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HomeMy WebLinkAboutGeotech BLD2006-00048 - BLD Engineering / Geo-tech Reports - 12/31/2006 f sTgT MASON COUNTY �P M o PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER r o T Shelton, Washington 98584 r2 N y 1W4 DATE: June 12, 2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Rebecca Hersha PARCEL # 12221-31-90141 FROM: John Sliva, Programs Engineer-PW BUILDING PERMIT NUMBER: BLD2006-00048 SUBJECT: Geo-Tech Report Review NAME: McFarland Greg & Larisa Rebecca, The Geotechnical Report prepared for the proposed new single-family residence located at 351 E. Victor Road near Belfair has been received and reviewed by Public Works. The report appears to satisfactorily address County requirements for Geotechnical Reporting. The author concludes the overall global stability of the ravine north of the proposed building area under the present site conditions and post construction appears good. Slope stability was modeled in both static and seismic conditions. As a result the building needs a set back of 50 feet from the top portion of the steep slope. Prior to construction NL Olson & Associates recommends field verification of the building setback from the top portion of the slope. Drainage, erosion control, earthwork, and structural recommendations are addressed by the author and should be followed. Adequate erosion and sediment control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. Based on the contents of this report, I recommend accepting this report as satisfying the County's requirements for stability investigation and geotechnical reporting. Recommendations contained in the report should be incorporated into the site development plans and made conditions for permit issuance. Please feel free to contact me at 724 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, John Sliva Programs Engineer TL CHNICAL ENGINEERING REPORT 351 EAST VICTOR ROAD Prepared For: Larisa and Greg McFarland 351 E. Victor Road - Belfair, WA 98528 A� &14ad H.L. Olson & Associates INC Engineering, Planning & Land Surveying SINCE 1973 Prepared By: N.L. Olson & Associates, Inc. 2453 Bethel Avenue Port Orchard, WA 98366 (360) 876-2284 / Fax: (360) 876-1487 Email: i IJi�C;i Giw►„� � , ;. F May 2006 I � GEOTECHNICAL ENGINEERING REPORT PROPOSED SINGLE FAMILY DEVELOPMENT 351 EAST VICTOR ROAD BELFAIR, WA CLIENT: LARISA AND GREG MCFARLAND 351 E VICTOR ROAD BELFAIR, WA 98528 BY: N.L. OLSON AND ASSOCIATES, INC. 2453 BETHEL AVE. SE PORT ORCHARD, WA 98366 (360) 876-2284 JOB NO. 6345-06 'P'. J p J 39359 NAL EN 7ii?ES 5/7/ MAY 2006 N.L. OLSON & ASSOCIATES, INC. Engineering, Planning and Surveying May 19, 2006 Project Number: 6345-06 Attn: Larisa and Greg McFarland 351 E Victor Road Belfair, WA 98528 Subject: Geotechnical Engineering Investigation Proposed Single Family Development 351 E Victor Road Belfair, WA Dear Mrs. & Mr. McFarland; This report presents our findings and recommendations for placement of the proposed structure as well as other geotechnical engineering aspects to this site development. We appreciate the opportunity to be of service to you on this project. If we can be of further assistance or if you have any questions regarding this project, please contact our office. Sincerely, Wesley R. Johnson, P.E. Project Engineer P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 CAProjects\6345 McFarland\McFarland\McFarland georepon doc t i . TABLE OF CONTENTS INTRODUCTION ......................................................................................................................1 SITE LOCATION AND SITE CONDITIONS...................................................................................... 1 SITECONDITIONS.................................................................................................................... 1 PROPOSEDDEVELOPMENT ...................................................................................................... 1 FIELD INVESTIGATION AND LABORATORY TESTING...................................................................... 2 SubsurfaceInvestigation.................................................................................................... 2 SiteSoil Conditions............................................................................................................ 2 Groundwater...................................................................................................................... 2 WATERWELL LOG INFORMATION............................................................................................. 2 AVAILABLE GEOLOGIC AND SOILS INFORMATION........................................................................2 EROSIONCONCERNS............................................................................................................... 3 SEISMICCONCERNS................................................................................................................ 3 SLOPE RECONNAISSANCE AND HISTORICAL LANDSLIDE RESEARCH............................................ 3 SlopeReconnaissance....................................................................................................... 3 Coastal Zone Atlas Information.......................................................................................... 3 SLOPESTABILITY ANALYSIS..................................................................................................... 3 CONCLUSIONS & RECOMMENDATIONS..............................................................................4 SITEPREPARATION AND GRADING............................................................................................4 Structuralfill....................................................................................................................... 5 PermanentCut and Fill Slopes........................................................................................... 5 SURFACEAND GROUND WATER............................................................................................... 5 FOUNDATIONSUPPORT ...........................................................................................................6 FootingDrainage................................................................................................................ 7 FLOORSLABS.........................................................................................................................7 CAST-IN-PLACE RETAINING AND SUBSURFACE WALLS ..............................................................7 Staticand Vehicle Loading................................................................................................. 