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HomeMy WebLinkAboutGEO2011-00003 COM2011-00006 - COM Engineering / Geo-Tech Reports - 2/24/2011 �p � Geotechnical Report for South Shore Enterprises Vehicle Storage Buildings 750 E Dalby Road Parcel No. 32232 43 90013 Union, Mason County, Washington February 24, 2011 Project#1120 Prepared For: South Shore Enterprises, LLC - YD P.O. Box 249 P�o�w SST9T� Union, Washington 98592 s: Prepared By: 43 Envirotech Engineering OA I STER�9 1 w PO Box 984 sS��NALti�G Belfair, Washington 98528 Phone: 360-275-9374 Fax: 360-275-4789 TABLE OF CONTENTS 1.0 INTRODUCTION.................................................»..............»........................................................1 1.1 PROJECTINFORMATION................................................................................................................ 1 1.2 PURPOSE OF INVESTIGATION AND SCOPE OF WORK..................................................................... 1 2.0 SURFACE CONDITIONS..............................................................................................................3 2.1 GENERAL OBSERVATIONS............................................................................................................3 2.2 TOPOGRAPHY.................................................................................................................I.............3 22.1 Upslope Geomorphology and Water Bodies..........................................................................3 2.3 SURFACE DRAINAGE.....................................................................................................................3 2.4 SLOPE AND EROSION OBSERVATIONS...........................................................................................4 3.0 SUBSURFACE INVESTIGATION.................................................................................................5 3.1 FIELD METHODS,SAMPLING AND FIELD TESTING........................................................................5 3.2 GENERAL GEOLOGIC CONDITIONS...............................................................................................5 3.3 SPECIFIC SUBSURFACE CONDITIONS.............................................................................................6 3.3.1 Groundwater......................................................................................................................... 6 3.4 SOILS TESTING.............................................................................................................................6 4.0 ENGINEERING ANALYSES AND CONCLUSIONS...................................................................7 4.1 SLOPE STABILITY.........................................................................................................................7 4.1.1 Slope Stability Analysis.........................................................................................................8 4.L2 Slope Stability Assessment.................................................................................................... 9 4.1.3 SepticDrainfield Impact to Critical Slopes............................................................................ 9 4.2 EROSION.......................................................................................................................................9 4.3 SEISMIC CONSIDERATIONS AND LIQUEFACTION......................................................................... 10 4.31 Liquefaction........................................................................................................................ 10 4.4 LATERAL EARTH PRESSURES...................................................................................................... 10 4.5 ON-SITE AND OFF-SITE IMPACTS............................................................................................... 10 5.0 ENGINEERING RECOMMENDATIONS.....................................»............................................ 11 5.1 BUILDING FOUNDATION RECOMMENDATIONS............................................................................ 11 5.1.1 Bearing Capacity................................................................................................................ 11 5.1.2 Settlement........................................................................................................................... 12 5.L3 Concrete Slabs-on-Grade.................................................................................................... 12 5.2 EARTHWORK CONSTRUCTION RECOMMENDATIONS.................................................................. 12 5.21 Excavation.......................................................................................................................... 12 5.22 Placement and Compaction of Native Soils and Engineered Ftll........................................ 13 5.2.3 Retaining Wall Backfill...................................................................................................... 14 5.24 Wet Weather Considerations............................................................................................... 14 5.3 BUILDING AND FOOTING SETBACKS........................................................................................... 14 5.4 SURFACE AND SUBSURFACE DRAINAGE...................................................................................... 14 5.5 VEGETATION BUFFER AND CONSIDERATIONS............................................................................. 15 6.0 CLOSURE..........».........................................................................................................................16 Appendix A-Site Plan Appendix B-Soil Information(Soil Profile; Soil Logs;Well Reports) Appendix C-Slope Stability Input&Output 1.0 INTRODUCTION Envirotech Engineering (Envirotech) has completed a geotechnical investigation for a commercial property located at 750 East Dalby Road, identified as parcel number 32232 43 90013, Union, Mason County, Washington. See the vicinity map on the following page for a general depiction of the site location. The geotechnical investigation was conducted at the request of the property owner,Rick Buechel, in support of the proposed development as detailed below. The proposed development, as provided herein,and the surrounding area is identified in this report as the Project. An initial geotechnical evaluation of the Project was conducted by Envirotech on March 18, 2010. The last site visit was completed on February 18, 2011. It was determined that slopes in excess of 40%with a vertical relief of at least 10 feet were present within 300 feet of the planned development. Based on this site characteristic, the proposed development will require a geotechnical report pursuant to Landslide Hazard Areas of Mason County Resource Ordinance (MCRO) 17.01.100. During the site visit by Envirotech, surface and subsurface conditions were assessed. After completion of the field work and applicable Project research,Envirotech prepared this geotechnical report which,at a minimum,conforms to the applicable MCRO. As presented herein,this report includes information pertaining to the Project in this Introduction Section; observations of the property and surrounding terrain in the Surface Conditions Section; field methods and soil descriptions in the Subsurface Investigation Section; supporting documentation with relation toslope stability, erosion, seismic considerations, and lateral earth pressures in the Engineering Analyses and Conclusions Section; and, recommendations for foundation, settlement, earthwork construction, retaining walls, erosion control, drainage, and vegetationin the Engineering Recommendations Section. 