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HomeMy WebLinkAboutGEOTech Assessment for SEP2005-00106 - BLD Engineering / Geo-tech Reports - 10/10/2005 �0 STA7-Foy MASON COUNTY �P A o N BLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER ° S N Shelton, Washington 98584 rZ N V y 0 OJ �O 1864 DATE: October 10, 2005 INTER-DEPARTMENTAL COMMUNICATIONS TO: Mike MacSems, DCD — Planner PARCEL 32344400010, 322353200130 322344400000 FROM: Patricia Carroll, PW BUILDING PERMIT NUMBER: SEP-2005-001006 SUBJECT: Geo-Tech Assessment Review NAME: Jerry Vermillion Hi Mike, A geotechnical assessment prepared for the proposed Single Family Residence at 8371 E. Highway 106 on a 2+ acre parcel which is part of a 34 acre site has been received and reviewed by Public Works. The residence and the road may be constructed at the location indicated based on the report from Geotechnical Testing Laboratory and SubTerra, Inc. Compliance in regard to their field observations, research, and understanding of the proposed design solution with the recommendations for managing and reducing the potential for surficial sloughing, shallow landsliding should be part of the condition for permit issuance. Adequate Erosion and Sediment (E&S) control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. A minimum 25' building setback from the top of the crest of slopes and other recommendations contained in the assessment should be incorporated into the site's development. I, therefore, recommend accepting the report as satisfying the County's requirement(s) for stability investigation and geotechnical reporting. Please feel free to contact me at ext. 523 or Bob Thuring ext. 452 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, Patricia Carroll �Ff 4 WORK ORDER . PUBLIC WORKS OEPT, PERMIT M �'...�.cr _ o l o.6 f 1Emben otk Or+dar . Requestad trlh4rltAd by, h Date: Type Of Work e� e ,ew• CHARGE TO: NAME �lr,►vi 0,, AGENCY/COMPANY - 131WNG ADDRESS PHONE _ 5 . Pub. 0: 0�3 ih i yuG • !01 a e: m.to es _ proHd WAI foil 1Fl h 0 EiTfMARO TOTAL n: TH , Lim mil' t�OTiu.S EQUIPMENT IJSE� ma 11 8 P1 Adud cost DAM: OAR ..� � —�--• Q gang •. . ;.,8,�!! Hour ,# F�l.lL TOTAL= . EQUIPMENT USED: MA MITAL al DILM DATE TOTAL ALL PAIDDATE lily _ ��✓ \ i i/ Sep 02 05 01:50p J0 s 360-262-9226 p.2 HUNGERFORD HOLDI G 0. INC. AND MONTANA , INC. SE1/4, SE114 SECT70N 34 AND SW1/4, SWI14 SECT70N 35 (22N 310 r� �J F- SWAY ($R �06) NAvy YA1� /T-4 NO ACTIVITY AREA DANGER TREE REMOVAL AREA j�- CONVENT70NAL HARVESTAREA FOREST PRO,INC. Grrglow 204 Senn Rd ChrhaBs WA 98S32 360-2629716 5-64JVERM.TRV SCALE UAIF- URAWN BY 0 300' 300 Ft/In 9-2-2005 Greg Jones 5 64 2 1/1 This map drawn with TRAVERSE PC,Software Traverse PC Geotechnical Report 8371 East Highway 106 Union, WA Prepared for: Jerry Vermillion by Geotechnical Testing Laboratory Olympia, Washington July 15, 2005 1 GEOTECHNICAL TESTING LABORATORY .TERRY VERMILLION 8371 EAST HIGHWAY 106 UNION, WA 98592 RE: GEOTECHNICAL REPORT 8371 EAST HIGHWAY 106 UNION, WA 98592 PARCELS 322344400000, 322344400010, 322353200130, & 322344470825 N47020.962' W 123°02.308' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed selective logging along State Highway 106 and one single-family residence to be located at the above referenced site, approximately 2.5 miles east of Union, Washington. 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 with a single-family residence. The 34-acre site is accessed by a driveway from State Highway 106. In general, grading will consist of the excavation of the foundation, footings, and access driveway. Selective logging will occur along State Highway 106 to remove hazard trees while the underbrush will remain. Verbal permission has been granted by the State to remove the hazard trees. The site slopes to the north from the southern, lesser-steep area toward the Hood Canal. The steepest slope measured onsite was in excess of 100 percent along State Highway 106. Most slopes are less than 62 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. In addition to previous reports supplied by Krazan and Associates, Inc., Geotechnical Testing Laboratory is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: 10011 Blomberg Street SW, Olympia, WA 98512 1 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 1. Review the available geologic, hydrogeologic, and geotechnical data for the site area. 2. Conduct a geologic reconnaissance of the site area and surrounding vicinity. 