleistocene). The Proglacial and recessional outwash is described as: Typically poorly to moderately sorted, rounded gravel and sand with localized coarser- and finer-grained constituents; lithologically varied mixture of mostly northern provenance clasts, especially containing granitic and metamorphic rocks that identify the unit as being deposited by the Puget lobe of the Cordilleran glacier; also contains varying amounts of locally derived Crescent Formation basalt, and in the Mox Chehalis Creek valley, central Cascade Range— derived andesitic clasts; typically shades of gray where fresh or brown where stained especially in proglacial and morainal areas; buff fJ'staining near the ground surface;fine sand, silt, and clay constitute local overbank sediments having relatively poor permeability or deltaic foreset bedding along north sides of valleys with higher permeability,porous and permeable enough to yield small to moderate quantities of groundwater; very poorly consolidated to loose; moderately to well-rounded clasts; mostly unweathered with rare weathered reworked clasts; thickness varies and is not well known; most commonly occupies outwash channels scoured into or through till. r SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed building site soil and reviewing available well logs. Depth to competent soil is approximately 18 inches throughout the site. Static groundwater is unknown but presumed to be beyond the scope of this project. SUBSURFACE CONDITIONS In general, undisturbed dense Cloquallum silt loam was observed throughout the site. 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. 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. 10011 Blomberg Street SW, Olympia, WA 98512 4 Phone#: (360)754-4612 Fax#: (360)7544848 GEOTECHNICAL TESTING LABORATORY 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. Landslide activity and erosion was not observed along the sloping portions of the site. Onsite trees were observed straight and vertical. 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 on sloping portions of the site. No surface water or active erosion was observed at the proposed building location. 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 slope. A drainpipe can be used to control the flow from top to bottom. Erosion control recommendations for the sloping areas are provided in the"Erosion Control'section of this report x y - 4 View Looking East CONCLUSIONS AND RECOWMNDATIONS 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 structure if our recommendations are respected. The proposed structure will not undermine adjacent structures. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope stability. Based on the results of our site reconnaissance and subsurface observations, and our experience in the area, it is our opinion that the site is suitable for the-proposed single-family residence. 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 Cloquallum soils observed at the site are not suitable for use as structural fill material. Saturated soil conditions may be associated with these soils during or following extended periods of rainfall. However, to reduce grading time and construction costs, we recommend that earthwork be undertaken during favorable weather conditions. 10011 Blomberg Street SW, Olympia, WA 98512 5 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECBmCAL TESTING LA BORATORY 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. LANDSLIDE—EROSION HAZARD AREAS CLASSIFICATION The Mason County Critical Areas Ordinance (17.01.100) defines a landslide hazard area as one containing slopes equal to or greater than 40 percent with more than a 10-foot vertical relief. The southeastern slope is in excess of 40 percent and the vertical relief is in excess of 10 feet. Based on this, this site does meet the technical criteria of a landslide hazard. The Mason County Critical Areas Ordinance(17.01.104)defines an erosion hazard area as: Areas in Mason County underlain by soils which are subject to severe erosion when disturbed. Such soils include, but are not limited to, those for which potential for erosion is identified in the Soil Survey of Mason County, USDA Soil Conservation Service, 1960, or any subsequent revisions or additions to this source. These soils include, but are not limited to, any occurrence of River Wash ("Ra') or Coastal Beaches ("Cg') and the following when they occur on slopes 15% or steeper: a.Alderwood gravelly sandy loam ("Ac"and "Ad') b. Cloquallum silt loam ("Cd') c. Harstine gravelly sandy loam ("Hb') d. Kitsap silt loam ("Kc') The soils at the site are mapped as Cloquallum silt loam (Q. This site does not 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 portions of the slopes on the lot exceed 40 percent, they are generally stable relative to deep- seated failure in their present configuration. 