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HomeMy WebLinkAboutGEOtechnical Report - GEO General - 1/26/2005 I z q,- Geotechnical Report 758 Promontory Road Hartstene Island Mason County, WA Prepared for Steve Miglia by Geotechnical Testing Laboratory Olympia, Washington January 26, 2005 GEOTECHNICAL TESTING LABORATORY STEVE MIGLIA 1630 WOODLAND STREET NE OLYMPIA,WA 98516 RE: GEOTECHNICAL REPORT 758 PROMONTORY ROAD HARTSTENE ISLAND PARCEL121195700013 N47017.724' W122051.758' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence to be located at 758 East Promontory Road at the north end of Hartstene Island. 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 Promontory Point Road. In general, grading will consist of the excavation of the foundation, footings, daylight basement, and driveway. A,t r A ax F View Looking Northeast The site slopes toward the north, northeast, and east from the proposed building location. The steepest slope measured onsite was in excess of 50 percent. Offsite, the steepest slope measured was in excess of 100 percent. Therefore, Mason County requires that a geotechnical report be prepared in accordance with the Critical Areas Ordinance. The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing geotechnical recommendations and design criteria for the project and to satisfy the requirements of the Mason County Critical Areas Ordinance. Geotechnical Testing Laboratory is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: 10011 Blomberg Street SW, Olympia,WA 98512 1 Phone#: (360)754-4612 Fax#: (360)7544848 GEOTECHNICAL TESTING LABORATORY 1. Review the available geologic,hydrogeologic, and geotechnical data for the site area. 2. Conduct a geologic reconnaissance of the site area and surrounding vicinity. 3. Investigate shallow subsurface conditions at the site by observing the exposed soil and reviewing published well logs. 4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations. 5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria (including hillside grading), temporary and permanent cut and fill slopes, drainage and erosion control measures. SITE CONDITIONS SURFACE CONDITIONS The proposed building site is located in an area of private community development in the Puget Sound glacial upland area located east of Pickering Passage and west of the Case Inlet. The proposed layout of the site is shown on the Site Plan, Figure 2. We conducted a reconnaissance of the site area on January 11, 2005. Site elevations range from approximately 80 to 94 feet. Elevations in the building area are roughly 8 feet in relief. 4.., The proposed building location has vegetation common to the Northwest. The vegetation includes fir, cedar, and hemlock trees as well as bracken ferns, sword ferns, huckleberry, salal,and Oregon grape. At the time of the site visit, we observed no evidence of surface erosion onsite. No evidence of deep-seated slope instability was observed. Minor sloughing was observed offsite along the eastern slope; see photo right. Surface water flow was not observed onsite at the time of our reconnaissance. The general topography of the site area indicates that drainage flows toward the east and ultimately to the Pickering Passage. Runoff from the community and roads is controlled by the existing stormwater system. 