3. Investigate shallow subsurface conditions at the site by observing the exposed soil and reviewing published well logs. 4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations. 5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria (including hillside grading), temporary and permanent cut and fill slopes, drainage and erosion control measures. SITE CONDITIONS SURFACE CONDITIONS The proposed building site is located in an area of sparse residential development in the glacial uplands overlooking the Hood Canal. The site has northern exposure. We conducted a reconnaissance of the site area on June 7, 2005. Site elevations range from approximately 20 to 500 feet. A septic system is proposed onsite. Exposed soil was observed along the southern slopes bordering State Highway 106. The site slopes are vegetated with a well-mixed variety of vegetation common to the Northwest. The vegetation includes fir, cedar, alder, maple, and hemlock trees as well as Scot's broom, sword ferns, bracken ferns, horsetail ferns, Oregon grape, skunk cabbage, devil's club, foxglove, holly, salal, huckleberry, blackberry, and grasses. a; r. al1�� e N a � At the time of the site visit, we observed no evidence of active surface erosion at or around the proposed building location. Minor sloughing and raveling were observed along the toe of the south facing slopes bordering State Highway 106. Most onsite trees were observed to be straight and vertical except along State Highway 106. Bowed trees were observed along State Highway 106 where the road cut oversteepened the slope. 10011 Blomberg Street SW, Olympia, WA 98512 2 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Surface water flow was observed as a spring approximately 1000 feet west of the proposed building location. The spring creates a class 4 stream, see photo right. Ponding was not } present throughout the site. Groundwater was expressed by seepage along the toe of the slope. The general topography of 4 , the site area indicates that drainage is toward the north. SITE GEOLOGY z ,, The site is generally situated within the Puget Sound glacial -- upland. The existing topography, as well as the surficial and shallow subsurface soils in the area, are the result of the most recent Vashon stade (stage) of the Fraser glaciation that occurred between about 8,000 and 11,000 years ago, and weathering and erosion that has occurred since. A description of the surficial soils is included in the"Site Soils" section of this report. In general, the soils are composed of glacial material. SITE SOILS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as an Alderwood gravelly sandy loam, 30 to 45 percent slopes (Ad), at the site. The report reads: 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. �. „y . 10011 Blomberg Street SW, Olympia, WA 98512 3 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY The Geologic Map of Washington—Northwest Quadrant(2002) has mapped the site geology as advance outwash deposits(Qga)of continental glacial origin. The report reads: Advance outwash — Glaciofluvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained, with interlayered coarser sand, gravel, and cobbles; locally contains nonglacial sediments and deposits mapped as transitional between glacial and nonglacial. Includes the Colvos and Esperance Sand Members of the Vashon Drift and part of the Vashon Drift undivided. The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site as glacial advance outwash(Qga). The glacial advance outwash is described as: Advance outwash, late Wisconsinan (Pleistocene)—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 and silt rip-up lag deposits at their base; may contain nonglacial sediments;generally overlain by till. F. F