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HomeMy WebLinkAboutGEOtech review SPI2003-00107 - SPI Letters / Memos - 10/8/2003 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Washington 98584 DATE: October 8`h 2003 INTER-DEPARTMENTAL COMMUNICATIONS TO: Grace'Miller, DCD- Planner FROM: Alan A. Tahja, P/W-Co. Hydr. Engr. WO#PLG-03 SUBJ: Geo-Tech Report Review NAME: Hamilton SFR&Hartstine Island SPI2003-00107 The geotechnical report prepared for the proposed residential development of the John&Donna Hamilton property located on Harstine Island, has been received and reviewed by Public Works. The report appears to satisfactorily address County requirements for geotechnical reporting. The report's author indicates that, in his opinion,the proposed development of the property will not cause stability problems for either the subject property or neighboring properties. From the contents of the report, I recommend accepting the report as satisfying the County's requirement(s) for stability investigation. Recommendations contained in the report should be incorporated into the site's development and made conditions for permit issuance. Recommendations of major concern are a 25' minimum building setback from the crest of the marine bluff, and a recommendation that roof and driveway stormwater runoff be tightlined to the base of the (marine) slope. With the engineer's recommendations incorporated into the site's development, stability issues appear to have been adequately addressed. 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. In summary, the geotechnical report appears acceptable, and the proposed FPA and residential development of the property should be allowed to proceed, subject to the engineer's recommendations. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sin rely, Alan A. Tahja File: H: \WP\GEO\Reviews\Hamilton.doc WORK ORDER - PUBLIC WORKS DEPT. Date: iv�(31 1 0 3 n Work Order r) PERMIT 5P1' oL03- lNumber. UJ ERequested by: iiiAuthorized by: Date: c1l) Rrype of Work: �HARGE TO: ui NAME C) AGENCY/COMPANY Q BILLING ADDRESS PHONE (B) Pub. Works Person In Charge: (c) Project Time Une: (from -to dates) 11#71 e- TO Project surt date: Estimated Firgsh Date: Apprmdrnate hours: ESTIMATED TOTAL$`S: E-- COST ESTIMATE (D) Employee lEaft Hours SUM31 Fringe% TOTAL t 10-9-0-3 EQUIPMENT USED: TOT Vs MATERIAL USED: �c .J,Y.;•r,G„.a-,<c:..,. ,,v,,.:•:.,:.,.-._-..-..v..�xz>;a.:: :w=:z::i.:?:i:s;+J'.^`?M:'"?.x::� ,3v>.;_:..,<-.,a�,,,..Xi:c;:v>:;:;:.M,. .,.- _. .: :.:-.::.:_.... fSx:'n;7!-mow-• 7F '�::..,: ..............�.�.....—.. •>....-.:moo+:-->:�-...)••... :�.-:�>.-:,-<�:J.'-:?:`:;8"-^�<.>::::::..::.:,�:.;;.:::...:.:.:.... J;:yi;:eV..;;.,�:: �'.,.. r;:;;f:.�l.':;",^-.<^.YT... -..AYE':-:�'.f rn.ewxevenJwk«wGwi.�^�vii•'aa47�r:`w.Miv. ...::..::... .. ���/.7�Vf ii..l .cam... 2-`.::^... "Z:;,3�.�: ::..< a�_...aY�� GFe`i.swr.QVY.�Y,CCar Y✓.eL>�i3f[tt✓J�C.C.,v...:.. � ,o v w..so t"''-ywa.` ... .,... �wK4-'ta:-:�n`).`�^��ii4le:Yf'c�i�R'iG`i�'a�.n�YS:wlis "<`�ir.-a-„-. a:��i3i.'eii��i�'-i':;�;<::µ,.> (F) Actual Cost $ BARS: PRGJ#-. DATE Emp" NUM dHours syt)(ow Frimm% TOTAL$ EQUIPMENT USED: at TOTAL S'S MATERIAL USED: TOTAL ALL (G) BILLED DATE INV 0 PAID DATE REC.0—CKN yoN-sTA c MASON COUNTY �P MC DEPARTMENT OF COMMUNITY DEVELOPMENT 4 O o N RE Planning Division N Y oy P 0 Box 279,Shelton,WA 98584 1864 (360)427-9670 Site Inspection October 09, 2003 JOHN HAMILTON US EMBASSY UNIT 3302 APO AA 34020 Case No.: SP12003-00107 Parcel No.: 221347690021 Project Description: DETERMINE SETBACKS, FROM SLOPE AND WATER Dear Applicant Pursuant to your application, a site pre-inspection (SPI)was performed on your property. Below you will find comments made regarding the proposed development and its critical values. In some cases, setbacks for development from shorelines, steep slopes, streams, and wetlands must be included in your specific proposal; these setbacks are included as part of the comments listed below. This information is based on County and State regulations as they exist to date. These regulations may change and may affect the requirements for development of the subject property. Please contact me at(360) 427-9670, ext 360 if you have questions. Sincerely, Grace Miller Land Use Planner Mason County Planning Department 10/9/2003 1 of 4 SP12003-00107 Site Inspection 10/9/2003 Case No.: SP12003-00107 Comments: The property was inspected by Planner, Grace Miller, on July 7, 2003. The property is located within a Rural shoreline environment as regulated by the Mason County Shoreline Master Program and is zoned as Rural Residential 5. Staff walked the recently graded access driveway that appears to have been done by the septic installer. This access stops in an area where presumably the applicants would like to place the residence. The site plan does not include dimensions of the property or a proposed site development plan. Between where the driveway ends now and the top of the marine bluff, the vegetation consisting of huckleberry and salal, is too thick to take measurements through to the top of the bank. Staff is normally able to forge my way through dense vegetation but in this case it is just too tall and thick. Although staff could see the adjacent residence to the north, it was not possible to view the residence on the third lot to the south. Staff will assume it is over 150' from the site. The shoreline setback is established by two chapters of the Mason County Resource Ordinance, the Landslide Hazard Area Chapter and the Fish and Wildlife Habitat Conservation Areas Chapter. Pickering Passage is considered to be a Type I water with a minimum development and buffer setback of 100' from the Ordinary High Water Mark (OHWM). The OHWM is located up on the side of the bank off the beach and can ususlly be measured from the top of the bank