10011 Blomberg Street SW, Olympia,WA 98512 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SITE GEOLOGY The site is generally situated within the 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 Vashon glacial till material. SITE SOILS The Mason County Soil Conservation Survey(1960) has mapped the site soils as a Sinclair shotty loam, 5-15 percent slopes (So), at the proposed building location. The Sinclair soils have typically developed from very compact Vashon gravelly till. Surface drainage is well to moderately well established. Internal drainage is restricted by the substratum of cemented till. Typically, there is no occurrence of a high water table. We observed no active erosion or slope disturbance in the site area during our reconnaissance. The Geologic Map of Washington—Northwest Quadrant(2002)has mapped the site geology as glacial till deposits (Qgt) of continental glacial origin. The report reads: Till— Unsorted, unstratfied, highly compacted mixture of clay, silt, sand, gravel, and boulders deposited by glacial ice; may contain interbedded stratified sand, silt, and gravel. Includes part of the Vashon Drift undivided. Y t. t xF, The Coastal Zone Atlas, Volume 9, Mason County (MA-14) maps the site as Pleistocene gravels (Qpd. Slope stability is described as "stable"at the building location and"unstable"offsite to the east. The chance of flooding is less than one percent. The advance outwash is further described at having "good to excellent foundation support", "good seismic stability", and"generally stable in slopes up to angle of repose." 10011 Blomberg Street SW, Olympia,WA 98512 3 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY - f*y Glacial Till on Lower Slope SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed building site soil and reviewing available well logs. Groundwater is presumed deep due to the topography. Depth to competent soil is approximately 12 inches throughout the site. SUBSURFACE CONDITIONS In general, undisturbed dense Sinclair shotty loam was observed throughout the site. Groundwater was not observed or encountered. No instances of groundwater seeps were observed on the slopes or adjacent to the parcel. Based on the site topography and the nature of the near surface soil, seasonally perched groundwater conditions are not expected during periods of extended wet weather. .a _ View Looking Southwest 10011 Blomberg Street SW, Olympia,WA 98512 4 Phone#: (360) 7544612 Fax k (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SLOPE STABILITY Slopes in excess of 100 percent were observed on the adjacent slope. 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 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. The near-surface soils are in a dense to very dense condition except at the ground surface. The surficial soils are generally in a medium dense condition. In general, the undisturbed native soils of the site consist of a mixture of variable amounts of sand, silt, and gravel. These soil materials are in a dense condition except where they have been disturbed by weathering activity. These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or significant erosion was observed on the site at the time of our investigation. Weathering, erosion, and the resultant sloughing and shallow landsliding are natural processes that can affect steep slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone, which has been disturbed and has a lower strength. Evidence of minor raveling and sloughing was observed on the offsite slopes during our investigative visit. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles, and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced by encouraging vegetation and discouraging runoff from the steep slope. Erosion control recommendations for the sloping areas are provided in the"Erosion Control"section of this report. View Looking West of Lower Slope 10011 Blomberg Street SW, Olympia,WA 98512 5 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 structure. 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. f M ' View Looking.South Ou In general, the Sinclair soils observed at the site are not 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. 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 eastern adjacent slope is in excess of 100 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. 