1.1 ProjectInformation Information pertaining to the Project was provided by the proponent of the property prior to and during the geotechnical investigation. The planned development consists of two 1-or 2-story high commercial buildings. Existing site features include one 2-story commercial building, septic system,paved and gravel parking/driveway,and an approximate 100ft by 60ft concrete slab.The concrete slab formerly housed a development,and will be the location for the proposed buildings. Approximate building footprint and other proposed features with relation to existing site conditions are illustrated on the Site Map provided in Appendix A of this report. 1.2 Purpose of Investigation and Scope of Work The purpose of this geotechnical investigation is to assess geological hazards, and evaluate the Project in order to provide geotechnical recommendations that should be implemented duringdevelopment. The investigation included characterizing the general Project surface and subsurface conditions, and evaluating the suitability of the soils to support the planned site activities. In order to fulfill the purpose of investigation, the geotechnical program completed for the proposed improvements of the Project include: Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 1 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 r • Review project information provided by the Project owner and/ or owner's representative. In addition, Envirotech prepared a Soils Report for this project, dated March 22, 2010; • Conduct a site visit to document the site conditions that may influence the construction and performance of the proposed improvements of the Project; • Define general subsurface conditions of the site by observing subsoils within test pits and/ or cut banks, review geological maps for the general area, research published references concerning slope stability, and review water well reports from existing wells near the Project; • Collect bulk samples at various depths and locations; • Perform soils testing to determine selected index and/or engineering properties of the site soils; • Complete an engineering analysis supported by the planned site alterations, and the surface and subsurface conditions that were identified by the field investigation, soil testing,and applicable project research; and, • Establish conclusions based on findings, and make recommendations for foundations, drainage, slope stability, erosion control, earthwork construction requirements, and other considerations. �Ho H� �F — Ro-- E 2NU sr e4 Project ' TM sr ------- E STH ST owe DR` -�TkMRSW _ _-:EILAWK AYE ¢ a � z E HYLAND DR e - T21NR3W- _T. - E MANZANRA DR TACDMA P !ACCESS RD_P _ --- T21NR41N _ E 0 5640ft > `� Vicinity Map from Mason County Website Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 2 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 1 2.0 SURFACE CONDITIONS Information pertaining to the existing surface conditions for the Project was gathered on March 18, 2010 by Michael Staten,geotechmcal engineer with Envirotech.During the site visit,the type of geotechnical investigation was assessed, site features were documented that may influence construction, and site features were examined that may be influenced by construction. This Surface Conditions Section provides information on general observations, vegetation, topography, drainage and observed slope/ erosion conditions for the Project and surrounding areas that may impact the Project. 2.1 General Observations The property is accessed from Dalby Road, an existing paved roadway. The Project is currently developed land as previously mentioned.The access road extends near the southproperty line,and a stream runs through the southern portion of the property. Beyond the property,rural residential and commercial development exists. Vegetation on and near the Project consists primarily of secondary growth firs, cedars, alders, and other trees and shrubbery common to this area of the Pacific Northwest. An aerial photo of the Project and immediate vicinity is provided on the following page. 2.2 Topography The topographic information provided in this section was extrapolated from a public lidar source, and incorporated observations and field measurements. Where necessary, slope verification included measuring slope lengths and inclinations with a cloth tape and inclinometer. See the Site Plan in Appendix A in this report for an illustration of general topography with respect to the planned development. The area of development has mild grades with steps in the terrain of up to 3.5 feet. Descending slopes are generally to the east,with maximum grades of approximately 20%, but generally less than 15%. 2.2.1 Upslope Geomorphology and Water Bodies Ascending grades are located to the northwest of the development with slopes ranging from less than 10%to just over 40%. The upland area of the property is situated on a hillside. Additional geomorphology that is pertinent to both upslope and downslope areas are provided in the Subsurface Investigation Section of this report. Although there is an upslo�e water body,there are no apparent water bodies or wetlands located upslope from the planned development that would significantly influence the Project. 2.3 Surface Drainage Stormwater runoff originating upslope from the anticipated development appears to be moderate to extreme. Drainage diversions and past drainage maintenance issues have been an on-going process. During the most recent site visit on February 18, 2011, it is apparent that drainage Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 3 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 . . mitigation has greatly improved,and is only causing minor concern to the existing building. 