into the lot. In cases where there is an adjacent residence within 150' of the proposed building site, such as there is to your north, the setback line is drawn between that roofline (on the waterward side of their house), to a default minimum setback of 100' on the lot to the south of yours. The measurement taken on your lot as this setback line crosses it, is your minimum shoreline setback. Staff was not able to physically take that measurement because of the dense vegetation. Enclosed please find the applicable chapter of the Mason County Resource Ordinance with the section on how to draw the shoreline setback highlighted. Please let me know if you have any questions interperting the example drawings and text. Staff recommends that once enough of the vegetation on this line is removed so that you are able to draw the line, you can mark it on the ground and I will conduct another site inspection to assure its adequacy. The site plan that you submitted does not show the width of the lot. The minimum sideyard setback is 10% of the width of your lot. 10/9/2003 2 of 4 SP12003-00107 Site Inspection 10/9/2003 Case No.: SP12003-00107 For example, if the lot is 100' wide, your side yard setbacks from the roofline to the property lines is 10'. There is a minimum 25' frontyard setback for all structures to the easment road. The property is also located within 250' of a potential landslide hazard area. The marine bluff is considered a potential landslide hazard area. Because the slopes exceed 40%, a Geotechnical Report will be required prior to all development of the site. The report should address the grading, location of the driveway, septic system, and all structures. Please see the enclosed landslide hazard area chapter of the Mason County Resource for the specific criteria, contents of the report and qualifications of the preparer. We have to refer you to the phone book for geologists. The closest to your property are located in Olympia. There is a 50' minimum vegetation buffer between the top of the slope and all development. The existing native vegetation buffer that will need to be maintained is going to be that measurement taken from the top of the bank to the line drawn between the adjacent residence and 100' back on the next lot to the south. Staff expects this measurement to be a diagonal line across your property and greater than 50'. Because it is most likely going to be greater, the vegetation between the top of the bank and this shoreline setback must be maintained as it exists. Please see the "Activities that do not require a Mason Environmental Permit" for tree limbing and removal, ect.. Thank you for the very good directions and let me know if you have any questions. Thank you. ADDENDUM TO PRE-INSPECTION FINDINGS, 10/9/03: Planning staff recieved the Geotechnical Report that was prepared by Harold Parks of Geotechnical Testing Lab,dated 8/25/03. Staff forwarded the report to Allan Tahja of the Public Works Department and he has completed his review. Please see attached comments. The recommendations made by the geologist will be made conditions of potential permit applications. A copy of the report has been forwarded to the Environmental Health Specialist who will be reviewing your septic system application so they are aware of compliance with the Landslide Hazard Area Chapter requirements. 10/9/2003 3 of 4 SP12003-00107 Site Inspection 10/9/2003 Case No.: Sp12003-00107 The Report will be placed in your parcel file awaiting potential in-coming building permits. If you have any questions please let me know. CC: Cindy Waite, EH Specialist Parcel file 10/9/2003 4 of 4 SP12003-00107 Case Activity Listing 101312003 2:06:20PM IPO Case #: SPI2003-00107 Assigned Done Activity Description Date 1 Date 2 Date 3 Hold Disp To By Updated Updated By SPIA600 SPI Letter-Field Review 7/16/2003 None DONE GBM GBM 7/16/2003 GBM The property was inspected by Planner,Grace Miller,on July 7,2003. The property is located within a Rural shoreline environment as regulated by the Mason County Shoreline Master Program and is zoned as Rural Residential 5. Staff walked the recently graded access driveway that appears to have been done by the septic installer.This access stops in an area where presumably the applicants would like to place the residence.The site plan does not include dimensions of the property or a proposed site development plan.Between where the driveway ends now and the top of the marine bluff,the vegetation consisting of huckleberry and salal,is too thick to take measurements through to the top of the bank.Staff is normally able to forge my way through dense vegetation but in this case it is just too tall and thick. Although staff could see the adjacent residence to the north,it was not possible to view the residence on the third lot to the south. Staff will assume it is over 150'from the site.The shoreline setback is established by two chapters of the Mason County Resource Ordinance,the Landslide Hazard Area Chapter and the Fish and Wildlife Habitat Conservation Areas Chapter. Pickering Passage is considered to be a Type I water with a minimum development and buffer setback of 100' from the Ordinary High Water Mark(OHWM).The OHWM is located up on the side of the bank off the beach and can ususlly be measured from the top of the bank into the lot. In cases where there is an adjacent residence within 15 0'of the proposed building site,such as there is to your north,the setback line is drawn between that roofline(on the waterward side of their house),to a default minimum setback of 100'on the lot to the south of yours.The measurement taken on your lot as this setback line crosses it,is your minimum shoreline setback.Staffwas not able to physically take that measurement because of the dense vegetation. Enclosed please find the applicable