7 EarthquakeLoading........................................................................................................... 8 Retaining Wall Subsurface Drainage.................................................................................. 8 RetainingWall Backfill........................................................................................................ 8 CONSTRUCTION CONSIDERATIONS...........................................................................................9 SPECIFICATIONS FOR FINAL DEVELOPMENT CONDITIONS...........................................................9 SETBACKREQUIREMENTS...................................................................................................... 10 REPORTLIMITATIONS.........................................................................................................10 VICINITYMAP............................................................................................................FIGURE 1 SITEPLAN.................................................................................................................FIGURE 2 SOILSURVEY MAP...................................................................................................FIGURE 3 SLOPESTABILITY MAP ...........................................................................................FIGURE 4 CROSSSECTION (A-A).............................................................................................FIGURE 5 APPENDIX A—TEST PIT LOGS APPENDIX B —SLOPE STABILITY ANALYSIS RESULTS i GEOTECHNICAL ENGINEERING INVESTIGATION PROPOSED SINGLE FAMILY DEVELOPMENT 351 EAST VICTOR ROAD BELFAIR, WA INTRODUCTION This report presents the results of our subsurface exploration and geotechnical engineering investigation for the referenced project. The geotechnical engineering investigation was done in general accordance to Mason County Resource Ordinance, Ordinance Number 77-93, dated February 28, 2006. In the following, we present our findings, conclusions and recommendations for the proposed development. SITE LOCATION AND SITE CONDITIONS The site is located at the address of 351 E Victor Road in Belfair, WA. The site is situated in the northwest quarter of the northwest quarter of Section 21, Township 22 North, Range 1 West, in Mason County, Washington. The Vicinity Map for the property has been illustrated on Figure 1. SITE CONDITIONS The site is bordered to the east by East Victor Road, to the north by a steep downward trending ravine, to the south by a single family residence and by undeveloped land to the west. The property is rectangular in shape, roughly one acre in size and previously developed with a single-family residence. The area of proposed development consists of a slope, which ascends down from the east to the west with gradients of about 516 1t'percent. Beyond the proposed building area to the west the slope increases downward in steepness with gradients of about 16°to 24D percent. Beyond the proposed building area to the north a ravine was observed along the north side of the property. The slope along the ravine increases in steepness as the slope descends down to bottom portion of a draw with gradients less than 40 to 56 pereent-,`The ravine's vertical slope height was on the order of 40 to 50 feet.' The developed portions of the site and areas west of the proposed building area have been cleared. In the undeveloped ravine area of the site, a secondary re-growth of cedar, Douglas fir, alder and large leaf maple was observed. PROPOSED DEVELOPMENT As presently conceived, a portion of the site is proposed for development with a single family residence. The building footprint will be roughly 1,900 square feet. The structure will be one to P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C\Projects\6345 McFarland\McFarland\McFarland geo report doc Project No. 6345-06 May 19, 2006 Page No. 2 two-stories and of light wood frame construction, daylight basement, floor slab and attached garage. The building's footing loads are anticipated to be light to moderate. We have shown the approximate building layout on the Site Plan - Figure 2. L cipate the cuts along the north, south and east side of the proposed structure-wilkbe-'e of 5 to 10 feet and daylight to the west. Minimal cuts are anticipated along the west he building. FIELD INVESTIGATION AND LABORATORY TESTING Subsurface Investigation The test pits were excavated using a track-hoe prove e y the client, and extended down 2 to 13 feet below current site grades. The approximate test pit locations are shown on shown on the Site Plan, Figure 2. Site Soil Conditions In general, our test pits revealed the site is underlain by silty sand, poorly graded sand and silt. Glacial till was encountered in ades ands e glacial till was underlain by dense to very dense silty sand with varying amounts of gravel and cobble. In test pit TP-2, loose to medium dense silty sand with gravel was encountered in the mil horizon. The silty sand with gravel was underlain by medium dense to dense well graded gravel with silt. Glacial till was not encountered in the test pit TP-2. For a more detailed description of the subsurface conditions, please refer to our test pit logs presented in Appendix A. Groundwater I FORMATION Based on the water well log information for this area, we anticipate a static around water_Jevel of about 200 feet below current site grades. At this time, NLO was unable to find water well log information for the well located along t e south side of the property. AVAILABLE GEOLOGIC AND SOILS INFORMATION The Washington Division of Geology and Earth Resource (WDGER), Geologic Map of Washington — Northwest Quadrant, dated 2002, has mapped the site as Quanternary sediments, dominantly glacial drift and includes alluvium. Glacial till consists of an unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel and boulders deposited by glacial ice. The Soil Survey, Mason County, Washington 1960 indicates the site is underlain k� j 15% slopes and Everett Gravely sandy loam, Eh and Ek, 5% to 15% and 15% to 30% slopes, respectively. T P.O. Box 637.2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C iProjeclsl6345 McFarlandUcFarlandlMCFarland geo report.doc f 7 , Project No. 6345-06 May 19,2006 Page No. 3 EROSION CONCERNS opinion that the proposed residence should have a minor influence on the present p�oten'a( for erosion and should not create a significant environmental impact during construction or post construction. The erosion risk can be mitigated