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Home My WebLink AboutBLD2002-00703 GeoTech Report - BLD Engineering / Geo-tech Reports - 5/17/2002 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Washington 98584 DATE: June 251", 2002 INTER-DEPARTMENTAL COMMUNICATIONS TO: Rick Mraz, DCD - Planner FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO# PLG-02 SUBJ: Geo-Tech Report Review NAME: Tingwall SFR core, Bald Point BLD2002-00703 Grace, The geotechnical report prepared for the proposed Del Tingwall Single Family Residence (SFR) replacement at 12881 North Shore Road, has been received and reviewed by Public Works. The report conforms with accepted standards of engineering/geotechnical principles and practices and appears in compliance with requirements of DCD for geotechnical reporting. The recommendations contained in the report should be made conditions for project approval. The applicant and their contractor should be aware of their responsibility to protect neighboring properties and State waters from construction silt and stormwater runoff impacts. Delivery of silty water to Hood Canal would be a violation of both State and County water quality regulations. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Si cerely, Man A. Tahja File: H:\WP\GEO\REVIEWS\Tingwall.doc ISGVGI v L-I-0 JUN 24 2002 1 .�. MtVAT.. Al M EE]LN Pt""ed . « ,�MzSON COUNT`!PUBLICWORKS ea' - -t • ugmt d by: Date: Type ofWodc r.sa� rL€p�� i CHARGE TO.- NAME AGENCYICOMPANY - BiLUNG ADDRESS PHONE G-) Pub.Works Person in Charge: aN Project Time Une: (from-to dates) TO Pro}oct Start date: 4pZ25 OZ EstSctuted FinFsh Dsbc Apprwdr�tbus: ESTIMATED TOTAL VS: COST ESTIMATE (D) GYM LEAli How EM Fffnat% TOTAL$ TOTAL n EOMMENT USED: MATERIAL USED: (F) Act"Cast BARS: DATE BW40y" YOE= Rzfe tours ;Sb( TOTAL f EQUIPMENT USED: Date Pitt TOTAL i'S MATERIAL USED: TOTAL ALL (G) SUED DATE INV 9 PAID DATE RECJ CKW i KEpT 1N THE I To BE E` F1`E PARC I'I Geological Report For Construction 12881 North Shore Road Mason County, Washington Prepared For: Del Tingwall By: Geotechnical Testing Lab Olympia, WA With: Spears Engineering & Technical Services May 17, 2002 GEOTECHNICAL TESTING LABORATORY DEL TINGWALL 4134 205'AVE. S E SAMMAMISH, WA 98075 Re: Geotechnical Report 12881 North Shore Road Mason County,WA INTRODUCTION This report summarizes the results of our geotechnical engineering services for the proposed remodel of a home located at 12881 North Shore Road in Mason County, WA. 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 and site meeting with you, our review of the site and explorations. We understand that the site is to be a remodel of the existing home and the building of a new garage on the north side of the North Shore Road. Stormwater runoff from the site, roof and hard surfaces, will be collected and directed to on-site discharge lines. The general layout of the site is shown on the Site Map, Figure 2. We further understand that very little grading is required at the site to reach design grades. In general, grading will consist of the excavation of the foundation for the remodel and little or no structural fill is anticipated. We understand that the site will be served by local utility companies. The building portion of the site has slopes that are greater than 45 percent. Mason County therefore 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 Lab is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: 1. Review the available geologic, hydrogeologic and geotechnical data for the site. 2. Conduct a geologic reconnaissance of the site area. 3. Explore the shallow subsurface conditions at the site. 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, sub-grade preparation, fill placement criteria (including hillside grading), suitability of on-site soils for use as structural fill, temporary and permanent cut and fill slopes, drainage and erosion control measures. 6. Provide recommendations and design criteria for the structural foundation and floor slab support, including allowable bearing capacity, sub-grade modulus, lateral resistance values and estimates of settlement. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206)754-4612 Fax#: (206) 754-4848 GEOTECHNICAL TESTING LABORATORY 7. Provide recommendations and design criteria for design of conventional retaining walls, including backfill and drainage requirements, lateral design loads, and lateral resistance values. 