10011 Blomberg Street SW, Olympia,WA 98512 6 Phone#: (360)7544612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY 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 r Cd') c. Harstine gravelly sandy loam ("Hb') d. Kitsap silt loam ("Kc') The soils at the site are mapped as Sinclair shotty loam (So). 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 adjacent slopes on the lot exceed 100 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. 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. A setback of 25-feet from the crest of the northeastern slope to the bottom of the footing should otherwise be observed. The building setback may be setback measured from the bottom of the footing to the face of the steep slope in accordance with the Unified Building Code. 10011 Blomberg Street SW, Olympia,WA 98512 7 Phone#: (360)7544612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY Slope stability was modeled using the GEO- SLOPE/W program (version 5.18) in both static and Peak Shear Stress vs.Normal Stress extreme dynamic conditions (ca = 0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price methods. The site was � modeled using two soil layers. The shotty loam was a determined to have a unit weight of 117 pcf, cohesion g of 300 psf, and a shear angle (�) of 30°. The 1500 underlying glacial till material was determined to have a unit weight of 130 pcf, cohesion of 200 psf, r ,ODO and a shear angle (�)of 50°. Under static conditions, the slopes remained stable to deep-seated and shallow ° +,µ- Mj failure. Under dynamic loading, the 3328 500 };';, computations demonstrated that the slope is not susceptible to surficial raveling. Large deep-seated o ,eoo 2000 �soo failure was not demonstrated by our model. The Normal o soo ,000 0 Suess(psf)following figure illustrates a moment F.S. of 1.09, the lowest value derived from modeling the proposed building location. This solution of greatest concern exhibits the need for a building setback of 25-feet. .• �• y Miglia Site — Slope A �o• �. Analysis Method: Morgenstern-Price b • . . . a • Direction of Slip Movement: Left to Right •• • •� . ,� Seismic Coefficient: Horizontal and Vertical ,• . .aWNT • 1.09/� Sinclair Shotty Loam .•• .• ' 100 Soil Model: Mohr-Coulomb l 90 Cohesion: 300 45 80 Phi: 30 • ti C 70 60 Till > 50 Sail Model: Mohr-Coulomb N Unit Weight: 130 W 40 Cohesion: 2'00 h 30 —Phi: 50 20 0 50 75 100 125 150 175 200 Distance (ft) 10011 Blomberg Street SW, Olympia,WA 98512 8 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are natural processes that affect slope areas. No significant surficial raveling or sloughing was observed offite. Surficial raveling and sloughing was observed offsite to the northeast. To manage and reduce the potential for these natural processes,we recommend the following: 1. No drainage of concentrated surface water or significant sheet flow onto the sloped areas. 2. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill. 3. Trees may be removed on sloped areas as long as the stumps remain. SEISMIC—LIQUEFACTION HAZARD According to the Seismic Zone Map of the United States contained in the 2003 International Building Code (IBC), the project site is located where the maximum spectral response acceleration is 45 percent of gravity(g). 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 '/z-inch diameter steel probe rod. The shallow soil conditions were assumed to be representative for the site conditions beyond the depths explored. Based on our review of the subsurface conditions, we conclude that the site soils are only mildly susceptible to liquefaction. The near-surface soils are generally in a dense condition and the static water table is located well below the surface. Shaking of the already dense soil is not apt to produce a denser configuration and subsequently excess pore water pressures are not likely to be produced. a 4 C I 10011 Blomberg Street SW, Olympia,WA 98512 9 Phone#: (360)754-4612 Fax#: (360)7544848 