through normal landscaping and the control of surface runoff. During construction and until fully surfaced and/or landscaped, the exposed site soils may be subject to minor erosio . n of the e is would be most noticeable during periods of intense raanfall ands al erosion control measures, i.e., silt " ces, hay bales, mule thing, and contour furrowing. SEISMIC CONCERNS NLO has reviewed the 1997 Uniform Building Code (UBC) for seismic design criteria for the proposed construction. The UBC seismic design parameters for this site include a seismic zone soil profile type of (SD), in the u er 100 feet of the rofile. ed on the encountered nt appears low. The site's ground acceleration was determined from the 2002 USGS Earthquake Hazard Program. The interpolated probabilistic ground motion values (PGA), in %g, for the 10% probability of exceedance in 50 years was PGA=32.88%. The PGA was based on the following location 47.3816 Latitude and 122.8123 Longitude. The maximum horizontal ground acceleration (Kh= 0.16) was determined by dividing the PGA by 2. SLOPE RECONNAISSANCE AND HISTORICAL LANDSLIDE RESEARCH Slope Reconnaissance As part of our fieldwork, the slope areas were examined for indications of slope instability during our reconnaissance performed May 12, 2006. Indications of slope instability include head scarps, hummocky terrain, inconsistent patterns of vegetation, tension cracks, _seep. ge zones and course grain_material overlaying silt and cla� soils. t , Wnee, no -ems-or erosion s ine and the ravin Coastal Zone Atlas Information A review of Department of Ecology, Slope Stability Maps — Coastal Zone Atlas, Volume 9, 1979 (Mason County)" indicates the area has been classified as stable, and intermediate stability. Slopes _classified as intermediate stability (1) are generally steeper than 15 percent except where conditions such as weaker material and/or abundan groundwater exist. Identified areas include slopes of sand and gravel, till, or thin soils over bedrock, which have no known failures. Stable (S) is defined as having slopes of less than 15 percent. Slope stability mapping for the site has been illustrated on Figure 4. SLOPE STABILITY ANALYSIS Slope stability analysis was performed on cross section A-A, utilizing a 2 ft contour map developed from LIDAR. The analysis was preformed with (PCSTABL7-Version 2.0), a slope stomputer program using the Modified Bishop Method of Slices. This method of analysis P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C\Projects\6345 McFarland\McFarland\McFarland geo report doc r , Project No. 6345-06 May 19,2006 Page No. 4 provides a number failure surfaces to determine the critical surface and associated factor-of- safety (FS). The FS is determined from the ratio of shear strength (the frictional resistance and soil cohesion resisting the down slope movement) to shear stress - (gravitational forces that initiate slope movement) or FS = Shear Strength/Shear Stress. A FS equal to 1.0 is considered e�m and n 1.0 indicates failure. Based on general slope stability guidelines - _ - and FS of 1.1 or greater for seismic is considered adequate. The building setback was determined by extending the critical failure surface from the toe of slope uphill toward the structure until an adequate factor of safety for static and seismic loading was achieved. The soil parameters utilized for our slope stability analysis and discussion of our slope stability analysis methodology can be found in Appendix B. The proposed slope configuration and soil conditions utilized in our analysis are shown in Cross Section A-A', Figure 5. CONCLUSIONS & RECOMMENDATIONS Following our review of Mason County Resource Ordinance, Ordinance Number 77-93, we `ne that nstro`n appears T glstabt n' ed building area under „ itions I bPost constri bn a We understand that the proposed_residence will utilize the_existing septic _drainfield area, which previously has not 6 exhibited signs of slope instabilitor erosion. We recommend vegetation removal only in areas - ` proposed for grading, paved areas and building placement. NLO has provided the o owing recommendations for the project. --- SITE PREPARATION AND GRADING pavement, fill and/or building areas should be stripped of all sod, organic soil, existing fill and bris. In most areas, a minimal stripping depth should be anticipated. However, deeper avations will be required to remove large tree root-balls, existing fill, foundations, septic t ks and associated drainfields, or pockets of unsuitable soils. Stripped soils, contaminated I t rth organics or debris, should be wasted off site or used in landscape areas. Following site stripping, and prior to fill placement, the exposed subgrade should be proof rolled and compacted to a firm, unyielding condition using vibratory equipment of appropriate size and e type capable of developing a minimum dynamic compaction effort rating of at least 25,000 pounds with a static drum weight of 13,000 pounds. Compaction of the stripped subgrade should be continued until field density tests show that a minimum compaction of 95% of the maximum dry density, as determined by ASTM method D-1557, has been achieved in all fill, building, roadway, and parking areas, or NLO indicates a firm unyielding subgrade has been obtained. Any soft or weaving areas disclosed during proof rolling should be excavated and replaced with compacted structural fill. We recommend that all site grading and preparation be undertaken and completed during dry weather. If grading in building or pavement areas is necessary during wet weather, and time does not permit allowing the on-site soils to drain, we recommend that all excavated soil be removed from the site or set aside in covered stockpiles, P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C\Projects\6345 McFarland\McFarland\McFarland geo report.doc Project No.6345-06 May 19, 2006 Page No. 5 and imported materials for structural fill. The structural fill must meet the requirements presented below. Structural fill n Structural fill is defined as compacted fill placed under buildings or pavement that consist of free draining grave Ty saMr-I`faving-a maximum size of 1-1/2 inches and with not more than 5.0% fines passing the U.S. No. 200 sieve. All imported fill material should conform to the above recommendation regardless of present weather conditions. All structural fill should be placed on a firm, properly prepared subgrade. Fill materials should be placed in approximately 8 inch thick layers, moisture conditioned, and compacted to 95% of the maximum dry density as determined by