10011 Blomberg Street SW, Olympia, WA 98512 6 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY To prevent minor sliding, uncompacted fill material and any underlying vegetation shall be removed in order to construct the foundation. Excavation and back-filling will occur based on appropriate engineering and earthwork recommendations found in the following"Earthwork" section. Grading in the building portion of the site should be conducted in accordance with geotechnical recommendations provided herein. As previously discussed, weathering, erosion, and the resultant surficial sloughing and landsliding are natural processes that affect slope areas. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles and freezelthaw 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 ands 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. A setback of 15-feet from the crest of the slope (located southeast of the proposed building location)to the bottom of the footing should otherwise be observed. The building setback may be measured from the bottom of the footing to the face of the steep slope in accordance with the 2003 International Building Code(IBC). Peak Shear Stress vs. Normal Stress Silt Loam 3000 2500 35] c a 2000 n a a 1500 0 t 1000 a 500 +1/4 ton ---1r2ton w -1 ton 0 0 500 1000 1500 2000 2500 3000 Normal Stress(p4 10011 Blomberg Street SW, Olympia, WA 98512 7 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHmcAL TESTING LABORATORY Slope stability was modeled using the GEO-SLOPE/W program (version 5.18) in both static and extreme dynamic conditions(ca=0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price methods. The silt loam was determined to have a unit weight of 124 pcf, cohesion of 300 psf, and a shear angle (�) of 35°. Under static conditions, the slopes were stable to shallow failure. Under dynamic loading, the 3328 computations demonstrated that the slope is not susceptible to surficial raveling and deep-seated failure. The following figure illustrates the moment factor of safety for slope A. The figure below is the solution of greatest concern and exhibits the need for a building setback of 15-feet. Ashby Homes Lot C-4— Slope A • �, ' Analysis Method: Morgenstern-Price Direction of Slip Movement:Left to Right Slip Surface Option:Grid and Radius Seismic Coefficient:Horizontal and Vertical 210 •� 1.51 1:�j• 0 19 �$\• . � 0 . 180 = 170 O 160 Cloquailum Soil Model: Mohr-Coulomb > 150 Unit Weight: 124 4) 140 Cohesion: 300 L1J 130 Phi: 35 120 110 100 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 Distance (ft) As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are natural processes that affect slope areas. Surficial raveling and sloughing was not observed in the sloping portions of the site. To manage and reduce the potential for these natural processes,we recommend the following: 1. No drainage of concentrated surface water or significant sheet flow onto the sloped areas. 2. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill. 3. Trees may be removed on sloped areas as long as the stumps remain. 10011 Blomberg Street SW, Olympia, WA 98512 8 Phone#: (360)754-4612 Fax#: (360)754-4848 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). Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic Soil Profile Type C, for Very Dense Soil, as defined by Table 1615.1.1 (IBC). This is based on the range of SPT (Standard Penetration Test) blow counts and/or probing with a 'h-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. 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. Trees located on steep slopes may be removed only if the stumps remain to deter erosion. Temporary and permanent erosion control measures should be installed and maintained during construction or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include, but not be limited to, silt fences, berms and swales with ground cover/protection in exposed areas. A typical silt fence detail is included on Figure 2. Any re-contouring of the site will create a need for erosion control measures as listed above. F r� r k View Looking Southwest 10011 Blomberg Street SW, Olympia, WA 98512 9 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTEcBmcAL TESTING LABORATORY 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 