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HomeMy WebLinkAboutGeoTech Assessment for BLD2005-01356 - BLD Engineering / Geo-tech Reports - 10/18/2005 ' N_STgTFO� MASON COUNTY MCp y PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER 0 s N i Shelton, Washington 98584 T�^�, Z7oJ � Y boy t„J gy h" pT / ,IV DATE: October 18, 2005 � Tf�r INTER-DEPARTMENTAL COMMUNICATIONS TO: Planning PARCEL # 123093490030 FROM: Robert A. Thuring, PW BUILDING PERMIT NUMBER: BLD2005-01356 SUBJECT: Geo-Tech Assessment Review NAME: Shane And Cassie Nagle Hi Planning; The geotechnical assessment prepared for the proposed single-family residence for Shane and Cassie Nagle at 415 Bear Creek Dewatto Road has been received and reviewed by Public Works. Although no surficial raveling and sloughing were observed onsite, following the recommendations of Geotechnical Services to manage and reduce the potential for these natural processes is advisable. No drainage of concentrated surface water or significant sheet flow on the sloped areas. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill. Trees may be removed on sloped areas as long as the stumps remain. The recommendation that earthwork should be undertaken during favorable weather conditions should be part of the requirements. Retaining walls may be utilized on the sloping portion of the site to retain fill material. The applicant and his contractor should be alerted to their responsibility to protect neighboring properties during and after construction, from adverse stormwater runoff impacts. The escape of silt or mud from the subject property constitutes a violation of both State and County stormwater quality protection regulations, and could subject violators to fines and penalties. The report appears to satisfactorily fulfill County requirement(s). Requirements contained in the Geotechnical Report by Geotechnical Services should be adhered to and incorporated into the site's development and made part of the conditions for permit issuance. I recommend accepting the report as satisfying the County's requirement(s). Please feel free to contact Bob Thuring ext. 452 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, ✓ ` Robert A. Thuring, PE Engineering and Construction Manager 1 1 , 1 ro rfj� Geotechnical Report ' 415 NE Bear Creek Dewatto Road Belfair, WA Prepared for: Shane & Cassie Nagle Belfair, WA by Geotechnical Testing Laboratory Olympia, Washington October 7, 2005 GEOTECHNICAL TESTING LABORATORY SHANE AND LASSIE NAGLE P.O.Box 778 BELFAIR,WA 98528 RE: GEOTECHNICAL REPORT 415 NE BEAR CREEK DEWATTO ROAD BELFAIR,WA 98528 PARCEL 123093490030 N47029.637'W 122°48.947' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence, attached garage, and shop to be located along the south-facing hillside overlooking the Union River, approximately 3 miles north of Belfair, Washington. The location of the site is shown relative to the surrounding area on the Vicinity Map,Figure 1. ria 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 Bear Creek Dewatto Road. In general,grading will consist of the excavation of the foundation and footings. All grading has been performed in anticipation of concrete placement. The approximate layout of the site is shown on the Site Plan,Figure 2. The site slopes toward the southeast from the proposed building location. The steepest slope measured onsite was in excess of 70 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 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 moderate residential development in the Puget Sound glacial upland overlooking the Union River. The site has a southeastern exposure. We conducted a reconnaissance of the site area on October 4,2005. Site elevations range from approximately 80 to 284 feet. The building area of the site has vegetation common to the Northwest. The vegetation includes fir, cedar, alder, and maple trees as i '11 well as Scot's broom, sword fern, bracken t fern, huckleberry, salal, blackberry, and grasses. At the time of the site visit, we observed no r= evidence of active surface erosion along the undisturbed slopes. Erosion was observed in a small area of fill material. -Silt fences will virtually eliminate the erosional concern. No evidence of deep-seated slope instability was observed. Sloughing and sliding was not observed onsite. Surface water flow was not observed onsite at the time of our reconnaissance. Evidence of previous surface water flow was observed southeast of the proposed building location where fill material was placed. The general topography of the site area indicates that drainage flows toward the southeast from the proposed building location. 