8. Provide our opinion regarding the feasibility of the location of the stormwater outfall. SITE CONDITIONS SURFACE CONDITIONS The proposed home is located in the Hood Canal glacial upland area. The site is situated in an area of moderate development. The site is bounded by homes on the east and west sides of the property. The proposed layout of the site is shown on the Site Plan, Figure 2. We conducted a reconnaissance of the site area. Elevations in the site area range from approximately 0 feet on the shoreline on the south to about 45 feet on the north portion of the site where the garage is anticipated. The majority of the site is located in the northern portion of the upper area, where the garage and drainfield are. A localized area in the northern portion of the site steeps to between 45 and 90 percent. This area is outside of the proposed development area. Site topography and slopes of 30 to 45 percent or greater are shown on the Site Plan, Figure 2. We observed no evidence of erosion. Surficial sloughing and soil movement was observed on the steeper portions of the site and adjacent areas. No evidence of deep-seated slope instability was observed in the site area at the time of our site visit. The site is vegetated with fir, cedar and Madrona trees. A moderate to dense understory consists of grass, brush, young alder trees, salal and Oregon grape with local areas of Scotch broom, and blackberry. No evidence of surface water flow was observed in the site area at the time of our reconnaissance. The general topography of the site area indicates that the site drains towards the south. SITE GEOLOGY The site is generally situated within the Hood Canal 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 of the Fraser glaciation that occurred between about 12,000 and 15,000 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, Vashon glacial till underlay the upper northern portions of the site. The till is absent from the lower southern portion of the site where advance sand with gravel is occurring near the ground surface. SITE SOILS The Mason County Soil Conservation Survey(1960)has mapped the site soils as Everett gravelly sand(Ek) in the building area of the site. The Everett soils typically form in sandy glacial till areas and are described as having a moderate permeability and a high erncinn hazard 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206)754-4612 Fax#:(206)754-4848 GEOTECHNICAL TESTING LABORATORY These soils are typically classified as a "Group C"relative to surficial runoff. We observed no active erosion or slope disturbance in the site area during our reconnaissance. SUBSURFACE EXPLORATIONS Subsurface conditions at the sites were evaluated by observing exposed slopes and outcrops. The exposed outcrops were as much as 20 feet in height. A log of the exposed outcrop is included in the appendix. SUBSURFACE CONDITIONS The subsurface conditions at the site were evaluated by observing exposed soils. In general, soil creep was evidenced by pistol butt tree growth. This usually implies that between 2 and 3 feet below the existing ground surface lies a very dense till. No groundwater seepage was observed during our site visit. Based on the nature of the near surface soils, intermittent outwash and weathered sand over undisturbed sand and gravel in the building area, seasonally perched groundwater conditions should not be expected even during periods of extended wet weather. SLOPE STABILITY Slopes as steep as 45 percent were observed on the site. Since slopes of 45 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 as per the Critical Areas Ordinance. In general, the undisturbed native soils to the north of North Shore Road consist of silty sand with variable amounts of gravel. These sandy soil materials are in a dense to very dense condition except where they have been disturbed by man or weathering activity. The near-surface recessional, weathered advance outwash are in a medium dense to dense condition except at the ground surface. The surficial soils are generally in a loose to medium dense condition. These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or significant erosion was observed at the site at the time of our site visit. Weathering, erosion, and the resulting 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. Very little local surficial erosion, raveling or sloughing was observed in the site area at the time of our site visits. 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 through proper design and construction of the storm water systems. Erosion control recommendations for the sloping areas are provided in the Building Setback and Erosion Control sections of this report. