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Home My WebLink AboutBLD2009-00088 Geotechnical Report • GeoR€ urces, LLC Ph. 253-896-1011 5007 Pacific Hwy. E., Ste. 20 Fx. 253-896-2633 Fife, Washington 98424-2649 March 04, 2009 The Rembaugh's CEDV 1 ; c/o Linda! Cedar Homes 3726 Pacific Highway East Tacoma, WA 98424 MAR 2 4 2C"1 (253) 922-0220 �1 ' Attn: Mr. Bud Gallup EFFC C9IFTY DCD Geological Assessment— Geotechnical Report Proposed Single Family Residence 131 Shore Drive Jefferson County, Washington PN: 983401-310, -313 Job#: Lindal.Rembaugh.LHGL INTRODUCTION This report presents the results of our landslide hazard assessment for the proposed single-family residence to be constructed at 131 Shore Drive in the Port Ludlow Area of Jefferson County, Washington. The location of the site is shown on the Vicinity Map, Figure 1. We completed our site evaluation on March 04, 2009. Based on our discussions with you, we understand that you propose to replace the existing cabin with a new single-family residence with and deck. The location of the new residence will be in the upper, western portion of the lot, in the approximate location of the existing cabin, using conventional construction practices. Grading at the site will consist primarily of excavation of the building foundations, driveway, and typical utilities. The site is rectangular in shape, situated on the western bank of Hood canal. The site generally slopes down to the east towards Hood Canal with slope inclinations ranging from 5 to 35 percent to the top of bank. The low bank is approximately 7 feet in height. There is a localized steep slope in the central portion of the southern parcel with a slope of 65 percent and 10 feet of vertical relief. Because of the steepness and height of the slope, we understand that a Geotechnical Report is being required per the Jefferson County Critical Areas Ordinance Chapter 18.22. SCOPE The purpose of our services is to evaluate the site conditions as a basis for satisfying the Jefferson County requirements and to provide geotechnical recommendations and design criteria for the long term stability of the structures. Specifically, our scope of services for this project included the following: 1. A visit the site to conduct a geologic reconnaissance to assess the site's slope, soil and ground water conditions. 2. Reviewing available surface and subsurface soil and ground water information, including the WADNR, Division of Geology and Earth Resources, Geologic Maps of Eastern Jefferson County, the USDA, Soil Conservation Service, Soil Survey for Jefferson County, and the DOE Coastal Zone Atlas for Jefferson County. 3. Assessing the landslide hazards in accordance with Jefferson County, Chapter 18.22, Lindal.Rembaugh.LHGL RECEIVE.j March 04, 2009 Page 2 MAR 2 1 22uj Critical Areas Ordinance. 4. Providing stormwater recommendations for on-site stormwater corYfr4irOnliVr00f'7 [in water. The services described in this report were prepared under the responsible charge of Keith S. Schembs, LEG and W. Glen Coad, PE. Mr. Schembs and Mr. Coad meet the qualifications contained in Title 18, Section 18.22.420 to prepare a Geotechnical report. Mr. Schembs and Mr. Coad understand the requirements of the current Critical Areas Chapter 18.22 and the definitions of the applicable terms contained within Chapter 18.22. Individuals under the responsible charge of Mr. Schembs and Mr. Coad have performed a landslide hazard geological assessment, conducted a field investigation, and researched historic records on or in the vicinity of the above referenced site. SITE CONDITIONS Surface Conditions The site is located on the western bank of Hood Canal in an area characterized by residential development. The site consists of two adjacent parcels that are rectangular in shape. When combined they measure approximately 180 feet (east to west) by approximately 100 feet of frontage along Shore Drive to the west and 110 feet of shoreline along Hood Canal to the east, and encompasses approximately 0.41 acres. The site is rectangular in shape and situated on the western bank of Hood canal. The site generally slopes down to the east towards Hood Canal. The site initially slopes from Shore Drive to the east at slope inclinations ranging from 0 to 5 percent for approximately 100 feet. The site then transitions to slopes ranging from 25 to 35 percent for approximately 70 feet and then back to slopes ranging from 0 to 5 percent for approximately 25 feet to the top of bank. The low bank is approximately 7 feet in height. There is a localized steep slope in the central portion of the southern parcel with a slope of 65 percent and 10 feet of