A, l �1 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 6 inches throughout the proposed building location. Static groundwater is unknown but presumed deep at the proposed building location. SUBSURFACE CONDITIONS In general, undisturbed dense gravelly sandy loam was observed throughout the proposed building location. Groundwater seepage was observed in a localized area in the northwest portion of the site approximately 1000 feet west of the proposed building location. Based on the site topography and the permeability 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 geotechnical report be completed according to the Critical Areas Ordinance. 10011 Blomberg Street SW, Olympia, WA 98512 4 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 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. 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. No ponding, 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. Erosion control recommendations for the sloping areas are provided in the"Erosion Control" section of this report. CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on the results of our site reconnaissance, subsurface observations, and our experience in the area, it is our opinion that the site is suitable for the proposed project. The slopes bordering Highway 106 are stable relative to deep-seated instability and will not be affected by the proposed logging if the stumps remain to deter erosion. The building location slopes are 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. 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 glacial soils observed at the site are 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 GEOTECHNICAL TESTING LABORATORY 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 north-facing slope is in excess of 100 percent along State Highway 106 and the vertical relief is in excess of 10 feet. Most slopes are less than 60 percent. Based on this,this site does meet the technical criteria of a landslide hazard. 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 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 f3 , ("Hb') d. Kitsap silt loam ("Kc') 'Tahu.va 5 Scale 1-24,000 �� � The central site soils are mapped as Alderwood gravelly a „� ,m ,.a Md sandy loam (Ad). This site does meet the technical s criteria of an erosion hazard area. SLOPE STABILITY Based on our field observations, explorations and our S experience with the soil types encountered on the property, we conclude that although portions of the slopes on the lot exceed 100 percent, the site is generally stable relative to deep-seated failure in its present configuration. 10011 Blomberg Street SW, Olympia, WA 98512 6 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY The Coastal Zone Atlas, volume 9, Mason County (MA-8) maps the northern site material as Pleistocene gravel deposits (Qpg). The advance outwash is described at having"good to excellent foundation support," "good seismic stability,"and"generally stable in slopes up to angle of repose." The slope stability is described as"stable." The Coastal Zone Atlas, Volume 9, Mason County(MA-8) maps the site as Vashon Advance Outwash(Qva)along the upper(southern) portion of the slope. The chance of flooding is less than one percent. Permeability is described as high, while runoff potential is low. Infiltration is moderate on natural slopes and high on cut slopes. Springs at the bases of slopes are common (springs or seeps were observed during the site reconnaissance). The slope stability is described as"intermediate." 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 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 building setback of 35 feet from the crest of the slopes to the bottom of the footings 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 2003 International Building Code (IBC). All foundation elements shall be founded in native material or engineered fill material. 