2.4 Slope and Erosion Observations The slope grades near the Project signal a potential landslide or erosion hazard area. Some indicators that may suggest past slope movements include: • Outwash of sediments near the bottom of the slope, • Fissures,tension cracks,hummocky ground or stepped land masses on the face or top of the slope,and parallel to the slope, • Fine, saturated subsurface soils, • Old landslide debris, • Significant bowing or leaning trees,or, • Slope sloughing or calving. These slope instability indicators or other significant mass wasting on the property or within the general vicinity of the Project were not observed or discovered during research. Indications of past landslides, current unstable slopes, deep-seated slope problems, or surficial slope failures were not observed during the site visit. f' r Ji o �y - m �. s - K - A Vi r._ _ E DALBY RD _. ._._. Aerial Photo from Mason County Website Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 4 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 3.0 SUBSURFACE INVESTIGATION Information on subsurface conditions pertaining to the Project was primarily gathered on March 18, 2010and February 18, 2011 by Michael Staten, geotechnical engineer with Envirotech. Specific information on field methods, sampling, field testing, general geologic conditions, specific subsurface conditions, and results from soil testing are presented in this section of the report. Appendix B of this report includes pertinent information on subsurface conditions for the Project, such as subsoil cross-section(s), test pit log(s), and water well report(s). Applicable test pit locations are depicted on the Site Plan provided in the appendix of this report. 3.1 Field Methods,Sampling and Field Testing Information on subsurface conditions for the Project was accomplished by examining soils within test pits extending to depths of up to 5.5 feet below the existing ground surface,including observing cut slopes. Information on subsurface conditions also included reviewing geological maps representing the general vicinity of the project, and water well reports originating from nearby properties. One bulk sample was collected at the Project site at approximately 18 inches below the existing ground surface near the anticipated building location. The soil sample collected was secured and transported for possible laboratory testing. Envirotech measured the relative density of the near-surface in-situ soils by gauging the resistance of hand tools.Within testing locations, field testing results generally indicated loose to medium dense soils in the upper 24 inches, and dense to very dense soils from 24 inches to the depth of terminous. 3.2 General Geologic Conditions In general, soils at the project are composed of materials from glacial advances. The geologic conditions as presented in the "Geologic Map of Washington," compiled by J. Eric Schuster, 2002 indicates Quaternary sediments, Qg. Quaternary sediments are generally unconsolidated deposits,and dominantly deposited from glacial drift,including alluvium deposits. This project is located within the Puget Lowland. Typically, "lower tertiary sedimentary rocks unconformably overlie the Crescent Formation."as revealed in the Geologic Map. Initial sedimentary rocks were formed from shales, sandstones and coal deposits from rivers. During the Quaternary period, the Puget Lowland was covered by numerous ice sheets,with the most recent being the Fraser glacier with a peak of approximately 14,000 years ago. Upon the glacial retreat, the landscape was formed by glacial erosion glacial drift deposits. According to the "Geologic Map of the Shelton 1:100,000 Quadrangle, Washington," by Robert L. Logan, 2003, the site soils are grouped as Continental Glacial Deposits from the Fraser glaciation, Vashon Stade. Specific units for this Project include advance outwash, late Wisconsinan (Pleistocene), Qga. From this geologic map, Qg. is "glaciological sand and gravel and latchstring 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 no glacial sediments; generally overlain by till." Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 5 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 t 3.3 Specific Subsurface Conditions The following subsurface conditions are estimated descriptions of the Project subgrade utilizing information from the depth of penetration at all testing, sampling, observed and investigated locations. Soils for this project were primarily described utilizing the Unified Soil Classification System(USCS)and the Soil Conservation Service(SCS)descriptions. The Project is composed of native soils with indications of possible fill near the downslope side of the building pads.For engineering purposes,these native soils consist of distinguishable layers, as presented below. Specifically, soils for this project were described utilizing the Unified Soil Classification System (USCS)and the U.S. Department of Agriculture(USDA)Textural Classification System. Soils within the upper 5.5 feet of natural ground were observed to be moist to wet,brown to red, loose to very dense silty sand with gravel (SM). Soils at deeper depths are believed to be a conglomerate of advanced outwash materials. Expanded and specific subsurface descriptions, other than what is provided in this section, are presented in the soil logs located in Appendix B of this report. According to the USDA Textural Classification System, the upper 36 inches of soil were classified as sandy loam. Per the SCS classification, the site soils where drainage features will exist were classified as Alderwood Gravelly Sandy Loam,Ab. 3.3.1 Groundwater Per our site visit, groundwater was encountered at a depth of 3 feet below the existing ground surface near anticipated building locations. Shallower groundwater, as little as 12 inches below the ground surface, was observed beyond. Upslope soil conditions did not exhibit perched groundwater. 3.4 Soils Testing The soil samples obtained at the Project site during the field investigation were preserved and transported for possible laboratory testing. Visual classification of soils was performed in the field at all observed soil profiles. Visual classifications were performed in accordance with the American Standards for Testing and Materials(ASTM D2488). The general results from the visual classification are presented above in the Subsurface Conditions Section. Specifically,soils within the upper 4 feet in one testing location consisted of approximately 20% gravel, 60% sand-sized soils, and 20% fines with medium plasticity indicating a high content of clay within the fine fraction. Minor variations observed during the visual classification of particle size content(i.e.gravel, sand,fines),or isolated pockets within the soil stratification were insignificant in relation to the overall engineering properties of the soil. Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 6 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 4.0 ENGINEERING ANALYSES AND CONCLUSIONS The following sections present engineering analyses and conclusions with relation to the existing conditions and proposed improvements of the Project. This section includes slope stability, erosion, seismic considerations, lateral earth pressures, and impacts to both on-site and off-site properties. 