vertical relief. The proposed site development, along with the site topography are identified on the Site Plan, Figure 2. The site is currently vegetated with typical residential landscaping and native vegetation. The majority of the site is covered with low grass. The low bank cover consists of moderately dense native vegetation. Site Soils The Soil Survey of Jefferson County (USDA Soil Conservation Service) indicates that the property is underlain by the Olete very gravelly silt loam soils (OeD) that forms on 0 to 30 percent slopes. These soils were derived from colluvium and residuum from basalt and are listed as having a "slight to moderate" erosion hazard. A copy of the SCS soils map for the site area is included as Figure 3. We observed no evidence of surficial erosion on the site or within 200 feet of the site at the time of our site visit. Geologic Conditions According to the Geology Map of the Eastern Jefferson County, Jefferson County, Washington, by Jefferson I.D.M.S., revised February 21, 1995, our site observations, and our geologic reconnaissance of the site area, the near surface soils at the site generally consist of basalt deposits (Tb). An excerpt of the above reference geologic map is included as Figure 4. A review of the Coastal Zone Atlas for Jefferson County indicates that the site is located in an area mapped as "S"for stable. No evidence of active and ongoing shoreline erosion was observed along the shoreline or evidence of larger deep-seated rotational failures were observed. No areas of mapped recent (Urs) or older (Uos) landslides are shown on the Coastal Zone Atlas for the site vicinity. A copy of the Coastal Zone Atlas is attached as Figure 5. Lindal.Rembaugh.LHGL • • March 04, 2009 Page 3 GEOLOGICALY HAZARDOUS AREAS «r The Jefferson County Municipal Code, Chapter 18 classifies a geblogically hazardous area based upon a combination of erosion, landslide, and seismic hazards. The following erosion, landslide, seismic, and channel migration zone (CMZ) hazard areas shall be subject to the standards of Article V (Geologically Hazardous Areas). These areas may be identified by the presence of any of the following indicators: Erosion Hazard Areas— per Jefferson County Section 18.22.160 Areas containing soils or soil complexes described and mapped with the United States Department of Agriculture, Soil Conservation Service, Soil Survey for Jefferson County as having severe or very severe erosion hazard potential. Landslide Hazard Areas— per Jefferson County Section 18.22.160 Areas potentially subject to mass movement due to a combination of geologic, topographic, and hydrologic factors including: (i) Areas of historic failures or potentially unstable slopes, such as: (A) Areas described and mapped as having severe or very severe building limitations for dwellings without basements within the United States Department of Agriculture, Soil Conservation Service, Soil Survey for Jefferson County; (B) Areas described and mapped as recent or old landslides or slopes of unstable materials within the Washington State Department of Ecology Coastal Zone Atlas of Jefferson County; and (C) Areas described and mapped as areas of poor natural stability, former landslides and recent landslides by the Washington State Department of Natural Resources, Division of Geology and Earth Resources; (ii) Areas potentially unstable as a result of rapid stream incision, stream bank erosion, or undercutting by wave action; and (iii) Areas with any indications of earth movement, such as: (A) Rockslides; (B) Earthflows; (C) Mudflows; and (D) Landslides. Seismic Hazard Areas — per Jefferson County Section 18.22.160 Areas subject to severe risk of damage as a result of earthquake-induced ground shaking, slope failure, settlement, soil liquefaction, or surface faulting. These areas are identified by the presence of: poorly drained soils with more than 50 percent silt and very little coarse material; loose sand and gravel, peat, artificial fill and landslide materials; or soil units with high organic content. Channel Migration Zones (CMZs) — per Jefferson County Section 18.22.160 Areas subject to the natural movement of stream channel meanders. In the delineation high risk CMZ area, channel migration is likely within the next 100 years. Areas protected from channel movement due to the existence of permanent levees of infrastructure improvement such as roads and bridges constructed and maintained by public agencies are excluded from the high or moderate risk designation. • Mach 04, 2009 Lindal.Rembaugh.LHGL • • JLECEI�C JJ.,+ f`) Page 4 11 1l Y [� l MAR 2 4 21D3 CONCLUSIONS Jefferson County, Chapter 18.22, Section 