10011 Blomberg Street SW, Olympia, WA 98512 7 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Peak Shear Stress vs. Normal Stress 3000 - 39° 25M 2MO 15M c` y 1000 O. 5C0 +1l1 ton 1 ton 0 0 5W 1000 1500 2000 2500 3000 Normal Stress(pan Slope stability was modeled using the GEO-SLOPE/W program (version 5.20) in both static and extreme dynamic conditions (Ca= 0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price methods. The gravelly sandy loam was determined to have a unit weight of 129 pcf, cohesion of 200 psf, and a shear angle(+) of 39°. Under static conditions, the slopes were stable to shallow failure. Under dynamic loading, the 3328 computations demonstrated that the slopes are susceptible to surficial raveling but not deep-seated failure. The following figure illustrates the moment factor of safety for slope"A" under the existing conditions. The figure is the solution of greatest concern and exhibits the need for a building setback of 35-feet from the crest of the slope. All foundation elements must be founded in native material or engineered fill material. Jerry Vermillion Site—Slope A Analysis Method: Morgenstern-Price Direction of Shp Movement: Left to Right Slip Surface Option:Grid and Radius • y . . . Seismic Coefficient: Horizontal and Vertical 250 230 210 /�e . . �-. 190 C 170 150 • 0.87 N 130 Gravelly Sandy Loam W 110 Unit Weight:129 •• '. Cohesion:200 gp Phi:39 70 50 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 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. Surficial raveling and sloughing was only observed along the south-facing slope bounding State Highway 106. Slumping was observed along the toe of the south-facing slope. 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 '/2-inch diameter steel probe rod. The shallow soil conditions were assumed to be representative for the site conditions beyond the depths explored. Based on our review of the subsurface conditions, we conclude that the site soils are not 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. The Liquefaction Susceptibility Map of Mason County, Washington by Palmer, Magsino, Poelstra, Bilderback, Folger, and Niggemann(September 2004)maps the site area as having a very low to low liquefaction potential. The Site Class Map of Mason County, Washington by Palmer, Magsino, Bilderback, Poelstra, Folger, and Niggemann (September 2004) maps the site area as site class C to D. Site class C is a very stiff soil or soft rock and site class D is a stiff soil. --n ++ a 10011 Blomberg Street SW, Olympia, WA 98512 9 Phone#: (360) 754-4612 Fax#: (360)754-4848 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 structure. Removal of natural vegetation on the slope 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 3. Any re-contouring of the site will create a need for erosion control measures as listed above, see Figure 2. a� t� a. 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 16 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 20 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. 10011 Blomberg Street SW, Olympia, WA 98512 10 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. 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 7 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. 46 4 ".: �I v 10011 Blomberg Street SW, Olympia, WA 98512 11 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SUITABILITY OF ONSITE SOILS AS FILL Onsite soils may be considered for use as structural fill. In general, the native soils (sand, loam, and gravel) encountered onsite must have less than 10 percent fines (material passing the US No. 200 Sieve) to be suitable for use as structural fill. CUT AND FILL SLOPES All job site safety issues and precautions are the responsibility of the contractor providing services and/or work. The following cut/fill slope guidelines are provided for planning purposes. Temporary cut slopes will likely be 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 shall 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. 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%2 inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation subgrade during construction could result in larger settlements than predicted. 