4.1 Slope Stability Landslides are natural geologic processes, and structures near slopes possess an inherent risk of adverse settlement, sliding or structural damage due to these processes. Geotechnical engineering cannot eliminate these risks for any site with sloping grades because gravity is constantly inducing strain on the sloping soil mass. Excessive wet weather and/ or earthquakes will exacerbate these strains. Geotechnical engineering considers excessive wet weather and `design' earthquakes in order to provide an acceptable factor of safety for developing on or near sloping terrain with relation to current engineering protocol. These factors of safeties are based on engineering standards such as defining engineering properties of the soil, topography, water conditions,seismic acceleration and surcharges. Surface sloughing or other types of surficial slope movements usually do not affect the deep- seated structural capability of the slope. However, excessive and/or repeated surficial slope movements, if not repaired, may represent a threat to the structural integrity of the.slope. If this situation does arise, the slope shall be inspected by a geotechnical engineer. Subsequently, maintenance may be required in order to prevent the possibility of fixrther surficial or deep seated slope movements that may be damaging to life and property. According to the Resource Map from the Washington State Department of Natural Resources (DNR), the Project is not within terrain labeled `highly unstable' relating to soils. DNR labeled portions of this project as medium and high slope instability with relation to slopes. This delineation is primarily dependent upon slopes and convergence. Secondly, lithology and precipitation are modeled within this delineation. In summary, this designation is based on mapping without field observations or knowledge of the specific site geology or soils. A Resource Map from the DNR Forest Practices Application Review System is provided below: Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 7 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 t � +/95908 +/95906 +1705000 &Peget S m ad i Pe Set 5—d I - Project 79498, + 04080 1704050 4 i,S yeb 4 IF 7 - _...794998 / .. -y 1704040 f + I y YiJJ r � Resource Map from Washington State Department of Natural Resources Website 4.1.1 Slope Stability Analysis Based on site geology, a non-circular slope stability analysis should be performed. However,the Simplified Bishop Method, as presented herein, was utilized. Although the method of circles could be an inappropriate tool, it is almost invariable much more conservative in these situations than other conforming slope stability models. For this Project and level of geotechnical investigation, our conclusions or recommendations would not be changed by this variation in analysis. Where applicable, ourslope stability analysis utilizes the subsurface angle of repose. The Simplified Bishop Method, utilizing `STABLE' software, was used to analyze the static stability of the site slopes. Seismic conditions were estimated utilizing worst case scenario values from the static analysis,a quasi-static analysis coefficient of at least 0.15, and applying the applicable values to STABLE software. Various radii's and center points of the circle were automatically selected, and produced factor of safeties in a graphical and tabular format. Worst case scenario values were used in the slope stability analysis in regards to topography, surcharges, water content, internal friction and cohesion of the site soils. STABLE software has been repeatedly checked with manual calculations, and consistently proved to be a very conservative program. The following Envirotech Engineering South Shore Enterprises Geotechnical Report PO Boa 984 page 8 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax:360-275-4789 February 24,2011 I• soil properties were used in the analysis, and are based on observed conditions, Down geology,and/or published parameters: Upper 6 feet soil depth Soil unit weight: 135pcf Angle of internal friction: 34 degrees Cohesion: 100 psf Soils below 6 feet in depth Soil unit weight: 138pcf Angle of internal friction: 38 degrees Cohesion: 200 psf Based on the slope stability analysis, a minimum factor of safety was determined to be 2.1 relative to static slope failures, and 1.4with relation to seismic conditions. See the slope stability information in Appendix C for a depiction of input parameters and example of outputs. 4.1.2 Slope Stability Assessment DNR did not indicate previous landslide activity or concerning slope problems near the Project.Based on this information, results of the aforesaid slope stability analysis, and present site conditions, it is our opinion that the proposed development should occur in accordance with this geotechnical report. 4.1.3 SepticDrainfield Impact to Critical Slopes The approximate location of the existing septic drainfield is presented on the Site Plan in Appendix A of this report. Based on the septic drainfield location with relation to the proposed addition,the drainfields are not expected to adversely influence the structure. 4.2 Erosion Based on the USCS description of the Project soils,the surface soils are considered moderately erodible. According to the Resource Map from the Washington State DNR, as provided above, the Project is not within terrain labeled `highly erodible.' This Project is not within an erosion hazard area as defined by the MCRO. Erosion hazard areas are those with USDA SCS designations of River Wash (Ra), Coastal Beaches (Cg), Alderwood Gravelly Sandy Loam on slopes 15% or greater (Ac and Ad), Cloquallum Silt Loam on slopes 15% or greater (Cd), Harstine Gravelly Sandy Loam on slopes 15% or greater (Hb), and Kitsap Silt Loam on slopes 15%or greater(Kc). A drainage and erosion control plan is required for this project, and has been prepared by Envirotech under a separate cover. Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 9 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 4.3 Seismic Considerations and Liquefaction Soils immediately below the expected foundation depth for this Project are generally Type D, corresponding to the International Building Code(IBC) soil profiles. Soils below a depth of 5 feet from the existing ground surface may be considered Type C. According to the IBC,the regional seismic zone is 3 for this Project. The estimated peak ground acceleration ranges from 0.50g to 0.60g. This estimation is based on the United States Geological Survey(USGS)National Seismic Hazard Project in which there is an estimated 2% probability of exceedance within the next 50 years. There are no known faults beneath this Project. The nearest Class `A' or Class `B' fault to this property is the Hood Canal Fault Zone, in which the distal end is approximately 4 miles to the northwest of this Project. This information is based on the USGS Quaternary Fault and Fold Database for the United States. 