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206)754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY Proper planning, design and construction techniques will reduce the risk of surficial erosion or movement in these areas. CONCLUSIONS AND RECOMMENDATIONS GENERAL 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 remodel of the home and removal of the existing garage. The slopes located in the building portion of the site area and the adjacent property are stable relative to deep-seated instability and will not be affected by the proposed remodel and development. Proper erosion and sediment and drainage control measures will reduce or eliminate the potential for erosion in this area, and improve slope stability. In general, the sand and gravel soils observed at the site are suitable for use as structural fill material. Material with less than 10 percent fines should be considered equivalent to gravel base material. The sandy soils that occur on the site are moisture-sensitive and susceptible to disturbance when wet. Saturated soil conditions may be associated with these soils during or following extended periods of rainfall. 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 adjusted wall lines for support of the remodeled structure. We do recommend that roof and footing drams be installed on all repaired footings and extended roof lines. A vapor barrier is recommended for all slab-on- grades. Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed remodel are presented below. LANDSLIDE—EROSION HAZARD AREAS Classification The Mason County Critical Areas Ordinance defines a landslide hazard area as 1)one containing slopes equal to or greater than 30 percent with more than a 10-foot vertical relief, and 2)one containing soils described by the Soil Conservation Service(SCS) Soil Survey as having a"severe"limitation for building site development due to slope. The slopes located in the area of the site are in excess of 30 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 soils at the site are mapped as Everett gravelly sand(Ek) in the building portions of the site. The Everett soils are described as having a rapid erosion hazard, based on the present slope inclination. These soils do meet the technical criteria of an erosion hazard. Slope Stability Based on our field observations, explorations and our experience with the soil types encountered on the property, we conclude that although portions of the slopes exceed 30 percent, they are generally stable relative to deep-seated failure in their present configuration. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206)754-4612 Fax#:(206)754-4848 GEOTECHNICAL TESTING LABORATORY No changes in slope stability are expected as a result of the proposed remodel of the home. Grading in the building portions of the site should be conducted in accordance with geotechnical recommendations provided herein. Site drainage will be collected and directed to the site's stormwater system. As previously discussed, weathering, erosion, and the resulting 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. These processes can be managed and the risk reduced through proper construction of the residence, including the stormwater system. 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 area from landslide hazard areas is required unless evaluated and reduced by an engineering geologist or a licensed professional engineer. Clearing, grading and filling within the setback area may not be allowed because slope stability or the erosion hazard will be adversely impacted. Based on our geotechnical evaluation of the site and our experience in the area, a building setback is not needed for the remodel because of a functional reinforced concrete bulkhead on the shoreline. This bulkhead has functioned successfully in the past preventing undercutting by wave action. The building setback for the proposed garage, north of the North Shore Road should be 30 feet and may be measured from the bottom of the footing to the face of the slope, in accordance with the U.B.C. As previously discussed, weathering, erosion and the resulting surficial sloughing and shallow landsliding are natural processes that affect slope areas. As noted,very little evidence of surficial raveling or sloughing was observed in the sloping portions of the site. To manage and reduce the potential for these natural processes, we recommend the following: 1. No drainage of concentrated surface water or significant sheet flow onto or near the slope area. Drainage from the roof and driveway area should be collected and tightlined to a disposal pipe discharging to the shoreline. 2. No filling within the buffer or setback zone for the garage unless retained by retaining walls or constructed as an engineered fill. 3. No percolation of surface water within 20 feet of the proposed garage building setback. SEISMIC—LIQUEFACTION HAZARD According to the Seismic Zone Map of the United States contained in Figure 16-2 of the 1997 UBC (Uniform Building Code), the project site is located within Seismic Risk Zone 3. Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic Soil Profile Type Sc, for Very Dense Soil, as defined by Table 16-J(UBC). 