GEOTECHNICAL TESTING LABORATORY EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development. Removal of natural vegetation should be minimized and limited to the active construction areas. Yard landscaping around the home is permissible, but understory growth on the slopes should be encouraged as much as possible as a deterrent to erosion. Hazard trees located on steep slopes may be removed only if the stumps remain to deter erosion. Temporary and permanent erosion control measures should be implemented and maintained during construction and/or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include, but not be limited to, silt fences, berms, and swales with ground cover/protection in exposed areas. A typical silt fence detail is included on Figure 2. Any re-contouring of the site will create a need for erosion control measures as listed above. EARTHWORK SITE PREPARATION All areas to be excavated should be cleared of deleterious matter including any existing structures, debris, duff, and vegetation. Based on our observations, we estimate that stripping on the order of 6 to 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 1 foot 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 zompaction-equipment used-: We- -- -recommend-that-the appropriate rift-thickness be evaluated by our field representative during construction. 10011 Blomberg Street SW, Olympia,WA 98512 10 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend the use of well-graded sand and gravel with less than 5 percent (by weight) passing the No. 200 sieve based on that fraction passing the'/,-inch sieve. If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a somewhat higher(up to 10 percent)fines content will be acceptable. Material placed for structural fill should be free of debris,organic matter,trash, and cobbles greater than 6 inches in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction. SUITABILITY OF ON-SITE SOILS AS FILL On-site soils should not be considered for use as structural fill. In general, the native soils (sand and loam) encountered on the site should have less than 10 percent fines (material passing the US No. 200 Sieve) and are not suitable for use as structural fill. CUT AND FILL SLOPES All job site safety issues and precautions are the responsibility of the contractor providing services and/or work. The following cut/fill slope guidelines are provided for planning purposes. Temporary cut slopes will likely be 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 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 of 2 feet for isolated footings and at least 14 inches for continuous wall footings or according to the UBC. Footings founded as described above can be designed using an allowable soils bearing capacity of 2000 psf(pounds per square foot) for combined dead and long-term live loads in areas of medium dense to dense soils. 10011 Blomberg Street SW, Olympia,WA 98512 11 Phone#: (360)7544612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY 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 150 pcf(pounds per cubic foot). We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch for the anticipated load conditions, with differential settlements between comparably loaded footings of '/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 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:1V 25% 44 pcf 2H:l V 50% 53 pcf lH:1V 75% 61 pcf 10011 Blomberg Street SW, Olympia,WA 98512 12 Phone#: (360)754-4612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY 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. 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, manufactured 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 home and garage. The roof drain should not be connected to the footing drain. For footing drains, the drain invert should be below the bottom of the footing. We recommend that the collected stormwater runoff be directed to an infiltration galley located in the northern portion of the site by tight-line, see Figure 2. 