8 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 16 inches may occur in these areas. These materials may be stockpiled and later used for erosion control and landscaping. Materials that cannot be used for landscaping or erosion control should be removed from the project site. Where placement of fill material is required, the exposed subgrade areas should be proof-rolled to a firm and unyielding surface prior to placement of any fill. We recommend that trees be removed with the roots, unless located on a slope. Excavations for tree stump removal in any building area should be backfilled with structural fill, compacted to the density requirements described in the"Structural Fill" section of this report. If structural fill is needed, we recommend that a member of our staff evaluate the exposed subgrade conditions after removal of vegetation and topsoil stripping is completed. 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. STRUCTURAL FILL All fill material should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least 90 percent of MDD (maximum dry density as determined in accordance with ASTM D-1557) to within 2 feet of subgrade and 95 percent MDD in the upper 2 feet. The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend the use of well-graded sand and gravel with less than 5 percent (by weight) passing the No. 200 sieve based on that fraction passing the 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. 10011 Blomberg Street SW, Olympia, WA 98512 10 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHMCAL TESTING LABORATORY SUITABILITY OF ONSITE SOILS AS FILL Onsite soils should not be considered for use as structural fill. In general,the native soils (sand, loam, and gravel) encountered on the site have more than 10 percent fines (material passing the US No. 200 Sieve)and are unsuitable for use as structural fill. CUT AND FILL SLOPES All job site safety issues and precautions are the responsibility of the contractor providing services and/or work. The following cut/fill slope guidelines are provided for planning purposes. Temporary cut slopes will likely be 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 of 5 percent or more, 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 of 2 feet for isolated footings and at least 16 inches for continuous wall footings. Footings founded as described above can be designed using an allowable 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. Passive pressure may be determined using an allowable equivalent fluid density of 300 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%z inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation sub-grade during construction could result in larger settlements than predicted. 10011 Blomberg Street SW, Olympia, WA 98512 11 Phone#: (360)754-4612 Fax#: (360) 754-4848 1 GEOTECUMCAL 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 3 percent fines(by weight). The drainage material should be placed in one lift and compacted to an unyielding condition. A synthetic vapor barrier may be used for the control of moisture migration through the slab, particularly where adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier could result in wet spots on the slab, particularly in storage areas. RETAINING WALLS Retaining walls may be utilized on the sloping portion of the site to retain fill material. The lateral pressures acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space is backfilled with clean granular, well-drained soil (washed rock), the design active pressure may be taken as 35 pcf(equivalent fluid density). 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: 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. 10011 Blomberg Street SW, Olympia, WA 98512 12 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECIINICAL TESTING LABORATORY 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. Passive pressure may be determined using an allowable equivalent fluid density of 35 pcf(pounds per cubic foot). Factors of safety have been applied to these values. 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 an appropriate infiltration area. 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 at the site be directed, if possible, to the level area located in the eastern portion of the site 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. LIMITATIONS We have prepared this report for Gale Ashby 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. j Variations in subsurface conditions are possible and may occur with time. A contingency for unanticipated t and schedule. Sufficient consultation with our firm during conditions,should be included in the budge g construction should continue, to confirm that the conditions encountered are consistent with those indicated by our observations, to provide recommendations 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 our specifications. 