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 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 Vashon glacial till material. 10011 Blomberg Street SW,Olympia,WA 98512 2 Phone#: (360)754-4612 Fax#: (360)754-4848 �• 1 GEOTECHNICAL TESTING LABORATORY SITE SOILS The Soil Survey of Mason County, USDA Soil Conservation Service(1960)has mapped the site soils as an Everett gravelly sandy loam, 15 to 30 percent slopes(Ek), at the site. The report reads: This soil is on steeper slopes of glacial moraines, sides of gullies, and terrace fronts. It is closely associated with other Everett soils and the Alderwood gravelly sandy loams. This soil is more variable than Everett gravelly sandy loam S to 15 percent slopes. The depth to substratum ranges from 12 to 36 inches, and the amount of gravel is the surface soil and subsoil varies greatly from place to place. Where the soil is in close association with the Alderwood soils, the substratum, in place, is compact and weakly cemented. Included are a few areas having slopes slightly greater than 30 percent. This soil is suitable only for forestry because it is strongly sloping, droughty, and low infertility. It is in capability subclass VIs and in site class S for Douglas-fir. Aff NC ' bc �` [,,,,�V-. 't x3 7s. �j. '�ri �� y !•i p K.."��f".7<� , 161 a.�� w rap r a.✓ �� 'II ' �► :.fir} � � -��` � k `.l d�. � e "- � 151 } e �" 'l? rr � }'r� �` • *1�5 - f. t'G ^.-�`+- ,} ; • � j.r .Y �,= i r3�ti fey'!z -.1y 'l, i,%. = y'„s t I� �t- �„�r ,. i .'ems .til�J_ .�, !Zr re.�.i .�•,. .y *Y i e(r-- ��.�r" �. �•«:�. '.f 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, unstratifted, 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. �1� i i1. lr� y ,,� is� p`� • l f ,1 M'�.� �� �1 �, t L( �r lJ' k y�-�'�Si f� 1'° � SC �, • �1 �� f 1 a'c'► e..r �� ,+�'�f4 } r� � 10011 Blomberg Street SW,Olympia,WA 98512 3 Phone#: (360)754-4612 Fax#: (360) 754-4848 G EOTECHNICAL TESTING LABORATORY �� SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed `.. building site soil and reviewing available well logs. The well log for the site indicates that static groundwater was 145 feet below the ground surface on _ August 29, 2005. Groundwater is deep and beyond the scope of this report. Depth to competent soil is approximately 8 inches throughout the proposed building location. SUBSURFACE CONDITIONS In general, undisturbed dense Everett gravelly sandy loam was observed in the undisturbed portions of the site. Glacial till was observed below the Everett material. Groundwater was not observed or encountered. Groundwater seepage was not observed onsite. Based on the site topography and the nature of the near surface soil, seasonally perched groundwater conditions may not be expected during periods of extended wet weather. a ! •e.e .. A Q: SLOPE STABILITY i } Slopes in excess of 70 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. 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 onsite at the time of our investigation. Weathering, erosion, and the resultant sloughing and shallow landsliding are natural processes that can affect steep slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone, which has been disturbed and has a lower strength. Raveling, sloughing, and sliding were not observed on undisturbed slopes throughout the site. 10011 Blomberg Street SW,Olympia,WA 98512 4 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles, and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced by encouraging vegetation and discouraging runoff from the steep slopes. Erosion control recommendations for the sloping areas are provided in the"Erosion Control"section of this report. B ati 3. Yw y R Mpt F KE 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 slopes. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope.._._ stability. The hazards of the landslide area can be overcome in such a manner as to prevent harm to property and public health and safety, and the project will cause no significant environmental impact. In general, the Everett soils observed at the site may be suitable for use as structural fill material. Saturated soil conditions are not associated with these soils during or following extended periods of rainfall. However, to reduce grading time and construction costs, we recommend that earthwork be undertaken during favorable weather conditions. Conventional construction equipment may be utilized for work at the site. Conventional spread footings may be utilized at the site for support of the structure. We do recommend that roof and footing drains be installed for the structure with conventional spread footings. A vapor barrier is recommended for all slab-on-grades. Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed single-family residence are presented below. 10011 Blomberg Street SW,Olympia,WA 98512 5 Phone#: (360)754-4612 Fax#: (360)754-4848 , II G EOTECHNICAL TESTING LABORATORY 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 southern 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 1 S% 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 Everett gravelly sandy loam (Ek). This site does not meet the technical criteria of an erosion hazard area. SLOPE STABILITY The Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977)describes the site area as Class 1. Class 1 is expressed as: Areas believed to be stable. Slopes generally less than IS percent, but may be greater locally in areas too small to be shown at the map scale. Largely comprises rolling uplands underlain by very stable material such as young glacial till, mantled in places by a thin layer of sandy gravel or other permeable material; also includes flood plains, deltas, alluvial fans, and some beach deposits. Class I areas immediately adjacent to steep slopes of class 3 areas may be threatened by potential landsliding. Normal,proper engineering practices generally are adequate to insure stability in these areas. 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 approach 70 percent,they are generally stable relative to deep-seated failure in their present configuration. Excavation and backfilling will occur based on appropriate engineering and earthwork recommendations found in the following"Earthwork" section. Grading in the building portion of the site should be conducted in accordance with geotechnical recommendations provided herein. As previously discussed, weathering, erosion, and the resultant surficial sloughing and landsliding are natural processes that affect slope areas. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation,root penetration,wet/dry cycles and freeze/thaw cycles. Over excavation may be necessary to ensure the removal of deleterious material. 10011 Blomberg Street SW,Olympia,WA 98512 6 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY These processes can be managed and the risk reduced through proper construction of the residence. Erosion control recommendations in the slope and buffer areas are provided in the "Building Setback" and "Erosion Control"sections of this report. BUILDING SETBACK A building setback from landslide hazard areas is required unless evaluated and reduced by an engineering geologist or a licensed professional engineer. Based on our geotechnical evaluation of the site and our experience in the area, a building setback will be needed for this lot. The building setback may be measured from the bottom of the footing to the face of the steep slope in accordance with the International Building Code (1805.3.1). The following figure represents a shear angle for the gravelly sandy loam. Shear angle and cohesion are variables used to model the site. Peak Shear Stress vs. Normal Stress 3000 Gravelly Sandy Loam — 41° 2500 c S 2000 N Hl d 1500 e-ZN Y a� 1000 a 500 -1/4 ton f V2 ton 1 ton 0 0 500 1000 1500 2000 2500 3000 Normal Stress(psf) Setback Setback 10011 Blomberg Street SW, Olympia, WA 98512 7 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 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 site was modeled using a monolithic layer of glacial till. The glacial till was determined to have a unit weight of 135 pcf, cohesion of 200 psf, and a shear angle (�) of 41°. Under static conditions, the slopes remained stable to deep-seated and shallow failure. Under dynamic loading,the 3,328 computations demonstrated that the slope is not susceptible to surficial raveling and large deep-seated failure. The following figures illustrate the moment factors 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 30 feet from the crest of the southern slope and a building setback of 5 feet from the toe of the northern slope. All foundation elements shall be constructed on native material or engineered fill material. The current building location meets these building setback requirements. f f • Nagle Site Analysis Method: Morgenstern-Price Direction of Slip Movement Left to Right •'' Slip Surface Option: Grid and Radius Seismic Coefficient: Horizontal and Vertical f 290 270 250 230 210 c 190 o Glacial Till 170 Soil Model: Mohr-Coulomb Unit Weight: 135 (D 150 Cohesion: 200 LLJ 130 Phi:41 110 90 L 70 1' 50 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 525 550 575 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, landsliding, or sloughing was not observed onsite. 