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. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206) 754-4848 GEOTECHNICAL TESTING LABORATORY 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 conditions and the static water table is located below the surface. Shaking of the already stiff/dense soil is not apt to produce a denser configuration and subsequently excess pore water pressures are not likely to be produced. EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed remodel or garage construction. Removal of natural vegetation should be minimized and limited to the active construction areas. It is our opinion that seven fir trees located south of the North Shore Road and very near the present home are a danger to people and property, including passing motorists. Temporary and permanent erosion control measures should be installed and maintained during construction of the garage 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, berms and swales with ground cover/protection in exposed areas and silt fences. Graded areas should be shaped to avoid concentrations of runoff onto cut or fill slopes, natural slopes or other erosion-sensitive areas. Temporary ground cover/protection such as straw or clear plastic sheeting should be used until permanent erosion protection is established. No earth work is anticipated on the steep portions of the site. EARTHWORK Site Preparation All areas to be excavated should be cleared of deleterious matter including any existing structures, foundations, abandoned utility lines, debris and vegetation. Based on our explorations, we estimate that stripping on the order of 4 to 6 inches will be necessary to remove the root zone and surficial soils containing organics in the garage area. 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 sub-grade areas should be proof-rolled to a firm and unyielding surface prior to placement of any fill. We recommend that trees be removed in such a manner so that a majority of the roots are removed(garage area) unless located on a slope. Excavations for tree stump removal in the building area should be backfilled with structural fill compacted to the density requirements described in the "Structural Fill"section of this report. We recommend that a member of our staff evaluate the exposed sub-grade conditions after removal of vegetation and topsoil stripping is completed and prior to placement of structural fill (if needed). The exposed sub-grade soil should be proof-rolled and tested for compaction by nuclear densometer during dry weather or probed with a %-inch-diameter steel rod during wet weather conditions. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206) 754-4848 GEOTECHNICAL TESTING LABORATORY Any soft, loose or otherwise unsuitable areas delineated during proof-rolling or probing should be re-compacted. 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-1557/698)to within 2 feet of sub-grade 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. We recommend that our representative be present during site grading activities to observe the work and perform field density tests. 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 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 12 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 During dry weather construction, any non-organic on-site soil may be considered for use as structural fill, provided it meets the criteria described above in the structural fill section and can be compacted as recommended. If the material is over-optimum moisture content when excavated, it will be necessary to aerate or dry the soil prior to placement as structural fill. The workability of a material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines increase, soil becomes more sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. In general,the native soils(sand and gravel)encountered in the test pit explorations at the site with less than 10 percent fines(material passing the US No. 200 Sieve)are suitable for use as structural fill. This material is comparable to WSDOT "gravel base". Material with less than 5 percent fines will be suitable as structural fill during wet weather conditions. If fill material is imported to the site for wet weather construction, we recommend that it be a sand and gravel mixture such as high quality pit run with less than 5 percent fines. 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. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206) 754-4848 GEOTECHNICAL TESTING LABORATORY 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 gravels or till. 