10011 Blomberg Street SW, Olympia, WA 98512 13 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY View Looking East ' - If our analysis and recommendations are followed, we do not anticipate any onsite or offsite impact from the proposed construction. It is our conclusion that potential landslide hazards can be overcome so as not to cause harm to property, public health and safety, or the environment. The scope of our services does not include services related to environmental remediation and construction safety precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures, except as specifically described in our report for consideration in design. If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. Respectfully submitted, •M W as y' GEOTECHNICAL TESTING LABORATORY Acaa (WIL4 Harold Parks, L.G., L.E.G. 27 �b Senior Engineering Geologist Geo HARCLD PARKS y.7- 3/-d�. 10011 Blomberg Street SW, Olympia, WA 98512 14 Phone#: (360)754-4612 Fax#: (360)754-4848 J GEOTECIINICAL TESTING LABORATORY VICINITY MAP Gmva 27, Tom+ "1 F. rK i. 1 ! i _ P 1. 6 r _. Figure 1 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (360)754-4612 Fax#: (360) 754-4848 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH Cp RRU M�IVNM MINIMUM,6 INCH SUGGESTED/ Sp 10"c FFr _ HF TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL 'FoorMM OR ENERGY DISPERSION DEVICE IFOOT MIN 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 Blombery SL SWO"s 512 FIGURE 3 QWQC Services Phwe:(vw se46 12 Testing Services Fax:(300)7 T54A 848 Not to scale DRAINAGE DETAILS RLTER FABRC MATERIAL BPVMIEROLIS USE STAKES°�� '�"��' Geotechnical FABRICTOY'RiE "7C R BOEVALI FABRIC OR EQUIVAIJBIT Y Testing � s-a ALE Laboratory 00 ; 61 MAX 2-XV WOOD POSTS.STA DARDOR BJRV BOTTOM OF FlLTEi ' BETTER OR EQUAL ALT07NATE MATERIAL IN S'X17TRENCHH STEEL FENCE POSTS I Il % I ' 0s 6 j' ( FILTER FABRIC e• 2-X7X14 GAl1GEVMRE FABRIC OR EQUIVALENT 2J- 1 GROUND SURFACE S-P PROVIDE YP-1 VTWASH� GRAVEL BACKALL NTRENC H 17 I t 1 1 I i I it i AND ON BOTH SIDESOFRLTER FENCE FABRIC ON THE Al7FKE S..MN I 11 I;f I , / STEEL POSTS SfS ' l '' I FILTER FABRIC FENCE NOTES GeoteChnlCai Services i __ l T,\\ \\\\\ ` I' / lI ! I i TLTERFFG�OFSHALLBRRIERTO EDINAE�OFR VALLCUMTHEN IS QA/� Services /' �' ARENECESSMY.FlLTERCLOTHSHALLBESaLI(IDTOGETI87OHL A Testing Services A SUPPORT POST WITH A MINIMUM&INCH OVERLAP MD SECUBV FASTENED AT BOTH E DSTO THE POST. 2.POSTS SHALL BE SPACED A MAXIMUM OF 6 FEET APART ADDRIVEN SECURELY INTO THE GROUND(MNMIMCF301146ES). 3.A TRENCH SHALL BE EXCAVATED APPROMMATELYBIND-ESWDEADI2 10011 Blomberg St.SW INCHES DEEP ALONG THE LINE OF POSTS ADUP30PE FROM THE BWPoER Oympia,WA 98512 4 WHEN STANDARD STRENGTH FILTER FASNC ISUSED.AWARE MESH SUPPORT FENCE SHALL BE FASTENED SECURELY TO THE UPSOPESIDE Phone:(360)754-4612 \ 1 I ) I I I l OF THE POSTS USING HEAW-DUTY WIRE STAPLES AT LEASTIINCH LONG,TIEWIRESORHOGRMGS.THENRESFWLEXTEDINTOTIE Fax:(360)754-4848 96 MINIMUM INCHES NOT EX INCHES ABOVE THE ORIGINAL GROUDSURFACE EXTEND MOREIH THAN Q `\ j HI J I l _ ,' 1, 5.THE STANDARD STRENGTH FILTER FABRICSHALLBESTAPUED OR WRED T I I ) ; --' , I TO THE FENCE AND 20 INCHES OFFPHdC SMALL BEEXTEDED Date: 10/06/2004 fl-N ; W ; I NTCHES ABOVE THE ORIGIOTH TRENCH THE N�IGROUND C SHALL�SURF RTERFAazCMORE THAN Sa Designed by: LL \ / ) I // l S ; r I % NOT BE STAPLED TO THEE7STING TREES. Drawn by: LL % l 'W^ I ; 7 l 8.Um EXTRkSTRENGTH ESHSFILTER FABRIC AND BECLOSEREUMI ATED,ALONG Is Checked by: LL i, % DISPERSt�N j li vJ ; 1 / I I USED,THE WIRE MESH SUPPORT FENCE MAP BE ELMNATED,N SICTI I A CASE.THE FILTER FABRIC IS STAPLED OR WIRED CNRECTLY TO THE Dwg#:10-06-04-070 EA AA i POSTS NTH ALL OTHER PROVISIONS OR ABOVE NOTES APPLYING FILTER FABRIC FENCES SHALL NOT BE REMOVED SORE THE LPSLOPE AREA HAS BEEN PERMANENTLY STABILIZED 8.FILTER FABRIC FENCES SHALL BE INSPECTED IMM®IATELY AFTER EACH W RAINFALL AND AT LEAST DAILY RING PROLONG®RNNFN.L ANY \\I REQUIRED REPAIRS SHALL BE MALE IMMEDIATELY. 1 I / ✓J / / l I � ! I I GENERAL EROSION CONIROLNOTES: 1 I i. EROSION CONTROL MEASURES SHALL BEN PLACE PRIOR TO THE BEGINNING OF CONSTRUCTION.THE PROJECT ENGINEER AHDTHE COUNTY SHALL INSPECT AND APPROVE 11E INSTALLATION OF EROSI ON CONTROL MEASURES PRIOR TO BE I KING CONSMUCIION. 