4.3.1 Liquefaction The potential for liquefaction is believed to be low for this Project. This is based, in part, on the subsurface conditions such as soil characteristics and the lack of a permanent shallow water table. Subgrade characteristics that particularly contribute to problems caused from liquefaction include submerged, confined, poorly-graded granular soils (i.e. gravel, sand, silt). Although gravel-and silt-sized soil particles could be problematic,fine and medium grained sands are typically subjected to these types of seismic hazards. No significant saturated sand stratifications are anticipated to be within the upper 50 feet of the subsoil for this Project. 4.4 Lateral Earth Pressures Lateral earth pressures exerted through the backfill of a retaining wall are dependent upon several factors including height of retained soil behind the wall, type of soil that is retained, degree of backfill compaction, slope of backfill, surcharges, hydrostatic pressures, earthquake pressures, and the direction and distance that the top of the wall moves. Significant retaining structures are not anticipated for this Project. Ifretaining walls are later planned for this Project, prescriptive requirements from the County should be adhered to. For retaining structures with a height exceeding County prescriptive requirements, additional design parameters must be accounted for in the retaining wall analysis, and recommendations should only be provided by a qualified engineer after the type of backfill is acquired, inclination of backfill slope is estimated, and the final wall height is determined. 4.5 On-Site and Off-Site Impacts From a geotechnical position, it is Envirotech's opinion that the subject property and adjacent properties to the proposed development should not be significantly impacted if all recommendations in this report are followed. This is based on the expected site development, existing topography,land cover,and the recommendations presented in this report. Em7rotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 10 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax:360-275-4789 February 24,2011 5.0 ENGINEERING RECOMMENDATIONS The following sections present engineering recommendations for the proposed improvements of the Project. These recommendations have been made available based on the planned improvements as outlined in the Introduction Section of this report; general observations including drainage and topography as recapitulated in the Surface Conditions Section; soil/ geologic conditions that were identified from the geotechnical investigation that is summarized in the Subsurface Investigation Section; and, Project research, analyses and conclusions as determined in the Engineering Analysis and Conclusions Section. Recommendations for the Project that is provided herein, includes pertinent information for building foundations, earthwork construction, building and/ or footing setbacks, drainage, vegetation considerations, and erosion control. 5.1 Building Foundation Recommendations Recommendations provided in this section account for the site development of a typical one- or two-story structure. The recommended allowable bearing capacities and settlements as presented below, consider the probable type of construction as well as the field investigation results by implementing practical engineering judgment within published engineering standards. Evaluations include classifying site soils based on observed field conditions and soil testing for this Project. After deriving conservative relative densities, unit weights and angles of internal friction of the in-situ soils, the Terzhagi ultimate bearing capacity equation was utilized for determining foundation width and depth. Foundation parameters provided herein account for typical structural pressures due to the planned type of development. A structural analysis is beyond the scope of a geotechnical report, and a structural engineer may be required to design specific foundations and other structural elements based on the soil investigation. Stepped foundations are acceptable, if warranted for this Project. Continuous,isolated, or stepped foundations shall be horizontally level between the bottom of the foundation and the top of the bearing strata. The frost penetration depth is not expected to extend beyond 12 inches below the ground surface for this Project under normal circumstances and anticipated design features. The soils on-site have low to moderate frost susceptible characteristics and should be used only to the extents provided in this report. 5.1.1 Bearing Capacity Existing in-situ soils for this Project indicates that the structure can be established on shallow, continuous or isolated footings. Foundations shall be established on relatively undisturbed native soil. Alternatively, foundations may be constructed on selective re- compacted native soil or compacted engineered fill as described in the Earthwork Construction Recommendations Section of this report. Since the proposed buildings are pre-engineered, specific foundation requirements are expected to be provided with the building plans. For a bearing capacity requirement of no more than 1500 psi a minimum continuous footing width of 15 inches shall be placed at a minimum of 18 inches below the existing,native ground surface. For a bearing capacity requirement of no more than 2000 psi=,a minimum continuous footing width of 18 inches Envirotech Engineering South Shore Enterprises Geotechuucal Report PO Box 984 page 11 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax:360-275-4789 February 24,2011 shall be placed at a minimum of 18 inches below the existing, native ground surface. Larger bearing pressures will require additional geotechnical studies. These bearing capacity requirements also apply to isolated footings, except the width should be increased to 24 inches for both round and square foundations. Foundation recommendations are made available based on adherence to the remaining recommendations that are provided in this report. Alterations to the aforementioned foundation recommendations may be completed upon a site inspection by a geotechnical engineer after the foundation excavation is completed. 