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). 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 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. Site class C is a very stiff soil. Based on the subsurface conditions observed at the site,we interpret the site conditions to correspond to a seismic Soil Profile Type D, for Stiff Soil, as defined by Table 1615.1.1 (IBC). This is based on the range of SPT (Standard Penetration Test) blow counts and/or probing with a %-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. 44. e 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 development. Removal of natural vegetation should be minimized and limited to the active construction areas. Yard landscaping around the home is permissible, but understory growth on the slopes should be encouraged as much as possible as a deterrent to erosion. Hazard trees located on steep slopes may be removed only if the stumps remain to deter erosion. Temporary and permanent erosion control measures should be implemented and maintained during construction and/or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include, but not be limited to, silt fences, berms, and swales with ground cover/protection in exposed areas. A typical silt fence detail is included on Figure 2. Any re-contouring of the site will create a need for erosion control measures as listed above. EARTHWORK SITE PREPARATION All areas to be excavated should be cleared of deleterious matter including any existing structures, debris, duff, and vegetation. Based on our observations, we estimate that stripping on the order of 2 to 6 inches will be necessary to remove the root zone and surficial soils containing organics. All grading performed exceeded our recommendations. 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. s 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 A the recommendations of our report. P r 10011 Blomberg Street SW,Olympia, WA 98512 10 Phone#: (360)7544612 Fax#: (360)7544848 GEOTECHNICAL TESTING LABORATORY STRUCTURAL FILL All fill material should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least 90 percent of MDD (maximum dry density as determined in accordance with ASTM D-1557)to within 2 feet of subgrade and 95 percent MDD in the upper 2 feet. The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather,we recommend the use of well-graded sand and gravel with less than 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. SUITABILITY OF ONSITE SOILS AS FILL Onsite soils may be considered for use as structural fill. In general, the native soils (sand, loam, and gravel) encountered on the site must have less than 10 percent fines (material passing the US No. 200 Sieve) to be suitable for use as structural fill. � a 4 s. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 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. 4r r X 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. 10011 Blomberg Street SW,Olympia, WA 98512 12 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY Lateral loads may be resisted by friction on the bases of footings and floor slabs and as passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.40 be used to calculate friction between the concrete and the underlying soil. Active pressure may be determined using an allowable equivalent fluid density of 150 pcf(pounds per cubic foot). We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions, with differential settlements between comparably loaded footings of '/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. FLOOR SLAB SUPPORT Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared as described in the "Structural Fill" section of this report. We recommend that floor slabs be directly underlain by a minimum 6-inch thickness of coarse sand and/or gravel containing less than 5 percent fines (by weight). The drainage material should be placed and compacted to an unyielding condition. A synthetic vapor barrier may be used for the control of moisture migration through the slab, particularly where adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier could result in wet spots on the slab, particularly in storage areas. 