10011 Blomberg Street SW, Olympia, WA 98512 12 Phone#:(360)754-4612 Fax#: (360)754-4848 I GEOTECHNICAL TESTING LABORATORY FLOOR SLAB SUPPORT Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared as described in the"Structural Fill" section of this report. We recommend that floor slabs be directly underlain by a minimum 6- inch thickness of coarse sand and/or gravel containing less than 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. / t- � , = F 7 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 taken as 0.40 (coefficient). 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 I (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 10011 Blomberg Street SW, Olympia, WA 98512 13 Phone#:(360)754-4612 Fax#: (360)754-4848 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. 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 be directed, if possible, to the northern 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. PROPOSED LOGGING Logging is proposed along State Highway 106 to remove danger and hazard trees. The underbrush vegetation must remain with minimal disturbance. We expect impacts to slope stability to be negligible. Straw bales or silt fences shall be used at the inlets of culverts to prevent sediment from entering the Hood Canal. Sediment migration will be arrested within the roadside ditch and must not be allowed to enter the Hood Canal. 10011 Blomberg Street SW, Olympia, WA 98512 14 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Additionally, all hazard trees (leaning, rotten, or dead) may be removed to increase slope stability throughout the site. All logging must be performed by a qualified or licensed logging professional. SEPTIC IMPACT The proposed location for the septic drainfield was inspected in regard to slope stability. If the location satisfies the building setback requirement from the top of slopes, the slope stability will not be compromised. LIMITATIONS We have prepared this report for Jerry Vermillion 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 with our firm during construction should continue, to confirm that the conditions encountered IL 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 _ , I and foundation installation activities comply with our specifications. If our analysis and recommendations are followed, we do not anticipate any offite 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. �0 Ct VV8S/y!� f0 Respectfully submitted, GEOTECHNICAL TESTING LABORATORY fi a�0 100-� 027 Harold Parks, L.G., L.E.G. a�p Senior Engineering Geologist 14, SW, Olympia, WA 98512 15 Fax#: (360)754-4848 sr - •�M�����r�' ■ .�/`yam . f ��4i• r rt r FILTER FABRIC MATERIAL W'WICEROLLS 'J SE STAPL WIRES OR WIRE RIG TO ATTACH G e o to c h n i c al FABRIC TO E 2'%2"X14 GAUD VARE FABRIC OR EWYABNi 2- Testing S-P Laboratory 2. 8 MAX 2-)W WOOD POSTS,STADATDOR BURY BOTTOM OF FILTER A BETTER OR EQUAL ALTERNATE MATERIAL IN 8"XITTRBNCH STEEL FENCE POSTS N FILTER FABRIC 8 2'X2'X14 GAUGE WIRE FABRIC OR EQUIVALENT 2- GROUND SURFACE S-P ♦' PROVIDE S4•.11?WASED GRAVEL BACKFILL IN 17R9NOR 12' G AND ON BOTH SIDES OF FILTER FENCE FABRIC ON THE SRFACE 8•MN _ If 7YA'WOOD POSfS ALT.STEEL ROW POSTS Geotechnical Services FILTER FABRIC FENCE NGTBE: I FILTERFABRICSHALLBEPURCHASEDINACONRNJOUSROLLCUTTO �� " Services THE LENGTH OF THE BARRIER TO AVOID USE OF JOINT$wHENJOINT9 Testing Services ARE NECESSARY.FILTER CLOTH SHALL BE SR1C®TOGETFEt ONLY AT A SUPPORTPo6<WITHA MINIMUM BNNgIOVBRUP AlDSBCLPflY FASTENED AT BOTH ENDS TOTHE POST. 2 POSTS SHALL BE SPACED A MAMMUM OF BFEET MART MDCRIVEN SECURELY INTO THE GROUND MNMUA OF 3DINOEST. 3 A TRENCH SHALL BE EXCAVATED APPROXIMATELY SINCHESWIDE AND 12 10011 Blofterg St.SW INCHES DEEP ALONG THE LINE OF POSTS AND UPSLOPE FROM THE BARRIER Olympia,WA 98512 WHEN STANDARD STRENGTH FILTER FABRIC IS USE),AWARE MESH 22OJ�• SUPPORT FENCE SHALL BE FASTENED SECURELY TO THE UPSLOPE SIDE Phone:(360)754-4612 LONG.TIE MR OR HOG RINGS�THE WRE SHALL AEXTEtDIT LEAST NTO THE INCH Fax:(360)754-4848 TRENCH A MINIMUM OF 4INC 4ES AND SHALL NOT EXTEND MORET AN 38 INCHES ABOVE THE ORIGINAL GROUND SRFACE. 