ASTM D-1557. Permanent Cut and Fill Slopes Permanent cut slopes and structural fill slopes shall not exce nt of 2HAV (50%). Permanent fill slopes should be placed in accordanceNMMWe TM pp" resented in this report. In areas where c u steeper slopes are required, retaining strures s ould be provided. SURFACE AND GROUND WATER Only minor storm water related problems are anticipated if grading operations and site preparation work are undertaken during the normally drier portions of the year, May 1 through Nov 1. However, if site work is undertaken during wet weather, typically Nov 1 through May 1, it should be anticipated that the near surface fine-grained soil will become over-saturated and unworkable. If the contractor should undertake the site work during wet weather, they should be fully prepared to deal with wet soil conditions and water problems associated with wet weather work, including the filtering of runoff, as needed to prevent the siltation of down slope areas miniaziing potential erosion concerns, `''is recom d that to should'no e Whpped and left without erosion protection for an extend Yiod of time` prior to the actual start of construction and/or landscaping. Silt fencing and other erosion control devices and megWres may be req _" rol AWer runoff and sedirtnt transport off the site. It should be anticipated that perched water flows or water flows developed during periods of wet weather may occur in excavations as shallow as one to two feet below current site grades or atop siltier zones at deeper depths. In that we are unable to predict where or when groundwater seepage might occur, we recommend that any development of seeps or flows be treated as a construction/maintenance problem. aft� W ht lining o runoff to th- arty would be" Q� u� However, such disposal sydwms should comply with all appficabl' ions and the pipes should discharge into a manifold-type structure or into an energy dissipater such as a pad of crushed rock to minimize erosion. If an energy dissipater pad is used it should be a minimum of three feet on a side and one foot thick, and comprised of two to four inch crushed roi k inside a stacked from to prevent down slope migration of the rock. P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C\Projects\6345 McFarland\McFarland\McFarland geo report.doc t Project No. 6345-06 May 19, 2006 Page No. 6 iag provided at convenient locations along the length of the storm drainage system for maintenance. Tight lines trending down to the base of the slope should be monitored annually or after significant precipitation events. If the tight lines are found faulty or inoperative they should be replaced immediately. Note: IV 9 _ wl, disch walls, or FOUNDATION SUPPORT Support for the planned residences can be provided using daylight basements in conjunction with conventional shallow foundation systems bearing on competent native soils or on structural fill used to modify site grades. For the residence's continuous and column footing system bearing on properly compacted structural fill or dense undisturbed native granular soils an allowable soil bearing pressure of 2,500 pounds per square foot (psf) can be used. For frost protections, footings should have a minimum embedment depth of 18 inches below adjacent grade. A base friction coefficient of 0.30 is considered appropriate for the expected dense site foundation support soils. An ultimate passive equivalent fluid earth pressure for retaining structures, considering a horizontal ground surface, of 250 pcf is available to develop additional resistance to lateral pressures. Passive pressures should be ignored or appropriately reduced in areas where the ground slopes downward on the resisting side of the wall within 4 times the footing embedment depth of the wall. The upper two feet of soil should be neglected when calculating the passive resistance. A 1/3 increase in the above value may be used for short duration, wind, and seismic loads. NLO recommends a footing subgrade inspection to verify if adequate foundation subgrade soils have been achieved. NLO may require additional overexcavation below the planned bottom level of footing if soft, loose, or organic laden soils are encountered. Prior to fill placement, all material intended for structural fill use will require verification and approval by a representative of our firm. Structural fill placement should be done in accordance to the structural fill section discussed in Site Preparation and Grading Section of this report. P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C\Projects\6345 McFarland\McFarland\McFarland geo report.doc r , Project No. 6345-06 May 19, 2006 Page No. 7 Footing Drainage To preclude the possible build-up of ground water or storm runoff in the soils adjacent to the structure, it is recommended that a four-inch diameter, SDR 35 (ASTM 3034), perforated, rigid pipe placed perforations down, around the perimeter of the building foundation at the footing subgrade elevation. The entire foundation drainage system should be bedded in gravel, drain rock) and designed to carry any accumulated water away from the structure to an appropriate discharge area. onnected to the footing drains but may use the same outfall rom the building such that roof water will not backup into the FLOOR SLABS Floor slabs may be supported on properly placed and compacted structural fill or on the medium dense to very dense in-situ native soils following preparation as outlined above. A capillary break/drainage layer consisting of six inches of pea gravel, or clean crushed rock should be placed below the floor slab. The capillary break material should contain less than 1.0% material passing a U.S. No. 200 sieve and less than 4.0% material passing a U.S. No. 10 sieve. A visqueen vapor barrier having a minimum thickness of 6-mils should be placed between the capillary break and the floor slab. We understand that a sand cushion between the vapor barrier and the base of the slab may improve the curing of the slab concrete. If a sand cushion is placed between the capillary break material or the vapor barrier and the slab, it should not contain free moisture when the slab is constructed. Excess moisture in the cushion could cause impervious floor coverings to bubble. CAST-IN-PLACE RETAINING AND SUBSURFACE WALLS The following earth pressures and design values are provided for cast-in-place retaining and subsurface walls up to 15 feet in height. We recommend that all foundations be designed as outlined above and bear on the dense native soils or structural fill placed and compacted as