4 � M y, RETAINING WALLS Retaining walls may be utilized on the sloping portion of the site to retain fill material. The lateral pressures acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space is backfilled with clean granular, well-drained soil (washed rock), the design active pressure may be determined using an active pressure coefficient equal to 0.25 (Ka= 0.25). This design value assumes a level backslope and drained conditions as described below. 10011 Blomberg Street SW,Olympia,WA 98512 13 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY 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 1H:1V 75% 61 pcf If the walls are greater than 4 feet in height, exclusive of the footing, additional design considerations should be applied. Positive drainage, which controls the development of hydrostatic pressure, can be accomplished by placing a zone of coarse sand and gravel behind the walls. The granular drainage material should contain less than 5 percent fines. The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should also extend from the base of the wall to within 1 foot of the top of the wall. The drainage zone should be compacted to approximately 90 percent of the MDD. Over-compaction should be avoided as this can lead to excessive lateral pressures. A perforated PVC pipe with a minimum diameter of 4 inches should be placed in the drainage zone along the base of the wall to direct accumulated water to an appropriate discharge location. We recommend that a non-woven geotextile filter fabric be placed between the drainage material and the remaining wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the drainage zone,with time, can reduce the permeability of the granular material. The filter fabric should be placed in such a way that it fully separates the drainage material and the backfill, and should be extended over the top of the drainage zone. Lateral loads may be resisted by friction on the bases of footings and as passive pressure on the sides of footings and the buried portions of the wall. We recommend that an allowable coefficient of friction of 0.40 be used to calculate friction between the concrete and the underlying soil RETAINING WALL ALTERNATIVES Typically, block wall systems are more cost-effective for long-term walls than the other options. Specific design criteria for these options can be provided at your request by the block manufacturers. 10011 Blomberg Street SW,Olympia, WA 98512 14 Phone#: (360) 754-4612 Fax#: (360)754-4848 G EOTECHNICAL TESTING LABORATORY _' IV .mac SITE DRAINAGE All ground surfaces, pavements and sidewalks should be sloped away from the residence and associated structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch basins and tight-lined into the existing drainage facilities. We recommend that conventional roof drains be installed. Footing drains shall be installed for the single-family residence. The roof drain should not be connected to the footing drain. For footing drains,the drain invert should be below the bottom of the footing. We recommend that the collected stormwater runoff be directed to the potential infiltration location by tight-line. Alternatively, the stormwater may be transferred to the base of the southern slope 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. ! ,�, 'INK own SEPTIC IMPACT _ . - '`� `. The location of the existing septic drainfield was inspected in regards to slope stability. The proposed septic drainfield is located to the east of the proposed building location. Since the drainfield is located over 45 feet from the top of the southern slope,the slope stability will not be compromised. 