chapter of the Mason County Resource Ordinance with the section on how to draw the shoreline setback highlighted. Please let me know if you have any questions interperting the example drawings and text. Staff recommends that once enough of the vegetation on this line is removed so that you are able to draw the line,you can mark it on the ground and I will conduct another site inspection to assure its adequacy. The site plan that you submitted does not show the width of the lot.The minimum sideyard setback is 10%of the width of your lot.For example,if the lot is 100'wide,your side yard setbacks from the roofline to the property lines is 10'.There is a minimum 25'frontyard setback for all structures to the easment road. The property is also located within 250'of a potential landslide hazard area.The marine bluff is considered a potential landslide hazard area.Because the slopes exceed 40%,a Geotechnical Report will be required prior to all development of the site.The report should address the grading,location of the driveway,septic system,and all structures.Please see the enclosed landslide hazard area chapter of the Mason County Resource for the specific criteria,contents of the report and qualifications of the preparer.We have to refer you to the phone book for geologists.The closest to your property are located in Olympia. There is a 50'minimum vegetation buffer between the top of the slope and all development.The existing native vegetation buffer that will need to be maintained is going to be that measurement taken from the top of the bank to the line drawn between the adjacent residence and 100'back on the next lot to the south. Staff expects this measurement to be a diagonal line across your property and greater than 50'. Because it is most likely going to be greater,the vegetation between the top of the bank and this shoreline setback must be maintained as it exists.Please see the"Activities that do not require a Mason Environmental Permit"for tree limbing and removal,ect. Thank you for the very good directions and let me know if you have any questions.Thank you. SPIA400 Miscellaneous Action 9/24/2003 None DONE CMH 9/24/2003 CMH Geotech report submitted-forwarded to Grace. �r 3 Page 2 of 2 CaseActivity..rpt Case Activity Listing 10/3/2003 2:06/2003 IF914 Case#: SPI2003-00107 Assigned Done Activity Description Date l Date 2 Date 3 Hold„ By Updated Updated By SPIA010 Application Received 6/18/2003 0 IS 2003 None DONE hS 61Si2003 KS SPIA100 Site Inspection 6/18/2003 7/7/2003 None DONE GBM GBM 7/16/2003 GBM Page 1 of 2 caseAc6vity„rpt n� Geotechnical Report ' Parcel #221347690021 Hartstene Island Mason County, WA Prepared for John & Donna Hamilton by Geotechnical Testing Lab Olympia, WA August 25, 2003 GEOTECHNICAL TESTING LABORATORY JOHN HAMILTON U.S. EMBASSY UNIT 3302 APO, AA 34024 Re: Geotechnical Report Hartstene Island Parcel 221347690021 N47016.082' W122054.983' INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed single-family residence located along the western shore of Hartstene Island in Mason County,Washington. The location of the site is shown relative to the surrounding area on the Vicinity Map, Figure 1 View Looking East at Proposed Building Location Aerial Photo Our understanding of the project is based on our discussions with you and our explorations and review of the site. The site is accessed by a driveway from Sunset Hill Road. A septic system will be located onsite; drinking water will be provided by an onsite well. Stormwater runoff from the site, roof and hard surfaces, will be collected and controlled. The general layout of the site is shown on the Site Map, Figure 2. We further understand that minor grading will be required at the site to reach design grade. In general, grading will consist of the excavation of the foundation material and driveway. The site slopes gently toward the west except for the steep coastal bluff. The steepest slope(coastal bluff)measured on the site was in excess of 100 percent. Therefore, Mason County requires that a geotechnical report be prepared in accordance with the Critical Areas Ordinance. 10011 Blomberg Street SW, Olympia,WA 98512 1 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY View Looking Southeast The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing geotechnical recommendations and design criteria for the project and to satisfy the requirements of the Mason County Critical Areas Ordinance. Geotechnical Testing Laboratory is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: 1. Review the available geologic,hydrogeologic, and geotechnical data for the site area. 2. Conduct a geologic reconnaissance of the site area. 3. Investigate shallow subsurface conditions at the site by observing the coastal bluff and the exposed soil in test pits. 4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations. 5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria(including hillside grading), suitability of on-site soils for use as structural fill,temporary and permanent cut and fill slopes,drainage and erosion control measures. 6. Provide recommendations and design criteria for the structural foundation and floor slab support, including allowable bearing capacity, subgrade modulus, lateral resistance values and estimates of settlement. SITE CONDITIONS SURFACE CONDITIONS The proposed building site is located in an area of sparse residential development in the Puget Sound glacial upland. The site has western exposure, overlooking the Pickering Passage. The Hidden Acres Subdivision is accessed from Sunset Hill Road on the western side of Hartstene Island. The general layout of the site is shown on the Site Plan, Figure 2. We conducted a reconnaissance of the site area on July 30, 2003. Onsite elevations range from approximately 0 feet to 134 feet. The proposed building location gently slopes toward the west until the coastal bluff drops to the beach. The building area of the site has vegetation indigenous to the northwest. The vegetation includes a copse of cedar, fir, madrona and some small alder trees as well as ferns, blackberry, salal,and grasses. 