previously described. Static and Vehicle Loading Retaining and subsurface walls should be designed for an active equivalent fluid pressure of�5 .10 i, if the top of the wall is allowed to deflect, assuming a horizontal ground surface behind the wall. If the top of the wall is restrained an equivalent fluid pressure of 55 pcf is recommended. Active or at rest pressures will need to be increased for sloping ground or surcharge loads (such as vehicle traffic) behind the wall. Resistance to sliding can be developed by a combination of passive pressure and base friction. A base friction coefficient of 0.30 is considered appropriate for the anticipated dense foundation subgrade soils. For traffic surcharge loads near retaining structures an ultimate passive equivalent fluid earth pressure, considering a horizontal ground surface, of 300 pcf should be used. Passive pressures should be ignored or appropriately reduced in areas where the ground slopes downward on the resisting side of the wall within 4 times the wall footing embedment P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C\Prolects\6345 McFarland\McFarland\McFarland geo report doc Project No. 6345-06 May 19, 2006 Page No. 8 depth. Appropriate safety factors should be applied to the recommended base friction and ultimate passive pressure values. Earthquake Loading Earthquake loadings are also expected to increase the lateral pressures indicated above. The increases for most basement walls have historically been expected to be within limits that are generally compensated for with a reduced safety factor (Seed, H. B. & Whitman, R. V., Design ifoff Retaining Structures for Dynamic Loads, 1970 Specialty Conference on Lateral Stresses in the Ground and Design of Earth Retaining Structures, American Society of Civil Engineers, 1970). However, the increases in lateral loadings from earthquake forces are expected to provide a slightly increased component of the lateral pressures to be taken into consideration in the structural design of buried walls. Seed and Whitman discuss a procedure for determination of lateral loading following an approach suggested by Mononobe and Okabe. As input to the Mononobe-Okabe evaluation, a friction angle of 35 degrees for the backfill soils was used along with a horizontal and vertical earthquake acceleration of 0.16g (half of the peak ground acceleration for the 10% probability of exceedance in 50 years, as suggested by the USGS). Based on this input and some assumptions on wall friction, an earthquake loading surcharge of 7H (equivalent active fluid pressure), and 5.5H, for at-rest. This loading is additive to the static "active" and "at-rest" pressures indicated above. The application of this loading depends on the wall type chosen. The earthquake surcharge loading should be applied as a rectangular loading condition with the resultant loading pressure within the rectangular loading. The above-recommended pressures do not include the effects of hydrostatic pressure on the wall as they assume a drained condition exists. The maintenance of a dewatered/drained condition behind all retaining structures is required for the above values to be valid. The following drain system and backfill requirements are recommended. Retaining Wall Subsurface Drainage A longitudinal subdrain with a minimum diameter of 4 inches should be constructed at the base { of the footing elevation behind the walls. This drain should be constructed of Winch diameter "perforate n; bedded in an eighteen-inch envelope of free-draining sand and gravel. This system should be sloped to drain and the water disposed of in the storm drainage system. Clean-outs should be provided at bends and convenient intervals, so that the drainage system can be maintained in a well-functioning condition. Flexible plastic piping (such corrugated ADS-type piping) should not be used behind the wall. Retaining Wall Backfill All wall backfill over the gravel envelope should consist of clean, free-draining, well-graded sand and gravel containing less than 2.0% fines (material passing a U.S. No. 200 sieve). This material should extend out from the rear wall face a minimum of eighteen inches. The free- draining backfill should be placed to the surface in paved areas or to within eighteen inches of the surface in non-paved areas. Backfill should be compacted as recommended above for fills. P.O Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax. (360) 876-1487 C\Projects\6345 McFarland\McFarland\McFarland geo report doc + r Project No. 6345-06 May 19, 2006 Page No. 9 In non-paved areas, the final eighteen inches of backfill should consist of topsoil or native materials firmly tamped into place. CONSTRUCTION CONSIDERATIONS eline for temporary cut than 10 feet in height; dd tib-�rnade no steeper than 1HA1mtr the dense granular soils and no s eeper than 2HA V in medium dense soils or structural fill plac IQ nd compacted as outlined above. For tempor in existing fill, topsoil, or loose nica r tempora77M 1010he full height of the cut. Temporary slopes or excavations should be benched as required by safety regulations in effect at the time of construction. The provided temporary slope recommendations are for native soils and fill materials; flatter slopes may be required in wet weather or if soil conditions other than those previously described are encountered. The contractor should be aware that slope height, slope inclination, and excavation depths (including utility trench excavations) should in no case exceed those specified in local, state, or federal safety regulations; e.g., OSHA Health and Safety Standards for Excavations, 29 CFR Part 1926, or successor regulations. Such regulations are strictly enforced and, if not followed, the owner, the contractor, or the earthwork or utility subcontractors could be liable for substantial penalties. The contractor should be made responsible for the stability of all excavations and slopes during construction because they are continually on site and can observe the stability of the exposed soils. In addition, the contractor should be prepared to shore any unstable slope area and provide shoring as required by local, state, or federal laws or codes. The provision of shoring design recommendations is beyond the authorized scope of this report. In a disturbed condition the site soils may be eroded by channelized water or sheet flow storm runoff. Therefore, it is recommended that all site preparation and excavation work be completed during the normally drier portion of the year. During periods of heavy rainfall, ditching should be used