10011 Blomberg Street SW,Olympia,WA 98512 15 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY LIMITATIONS We have prepared this report for the use of Shane and Cassie Nagle and members of their design team, to use in the design of a portion of this project. The data used in preparing this report, and this report, should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and our site reconnaissance, and should not be construed as a warranty of the subsurface conditions. This report is quantified as a micro-study and not a macro-study. Geotechnical Testing Laboratory and its personnel cannot be responsible for unforeseen and widespread geologic events(such as earthquakes, large-scale faulting,and mass wasting)beyond the scope of this project. Variations in subsurface conditions are possible and may occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient consultation should be made with our firm during construction to confirm that the conditions encountered are consistent with those indicated by the recommendations and for design changes should the conditions revealed during the work differ from those anticipated,and to evaluate whether earthwork and foundation installation activities comply with contract plans. If our analysis and recommendations are followed, we do not anticipate any on site or off site impact from the construction. It is our conclusion that potential landslide hazards from the landslide area can be overcome so as not to cause harm to property,public health and safety,or the environment. The scope of our services does not include services related to environmental remediation and construction safety precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures,except as specifically described in our report for consideration in design. If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications,as appropriate. i wash Respectfully submitted, tie jh GEOTECM141CAL TESTING LABORATORY r0 0 Ham / aA4,,3 Harold Parks,L.G.,L.E.G. Senior Engineering Geologist ngineering Geologist Leo 827 sed Geo�o HAROLD PARKS c { A" 10011 Blomberg Street SW,Olympia, WA 98512 16 Phone#: (360)754-4612 Fax#: (360)754-4848 it ,4 ko „ram.. u � \?��1/'! lam/! +a r, n����.�_i_,�w�rii ��ass�1 �►y�� � �1�/ _-�, �� .� � ��,��try �� ► f . ;.�. I • ' / ! FITTER FABRIC MATERIAL SP WIDE ROLLS Geotechnical USE BTA OR WIRE RING TO ATTACH FABRIC.;PLE9HARE • / 4A , RIC OREQUI ALE Testing RIC OR EQUIVALENT / 7d Laboratory 7B' G POSTS,STANDARD OR -11 BOTTOM OF BETTE" OOREQUAL ALTERNATE: FILTER MATERIAL rX12'TRENCH STEEL FENCE POSTS FILTER FABRIC S' 29(TXII TUWE WIRE FABRIC OR EQUIVALENT 7 ,/ /'/���• / // / I'/ //' / // // ' �' GROUND SURFACE Sd PROVIDE 3/P-11?WASHED GRAVELSACKFILL IN TRENCH 17 AND ON BOTH SIDES OF FILTER FENCE FABRIC ON THE SURFACE S.MI 77I"WOOD PO5T8 ALT:STEEL FENCE POSTS Geotechnical Services FILTER FABRIC FENC[NOIEt: 1.FLTER FABRIC SHALL BE PURCHASED N A CONTINUOUS ROLL CUT TO QA/QC Services q // TE LENGTHAR THE BARRIER TO AVOID USE LI JOINTS WHEN JOINTS �// ,' // / /' / ,/ //�'/� ' � / ,/ / / /' //''' ' / ARE NECESSARY,FILTER CLOTH SHALL BE SPLICED TOGETHER ONLY AT Testing Services W A SUPPORT POST WITH A MINIMUM 64NCH OVERLAP AND SECURELY / FASTENED AT BOTH ENDS TO THE POST. I / /'POTENTIAL INFILTRATION 2.POSTS SHALL BE SPACED A MAXIMUM OF S FEET APART AND DRIVEN SECURELY INTO THE GROUND(MINIMUM OF 30INCHES). LOCATION p 3.A TRENCH SHALL BE EXCAVATED APPROXIMATELY S INCHES WIDE AND 12 10011 Blomberg St.SW f� POS II // I / MM \\ 1 1 / / INCES DEEP ALONG THE LIE OF POSTS AND UPSLOPE FROM THE BARRIER. / O \\ \ j ►SOTENTIAL,/' /� Olympia,WA 98512 / I I 11 \\ \ \ 1 'INFILTRATION ' 1.WHEN STANDARD STRENGTH FASTENED SECURELYBRIC IS TO THE UEMESH $HOP 1 \ \ 1 I SU OF FENCE INALLAVY-DUENEDSESTAPLSATLEUPIINCH ICE Phone:(360)754 4612 I \ 1 ILOCATIVN /' OF THE POSTS USING HEAVY-DUTY WARE STAPLES AT LEASTIINCH '' LONG,TIE WIRES OR HOG RINGS.THE WIRE SMALL EXTEND INTO THE Fax:(360)754-4848 TRENCH A INCHES ABOVNIMUME THE ORIGINAL GROUND SURFACE 4 INCHES AND SHALL NOT EXTEND MORE THAN 38 \\ 5.THE STANDARD STRENGTH FILTER FABRIC SHALL BE STAPLED OR MIRED I ' Date: 10/05/2005 __ --�� / // / / 1 1 1 1 I / / ,' TO THE TRENCH. 2TI FABRIC SHALL LN TEXTS BE EXTENDED TJ����/ '// / 1 \ ' INTOTETRENCH.TEFABRICSIALLNOTEXTENDMORETHANx Designed b LL '// / / / \\ \ \�\ // / I 1 I I I I ' ' / INCHES ABOVE TEORIGINAL GROUND SURFACE.FILTER FABRIC SHALL 9 Y• F,��L,/ 1 1 1 I I I % ,, /' / ' NOT SE STAPLED TO THE EXISTING TREES. Drawn by: LL -- ----' /' 6.WHEN EXTRA-STRENGTH UP FILTER FABRIC AND CLOSER POST SPACING IS SEPTIC USED.THE WIRE MESH SPORT FENCE MAP BE ELIMINATED,IN SUCH Checked by: LL A CASE,THE FILTER FABRIC IS STAPLED OR WIRED DIRECTLY TOTHE Dwg#: 10-05-05-079 OTHER LOCITION /' %'/' / ! / I 1 I / may/ POSTS WITH ALL OTHER PROVISIONS OR ABOVE NOTES APPLYING. 