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 site is serviced by community sewer and thus no septic drainfield is proposed onsite. 10011 Blomberg Street SW, Olympia,WA 98512 13 Phone#: (360)7544612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY LIMITATIONS We have prepared this report for the use of Steve Miglia and members of his design team, to use in the design of a portion of this project. The data used in preparing this report, and this report, should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and our site reconnaissance, and should not be construed as a warranty of the subsurface conditions. This report is quantified as a micro-study and not a macro-study. Geotechnical Testing Laboratory and its personnel cannot be responsible for unforeseen and widespread geologic events (such as earthquakes, large-scale faulting, and mass wasting)beyond the scope of this project. Variations in subsurface conditions are possible and may occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient consultation should be made with our firm during construction to confirm that the conditions encountered are consistent with those indicated by the recommendations and for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans. If our analvsis 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 propem, 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. a� Respectfully submitted, 7 GEOTECHNICAL TESTING LABORATORY A O sed G Harold Parks, L.G., L.E.G. 7_3/-05 d-IAROLD.PAf,?<5 I Senior Engineering Geologist 10011 Blomberg Street SW, Olympia,WA 98512 14 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY Vicinity Map s: Cs off /r4 t w �r Dougall Point Rock MIG Si jJ (/fir -- . '} �, Yr.• �� 1 r •S .f• f /f It ' t r j Figure 1 10011 Blomberg Street SW,Olympia,WA 98512 Phone#:(360)754-4612 Fax#: (360)754-4848 FILTER FABRIC MATERIAL17'WICEROLLS USE STAPLES OR WIRE RING TO ATTACH G e o to c li n i c al F FABRIC TO V.1RE " I 14 GAUGE WARE gBRgRIC OR EQU VALENT 7. Testing Laboratory MAX 1 _ OR T BOTTOM OFRLTER 1 BETTER OORDEQUAL ALTERNATE MATERIAL IN 8"X12'TRENCH 1 1 STEEL FENCE POSTS 1 I 1 1 1 1 1 1 ` ` FILTER FABRIC Y 1 I I I 1 2"X2"X14 GAUGE WIRE t7 FABRIC OR EQUIVALENT 7-P 1 ; 1 GROUND SURFACE5'-P PROVIDE 314"-11?WASHED GRAVEL BACKFILL INTRIENCH 12' AND ON BOTH SIDES OFRLTER 1 ; ; FENCE FABRIC ON THE SURFACE 8 M III 1 7LT TEFL FENSTS CE `� j? O A AT'STEE FENCEPOSS Geotechnical Services 1 POTENTIAL `� \ FILTER FABRIC FENCE NOTES INFILTRATION i i QA/QC Services 1 THELENGTH OF THE BA PURCHASED TO ED IN A CONTINUOUS ROLL CUT TO THE LENGTH OF THE BARRIER TO AVOIDUSEOF JOINTS.WA.IBN JOINTS LOCATION �` �\ ASUNPPORTSPOSTWThHA MINIMUM 6Np� pP °"`HAT Testing Services ` FASTENED AT BOTH ENDS TO THE POST. T O \\ v< ro ; 2.POSTS SMALL BE SPACED AMA%IMUM OFBFEfT APART AND DRIVEN v/- \ ` ; ` SECURELY INTO THE GR°UND(MMMIMOFWINOfS). 3.A TRENCH SHALL BE EXCAVATED APPROXIMATELY 8 INCHES WIDE AND 12 10011 Blomberg St.SW INCHES DEEP ALONG THE LINE OF POSTS MD UPSLOPE FROM THE BARRIER 1 1 1 \ ; 4.WHEN STANDARD STRENGTH FILTER F186CIS USED,AWARENISI Olympia,WA 98512 SUPPORT FENCE SHALL BE FASTENED SECURELY TO THE UPSLOPE SIDE Phone:(360)754-4612 OFTHE POSTS USING HEAW.DUTY WIRE STAPLESAT LEAST I INCH LONG,TIEWIRESORHOGRINGS THEVARESIiN1EMBDINTOTHE Fax:(360)754-4848 TR NENCHAMINIMUMOF4I NCHESANOSHALLNOTEXTEDMORETHMN36 INCHES ABOVE THE ORI GINALGROUNDSURFACE THE STANDARD STRENGTH FILTER FABRIC SHNLEE STAREDORWARED \ ► 20 Date: 01l17/2005 1 ` IN THE FENCE AND THEFA RI OF ALLN TELLN EORETHA INCHESA RENCHABOVE THE THE ORIGINAL GROUND SURFACE MORETFLPN% ^ }� \\�\ \\ ; 1 ; INdHESABOVETHEORIGINALGROUNDSURFACE.RLTE7FAE8CSHALL Designed by: LL PRO, \ E \ , NOT BE STAPLED TO THE EXISTING TRIES Drawn