to divert water away from stripped areas and visqueen should be used to cover the slopes ® and soil stockpiles to aid in preventing excessive surface erosion. This covering also aids in preventing infiltration of water into the unprotected soils. All disturbed soil areas and slopes should be replanted with fast-growing, deep-rooted grass, shrubs and other ground cover as soon after final grading as possible. If the vegetation is not fully established prior to the on set of wet weather, the slopes should be covered with visqueen to aid in preventing excessive erosion and water infiltration. It should be anticipated that there could be a number of additional site development or construction problems, particularly if the earthwork has not been completed and the site properly protected at the onset of wet weather. It is recommended that a qualified representative of the architect or engineer make periodic inspections of all excavations and slopes to provide early recognition and recommendations. SPECIFICATIONS FOR FINAL DEVELOPMENT CONDITIONS NLO should observe the site prior to project completion to determine if the present erosion control, and re vegetation plan is adequate. We anticipate that areas outside the proposed �v building area will consist of lawn and landscapin . I � P.O. Box 637e 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C Trolects\6345 McFarland\McFarland\McFarland georepon.doc + Project No. 6345-06 May 19, 2006 Page No. 10 • Exposed soil areas should be hydroseeded or covered with straw or mulch. Footing drains and downspout tightlines, and graded areas will be observed after completion of the residence for potential surface runoff and erosion issues. Vegetation in the building setback and the creek buffer/setbacks should not be disturbed. Disturbed areas associated with this development should be seeded with grass and covered with 2 to 3 inch thick layer of straw. Mulch can also be used in lieu of straw in non-seeded areas. • The sites permanent erosion control measures, lawn and landscaping should be completed prior to November 1. • `Verify°footing subgrade area and building setbacks prior to placement of footing forms and rebar. SETBACK REQUIREMENTS At this time, we ave utilized slope stability analysis to determine the building's setback, distance of 50 feet from the top portion of the steep slope for the proposed residence. The setback distance shall be determined by measuring between the furthest projecting footing element to the top portion of slope identified on the Site Plan, Figure 2. Prio[ ,ction, NLO recommends field verification of the building setback from the top portion of the slope. 1 �J Per Mason County's comments (2/17/06) case number, BLD2006-00048, NLO has provided as a LIDAR map illustrating buffer and setback requirements for the propped building.area near the inte ittent stream. The stream buffer requirements are 75 feet with ;a' 5 ee M ng ufr. a buffers and setbacks for the intermittent stream have been defined on the Site flan igure 2. REPORT LIMITATIONS This report has been prepared for the client regarding the subject project. Information presented in this report has been collected and interpreted in a manner consistent with the level of care and skill ordinarily exercised by members of the profession currently practicing under similar conditions, and in accordance with sound and generally accepted principles consistent with normal consulting practice. No other warranty, expressed or implied, including (but not limited to) any warranty or merchantability or fitness for a particular use has been made. In the event that change in the nature, design, or location of the proposed construction is made, or any physical changes to the site occur, recommendations are not be considenless the changes are reviewed by NLO and conclusions of this report are modified or verified in writing. NLO should be retained to provide geotechnical services during construction. This is to observe compliance with the design concepts, specifications or recommendations and to allow design changes in the event subsurface conditions differ from anticipate for to the start of construction. We do not accept responsibility for the performance o e oundation or earthwork unless we are retained to review the construction drawings and specifications, and to provide construction observation. P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax (360) 876-1487 C.1Projects�6345 McFarland\McFarland\McFarland geo report doc Project No. 6345-06 May 19, 2006 Page No. 11 Any site involving sloping terrain has inherent risk of earth movement. As a result, the CLIENT agrees to accept full responsibility for all risks associated with steep slopes. The CLIENT acknowledges that this risk cannot be completely eliminated and that engineering and geologic analysis is intended to reduce the inherent risk associated with slopes. No amount of geotechnical engineering and geologic analysis can provide a guarantee of stable slopes. Geotechnical engineering and geologic analysis are based heavily on subjective interpretation, professional judgment, and opinion regarding the physical conditions at a specific site. Subsurface conditions are only documented at those points where samples were taken and interpolation and extrapolation is necessary between and around sample locations. Conditions can vary between samples and can change over time due to natural processes and/or human activity. Analyses and recommendations provided in this report are based in part upon the data obtained from the subsurface explorations. P.O. Box 637. 2453 Bethel Avenue • Port Orchard, Washington 98366 Phone: 1(800) 755-1282 Fax: (360) 876-1487 C:\Projects\6345 McFarland\McFarland\McFarland georeport.doc Y � 1^ d a 144TH ST O _BAY_:., - TOR RD SITE J 3 a a m E VICINITY MAP �U ' C (0 C (0 LL U f0 N U N O a` v I • t o LIDAR INFORMATION PROVIDED BY ALKAI CONSULTING LLC /50 - 6° TEST PIT LOCATION Uc nnoN uC 1 4 o c i I � ID 5 4• REVISIONS BY DATE A FOR: ATTN: LARISA A DATE I BY DESCRIPTION DESIGNED .k,N1.,01 GREG MCFARLA DRAYM Enginee CHECKED 351 E. VICTOR RI APPROVED BELFAIR, WA 98 ACCEPTED 2453 8"k w ' c + r �aF - v .� t n ,y�i,. v k•§ tin: Xm 4- 2- ILA# NY t i• :.°o�+'i ' ,fir�'�! Y�d ;;�,,}} � .htr., fh r xtkr�. a a'+p 0 i5 , It i � # x - - •. y • ••- • • •. 0 Mm s A review of Department of Ecology, GlopoStability Maps - Coastal Zone atlas, Volume 9, 1979 (Mason County)" � ndicates the area has been classified as -,table, and intermediate stability. 