7.FLTETHER FABRIC FENCES SMALL NOT 8E REMOVED BEFORE T UPBLOPE M AREA INS BEEN PERMANENTLY STABUMD. POSE j /'/ // ,// '/�/ ',//' / j / I I �/ W / S FILTER ALL AND AT LEAST DAILY FABRIC FENCES SHALL BOURINOPROLONGED RAINFALLE IN FOOTED IMMEDIATELY .ANY EACH 00 -- B U L N G / Co / REQUIRED REPAIRS SMALL BE MADE IMMEDIATELY. / --- O CAT I /' / '' ''/'/ % ,' % % % / % % % ! / / / GENERAL EROSION CONTROL NMO: 1. EROSION CONTROL MEASURES SMALL BE IN PLACE PRIOR TO TE BEGINNING OF CONSTRUCTION.THE PROJECT ENGINEER AND THE COUNTY SHALL INSPECT OL MEASURE PRIHE OR BEGINNING EROSION CONTROL MEASURES PRIOR TO BEGINNING CONSTRUCTION. -- -- -- _-- VARAV ' / /' ' / ' / / / / / / / / / / / 2.EROSION CONTROL MEASURES ARENOT LIMITEDPONSIB E OR THE / // //',' ; // / / IN THIS PLAN.THE CONTRACTOR ISRESPOROSIONORTE PROJECT NAME: INSTALLATION F D STING NANCE OF ALL DRAINAGECONTROL MEASURES. FACILITIES SSHHALLLTBEALALLOWED.ISCARESHALLBE OR OAKEN�TOIPRGEVENTMIGRATION NAGLE SITE NORTH W '/ % '/ ' ' '/' / ' '� '/ ' '/ / ' ' ' / / / ! OF SILTS TO OFF SITE PROPERTIES. NA NE BEAR CREEK- ' / / / /' / / / 3.THECONTRACTOR SHALL FAKE DAILY SURVEILLANCE OF ALL EROSION 415 SCALE 1 =SO / / / / CONTROL MEASURES RO MAKE ANY NECESSARY REPAIRS S A RIO _ TO THE EROSION CONTROL HILL MEASURES.THE CONTRACTOR SHALL DEWATTO ROAD C.I.=7 _ -�- ______ , ADDITIONAL EROSION CONTROL MEASURES AS DETERMINED NECESSARY DATUM ASSUMED 1 / / ' / ! BY THE COUNTY INSPECTORANDO THE PROJECT ENGINEER,FAILURE BELFAIR,WASHINGTON / / / / / / / / / / / TO COMPLY WITH ALL LOCAL AND STATE EROSION CONTROL 1 ' / / ' 'THIS IS NOT SURVEY REQUIREMENTS MAY RESULT IN CIVIL PENALTIES BEING LEVIED 1 / / / / / / / j ; ; ; / AGAINST THE CONTRACTOR AND/OR PROJECT OWNER PARCEL 123093490030 1 / / / / / / / / / / CIVIL ---C>-- I /' / / / / % / / / / / / 1.DURING THE WET SEASON NOVEMBER TO IAARCH)ALL DISTURBED SOILS 10 \ce) \ / / / / / MEASCONTROL URES SHALL INCLUDE,BUT NOT BE LIMITED 0 SHALL LSTABI[ZED WI DK EROSION RGA/ NMML.IC COVERINGTHE EFFECTEDAREA INCLUOINGSPOIL PILESWITH "c• �" PLASTIC SHEETING,STRAW MATTING.JUTE MATTING.STRAW MULCK \\ 1 \ WELL 40 / / / / / / / / / / / / / / / , / , / / OR WOOD CHIPS.SEEDING OF THE DISTURBED AREAS SHALL TAKE / / , PLACE AS WEATHER PERMITS. `.LOCATION,, / / / / / / , / , , / / SHALL __ _______ \\ S.ALL S�VEGETATTIVE CCOSVERA 13 COALETED R AREAS EAS LY SHALL,BE REPAIRED,RESEEDED.AND FERTILIZED AS REQUIRED. TRACKING OF SOIL OFFSITE WILL NOT BE ALLOWED.IF ANY SOIL IS 1_____ \ / / / / / / , TRACKED ONTO A COUNTY STREET,IT SHALL BE REMOVED BY T ENO \\ \\ / / / / / / / / / , / BEOF THAT WOR EVENTEDBVGSWEEPINO OR WASH OF THE VEKCLE3 TIRES DAY.ANY FURTHER TRACKINGG OF MUD WLL N BEFORE DRIVING ON A COUNTY STREET. //� /ryb /N ^�/ ^b�/ 7.NO MORE THAN 500 LF OF TRENCH ON A DOIMIBLOPE OF MORE THAN -- ----- \ ��_______'' // / / / AJ A ^ / d / PERCENT 9HALLB OPEEDATOE TIME. Ad S.EXCAVATED MATERIAL SHALL B PLACED ON THE UPHILL SIDE OF TRENCHES. I.TRENCH DEVMTEPoNG DEVICES SHALL BE DISCHARGED N A MANNER THAT WILL ____-- ADVERSELY AFFECT FLOWING STREAMS.-SYSTEMS OR OFFSITE PROPERTIES. / / f SCALE:1 k1Ch-50 feet _- -------- _ // 10.ALL STORM SE SEMR INLETS RECEIVING RUNOFF FROMHE PROJECT O CONSTRUCTION SHAL BEPROTECTED60 THAT SEOMENTNVATER MLLBE FILTERED BEFORE ENTERING THE CONVEYANCE SYSTEM. 11.ALL OFf3RE CATCH BASINS IMMEDIATELY ADJACENT TO THE SITE / ' i i POMrENTIAIIINFILTRATION' , SHALL BE PROTECTED FROM SILTATION. ' /' CATIO AT BASE OF PE FIGURE 2 / 17 ALL DISTURBED AREAS SHALL BE SEEDED OR BOOOEO UPON COMPLETION ' COMPLETE COVTHEERAGE OF WORK.THE OF THE DISTURBED BE D ARONBIBLPlO PROVIDED ENSUR THAT TES ETLMB0 AREAS q FRONDED S THAT GROWTHOFSS ALL TAP SEDIMENT REENTOR HITS SITE PLAN --� , / / / / / / 13.CATCH BASINS SHALL TRAP SEDIMENT OR FRIER FABRIC MUST B - , / / / / , / % / PLACED UNDER GRATE UNTIL VEGETATION IS ESTABLISHED. 112 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH ;fir coRRv M/HS vM'o MINIMUM,6 INCH SUGGESTED 9 C F - •:x:_i'.��fit!=^Y" _ ��� +-:::;..ti. _ •.•-a>>`.:-{1•T�:�^i' t 1 �d".:i' �_'.�.u.S. +V:7 :'F''o vc e�.�:^,:c', ��ti;s:`.�t: .._<:+j :xr -i`�� •tip'' �=�. +.fit'-'. _ l�'a.`'- _ _ .-t.=:`•.y: TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. �Cay FLARE END SECTION QUARRY SPALL :ft'dW* s �:.'� OR ENERGY DISPERSION DEVICE •.� •`= :xte `_: �•P 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 1001--g s.sw QAIQC Services �t'W 9612 FIGURE 3 Testing Services Fa:(NO)754-4M Not to scale DRAINAGE DETAILS