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. We recommend a maximum slope of 2 to 1 for permanent cut and fill slopes. Where 2 to 1 slopes are not feasible, shoring of the slopes should be considered. Fill placed on slopes that are steeper than 4 to 1 should be"keyed" into the undisturbed native soils by cutting a series of horizontal benches. The benches should be 1 '/z times the width of equipment used for grading and a maximum of 3 feet in height. Subsurface drainage may be required in seepage areas. Surface drainage should be directed away from all slope faces. Some minor raveling may occur with time. All slopes should be seeded as soon as practical to facilitate the development of a protective vegetative cover or otherwise protected. FOUNDATION SUPPORT All new exterior footing elements should be embedded as least 18 inches below grade for frost protection. Where these new foundation elements are located near slopes of 5 percent or more, the footings should be located a minimum of 2 times the footing width from the slope face(horizontally), and founded in medium dense or denser native soils or properly prepared structural fill. We recommend a minimum width of 2 feet for isolated footings and at least 16 inches for continuous wall footings. Footings founded as described above can be designed using an allowable soil bearing capacity of 2,000 psf(pounds per square foot)for combined dead and long-term live loads in areas of medium dense to dense soils. The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be increased by one-third for transient loads such as those induced by seismic events or wind loads. Lateral loads may be resisted by friction on the base 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 sub- grade during construction could result in larger settlements than predicted. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206) 754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY FLOOR SLAB SUPPORT Slabs-on-grade(garage)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 should be used for the control of moisture migration through the slab, in particular 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. A sub-grade modulus of 400 kcf(kips per cubic foot)may be used for floor slab design. We estimate that settlement of the floor slabs designed and constructed as recommended, will be % inch or less over a span of 50 feet. Retaining Wall Retaining walls will likely be utilized in the east portion of the site to retain fill material, and in the below grade parking garage in the west and central portions of the building. The lateral pressures acting on sub-grade 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. The design for active pressure assumes the walls can yield 0.001 times the wall height. Stiffer walls or walls restrained from movement by diaphragms or floors, should be designed to resist at-rest pressures of 50 pcf.. Retaining walls located on or near the toe of the 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 of 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 upwards from the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical)to a point where the line intersects the ground surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by the percentage given in the following table: Slope Inclination:Equivalent Fluid Pressure Slope Angle Percent Increase Equivalent Fluid Pressure Horizontal 0% 35 pcf 3H:1 V 25% 44 pcf 2H:1 V 50% 53 pcf 1 H:1 V 75% 61 pcf 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)7544612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY If the walls are greater than 10 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 so 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 base of footings and as passive pressure on the sides of footings and the buried portion of the wall. We recommend that an allowable coefficient of friction of 0.35 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). Factors of safety have been applied to these values. Retaining Wall Alternatives: Retaining walls will likely be utilized on this site. We understand that structural fill will likely be placed in the area where the garage is to be built. Options for retaining this material other than conventional concrete retaining walls include reinforced earth systems such as small/large block walls, rolled-faced walls or above grade pile systems with lagging. Typically, reinforced-earth 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. PAVEMENT SUB GRADE We recommend that pavement sub-grades be prepared in accordance with the previously described site preparation and structural fill recommendations. The upper 2 feet of roadway sub-grade should have a density of at least 95 percent of the MDD(ASTM D-1577) SITE DRAINAGE All ground surfaces, pavements and sidewalks should be sloped away from the residences and associated structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch basins, and conveyed to the site's retention system. We recommend that conventional roof and footing drains be installed for the home and garage. Drains should be provided behind all retaining walls. Roof drains should not be connected to the footing drain. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY We recommend that the collected stormwater runoff at the site be directed to the site's existing stormwater system. LIMITATIONS We have prepared this report for use by Del Tingwall and members of his design team, for 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. Variations in subsurface conditions are possible between the home and the garage. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient monitoring,testing and consultation should be provided by our firm during construction to confirm that the conditions encountered are consistent with those indicated by the study, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans and specifications. When the design is finalized, we recommend that the design and specifications are reviewed by our firm to see that our recommendations have been interpreted and implemented as intended. 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 type of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. Respectfully submitted , A,,U P.,� Harold Parks , Engineering geologist 777 r 770 rO 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206)754-4848 G EOTECHNICAL TESTING LABORATORY VICINITY MAP 0 Paiwch 1 p_ Bend Hood Canal � 9V 2 ocd � 1 O 10011 Blomberg Street SW, Olympia, WA 98512 Boring Log 1 Date: May 1002 File M Boring Log#: 1 Client: Tingwall Boring Type: Outcrop North Shore Rd. Depth Drilled: 20 feet Depth Field Change (Ft) Description in Soils %M N %'/." %44 %-#200 Comments 1.0 Topsoil 2.0 3.0 Silty Sand SS,some organics,dry 4.0 medium dense 5.0 to dose 6.0 7.0 8.0 Senii-ectnented SS,dark brown,dry, 9.0 sand with gravel homogenous, 10.0 very dense 110 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 end 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0 31.0 Page 1 TINGWALL j angle: 34.6° Unit Weight: 128.2 Critical Slope Angle,Saturated: 19.51 Horizontal Sectional Sectional Angle or Total Saturated Saturated Unsatoratec Unsaturated X Y Z Elevation Distance % Slope Factor Total Total Total Total Internal Factor Section Total Section Total Sectional Grid Station Elevation Change From Last Slope Angle of Safety Horizontal Change Slope Angle Friction of Safety P> P> > > Factor Line Point Feet Feet Sta.pt.(ft) 0 F Feet Feet % 0 j' F Critical Critical j j of Safety From To 1 0 82.00 0.00 0.00 0 0.0° n/a 0 0 0 0.01 17.3 n/a F Sta. Sta. 1 1 78.00 4.00 12.00 33.3% 18.41 0.93 12.00 4 33.3% 18.41 17.3 0.93 Safe Safe Safe Sale 0.93 0 1 1 2 74.00 4.00 12.00 33.3% 18.4- 0.93 24.00 8 33.3% 18.4° 17.3 0.93 Safe Safe Safe Safe 0.93 0 2 1 3 70.00 4.00 12.00 33.3% 18.4' 0.93 36.00 12 333% 18.4° 17.3 0.93 Safe Safe Safe Safe 0.93 0 3 l 4 66.00 4.00 12.00 33.3% 18.4' 0.93 48,00 16 13.3% 18.4° 17.3 0.93 Safe Safe Safe Safe 0.93 0 4 1 5 62.00 4.00 12.00 31.3% 18.41 0.93 60.00 20 33.3% 18.4° 17.3 0.93 Safe Safe Safe Safe 0.93 0 5 1 6 58.00 4.00 10.00 40.0% 21.8° 0.79 70.00 24 34.3% 18.9° 17.3 0.91 Yes Safe Safe Safe 0.78 0 6 1 7 54.00 4.00 10.00 40.o% 21.81 0.79 80.00 28 35.0% 19.3° 17.3 0.89 Yes Safe Safe Safe 0.78 0 7 1 8 30.00 4.00 8.00 30.0% 26.(1° 0.62 88.00 32 36.4% 20.0° 17.3 0.86 Yes Yes Safe Safe 0.62 0 8 1 9 48.00 2.00 6.00 11.3% 18.41 0.93 94.00 34 36.2% 19.9° 17.3 0.86 Safe Yes Safe Safe 0.73 8 9 1 10 45,00 3.00 6.00 50.0% 26.61 0.62 100.00 37 37.0% 20.30 17.3 0.84 Yes Yes Safe Safe 0.62 0 10 I 11 45.00 0.00 18.00 0,0% 0.0° n/a 118.00 37 31.4% 17.4° 17.3 0.99 Safe Safe Safe Safe 0.99 I 11 1 12 42,00 3.00 15.00 20.0% 11.31 1.66 133.00 40 30.1% 16.7° 17.3 1.04 Sato Safe Safe Safe 1.04 1 12 1 13 40,00 2.00 5.00 40.0% 21.81 0.78 138.00 42 30.4% 16.9° 17.3 1.02 Yea Safe Safe Safe 0.78 0 13 1 14 35.00 5.00 5.00 100.0% 45.0° 0.31 143.00 47 32.9% 18.2° 17.3 0.95 Yes Safe Yes Safe 0.31 0 14 1 15 30.00 5.00 5.00 100.0% 45.01 0.31 148.00 52 351% 19,4° 17.3 0.89 Yes Safe Yes Safe 0.31 0 15 1 16 28.00 2.00 4.00 $0.0% 26.60 0.62 152.00 54 35.5% 19.6° 17.3 0.88 Yes Yes Safe Safe 0,36 14 16 1 17 30.00 .2.00 4.00 -50.0% -26.6° -0.62 156.00 52 33.3% 18.4° 17.3 0.93 Safe Safe Safe Safe 0.56 14 17 1 18 30.00 0.00 35.00 0,0% .0.0, o/a 191.00 52 27.2% 15.2° 17.3 1.14 Safe Safe Safe Safe 1.14 1 18 1 19 25.00 5.00 12.00 41.7% 22.6° 0.7E 203.00 57 28.1% 15.7° 17.3 1.11 Yes Safe Safe Safe 0.75 0 19 1 20 20.00 5.00 12.00 41.7% 22.61 0.7E 215.00 62 29.8% 16.1° 17.3 1.08 Yes Safe Safe Safe 0.75 0 20 Slope Profile oo.00 e0.00 70.00 80.00- 50.00 to ation of garage Imo) 40.00 Nort Shore Rd . 30.00 20.00 10.00 o.00 - 0 100 200 300 Horhoreat Distanaa(Pear)