10011 Blomberg Street SW, Olympia,WA 98512 2 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY At the time of the site visit,we observed no evidence of surface erosion. No evidence of deep-seated slope instability was observed on the site slopes or areas adjacent to this site at the time of our investigation. The general topography of the site area indicates that surface drainage flows toward the west. No evidence of surface water flow was observed in the site area at the time of our reconnaissance. SITE GEOLOGY The site is generally situated within the lower Puget Sound glacial upland. The existing topography, as well as thei surficial and shallow subsurface soils in the area, are the result of the most recent Vashon stade (stage) of the Fraser glaciation that occurred between about 10,000 and 12,000 years ago, and weathering and erosion that has occurred since. A description ` of the surficial soils is included in the "Site Soils" section of this report. In general, the soils on the site are predominantly represented by cemented Vashon glacial till. Cemented Glacial Till Under Cutting by Wave Action SITE SOILS .., The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as a Harstine gravelly sandy loam, 15 to 30 % slopes (Hb). The Harstine soils are described as "well-drained, brown soils of the uplands. They have developed from softly cemented, sandy glacial till that high in particles of quartzite and granite. The Harstine soils�•;Y F__ .,> - �, contain more gravel than the Indianola soils and have harder,or more compact, underlying till. This soil is on the stronger slopes between the high moraines of the Harstme gravelly sandy loam, 5 to 15 % slopes, and Puget Sound. At depths of y 24 to 32 inches, there is an abrupt change to weakly cemented Harstine Gravelly Sandy Loam till. Natural drainage is described as good. Occurrence of a high water table is none." 10011 Blomberg Street SW, Olympia,WA 98512 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY The Coastal Zone Atlas, Volume 9, Mason County (MA-17) maps the site as Vashon till(Q,,). Till is tough,dense material, of low permeability. It provides excellent foundation support. Slope stability is described as "intermediate" at the building location, but "unstable" along the coastal bluff. Sloughing or slumping was not evident along the coastal bluff. SUBSURFACE EXPLORATIONS Subsurface conditions at the site were evaluated by observing the exposed foundation material and the exposed coastal bluff. Cemented glacial till was observed at the building location. Well drilling records for the area indicate that the glacial till Ceme»ted Glacial Till extends at least 15 feet below sea level. SUBSURFACE CONDITIONS In general, undisturbed cemented glacial till was observed throughout both the site and the proposed building location. Groundwater seepage was not observed at the site. Seasonally perched groundwater conditions are not expected during periods of extended wet weather. Well drilling records for the area indicate that groundwater is found at least 80 feet below the ground surface. SLOPE STABILITY Slopes in excess of 100 percent were observed on the site. Since slopes of 40 percent or greater with 10 feet or more of vertical relief occur on portions of the site, Mason County requires that a geologic hazards report be completed according to the Critical Areas Ordinance. The near-surface till soils are in a dense to very dense condition except at the ground surface. The surficial soils are generally in a medium dense condition. In general, the undisturbed native soils of the site consist of a mixture of variable amounts of sand, silt, and gravel. These soil materials are in a dense condition except where they have been disturbed by weathering activity. These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or significant erosion was observed at the site at the time of our investigation. Weathering, erosion, and the resultant sloughing and shallow landsliding are natural processes that can affect steep slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone, which has been disturbed and has a lower strength. Evidence of minor surficial erosion, raveling and sloughing was not observed on the lower coastal bluff at the time of our investigative visit. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles, and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced by encouraging vegetation and discouraging runoff from the steep slope. A drainpipe can be used to control the flow from top to bottom. Erosion control recommendations for the sloping areas are provided in the"Building Setback"and"Erosion Control"sections of this report. 10011 Blomberg Street SW, Olympia,WA 98512 4 Phone#: (360) 7544612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on the results of our site reconnaissance and subsurface observations, and our experience in the area, it is our opinion that the site is suitable for the proposed single-family residence. The slope is stable relative to deep-seated instability and will not be affected by the proposed single-family residence. Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope stability. In general, the site soils are suitable for use as structural fill material. Although saturated soil conditions are not associated with these soils during or following extended periods of rainfall, we recommend that earthwork be undertaken during favorable weather conditions to reduce grading time and construction costs. Conventional construction equipment may be utilized for work at the site. Conventional spread footings may be utilized for support of the structure. We do recommend that roof and footing drains be installed. Footing and roof drains should not be connected. A vapor barrier is recommended for all slab-on-grades. Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed single-family residence are presented below. LANDSLIDE—EROSION HAZARD AREAS Classification The Mason County Critical Areas Ordinance (17.01.100) defines a landslide hazard area as one containing slopes equal to or greater than 40 percent with more than a 10-foot vertical relief. The western slope is in excess of 100 percent and the vertical relief is in excess of 10 feet. Based on this, this site does meet the technical criteria of a landslide hazard. The Relative Slope Stability of the Southern Hood Canal Area, by Smith&Carson(1977), categorizes the site as a Class 1 and Class 2. The classifications indicate the site is stable under normal conditions. The Mason County Critical Areas Ordinance(17.01.104)defines an erosion hazard area as: Areas in Mason County underlain by soils which are subject to severe erosion when disturbed. Such soils include, but are not limited to, those for which potential for erosion is identified in the Soil Survey of Mason County, USDA Soil Conservation Service, 1960, or any subsequent revisions or addition to this source. These soils include, but are not limited to, any occurrence of River Wash ("Ra') or Coastal Beaches rco and the following when they occur on slopes 1 S%or steeper: a. Alderwood gravelly sandy loam ("Ac"and "Ad') b. Cloquallum silt loam ("Cd') c. Harstine gravelly sandy loam ("Hb') d. Kitsap silt loam ("Kc') The soils at the site are mapped as Harstine gravelly sandy loam (Hb). This site does meet the technical criteria of an erosion hazard area. With proper drainage control and re-vegetation, erosion hazard concerns may be overcome. 10011 Blomberg Street SW, Olympia,WA 98512 5 Phone#: (360) 754-4612 Fax#: (360) 754-4848 - r� wd L GEOTECHNICAL TESTING LABORATORY Slope Stability Based on our field observations, explorations and our experience with the soil types encountered on the property, we conclude that although portions of the slopes on the lot exceed 100 percent,they are generally stable relative to deep- seated failure in their present configuration. The following figure represents a shear angle for the glacial till. Shear angle and cohesion are variables used to model the site. Peak Shear Stress vs. Normal Stress 3" 41° 25M 0Z c a �.. 2000 a a as 1500 a m L U) 1000 Q1 a 500 —0 1/4 ton f 1/2 ton 0 --�1 ton 0 500 1000 1500 2000 2500 3000 Normal Stress(ps1) These processes can be managed and the risk reduced through proper construction of the residence. Erosion control recommendations in the slope and buffer areas are provided in the `Building Setback" and "Erosion Control" sections of this report. Building Setback Slope stability was modeled using the GEO-SLOPE/W program (version 5.13) in both static and dynamic conditions (ce=0.3). Factors of safety were determined using Bishop's,Janbu, and the Morgenstern-Price methods. The site geology was modeled using a monolithic layer of glacial till. The glacial till was determined to have a unit weight of 132 pcf, cohesion of 200 psf, and a shear angle (�) of 41°. Under static conditions, the slopes remained stable to deep-seated and shallow failure. Under dynamic loading, the 4096 computations demonstrated that the slope might be susceptible to surficial raveling; large deep-seated failure was not demonstrated by our model. The following figure illustrates--a manent_F.S. for o_cress-sections.. This solution is the lowest factor of safety generated 10011 Blomberg Street SW, Olympia,WA 98512 6 Phone#: (360)7544612 Fax#: (360) 7544848 i •. A' vL } owsoe v t • - i - 1_ t 77 GEOTECHNICAL TESTING LABORATORY I . . . . . . . . . . . Hamilton - Analysis Method: Morgenstern-Price Direction of Slip Movement: Left to Right , Slip Surface Option: Grid and Radius Seismic Coefficient: Horizontal and Vertical 200 160 ISO 140 !/ . � 120j L u 100 > B0 ~ m w 60 Harstine G.S.L. 40 Soil Model: Mohr-Coulomb Unit Weight: 132 20 Cohesion: 200 0 Phi:41 —— _p 0 50 100 150 200 250 300 3W 4W 450 5W sm 6W Distance(R) A building setback from landslide hazard areas is required unless evaluated and reduced by an engineering geologist or a licensed professional engineer. Based on our geotechnical evaluation of the site and our experience in the area, a building setback will be needed for this lot along with the use of pin-pile to support the footing. 3 Jpottom of the footing should otherwise be observed. The building setback may e measurea from me Bottom of the footing to the face of the steep slope, in accordance with the Unified Building Code. As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are natural processes that affect slope areas. No significant surficial raveling or sloughing was observed in the sloping portions of the site. To manage and reduce the potential for these natural processes, we recommend the following: 1. No drainage of concentrated surface water or significant sheet flow onto the sloped areas. 2. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill. linghould be collected and tight-lined to the base of the slope. SEISMIC—LIQUEFACTION HAZARD According to the Seismic Zone Map of the United States contained in Figure 16-2 of the 1997 UBC (Uniform Building Code),the project site is located within Seismic Risk Zone 3. Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic Soil Profile Type Sc, for Very Dense Soil, as defined by Table 16-J (UBC). This is based on the range of SPT 10011 Blomberg Street SW, Olympia,WA 98512 7 Phone#: (360) 7544612 Fax#: (360) 754-4848 Aftk Ank tic �: ;^ _ _ L. L;• � - ! � � � Vie. 27 --M► IV GEOTECHNICAL TESTING LABORATORY (Standard Penetration Test) blow counts and/or probing with a '/z-inch diameter steel probe rod. The shallow soil conditions were assumed to be representative of the site conditions beyond the depths explored. Based on our review of the subsurface conditions, we conclude that the site soils are not susceptible to liquefaction. The near-surface soils are generally in a dense condition and the static water table is located well below the surface (over 80 feet deep). Shaking of the already dense soil is not apt to produce a denser configuration and subsequently excess pore water pressures are not likely to be produced. EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development. Removal of natural vegetation should be minimized and limited to the active construction and living areas. Yard landscaping around the home is permissible, but understory growth on the slopes should be encouraged as much as possible as a deterrent to erosion. Trees located on steep slopes may be removed only if the stumps remain to deter erosion. Temporary and permanent erosion control measures should be implemented and maintained during construction and/or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include, but not be limited to, silt fences, berms and swales with ground cover protection in exposed areas. A typical silt fence detail follows this report. Any re-contouring of the site will create a need for erosion control measures as listed above. EARTHWORK SITE PREPARATION All areas to be excavated should be cleared of deleterious matter including any existing structures, debris, duff, and vegetation. Based on our observations, we estimate that stripping on the order of 6 to 8 inches will be necessary to remove the root zone and surficial soils containing organics. Areas with deeper, unsuitable organics should be expected in the vicinity of depressions or heavy vegetation. Stripping depths of up to 1 foot may occur in these areas. These materials may be stockpiled and later used for erosion control and landscaping. Materials that cannot be used for landscaping or erosion control should be removed from the project site. Where placement of fill material is required, the exposed subgrade areas should be proof-rolled to a firm and unyielding surface prior to placement of any fill. We recommend that trees be removed with the roots, unless located on a slope. Excavations for tree stump removal in any building area should be backfilled with structural fill, compacted to the density requirements described in the"Structural Fill'section of this report. If structural fill is needed, we recommend that a member of our staff evaluate the exposed subgrade conditions after removal of vegetation and topsoil stripping is completed. Any soft, loose or otherwise unsuitable areas delineated during foundation preparation or probing should be compacted, if practical, or over-excavated and replaced with structural fill, based on the recommendations of our report. 10011 Blomberg Street SW, Olympia,WA 98512 8 Phone#: (360) 754-4612 Fax#: (360)754-4848 1 7 , ro. GEOTECHNICAL TESTING LABORATORY STRUCTURAL FILL All fill material should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least 90 percent of MDD (maximum dry density as determined in accordance with ASTM D-1557) to within 2 feet of subgrade and 95 percent MDD in the upper 2 feet. The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines (material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend the use of well-graded sand and gravel with less than 5 percent (by weight) passing the No. 200 sieve based on that fraction passing the'/4-inch sieve. If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a somewhat higher(up to 10 percent)fines content will be acceptable. Material placed for structural fill should be free of debris, organic matter,trash and cobbles greater than 6 inches in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction. Suitability of On-Site Soils as Fill On-site Harstine soils may be used as structural fill. In general, the native soils (gravelly sandy loam) encountered on the site should have less than 10 percent fines(material passing the US No. 200 Sieve)and are suitable for use as structural fill. CUT AND FILL SLOPES All job site safety issues and precautions are the responsibility of the contractor providing services and or work. The following cut/fill slope guidelines are provided for planning purposes. Temporary cut slopes will likely be necessary during grading operations. As a general guide, temporary slopes of 1.5 to 1 (horizontal to vertical) or flatter may be used for temporary cuts in the upper 3 to 4 feet of the glacially consolidated soils that are weathered to a loose/medium dense condition. Temporary slopes of 1 to 1 or flatter may be used in the unweathered dense to very dense sands and gravels or till. These guidelines assume that all surface loads are kept at a minimum distance of at least one half the depth of the cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slopes will be necessary where significant raveling or seepage occurs. Subsurface drainage may be required if seepage areas are discovered. Surface drainage should be directed away from all slope faces. Some minor raveling may occur with time. All slopes should be seeded as soon as practical to facilitate the development of a protective vegetative cover or otherwise protected. 