31s classified as intermediate stability (1) are generally steeper than 15 n' -)ercent except where conditions such as Neaker material and/or abundant groundwater exist. Identified areas nclude slopes of sand and gravel, till, or hin soils over bedrock which have no known failures. Stable (S) is defined as K. q 'laving slopes of less than 15 percent. , f for w f $ o V� Y £14 p �� yx Site x , A� ,uw.x,ir: r # � § v. "q 4� ,. Figure 4 Slope Stability Mapping l ,� A'-`A N.L.Olson&Associates,Inc. Engineering.Planning and Surveying McFarland 2453 BETHEL AVENUE 351 E Victor Road P.O.BOX 637 PORT ORCHARD,WASHINGTON 98366-0637 Belfair, WA I ' i Building Setback I 50 ft I i Proposed esidence i i I l 60 Total Saturated Friction Unit Wt. Unit Wt. Angle i 47.5 ft (pct) (pco (deg) 135.0 145.0 35.0 f 30 I Suctace Silty Sand with Gravel 1\ure I I i i 0 0 30 60 90 120 150 180 210 240 i I Cross Section A-A k-`AN.L.Olson&Associates,Inc. McFarland Engineering,Planning and Surveying 351 E Victor Road 2413 BETHEL AVENUE I P.O.Box 637 — Belfair, WA — — — PORT ORCHARD,WASHINGTON 98366-0637 APPENDIX A TEST PIT LOGS The site soil conditions were explored on the site July 22, 2005 by excavating eight test pits throughout the site. The test pit excavation were excavated using a track-hoe provided by the client, and were extended to depths of 2 to 12 feet. The approximate test pits locations are shown on the attached Site Plan, Figure 2. the test pits soil logs are presented in this Appendix. Stratification lines designating the interface between soil types in subsurface exploration logs represent approximate boundaries. The transition between materials may be gradual. The test pit logs and related information depicts conditions only at the specific locations and at the particular time designated on the logs. The depths represented on our test pits logs were referenced to present site grades encountered during our subsurface exploration work. AZ-,'A N L.Olson&Associates,Inc. Test Pit Engineering,Planning and Surveying McFarland 1411 BETHEL AVENUE 351 E Victor Road P.O.BOX 637 PORT ORCHARD,`•NASHINGTON 98366-0637 Belfalr, WA Job Number. Logged By: Subsurface Exploration Ground Surface Elevation Page 6345 WRJ Start Date:Mar 14,2006 1 End Date: Mar 14,2006 154 TP-3 1 of 1 General Surface Notes Conditions: Grab samples Area Cleared Test Pit Below Rock Wall Area "— � Moist taken at following n E USCS L Coisture SYMBOL mert Depths C (% TOPSOIL upper 2 to 4 inches Brown Silty SAND with gravel, dense to very dense, moist 2 ft sM - Contains cobbles 2- 4- 5- Test Pit terminated at 2 feet. 6- 7- 8- 9 10 11 12 13 I 14 15 16 17 18 Contractor Operators Name Sampling Method Drawn By: Date Hole Completion grab WRJ Dec 19,2005 ❑ Monitoring Well Equipment Groundwater Elevation Checked By: Date Piezometer Not Encountered ® Abanonded and backfilled Notes: Revision By: Date Inclinometer El Test Pit &!--'A N.L.Olson&Associates,Inc. Engineering,Planning and Surveying McFarland 2453 BETHEL AVENUE 351 E Victor Road P.O.BOX 637 PORT ORCHARD,WASHINGTON 98366-0637 Belfair, WA Joo Number. Logged By. Subsurface Exploration Ground Surface Elevation Page 6345 WRJ Start Date:Mar 14,2006 1 End Date: Mar 14,2006 141 TP-1 1 of 1 Surf General ace Notes Conditions: Grab samples a z Drive Area cleared of Vegitation j E a USCSt Moisture taken at following m E SYMBOL m Content 9 N p �� Depths j I Brown Silty SAND with gravel, loose to medium dense, j 1 ft 1 moist sM 2 - Contains cobbles i 3 3 to 4 It SP Brown poorly graded SAND with gravel and trace silt, 4 medium dense, moist 4 to 5 It ML - Contains cobbles 5-- 6- Dark Gray Silty SAND with gravel, dense to very dense 7 - Contains cobbles aft j - Appears to be a layer of glacial till 5 to 8 ft below current i 8 site grades between el 133 to el 136 SM I Becomes yellowish brown at roughly 8 feet and dense 9 - Cobbles not encountered below 8 feet Contains trace gravel 10 - At roughly 12 to 13 feet becomes dense to very dense 11 -Observed silt content 15 to 20 percent 12ft 12 13It 13 Test Pit terminated at 13 feet. 14 15 16 17 18 Contractor Operators Name Sampling Method Drawn By: Date Hole Completion grab WRJ Dec 19,2005 ❑ Monitoring Well Equipment Date ❑ Piezometer Groundwater Elevation Checked By: Not Encountered ® Abanonded and backfilled Notes: Revision By Date ❑ Inclinometer ( t Test Pit A'=`�N.L.Olson&Associates Inc. Engineering,Planning and Surveying McFarland 2453 BETHEL AVENUE 351 E Victor Road I P.O.BOX 637 PORT ORCHARD,WASHINGTON 98366-0637 Belfalr, VVA Job Number Logged By: Subsurface Exploration Ground Surface Elevation Page I 6345 WRJ Start Date:Mar 14.2006 End Date: Mar 14.2006 112 TP-2 1 of 1 Surface General Conditions: I Notes Area cleared along slope surface Grab samples -�$ USCS t Moisture taken at following E SYMBOL m Content Depths Brown Silty SAND with gravel, loose to medium dense, 2 ft 1 moist sM 2 - Contains cobbles 3 4 Yellowish brown well graded gravel with sand and silt, medium dense to dense, moist 5 - Contains cobbles I 6 7 ft GW-GM 8 I g I, 10 11 12 13ft 13 Test Pit terminated at 13 feet. 14 15 16 17 18 Contractor Operators Name Sampling Method Drawn By: Date Hole Completion grab WRJ Dec 19.2005 ❑ Monitoring Well Equipment Groundwater Elevation Checked By: Date ❑ Piezometer Not Encountered ® Abanonded and backfilled Notes: Revision By: Date ❑ Inclinometer El ❑ I APPENDIX B SLOPE STABILITY ANALYSIS DISCUSSION & RESULTS For the purposes of our slope stability analysis, we have assumed a pore pressure ratio (ru) of .25 for the groundwater water build up within the slope, which may occur with a typical 100 year 24 hour storm event for this area. The cross section illustrating the slope is shown on (Cross Section A-A' in Figure 5. The soil strength parameters utilized in the analysis are presented below. SLOPE STABILITY ANALYSIS SOIL PARAMETERS Soil Type Density Cohesion Friction YP (Ref) (Psf) (degrees) 1 Silty Sand with Gravel&Silty Sand 135(m) /145(s) 0 35 Soil strength parameters were developed based on our experience with similar soil conditions - and published values. The site soils consist of medium dense to dense soils in the upper 6 to 8 feet of the soil horizon becoming dense at roughly 8 to 12 feet. Based on the encountered soil conditions, we have provided a cons8R 35 degrees for our analysis of the entire slope profile detailed in Cross Section A-A. Note: y Therefore, the s went occurring- .,�y cad be �msidered. oil conditions encountered at the time of our subsurface exploration were utilized for our seismic analysis. The site's ground acceleration was determined from the 2002 USGS Earthquake Hazard Program. The interpolated probabilistic ground motion values (PGA), in %g, for the 10% probability of exceedance in 50 years was PGA=32.88%. The PGA was based on the following location 47.3816 Latitude and 122.8123 Longitude. The maximum horizontal ground acceleration (Kh= 0.16) was determined by dividing the PGA by 2. The building setback was determined by extending the slope failure planes from the toe of slope uphill toward the structure until an adequate factor of safety for static and seismic loading was achieved.