5 THE STANDARD STRENGTH FILTER FABRIC SRALBE STAPLED OR WIRED Date: 06/1612005 TO THE FENCE AND 201N0¢S OF FABRIC SEAL E EXTENDED INTOTHETRENCH THEFAMICSHALGTDOBDMORETHM38 Drawn by: JM is NOTESTAPLED INCHES ABOVTHE THE INNAL GHROTU 9JRFACE FILTER FABRIC SHALL 250 Checked by: KB 6 WHEN EXTRA-STRENGTH FILTER FABRIC AND CLOSER POST SPACING IS Revised by: LL USED,THE WIRE MESH SUPPORT FENCE MAP BE EUMINATED,IN SUCH A CASE,THE FILTER FABRIC STAPIIDORO ARMCIRECRY TO THE Dwg*:06-16-05-053 2 Q g POSTS WITH ALL OTHER PROVISIONSOR ABOVE NOTES APPLYING I& ACRES TO NL/Y lR o T FILTER FABRIC FENCES SHALL NOT BE RBAOVEDB�THE UPYOFE a AREA HAS BEEN PERMANENTLY STAffi IZED 300 +� 8 FILTER FABRIC FENCES SHALL BE INSPECTED IMMEDIATELY AFTER ELAN RAINFALL AND AT LEAST DAILY WRING PROLO GEDRANFALL.ANY REQUIRED REPAIRS SHALL E MADE IMMEDIATELY. O I O.OD' 1 d- 22'E �-21.E5 GENERAL E1081014 CONffROI NOI�'. 2 ��IY 1 EROSION CONTROL MEASURES SHALE IN PLACE PRIOR TO THE 350 EGINNIGOFCONSTRUCTION.THE PROJECT ENGIEER ADTHE COUNTY SHALL INSPECT AND APPROVE THE INSTALLATION OF EROSION CONTROL MEASURES PRI OR TO BEGINNING CONSTRUCTION. 2.EROSONCONTROLMEASURESAREGTUMTEDTOTHEITEMS PROJECT NAME: ONTHISPLAN.TECONTRACTORISRE5PONSIBIEFORiRE JERRY VERMILLION INSTALLATION AND MAINTAINANCE OF ALL EROSION CONTROL MEASURES NO SILTATION OF EXISTING OR PROPOSEDDRANAGEFAIUTIES 8371 EAST I"'IWY 106 SHALL E E ALLOWED.CARE SHALL TAHEN TO PREVENT MIGRATION OF SILTS TO OFF SITE PROPERTIES. UNION, WASHINGTON 40 3 THE CONTRACTOR SHALL MAKE DAILY SURVEILLANCE OF ALL EROSION CONTROL MEASURES AND MAKE ANY NECESSARY REPAIRS OR ACCITIONS PARCELS 322344400000, TO THE EROSION CONTROL MEASURES.THE CONTRACTOR SHALL PROVIDE ADDITIONAL EROSION CONTROL MEASRESASCETE2MINEDNECESSARY 322344400010 BY THE COUNtt INSPECTOR AND/ORTEPROJECTENGINER FAILURE , TO COMPLY WITH ALL LOCAL AND STATE EROSION CONTROL &322353200130 SCALE 1 INCH - 200 FEET REQUIREMENTS MAY RESULT IN pMLPBNALTIESEING LEVIED AGAINST THE CONTRACTOR MOM PROJECT OWNER. 0 50 NIX) 200 4 WRING THE WET SEASON(NOVEMBER TO MARCH)ALL OSRIREED SOILS SHALL E STABILIZED WITHIN 48 HOURS AFTER STOP OF WORK.EROSION CONTROL MEASURES SHALL INCLUDE,BUT NOT E UMTEXTO. Win: COVERING THE EFFECTED AREA INCLUDING SPOIL NLES'MTH ,IM��y1 Iry��/TA.AL�� G STRAW MATTING,JUTE MATTINIS,STRAW MLLCH. 4W ORAWOODCHIPSSTIC N SEEDINGOFT CISRR®AREASSALL TAKE ^Rim PACE AS WEATHER PERMITS 5 ALL SEEDED OR SODDED AREAS SHALL E CHECKED REGULARLY TO MAKE SURE VEGETATIVE COVERAGE IS COMLETE.AREAS S1AL E REPAIRED,RESEEDED,AND FEIMUZED AS REOURED. 8 TRACKING OF SOIL OFFSITE WILL NOT EALLOWED.IF ANY SOIL IS TRACKED ONTO A COUNTY STREET.IT SVLL E REMOVE)BY THE M' END .��AV OF THAT WORKING DAY AFURTHE2TRACXIGOFMUDWIILTHEN .WO E PREVENTED BY SWEEPING OR WASHING OF THE VEHICLES TIRES BEFORE DRIVING ON ACOUNTY STREET 1 G MORE THAN S00 LF OF TRENCH ON A DOWNSLOPE OF MORE THAN 5 PERCENT SHALL SHALL BE OPENED ATONE TINE. 1257.59• 8.EXCAVATED MATERIAL SHALL BE PACED ON THE UPHILL SIDE OF TRENCHES 9 TRENCH DEWATERtG DECODES SHALL BE DISOARGED IN A MANNER THAT WILL NOT ADVERSELY AFFECT FLOWING STREAMS.DRAINAGE SYSTBASOR OFFSITE PROPERTIES SCALE:1 WO-2W feet 10.ALL STORM SEWER INLETS RECEIVING RUNOFFFROMTHE PROJECT DJRG CONSTRUCTION SHALL BE PROTECTED SD THAT SEDIMENT-LADEN WATER WILL BE FILTERED RED BEFORE ENTERING THE CONVEYANCE SYSTEM 11.ALL OFF-SITE CATCH BASINS IMMEDIATELY ADIACE TTO THE SITE SEAL TU SED MTEDFROM SILTATION SEEDED EE FIGURE 2 12.ALL THE AREASSHALL S SEE DE DORSOWEDLPOf1COMPLETION Of-WORK COVERA EOFTRSEAL BEREEON9BETOENSUREHAT COMPLETECOVERAGETATE pSNEUSHEO SISPROVOED 81}UT GROWTH OF THE VEGETATION IS DIMENT ORRLT SITE PLAN 13.CATCH BASING SHALL TRM SEpMEM Oft flLTER FABfRIC MUST E PACED UNDER GRATE UNTIL VEGETATION ISESTAELI 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH C R MAN/ V MINIMUM,6 INCH SUGGESTED NF w TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL FON OR ENERGY DISPERSION DEVICE 1FOOT MIIN 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 Bbmbxg St SW FIGURE 3 QA/QC Services Phwe:(,wn 88512 12 Testing Services Ph c360)75360)4 848 DRAINAGE DETAILS Not to scale