10011 Blomberg Street SW, Olympia,WA 98512 9 Phone#: (360) 754-4612 Fax#: (360)754-4848 _ '+, i a. '�' v ` '. i _ fir• � N ti � `�• c. - - .. _ - yam. ctzL: _ M r. GEOTECHNICAL TESTING LABORATORY FOUNDATION SUPPORT Where foundation elements are located near slopes of 5 percent or more, the footings should be located a minimum of 2 times the footing width from the slope face (horizontally), and founded in medium dense or denser native soils or properly prepared structural fill. We recommend a minimum width of 2 feet for isolated footings and at least 16 inches for continuous wall footings. Footings founded as described above can be designed using an allowable soil bearing capacity of 2,000 psf(pounds per square foot)for combined dead and long-term live loads in areas of medium dense to dense soils. The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be increased by one-third for transient loads such as those induced by seismic events or wind loads. Lateral loads may be resisted by friction on the bases of footings and floor slabs and as passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.25 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 300 pcf(pounds per cubic foot). We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions,with differential settlements between comparably loaded footings of%inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation sub-grade during construction could result in larger settlements than predicted. FLOOR SLAB SUPPORT Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared as described in the"Structural Fill"section of this report. We recommend that floor slabs be directly underlain by a minimum 6- inch thickness of coarse sand and/or gravel containing less than 5 percent fines (by weight). The drainage material should be placed and compacted to an unyielding condition. A synthetic vapor barrier should be used for the control of moisture migration through the slab, particularly where adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier could result in wet spots on the slab,particularly in storage areas. RETAINING WALLS Retaining walls may be utilized on the sloping portion of the site to retain fill material,or for below grade parking garage or basements. The lateral pressures acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space is backfilled with clean granular, well-drained soil (washed rock), the design active pressure may be taken as 35 pcf(equivalent fluid density). This design value assumes a level backslope and drained conditions as described below. 10011 Blomberg Street SW, Olympia, WA 98512 10 Phone#: (360) 754-4612 Fax#: (360) 754-4848 Ly _ 1 l GEOTEC14NICAL TESTING LABORATORY Retaining walls located on or near the toe of a slope that extends up behind the wall should be designed for a lateral pressure, which includes the surcharge effects of the steep slope in proximity to the wall. Although not expected at this site,the following data is provided for planning purposes. For an irregular or composite slope, the equivalent slope angle may be determined by extending a line upward from the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical) to a point where the line intersects the ground surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by the percentage given in the following table: SLOPE INCLINATION: EQUIVALENT FLUID PRESSURE Slope Angle Percent Increase Equivalent Fluid Pressure Horizontal 0% 35 pcf 3H:1V 25% 44 pcf 2H:1V 50% 53 pcf 1H:1V 75% 61 pcf If the walls are greater than 8 feet in height, exclusive of the footing, additional design considerations should be applied. Positive drainage, which controls the development of hydrostatic pressure, can be accomplished by placing a zone of coarse sand and gravel behind the walls. The granular drainage material should contain less than 5 percent fines. The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should also extend from the base of the wall to within 1 foot of the top of the wall. The drainage zone should be compacted to approximately 90 percent of the MDD. Over compaction should be avoided as this can lead to excessive lateral pressures. A perforated PVC pipe with a minimum diameter of 4 inches should be placed in the drainage zone along the base of the wall to direct accumulated water to an appropriate discharge location. We recommend that a non-woven geotextile filter fabric be placed between the drainage material and the remaining wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the drainage zone can with time, reduce the permeability of the granular material. The filter fabric should be placed in such a way that it fully separates the drainage material and the backfill, and should be extended over the top of the drainage zone. Lateral loads may be resisted by friction on the bases of footings and as passive pressure on the sides of footings and the buried portions of the wall. We recommend that an allowable coefficient of friction of 0.50 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 35 pcf(pounds per cubic foot). Factors of safety have been applied to these values. RETAINING WALL ALTERNATIVES Typically, reinforced-earth block wall systems are more cost effective for long-term walls than the other options. Specific design criteria for these options can be provided at your request by the block manufacturers. 10011 Blomberg Street SW, Olympia,WA 98512 11 Phone#: (360)754-4612 Fax#: (360) 754-4848 !i3� 1, .. (". -. G I,JEJ'R .. .., i { :!� !ter '• ...1 "�/5 • - ' .,.ti' ::Y.,?. ;:�.. 'i ,,,ti.'I• .'�: . :(�� %h '! �: 1. f-; .i2 �+rll"3r: ,jGjT`' ,: .. �.. ..1; .. .17 ,;try:• !.'l",/I:r, ",..it ;e' .. :1 1E. ;fti3j'a.- )(' %r:!�, Ala. DqUIR JiC.iT.Son mle w- , , '}f, '10 , nis &Cr - ,.+r.;} :f t' :•ct: 1� T'L,')+; �? . ..'11'I:� iv.!{Ktatlt� +_> ! .! r 'LI,, T1. 'Dro ..',; .,. _a, ?' _,' ,. i Jr ud )+ e• aT u.. . ,. ,:a• ,- • 9, Ts.:. sC i I I:�1'. r'}! 'l.. . . G_1 ,-'tf,f)J:/ n .)'•�. P5ll.:ir? i'i i/• ! I t '�°'.T )A .W*"01 1 �n� I...Y .:'t 'J`11-E.i+'. r S 77 i AL: 1 r , { s,i1E:•iJ i;P)L..f'1`;,tit;=> >!� :f F lr! ;1 ;E l 1 - � _ t3 ti) `1�trif y'%",'s .. »�`I . 'II .. � !ir'. 1',it,.;'; Af." )` ! JL 'j J'., i};"��.. ;:� rir J'1ii22 i 3Ci'Weo b it j+ it{R,.ai "31i.' IV. JCliv ,r,,.