5.1.2 Settlement Total and differential settlement that a structure will undergo depends primarily on the subsurface conditions, type of structure, amount and duration of pressure exerted by the structure, reduction of pore water pressure, and in some instances, the infiltration of free moisture. Based on the expected native soil conditions, anticipated development, and construction abides by the recommendations in this report, the assumed foundation system may undergo a maximum of 1.0 inch total settlement,and a maximum differential settlement of 0.75 inch. 5.1.3 Concrete Slabs-on-Grade It appears that existing concrete slabs-on-grade are sufficient for the type and use of this project. Interior slabs,if constructed new,s ould be supported on a minimum of 4 inches of`compacted coarse,granular material (Passing U.S. Sieve #10 or greater)that is placed over undisturbed native subgrade or engineered fill.Native soils found at the Project site may be suitable for use as material directly beneath concrete slabs if it meets the aforesaid requirements or screened to meet these requirements. The top 2 to 6 inches of native soil should be removed prior to the placement and compaction of the aforementioned 4-inch coarse,granular material. The recommendations for interior concrete slabs-on-grade as presented herein are only relevant for the geotechnical application of this Project. Although beyond the scope of geotechnical engineering, concrete slabs should also be designed for structural integrity and environmental reliability. This may include some type of vapor barrier or moisture control for mitigating excessive moisture in the building. 5.2 Earthwork Construction Recommendations Founding material for building foundations shall consist of undisturbed native soils. Compacted engineered fill, or selective re-compacted native soils may be used to the extents provided in this Earthwork Construction Recommendations Section. The following recommendations include excavations, subgrade preparation,type of fill,and placement of fill for building foundations. 5.2.1 Excavation Excavation is recommended to remove any excessive organic content or other deleterious material, if present, beneath foundations and to achieve appropriate foundation depth. Additional sub-excavation will be required for this Project if the soils below the required Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 12 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 foundation depth are loose,saturated, or otherwise incompetent due to inappropriate land disturbing, or excessive water trapped within foundation excavations prior to foundation construction. All soils below the bottom of the excavation shall be competent, and relatively undisturbed or properly compacted fill. If these soils are disturbed or deemed incompetent, re-compaction of these soils below the anticipated footing depth is necessary. Excavations shall be completely dewatered, compacted, and suitable before placement of additional native soil, engineered fill or structural concrete. It is suggested that foundation excavations are inspected by a geotechmcal engineer or qualified professional in order to assess the bearing material prior to the placement of structural footings. 5.2.2 Placement and Compaction of Native Soils and Engineered Fill For engineered fill or disturbed native soils that will be utilized as fill material directly beneath foundations, observation and/ or geotechnical testing is required prior to foundation construction. The following placement and compaction requirements are necessary. For disturbed native soils or engineered fill beneath foundations, limits of compacted or re-compacted fill shall extend laterally from the bottom edge of the foundation at a rate of one foot for each foot of compacted or re-compacted fill beneath the foundation. See the illustration below. FOOTING COMPACTED NATIVE SOILS OR ENGINEERED 1 FILL 1 UNDi ISTURBED SUBGRADE Both engineered fill and native soils used as compacted fill should be free of roots and other organics, rocks over 6 inches in size, or any other deleterious matter. Engineered fill should consist of the following gradation: U.S. Standard Sieve %Finer(by weight) 6" 100 Y 60— 100 No. 4 20—60 No. 200 0-8 Table 1 Partical Size Distribution of Engineered Fill Compaction shall be achieved in compacted lifts not to exceed 6 inches and 12 inches for native soils and engineered fill, respectively. Each lift should be uniformly compacted to at least 95% of the modified Proctor maximum dry density (ASTM D 1557) and within Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 13 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 3% of optimum moisture content. Each lift surface should be adequately maintained during construction in order to achieve acceptable compaction and inter-lift bonding. Temporary earth cuts and temporary fill slopes exceeding 4 feet in height should be limited to a slope of 2:1 (horizontal:vertical). Utility trenches or other confined excavations exceeding 4 feet should conform to OSHA safety regulations. 5.2.3 Retaining Wall Backfill As previously mentioned, significant retaining structures are not anticipated for this Project. However, if used, native soils may be used as retaining wall backfill for this Project. Backfill may also consist of engineered fill or borrow materials approved by a geotechnical engineer. Placement, compaction and extents of retaining wall backfill should also be specified by a geotechnical engineer or qualified professional. 5.2.4 Wet Weather Considerations Due to the types of subsurface soils, additional provisions may be required during prolonged wet weather. Every precaution should be made in order to prevent free moisture from saturating the soils within excavations. If the bottom of excavations used for footing placement changes from a moist and dense/hard characteristic as presented in this report to muck or soft, saturated conditions, then these soils become unsuitable for foundation bearing material. If this situation occurs, a geotechnical engineer should be notified, and these soils should be completely removed and replaced with compacted engineered fill or suitable native material as presented in this section. 5.3 Building and Footing Setbacks Due to potential debris flow,the building location should have a minimum setback from the local ascending slope toe equal to %2 the slope height. The toe of the ascending slope is delineated as a grade break in which the ascending slope is in excess of 40%. Envirotech recommends the building setback to be at least 25 feet from the toe of the nearby ascending slope. See the Site Plan in Appendix A for an illustration o the s acks. 5.4 Surface and Subsurface Drainage Positive drainage should be provided in the final design for all planned residential buildings. Drainage shall include sloping the ground surface, driveways and sidewalks away from the Project structures.All constructed surface and.subsnrface_drains should be adequate]m named during the life of the structure.If drainage problems occur during or after construction,additional engineered water mitigation will be required. This may include a combination of swales, berms, drain pipes, infiltration facilities, or outlet protection in order to divert water away from the structures to an appropriate protected discharge