` on a 50 feet setback d the anticipated soil conditions, we In e stability results in the following_ Slope Stability Results of Existing Slope Condition Cross Section Slope Wet ru=.25 Slope Wet ru=0.0 Seismic FS Static FS Static FS Existing/Proposed 1.514 2.097 1.336 A-A' Required FS 1.5 (okay) ,Our Analysis indicates and adequate factor of safety for static and seismic ioadi I%Le isc his report with a 50 feet building setback. Note: the por"ROM yj9;y ratio (ru), governed e °etback distance for the proposed project. Slope Stability Graphical results are presented in this appendix. I pit! � f a a� _ o ' ^�o T22NR1W ro, .: Mir f, N^ r M �. 12p NN of .. i 4. Conten'of the Geoiogcal Assessrient A Geological Assessment shai nclude but not be limited to the fcli(xw ng: ;1) A discussion of geologic conditions in the general vicinity of the proposed development,with geologic unit designation consistent with terminology used in the Coastal Zone Atlas ;'Aash.ington Deparmen:of Natural Resources. 19A0)or in applicable U.S. Geologic Survey maps(e.g. Geological Map of North Central Mason County,by R.J. Carson, 1976, U.S. Geologic Survey GFR 76-2). Use of Soil Conservation Service soil layer terminology is considerea mopropriate`a ,his assessrnert:. (2) A discussion of the ground water conditions at the s::e,incud=ng the depth to water and the quan,N of surface seepage. (3) The appro'eiriate depth to hard or dense coniaetent soil,e.g.glac al till or outwash sand. (4) A discussion of any geomorphic expression of pas:slope instabil=:y(presence of hummocky ground or ground cracks.terraced topography indicative of landslide block movement. bowec or arched trees indicating clawnslooe moverie-t,etc.). (5) A discussion of the history o`landsl Je activity in the vicinity, as availa.*le in:the Coastal Zone Haas the ria�-. ..-"-: ,.ve Slooe Stability of the Southe^- Hood Canal Area,Washington is- 5•�i:n and R..; Carson. 197T and the -andslide records on file hith the Mascr, ::,:unty Department of Community;Development. ;6) An opinion on:he potential for landslide ac*iv=ty at the site in light of the proposed development. ;7) A recommencation by the preparer whether a Geotechnical Report should be required to fur-ner evaluate site conditions and'he proposed devetopment of the subect property. 5. Content of a Geo-echnical Repor, A G, chnica'Rep:,*t shall include but not be limited to the follow no: (1)✓ A discussion of general geologic conditions,specific sri ty p--s gro end water conditions and history of iandslide activity in fie v�cini:y as recl,irec for the Geologic Assessu`—n?e nTe-Tl n, d a)ove. P0111(2)✓ A si:e p:an vexh identifies the important development and geologic features. r 6 CZ �`CL— (3) t_oca:ions and ogs of exploratory holes or probes. (4) ✓A minimum of one cross section at a scale nhict;adequately depicts:he subsurface profile. and which incorporates he details of proposed grade changes. �y N. (5) v A description and results of slope stability analyses performed for berth static and seismic loading conditions. (6)✓ Approonate restrictions on placement of drainage features,septic dra n fields and compactec fills and footings,including recommended setbacks from shoreline bluffs ona the t;,,,%s o`oth si Pe the property A detailed ciea n i ai grad no p an r,h .h s_eci ically identifies vegetation to be ren'c ec,a sche-Lil.,fu vegresa:on re noval an -eplanting,inc the method of vegetaac removal (6);/ A detailed en�aerary erosion control plan which identifi s th-specific mitigating measures to be Implemented during construction to protect the slope from erosion, landslides and �'�i II harriful cons:ruction methods. PCr 49) ✓ An analysis of bob on-site and off-site iripa=of the proposed de; a.ri ent (10)1/Specifications of final development cond':ions such as.vegela'uh i3"aa6ment. drainage,erosion control, and buffer widths. �— � � I 1 \. 1 \� �, t t -� � .��.�4 � ��/ ,; ��- pip•--�� Q 00 LIDAR INFORMATION � � � � � �/ � Q�� ... �� � / �/ 15 0 30 60 o s ,./ / �—=`�� Q1 iJralr rn Frrl PROVIDED BY ALKAI CONSULTING LLC ILQIN A K — ET g0zi � � 1, � I '� � V `•'� , Qr - TEST PIT LOCATION Y TP- 2 - - `Q c 1 N C I C tfULDINC TRACK �. 6ET,ATION UFFE CKBE ! 1 / TO 0- / TH OF THIS O a n C) ! r t / Q `CD NQ ��� �✓ AL TiLL ^\ J/ 7I I 1�� v `t C T 4THISS U�NEE ATED II 1 i —TILL I To W CURRENT S17Ea co N QQ r to t co REVISIONS BY DATE A GEOTECHNICAL ENGINEERING INVESTIGATION FOR: ATTN: LARISA AND SCALE: AS SVOW DATE BY DESCRIPTION DESIGNED N.L.01son&Associates,lnc. PROPOSED SINGLE FAMILY DEVELOPMENT GREG McFARLAND DATE:May 16, 2006 DRAWN Engineering, Planning and Surveying 351 E. VICTOR ROAD DRAWING NUMBER CHECKED (360) 876-2284 351 VICTOR ROAD 066245— APPROVED BELFAIR, WA BELFAIR, WA 98528 xxxxxx ACCEPTED 2453 Be"km ,P.O.Box 637.Port Or&"d,WA m66 I I • •oa■a woa.m H i 1 150 150 SW Soil Tool S— Ftw P— Soi Soii T­ S-1-41 FMb.P— -1 Dw TyM U-M U,I- Antpe S�ItaCe cj. T�U.��U., N. (pollJP4 (.g) - No. (pcf) (pd) (ftgl P— N. 1 135c 145.0 35.0 0 snd gry 1 135.0 145.0 35.0 0.25 0 120 120 90 90 Global stability based on present soil conditions Global stability 1)asad on ru value or.251 Safety Factors Are Calculated By The Modified Bishop Method Safety Factors Are Calculated By The Modified Bishop Method i Proposed kesidence ZAsidence GSTABL7 v.2 FSmin=2.097 GSTABL7 v.2 FSmin=1.514 60 le 30 30 0 0 0 30 60 90 120 150 180 210 240 0 30 60 90 120 150 180 210 240 Note: Based on the propos ilU 0VLUC1%,rX L1 I will have a minor effect on the analyzed slope a 150 P The slope has been analyzed for static and seismic with an acceptable D Ty A141 s.� Peqk(A) 0.32ft) i — (P'� (P�lo ) N. kh C-f. OJCA(g)< snk!g�1 135.0 145.0 (3�ZO factor of safety achieved with a 50 ft setback. 120 go Global stability based on encountered oil conditions with d6sign acceleration Safety Factors Are Calculated By The Modified Bishop Method I i Proposed Residence GSTI-7 v.2 FSmin=1.336 iii 60 Slope Stability Results 3o L.Olson&Associates,I nc. Engineering,Planning and Surveying 0 2453 BETHEL AVENUE 0 30 60 90 120 ISO 180 210 240 P.O.BOX 637 Appendix PORT ORCHARD,WASHINGTON 98366-0637 B.1