(2T1 .i1 J'/1'• .r `j ;!"''sT. . EiF,;t: 8J' '1?.:,7`:�:: `;i„ •rf:. I:...:1J1. 3,tTrfilS"It� .,',t -jr!" •.k:'y rr. l.' rn Eir :;. • . -Ail • ri.:�i.J"L!}fi� ;}.,.c -,' "TTS:.;{ .{r i +li;'' :L i:, !�' : :ill `:) ,C•I. 1 fig'. r t: ., :1� . lift 'if�' Sal)l� PJ�,'J!Y`i ;,,/1new +11 ii:`)I r:S) AT %i. !..'n r ve hurl,J: ffort'i!' '?1C )- ' } (101A Ma It's Ii ii�i(1!!t iPa Vl "-'r- ':ill f,l'. :i}._S 0.'?E::)) ;; '7E irs•i1,111 !1 )oil.-. ;'.E,?;.! t 'fJ »' IL!i, "i(if;i r. ':, l a" } _)V'. 17, 1 To i.. -,;.1 r11i IC?.%+; frpt}r iat? Iey Fit— ir . 0 j ! :{,?tU 10 emu( J;(Iw isc ',, Am? ;7'r ') 7:if�1'• _. •/. ,r l': 'i, ., ..r 'ra _lu c';N[ tl::'. .!�U;(•I (?.1> ..�. S(;i;ti_ ,Ij. r.? .., �, -.f', .. .: �. "�' .. . . t£j`.. I':'i(• ..iE:_311-�' �r,i l '.r-. IX:I;•.:.. ., ', w.e.-..r........�.».....�...•...r..wr+�.......w• pw.r.....,...,.:.....•... hwi/wrw...,►.r...�►.......«.,,..i«..�.r..ws�w....�.....,e,ro•..•ww•�r�..w•r..w.•..n.....�,+.-.a --. GEOTECHNICAL TESTING LABORATORY SITE DRAINAGE All ground surfaces, pavements and sidewalks should be sloped away from the residences and associated structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch basins and tight lined to the base of the bluff. We recommend that conventional roof drains be installed. Footing drains shall be installed for the home and garage. The roof drain should not be connected to the footing drain. For footing drains,the drain invert should be below the bottom of the footing. lawn areas should be closely monito-r6d. We do not expect any adverse affects on the recharge condition of the groundwater system. LIMITATIONS We have prepared this report for the use of John Hamilton and members of his design team,to use in the design of a portion of this project. The data used in preparing this report, and this report, should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and our site reconnaissance, and should not be construed as a warranty of the subsurface conditions. Sufficient consultation with our firm during construction should continue,to confirm that the conditions encountered are consistent with those indicated by our observations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with our specifications. If our analysis and recommendations are followed, we do not anticipate any on site or off site impact from the construction. It is our conclusion that potential landslide hazards from the landslide area can be overcome so as not to cause harm to property, public health and safety, or the environment. The scope of our services does not include services related to environmental remediation and construction safety precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures,except as specifically described in our report for consideration in design. If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications,as appropriate. `•o� Was 0 Respectfully, GEOTECHNICAL TESTING LAB aecl Go(-"' Harold Parks, L.G., L.E.G. Senior Engineering Geologist 10011 Blomberg Street S ympia,WA 98512 12 Phone#: (360) 754-4612 Fax#: (360) 754-4848 • t� Mg�'�. GEOTECHNICAL TESTING LABORATORY Filter fabric material in continuous rolls. Use staples or wire rings to attach fabric to wire. Wire mesh support fence for filter fabric A —A�— —1 / z 2 ft. Ground surface 5 ft. 2.5 ft. 6 ft. max. Bury bottom of filter material in 8 2 in. by 2 in. wood posts. in. by 12 in.trench Standard or better or equivalent Wire mesh support fence(to be located on the downhill side of the filter fabric) 6 in. Filter fabric material 2 ft. 5 ft. Provide washed gravel backfill,3, 12 in. in. / to 3 in. in trench and on both sides of filter fence fabric on the surface —� 8 in. min. Bury bottom of filter material in 8 in. 2 in. by 2 in. by 5 ft. wood posts by 12 in. trench Standard or better or equivalent SILT FENCE DETAIL Not to scale 10011 Blomberg Street SW, Olympia,WA 98512 13 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY Geotechnical General note1 SOIL PROPERTY SYMBOLS N: Standard"N"penetration: Blows per foot of 140 pound hammer falling 30 inches on a 2 inch O.D. split-spoon. Q.: Unconfined compressive strength,tons/ft'- Qp: Penetrometer value,unconfined compressive strength, Ibs/ft2 V: Vane value,ultimate shearing strength, Ibs/ft2 M: Water content,% LL: Liquid limit,% PI: Plasticity index,% D: Natural dry density, lbs/ft3 WT: Apparent groundwater level at time noted after completion. DRILLING AND SAMPLING SYMBOLS SS: Split-Spoon- 1 3/8"I.D., 2"O.D.,except where noted. ST: Shelby Tube-3"O.D.,except where noted. AU: Auger Sample. GB: Grab Sample. DB: Diamond Bit. CB: Carbide Bit. WS: Washed Sample. RELATIVE DENSITY AND CONSISTENCY CLASSIFICATION Terms(Non-Cohesive Soils) Standard Penetration Resistance Very Loose 0-2 Loose 2-4 Slightly Compact 4-8 Medium Dense 8- 16 Dense 16-26 Very Dense Over 26 Terms(Cohesive Soils) Q._(tons/ft2) Very Soft 0-0.25 Soft 0.25-0.50 Firm(Medium) 0.50- 1.00 Stiff 1.00-2.00 Very Stiff 2.00-4.00 Hard 4.00-+" PARTICLE SIZE Boulders 8 in. + Coarse Sand 5 mm-0.6 mm Silts 0.074 mm -0.005 mm Cobbles 8 in.- 3 in. Medium Sand 0.6 mm -0.2 mm Clays 0.005 mm&Smaller Gravel 3 in.-5 mm Fine Sand 0.2 mm -0.074 mm - — _ 10011 Blomberg Street SW,Olympia, WA 98512 Phone##:(360)7544612 Fax#: (360)7544848 � � / •• if it C . � • - • . . ': Geotechnical Testing Laboratory Geotechnical Services QA/QC Services W Testing Services V 10011 Blomberg St.SW QOlympia,WA 98512 Phone:(360)754-4612 rn Fax:(360)754-4848 P Date: 07/30/2003 QDesigned by: ILL Drawn by:I Checked by:: LL W Dwg#:07-30-03-052 TP > Z T A Z W f- X U � � W PROJECT NAME: 0 10 20 30 40 50 60 70 / �. r1 80 DONNA HAMILTON 0— 9 100 110 120 1 0 HARTSTENE ISLAND,WA PARCEL 221347690021 Revisions: NORTH SCALE 1"=40' C.I. =2' SCALE:1 inch=40 feet DATUM ASSUMED ' THIS IS NOT A SURVEY FIGURE 2 0 10 20 30 40