18.22.160 uses the above referenced indicators to define a geologically hazardous area. Based on our observations of the site and review of published information, we offer the following comments. Erosion Hazard Classification No soils or soil complexes onsite are described or mapped as having severe or very severe erosion hazard potential. Landslide Hazard Classification No areas of historic failures or potentially unstable slopes were observed such as: Areas described and mapped as having severe or very severe building limitations for dwellings without basements within the United States Department of Agriculture, Soil Conservation Service, Soil Survey for Jefferson County; Areas described and mapped as recent or old landslides or slopes of unstable materials within the Washington State Department of Ecology Coastal Zone Atlas of Jefferson County; or Areas described and mapped as areas of poor natural stability, former landslides and recent landslides by the Washington State Department of Natural Resources, Division of Geology and Earth Resources. No areas potentially unstable as a result of rapid stream incision, stream bank erosion, or undercutting by wave action were observed. No areas with any indications of earth movement such as rockslides, earth flows, mudflows, and landslides were observed on site at the time of our visit. Based on the above, it does not appear that the site has any indications of a geologically hazardous area. Seismic Hazard Classification As stated above, the site is underlain by the Olete very gravelly silt loam soils. These soils are well drained, have less than 50 percent fines, and contain a significant amount of coarse material. The Olete soils do not contain artificial fill and landslide materials, nor is it a soils unit with high organic content. Based on the above, it is our opinion that the site does not meet the technical criteria of a Seismic Hazard Area. Based on our observation and the subsurface units mapped at the site, we interpret the structural site conditions to correspond to a seismic Site Class "C" in accordance with Table 1613.5.2 in the 2006 IBC (International Building Code) documents. This is based on the likely range of equivalent SPT (Standard Penetration Test) blow counts for the soil types observed in the site area. These conditions were assumed to be representative for the conditions based on our experience in the vicinity of the site. Channel Migration Zone Classification Based on the location of the site, the site is not within an area susceptible to the natural movement of stream channel meanders. Recommended Setback The Jefferson County building department may require a building setback in accordance with IBC (International Building Code) standard requirements. IBC section 1805 requires a building setback from slopes that are steeper than 3H:1V (Horizontal:Vertical) unless evaluated and reduced, and/or a structural setback is provided, by a licensed geotechnical engineer. The setback distance is calculated based on the vertical height of the slope. The typical IBC setback from the top of the slope equals one third the height of the slope while a setback from the toe of the slope equals one half the height of the slope. Vegetation in the setback area may be enhanced, if approved/required by the Jefferson County. Clearing, Lindal.Rembaugh.LHGL • • RECET[\TED March 04, 2009 1t Page 5 MAR 2 4 2C grading and filling within the setback area is allowed if it can be demonstrated that the existing vegetation will not be adversely impacted or that it can be mitigated (enhancgd). Based on our site observations, in accordance with IBC guidelines, we recommend a setback distance of H/3 for slopes greater than 10 feet in height to a maximum of 8 feet from slopes greater than 33 percent. Where this setback distance cannot be met, the foundation elements of the structure can be extended vertically to meet the horizontal setback distance. Where the foundation is extended vertically, we recommend that the setback be measured horizontally from the lower outside edge of the foundation element to the face of the slope. This structural setback is based on the foundation elements extending to the dense to very dense native soils. Once the final locations of the residences are determined and the setback criteria cannot be met, we can provide alternative foundation recommendations to address the setback criteria. Alternatively we can visit the footing excavations at time of construction and provide recommendations in the field at that time. Weathering, erosion and the resulting surficial sloughing and shallow land sliding are natural processes that affect