area. Roof drains are required for this Project. Subsurface water intercepted from potential footing penm re a drains, and stormwater collected from roof drains shall be separately tight-lined to an appropriate infiltration or dispersal location downslope of the buildings. A drainage plan has been prepared by Envirotech under a separate cover. Envirotech Engineering South Shore Enterprises Geotechnical Report PO Box 984 page 14 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 5.5 Vegetation Buffer and Considerations Vegetation is an excellent measure to minimize surficial slope movements and erosion on slope faces and exposed surfaces. By removing trees,the root strength is decreased over time, thereby lowering the `apparent' cohesion of the soil. Transpiration is decreased, which results in additional groundwater, increased pore water pressure and less cohesion/ friction of the soil particles. Stormwater runoff also increases, and, fewer plants will create less absorption of the force from raindrops,thereby creating the potential for erosion hazards. Vegetation shall not be removed from the face of the steep slope or withiY _stauQf 25_feet beyond the top of the slope. However, any tree deemed hazardous to life or property shall be removed. If tree removal is necessary, then stumps and roots shall remain in place, and the underbrush and soil shall remain undisturbed as much as possible. Any disturbed soil shall be graded and re-compacted in order to restore the terrain similar to preexisting conditions and drainage patterns. See the Site Plan in Appendix A of this report for a depiction of the vegetation buffer. Envirotech Engineering South Shore Enterprises Geotechnical Report PO Boa 984 page 15 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph. 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 6.0 CLOSURE Based on the project information provided by the owner, the proposed development, and site conditions as presented in this report, it is Envirotech's opinion that additional geotechnical studies are not required to further evaluate this Project. Due to the inherent natural variations of the soil stratification and the nature of the geotechnical subsurface exploration, there is always a possibility that soil conditions encountered during construction are different than those described in this report. Therefore, it is recommended that a qualified engineer performs a site inspection during the earthwork construction if subsurface conditions found on-site are not as presented in this report. This report presents geotechnical design guidelines, and is intended only for the owner, or owners' representative, and location of project described herein. This report should not be used to dictate construction procedures or relieve the contractor of his responsibility. Any and all content of this geotechnical report is only valid in conjunction with the compliance of all recommendations provided in this report. Semantics throughout this report such as `shall,' `should' and `recommended' imply that the correlating design and/or specifications must be adhered to in order to potentially protect life and/or property. Semantics such as `suggested' or `optional' refer that the associated design or specification may or may not be performed, but is provided for optimal performance.The recommendations provided in this report are valid for the proposed development at the issuance date of this report. Changes to the site other than the expected development, changes to ordinances or regulatory codes, or broadening of accepted geotechnical standards may affect the long-term conclusions and recommendations of this report. The services described in this report were prepared under the responsible charge of Michael Staten, a professional engineer with Envirotech. Michael Staten has appropriate education and experience in the field of geotechnical engineering in order to assess landslide hazards, earthquake hazards, and general soil mechanics. Please contact Michael Staten at 360-275-9374 if you have any questions, comments, or require additional information. Sincerely, Envirotec Engineering ...Z in� Michael Staten,P.E. Geotechnical Engineer Envirotech Engineering South Shore Enterprises Geotechnical Report PO Boa 984 page 16 750 E.Dalby Road Belfair,Washington 98528 Parcel 32232 43 90013 Ph 360-275-9374 MasonCounty,Washington Fax: 360-275-4789 February 24,2011 APPENDIX A SITE PLAN APPENDIX B SOIL INFORMATION VERTICAL AND HDRIZINTAL SCALE, I INCH = 40 FEET 0 10 20 40 LOOSE TO MEDIUM DENSE OVERBURDEN (SM) EXISTING GRADE 43,E PROPOSED BUILDING DENSE GLACIAL :. :•. ❑UTWASH GROUNDWATER SECTION A-A PROJECT/ OWNER/ LOCATION, COMMERCIAL BUILDING GEOTECHNICAL REPORT SOUTH SHORE ENTERPRISES PARCEL 32232 43 90013 MASON COUNTY, WASHINGTON NOTES, ENGINEER, ENVIROTECH ENGINEERING 1) THE SOIL PROFILE IS ACCURATE FOR THE DEPTH OF 9 84 BE THE OBSERVED TEST PITS AT THE SPECIFIED LOCATIONS. BOX 984 LOWER DEPTHS ARE BASED ON SITE GEOLOGY, LFAIR, WASHINGTON 98528 360-275-9374 WELL LOG(S), AND/OR EXPERIENCE IN THE GENERAL AREA. SOIL PROFILE TEST PIT LOG TEST PIT NUMBER TP-1 PROJECT: South Shore Soils Report DATE OF LOG: 3/18/2010 PROJECT NO: 1027 LOGGED BY: MCS CLIENT: South Shore Enterprises EXCAVATOR: N/A LOCATION: Parcel 32232 43 00010, Lot 3 DRILL RIG: None Mason County, Washington ELEVATION: N/A INITIAL DEPTH OF WATER: 12" FINAL DEPTH OF WATER: 12" STANDARD PENETRATION TEST SOIL STRATA DEPTH SAMPLERS USCS DESCRIPTION LL PI CURVE AND TEST DATA DEPTH N 10 30 50 0 . ......................................... . SM Brown, moist, wet at 1 ft, loose SILTY SAND with GRAVEL. Gravel is primarily fine and subangular. Sand is mostly 1 medium. Low plasticity. 2 3 Excavation terminated at approximately 3.0 feet 4 5 6 7 . 8 9 110 Groundwater Encountered ENVIROTECH ENGINEERING This information pertains only to this boring and should not be Geotechnical Engineering interpreted as being indicitive of the entire site. TEST PIT LOG TEST PIT NUMBER TP-2 PROJECT: South Shore Soils Report DATE OF LOG: 3/18/2010 PROJECT NO: 1027 LOGGED BY: MCS CLIENT: South Shore Enterprises EXCAVATOR: N/A LOCATION: Parcel 32232 43 00010, Lot 3 DRILL RIG: None Mason County, Washington ELEVATION: N/A INITIAL DEPTH OF WATER: 36" FINAL DEPTH OF WATER: 36" STANDARD PENETRATION TEST SOIL STRATA, DEPTH SAMPLERS USCS DESCRIPTION LL PI CURVE AND TEST DATA DEPTH N 10 30 50 0 . .................................................. SM Brown, moist, loose SILTY SAND Wth GRAVEL. Gravel is primarily fine and subangular. Sand is mostly medium. Low 1 plasticity. Medium dense 2 Wet 3 Excavation terminated at approximately 3.0 feet 4 5 6 7 8 9 10 Groundwater Encountered ENVIROTECH ENGINEERING This information pertains only to this boring and should not be Geotechnical Engineering interpreted as being indicative of the entire site. TEST PIT LOG TEST PIT NUMBER TP-3 PROJECT: South Shore Geotechnica! Report DATE OF LOG: 2/18/2011 PROJECT NO: 1120 LOGGED BY: MCS CLIENT: South Shore Enterprises EXCAVATOR: N/A LOCATION: Parcel 32232 43 90013 DRILL RIG: None Mason County, Washington ELEVATION: N/A INITIAL DEPTH OF WATER: N/A FINAL DEPTH OF WATER: N/A STANDARD PENETRATION TEST SOIL STRATA DEPTH SAMPLERS USCS DESCRIPTION LL PI CURVE DEPTH N AND TEST DATA 10 30 50 0 . .................................................. SM Brown, moist, loose SILTY SAND with GRAVEL. Gravel is primarily well graded - and subrounded. Sand is mostly medium. 