by: LL 1r V \�\ \\ ; \ 6 WHEN EXTRA.STRENGTH FILTER FABRIC AND CLOSER POST SPACING,IS Checked by: LL USED,THE WIRE MESH SUPPORT FENCE MAP BE ELIMINATED,IN 9141 - B U I L N G ` �\ POSTS WITH ALLTOTHER PROMSIo�AABOOVEOR E�NOTESDTE PLLYIINNG THE Dwg# 01-17-05-009 \\ T.F1 LTER FABRIC FENCES SHALL NOT BE REMOVED BEFORE THE UPSLOPE AREA HAS BEEN PERMANENTLY STABUZED � O A \ \ 8.FILTER FABRIC FENCES SHALL BE INSPECTEDIMAEDIATELY AFTER EACH so L TION \ \ REQUIRE REPAIRS ASTDAILY BEMADENGPROLONC>✓�RALN=NI.ANY \ \ REQUIRED REPNRS SHALL EEMACE IFAE]ATB-Y. GENERAL EROSION CONTROLNOTES: 1. EROSIONCONTROL MEASURES SHALL ffIN PUCE PRIOR TO THE BEGINNING OFCONSTRUCTION.THE PROJECT BIGNEER AND THE COUNTY O \ SHALL INSPECT AND APPROVE THE INSTALLATION OF \` EROSION CONTROL MEASURES PRIOR TO BEGIN I NG CONSTRUCTION. _ \ 2.EROSION CONTROL MEASURES ARE NOT UNITED TO THE ITEMS ONTHISPLAN.THECONTRACTORMRESPONSIBLE FOR THE INSTALLATION AND MAINTAINANCE OF ALL EROSION CONTROL MEASURES. SHALLBEALLOFE.CARSORPROPOS®ORNNAGEFAGUTE$ PROJECT NAME: ` OF SILTS TO OFFSTEPRROPERT S�TNFNTOPREVENTMGRATION MIGLIA SITE O 3.THE CONTRACTOR ESSHALL NMAKE AKEDAILY SURVSARYRE OF ALL AIRSO ADDn 758 PROMONTORY RD. CONTROL MEASURESANDMAZE UR NECESSARY REPAIRS ORALCITONS TO THE EROSION CONTROL MEASURES.THE CONTRACTOR SFUV1 PROVIDE SSARY BY ADDITIONAL SIONINSPECTOR CONTCTOR ALMEASIEPROJE ENGINED EER FALS/RY SHELTON, WASHINGTON NORTH BY THE COUNTY INSPECTOR AND/OR THE EROSION ENGINES FALL MiE TO REQUIREMENTS NTSWIT ALL LOCAL AND VIL EEA°g«N DON ROL LEVI PARCEL 121195700013 REQUIREMENTS MAY RESULT IN GML PENALTIES LNG LEVIED AGAINST THE CONTRACTOR ANCIOR PROJECT OWNER. ��� ELEC BOX SCALE 1" —2O' 4.DURING THE WET SEASON(NOVEMBER TO MARCH)ALL DISTURB®SOILS SHALL BE STABILIZED WITHIN 48 HOURSAFTER STOPOFWORK(.EROSION p�71� �I 9Q _ C.I. �] CONTROL MEASURES SHALL INCLUDE,ENTNOTEEUMTEDTO. ROsio IS: T - - C = 2' COVERING THE EFFECTED AREA INCLUDING SP01LPR6WITH PLASTIC SHEETING,STRAW MATTING.JJTE MATTING.STRAW M1LCi. OOCHIPS SEEDING OF THE OISRRBED TAKE AREAS SHALL TA DATUM ASSUMED OR WO PLACE AS WEATHER PERMITS, THIS IS NOT A SURVEY 5.ALL SEEDED OR SODDED AREAS SHALL IECEo®REGULARLY TO MAKE SURE VEGETATIVE COVERAGE IS COMETS AREAS 9AALL BE REPAIRED.RESEEDED,AND F Wn UZED ASREQU.IREJ. S.TRACKING OF SOIL OFFSTE WILL NOT BE ALLOWED.IFANYSCLIS TRACKED ONTO A COUNTY STREET.IT SMALL EE REMOVED BY THE END OFTHATWORKINGDAY.ANY FURTFERTRAC14NGOF MDVALLIHEN PREVENTED BY SWEEPING OR WASHING OF THE VEHICLES TIRES 0 10 20 30 YAO BEFORE DRIVING ONAOOUNTYSTREEET 7.NO MORE THAN SIX LF OF TRENCH ON ADOWNSLOPE OF MORETHNN 5 PERCENT SHALL BE OPEC AT ONE TIME. 8.EXCAVATED MATERIAL SHALL BE PLACED ON TIE UPIHLL SIDE OFTRE40ES. 8.TRENCH OEWATERING DEVICES SHALL BE 0I90HARG DNAMAIERTMATVALL NOT ADVERSELY AFFECT FLOWING STREAMS.DRAINAGE SYSTEMS OR OFFSTE PROPERTIES. SCALE:1 Inch=20 feet 10.ALL STORM SEWER INLETS RECEIVING RUNOFF R20M THE PROJECT WRING CONSTRUCTION SHALL BE PROTECTED 90 THAT SEDIMENT-LADEN WATER WILL BE FILTERED BEFORE ENTERING THE CONVEYANCE SYSTEM. 11,ALL OFF-SITE CATCH BASINS IMMEDIATELY ADJACENT TO THE SITE ECTEDFROM TION SHALL DISTURBED BED AREAS SHALL SE SEE RETHAT FIGURE 2 12.ALLDISTURBED AREAS SHALL S SEEDEDOR SODDED SEUE TOUPON CONPIPRON OF WORK THE COVERAGECO NTRACTOR SHALL BERE�NSISP O E PROVIDED COMPLETE COVERAGE OF THE DISTURBED AREAS IS FRONDED bTMAT GROWTHOFTIAEALL TRATI SEDIMENT OR®. SITE PLAN 19.CATCH BASINS SHALL TRAP SEDIMENT OR FILTER FERRIC MUST BE PLACED UNDER GRATE UNTIL VEGETATION IS ESTABUSI�. 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH MINIMUM,6 INCH SUGGESTED 10 TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL OR ENERGY DISPERSION DEVICE x .. - 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 Geatechnical Services l00l l Bl0fftM s.sw0VM FIGURE 3 QA/QC Services Phwe:(wa ses4z Testing Services Fa (360)754-az a 8 Not to scale DRAINAGE DETAILS