2 EROSION CONTROL MEASURES ARE NOT LIMITED TO THE ITEMS ONTHISPLAN.THE CONTRACTOR IS RE5PCNSftE FOR THE INSTLATION AND MAININNANCE OF ALL EROSION CONTROL MEWSLIFES NO SAL ATION OF EXISTING OR PROPOSEDORNNAGEFAUUTIIES SHALLBEALLOWED.CARE SHALLBETMIENTOPREVBNTMGRATION PROJECT NAME. OF SILTS TO OFF SITE PROPERTIES ASHBY HOMES SITE 9.THE CONTRACTOR SHALL MAKE DAILY SURV9t1AHCE OF ALL ER0.QON CONTROL MEASURES AND MAKE ANY NECESSARY RFPNRSORADDITIONS LOT C-4 OF SP#1233 TO THE EROSION CONTROL MEASURES.TFE COMRACTOF2 SViLPROMCE ADDITIONAL EROSION CONTROL MEASLRESASOETERMI€DNEDESSRY SHELTON, WASHINGTON BY THE COUNTY INSPECTOR ANLVOR THE PROJECT ENG04MR.FAILURE TO COMPLY WITH ALL LOCAL"STATE EROSION CONTROL -/ PARCEL 420252290231 REQUIREMENTS CONTRACTOR ANDIO PROJECT OWNER LEMED AGAINST THE CONTRACTOR MDR7R PROJECT OWNER. - / 4.WRING THE WET SEASON(NOVEMBFJR TO MARCH)ALL DISTURBED SOILS SHALL BE STABILIZED WITHIN 48 HOURS AFTER STOP OF WORK 870SONCO pL/I��/�A� 00 O i- / /�4 J - /- CONTROL MEASURES SHALL INCLUDE,BUT NOT BE UMITEDTO. Revisions: VERING THE/•' ' /' '- - /' ` - ' / ,/'- --i��� _—_• /, RLESWITH PLASTIC SHEETING,EFFECTED RAW MATTAREA IINHG,�IE fMmNG,STRAW MACH. ORWOODCHIPS.SEEDING OF THE DISTURBED AREAS SHALL TARE - ' PLACE AS WEATHER PHLATS - • 'j- %' �. //'✓'' �� --_ S.ALL SEEDED OR SODDED AREAS SHALL BE C ECI®REGUI-A LY TO MAKE SURE VEGETATIVE COVERAGE ISCOMEM AREASSALSE REPAIRED.RESEEDED,AND FE IIU EDASREQLARED. \ \` -/ ---"-' 8.TRACKING OF SOIL OFFSITE WILL NOT BE ALLOWED.IFANYSOILIS `\ I / - TRACKED ONTO A COUNTY STREET.IT SHALL B:REMOVED BYTHE END /' ' ' / OF THHAT WORIONG DAY.ANY FURTHER TRAOGNG OF MUD WILL THEN BE PREVENTED BY SWEEPING OR WA47NG OFTIE V84t5 CI11RE5 BEFOREDRIMNGONACCUNIYSR7EET. -/ 7./ - /- -/ /' , ' l' NOMORETHAN500LF OFTRENCHONADOIANSLOPEOFMOfETHM75 NORTH ' fE -/- - - / ,. % ; / �O PERCENT SHALL BE OPEEDATOTIME. SCALE V 40 I l i C.I.=2' 8.EXCAVATED MATERIAL SHALL BE PLACED ON THE UPHILL SICECFTRENQES. DATUM ASSUMED ' ' i' -� -/- - �' ,I i %, 9.TRENCH DEWATERING DEVICES SHALL BE DISC7ARGEDN AMARIE R THATWILL NOT ADVERSELY AFFECT FLOWING STREAMS DRAINAGE SYSTEMS OR THIS IS NOT A SURVEY OFFSTE PROPERTIES. SCALE:1 Inch=40 feet - /' I i i I / I i 1 j^ 10.ALL STORM SEWER INLETS RECEIVING RINOFF FROM THE PROJECT DURING - %' )' i i i I`. % l i j - CON BEFlLTEREDBEF R ENTERMGTHECONVEY� T SYSSrEM ER WAT 0 10 20 30 40 11.ALL OFF-SITE CATCH BASINS IMMEDIATELY AWACB7TTOTHE 9TE SHALL BE PROTECTED FROMSLTATION. R FIGURE 2 72 ALLDISTURBED AREASA BE cLPD OFWORK THE CONTRACTOR SHALLREAE5PONSIBEMENSIREHAT COMPLETE COVERAGE OF THE pSTURB50 PREASISPROMDBO L THAT GROWTH OF THE VEGETATION IS ESTAHISE). SITE PLAN 13.CATCH BASINS SHALL TRAP SEDIMENT OR FILTER FAE ICM)ST BE PLACED UNDER GRATE UNTIL VEGETATION ISESTABUSED. �0N_STpT�O� MASON COUNTY �P MC � PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER ° 0 N Shelton, Washington 98584 r T G 2 00 a0 1%4 DATE: April 25, 2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Tammi Clark PARCEL # 42025-22-90234 FROM: John Sliva, Programs Engineer-PW BUILDING PERMIT NUMBER: BLD2006-00556 SUBJECT: Geo-Tech Report Review NAME: Ashby Homes Tammi, The Geotechnical Report prepared for the proposed new single-family residence located at 110 W. Valley Heights Drive (Lot C-4 of SP#12233) has been received and reviewed by Public Works. The report appears to satisfactorily address County requirements for Geotechnical Reporting. The report's author indicates that if their analysis and recommendations are followed the site is suitable for the proposed single-family residence. The author does not anticipate any onsite or off site impact from the proposed construction. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope stability. Slope stability was modeled in both static and extreme dynamic conditions. The author needs a building set back of 15 feet from the crest of the slope to the bottom of the footing. Drainage, erosion control, earthwork, and structural recommendations are addressed by the author and should be followed. 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. Based on the contents of this report, I recommend accepting this report as satisfying the County's requirements for stability investigation and geotechnical reporting. Recommendations contained in the report should be incorporated into the site development plans and made conditions for permit issuance. 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. r°eF Sin rely, pi�R kFP;r. CFI F TyF John Sliva Programs Engineer