1 Low plasticity. Medium dense 2 3 Increasing gravel and density with depth 4 5 Excavation terminated at approximately g 5.5 feet 7 8 9 10 No Groundwater Encountered ENVIROTECH ENGINEERING Geotechnical Engineering This information pertains only to this boring and should not be interpreted as being indicitive of the entire site. 'File Original and First Copy with Application No Department of Ecology WATER WELL REPORT Second Copy—Owner's Copy Third Cqpy—Dri I ter*s Copy STATE OF WAS=qGTON Permit No. (1) owNEIL. Name. Gordon GerbJng 25806 S.E. . 192nd, Maple Valley, Wa. .. .. ...... Add rew.... (2) LOCATION OF WELL: county...... ..... .Ma6.Qn........................................... )Sec.32 T..22 ri.. R.31(..w.m. Bearing and distance from section or subdivision corner (3) PROPOSED USE: Domestic industrial 0 Municipal El (10) WELL LOG: Ifrigation. Q Test well 0 Other [I Formation:Describe by color•character,size of material and structure,and erg and show thickness of a the k. and nature of the material in each shiattim penetrated,q= at least one entry for each cUmg* of formation. (4) TYPE OF WORK' number of well _'E FROM TO I I mor,* th none).... ..... .................. MATERIAL New well than Dug (3 Bored 0 Deepened 0 Cable 0 Driven 0 Reconditioned 0 ;zx/ Jetted [3 Shot Clay Gravel & sand (5) DIMENSIONS: Diameter of well 6 83 inches. Clay--_- Drw,d..... ft. Depth of completed well.. _...._.--A- — Gra-v 1 & 212 ( Cemented grave 212 1 215 6) CONSTRUCTION DETAILS: Gravel & water ..220'. Casing installed: Diam. from ft. to .22Q... ft. Threaded 0 Disim. from .............. ft. to ._............ ft. Lj Welded Dkam. from .... ........ ft. to .............ft. Perforations: Yes Q No Type of perforator used..V.. - - - ... ... SIZE of perforations ................. in. by ...... ......... In. perforations from It. to .......... perforations from ......... ..... It.to ..................... ft. Tn .......... to .................... 0--.- ....... ............ perforstiom from 1Z Screens: yes 0 N Manufacturer's NY.-.. Type..._..._................. -..-.-­--­--­-­ Model No_........._ Diam. ............... Slot size ............... from ... - ....- ft. to ft. �iarn- Slot size . . ........ from ........... ft. to 7 P'al Gravel packed: Yes(] No Size of gravel; .............. Gravel placed from.............. ft.to- ft. —4— Surface seal: Yes No To what depth? ....... .......... ft. we ...... Material used in seal-... ntQn1tq........ Did any strata contain unusable water? Yes Type of water?. Depth of strata. ......... . Method of sealing strata off . . . .................... (7) PUMP: Manutacturer's Name.._......-... ------ Type: .... .......................... ..­..............................H.P........... .... .... (9) WATER LEVELS: Land-surface elevation above mean sea level.... Static level 175 .... ....ft. below top of well Date. 5/15/85­ Artesian pressure . . .............lbs. per square inch Date -—------- Artesian water is controlled by.. (9) WELL TESTS: Drawdown is a ount water level Is static level in lowered below Work started............. 5/. ....... .. Compitted was a pump test made? Yes 0 No/If yes.by whom?.. .. .. . --gal./min. with ft. drawdowri after hrs. WELL DRILLERS STATEMENT. This well was drilled under my jurisdiction and this report is true to the best of my knowledge and belici. Recovery data (time taken an zero when pump turned off) (water level measured from Well top to water level) n NAME......... 9- Time Water Level Time Water Level Time Water Level (Person. arm. or corporation) (Type or print) .... ........................... . ........... .. ..................................................... ............ ........................ Address....1-50L.B....Ar. ...nson ...........St. .............Shelton, .Wa... ....................... . ............... .... ................ . . .... ...................... .................................I...... Date of test [Signed]...... ...... ........... Hailer test gal/mtn. with. .40.. ft. drawdown after......I..........hre. Wall Driller) Artesian Row X.P.M. Date...... ...................._..._..._.......... Temperature of water.. Was a chemical analysis made?Yes C3 N11 License No.........00.32........................ Date. .. .5/17/85 APPENDIX C SLOPE STABILITY STABLE Slope Stability Analysis System New User Project Buechel(Gerving Site) Datafile: Dynamic Bishop STABLE Version 9.03.00u Bishop TITLE Dynamic UNITS (Metric/Imperial) = I GEOMETRY DEFINITION POINTS NO. X Y 1 0.000 0.000 2 102.000 -44.000 3 190.000 -63.000 4 0.000 -6.000 5 102.000 -50.000 6 190.000 -69.000 7 19.000 -8.200 8 27.000 -11.650 9 35.000 -15.100 10 43.000 -18.550 11 51.000 -22.000 12 59.000 -25.450 13 67.000 -28.900 14 75.000 -32.350 15 83.000 -35.800 16 91.000 -39.250 17 99.000 -42.710 18 107.000 -45.080 19 115.000 -46.810 20 123.000 -48.530 21 131.000 -50.260 22 139.000 -51.990 23 147.000 -53.720 24 155.000 -55.440 25 163.000 -57.170 26 171.000 -58.900 LINES Lo X Hi X SOIL 1 2 1 2 3 1 4 5 2 5 6 2 SOILS SOIL NAME LINETYPE-PEN COHESION FRICTION UNIT WT. 1 —.rh—ri— r..nMT TNT TOT T.Q-RT.A('K 1 on nn 'Ad n 1'Ar, nnn STABLE Slope Stability Analysis System New User Project Buechel(Gerving Site) Datafile: Dynamic Bishop 2 outwash CONTINUOUS-BLUE 200.00 38.0 138.000 ********************************************************** PORE PRESSURE SPECIFICATION SOIL PIEZO RU EXCESS Y/N/P Value Value 1 N 0.000 0.000 2 N 0.000 0.000 PIEZOMETRIC SURFACE POINT POINT PORE PRESSURES POINT PRESSURE SLIP DIRECTION (+/- X) = + SLIP-CIRCLES AUTOMATIC Circle Centre Grid Extremities 152.000 * 19.000 * * 171.000 * *************** 0.000 X spacing -- no. of cols (max 10)= 10 Y spacing -- no. of rows (max 20)= 20 Grid 1 Circles through point 7 Grid 2 Circles through point 8 Grid 3 Circles through point 9 Grid 4 Circles through point 10 Grid 5 Circles through point 11 Grid 6 Circles through point 12 Grid 7 Circles through point 13 Grid 8 Circles through point 14 Grid 9 Circles through point 15 Grid 10 Circles through point 16 Grid 11 Circles through point 17 Grid 12 Circles throuch point 18 i 00000000000 0 Nn 't0tDI", M0 0 N V) U c 0 j In L N � v -C CL 0 0 Q) +, - � 041 �"0 () o N 000 L 0 Cm 0- OQN 1 .0 0 1 . 1 0 1 . 20 1 . 30 1 . 40 1 S O 1 . 60 1 . 70 1 .80 i 1 . 90 2 .00 1 . 78 Project Buechel (Gerving Site) Datafile Dynamic Analysis Bishop STABLE.2002 MZ Associates Ltd