steep slope areas. As noted, no evidence of surficial raveling or sloughing was observed at the site. To manage and reduce the potential for these natural processes, we recommend the following: • No drainage of concentrated surface water or significant sheet flow onto or near the steep slope area. • No additional fill should be placed within the setback area. • Grading should be limited to providing surface grades that promote surface flows away from the top of slope to an appropriate discharge location beyond the toe of the slope, such as into Puget Sound. Site Drainage All ground surfaces should be graded such they slope away from the proposed residence. We recommend conventional roof and footing drains be installed for the residence, and that any subgrade wall be provided with a drain to prevent the build-up of hydrostatic pressure. The roof drain downspouts should not be connected to the footing drain unless adequate measures are taken to prevent a surcharge of the footing drain. Roof water can be dispersed onsite via splash blocks or collected and tightlined down the bluff to the shoreline and discharged to an appropriate location. Collected runoff from the driveway area may be directed to adjacent vegetated areas as sheet flow. LIMITATIONS We have prepared this report for use by Lindal Cedar Homes and members of their design team, for use in the design of a portion of this project. The data used in preparing this report and this report should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and limited site reconnaissance, and should not be construed as a warranty of the subsurface conditions. Variations in subsurface conditions are possible between the explorations and may also occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient monitoring, testing and consultation should be provided by our firm during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans and specifications. ' Lindal.Rembaugh.GR + • March 4,2009 Page 6 We have appreciated the opportunity to be of service to you on this project. Please do not hesitate to call with any comments or questions at your convenience. Respectfully submitted, GeoResources, LLC A.\e.. ....-.k R P. O'Rourke, EIT n T Staff Engineer ;3u.Wash/ ` 3�a�� f ., / , :.\:‘,....O �� !KEITH SCOTT SCHEMES 3/e' or Keith S. Schembs, LEG W. Glen Coad, PE Principal Principal RPO:KSS;WGC;rpo DocID:Lindal.Rembaugh.LHGL Attachments: Figure 1 -Site Vicinity Ma T' 1 Figure 2 Site Plan p JI \_1 � � T� 'r Figure 3-USDA Soils Map Figure 4-Geology Map Figure 5-Coastal Zone Atlas riA,R 2 4 209 t7FEfl ON CIIIN I DCP • • .._.., 1 -....... i-,444-t,.;___, '� A. ,i. 5 4.14._ t I ,0 I i NO TT'. W 110A,[)R titth Pf" iti:tall * trRi r) 1 WAinnx4f: r1'4, , tt ';'1'tt .4t4:E't'bt.- SPltUCT t 1 1►'ifrill.f11'k•S ff fjtx st I fifdl. '— r.j, A f Eau I . A�i,a 4f`ttZ 1 ---- — ` —� — ------ - �il B#K51�FR1YAYN,� t ''.it fiii �w..� ...g,i's, •,_: .. . .1 i Ow \ 4.,0<„ 21 ;# .4 20 CtSA% Q 1 5,..;,, e 44 144 1P. Air 11?— >A. ,, 6;r # i t`j g ! /44 4 V 4'ill, ``0 4A I1 t V # cro4 J.A____ _ t he Approximate Site Location ll-, 7,-,,,,----.._... •'C'1'J[V T `L a �l� lti�) tIAR24209 tX AV ,- JEFFERSON COUNTY z: 6 Not to Scale GeoResources, LLC Site Vicinity Map 5007 Pacific Highway East, Suite 20 Single-Family Residence Fife, Washington 98424 131 Shore Drive Phone: 253-896-1011 Jefferson County, Washington Fax: 253-896-2633 DocID:Lindal.Rembaugh.SVM March 2009 Figure 1 • iiii c c ^ V ` '`o '''''"N \-\\ } ` \ E A k?'!- ,_>< , :t 5 l‘ `i4, MAR 2 4 206A a\ JEEFERS Cr„ SCALE 1" = 20' Site Plan Single-Family Residence 131 Shore Drive Jefferson County, Washington dal.Rembaugh.SP March 2009 Figure 2 • • 04ft .., it 6 144010 :_• ik 44 -.1. ._ 11104..._ �� ' ta Alder St \\*- 11 4 Cf" A llit jilli it ( ' f4r . 41! ... . 41,,, , , 1111:41 Spruce St _ Ii 0 Approximate Site Location SCS SCS Parent Slopes Erosion Soil Soil Name Material (in percent) Hazard Type OeD Olete very gravelly silt loam Colluvium and residuum from basalt 0- 30 Slight- Moderate Co Coastal beaches -- (W iF MAR 2 4 2"03 S �! Not to Scale CutIN11 Ulu GeoResources, LLC USDA Soils Map 5007 Pacific Highway East, Suite 20 Single-Family Residence Fife, Washington 98424 131 Shore Drive Phone: 253-896-1011 Fax: 253-896-2633 Jefferson County, Washington DocID:Lindal.Rembaugh.SCS March 2009 Figure 3 • • ENLARGED . 2 ilk ' ' ?-,..._ 1 1 1. l , 11i) 'IN& MIL_, 1 ,j i if lkit Pi Itr.),:„‘ - i 4. , ,411AIPOir. , d __IAN. 144 ...._:..„ 1 A •IL 0061 01 1,,: til . . 11 . : Pi ' I I k tr.vii, al .. 1. I a I ( 1 I AI •- "I, li. MO '.414.. '4" 'lib 4L jt....... r. i I e rm. I ^ MAR 2C Approximate Site Location 2 4 ``9 JEff it j'' . • L._ L..;' " ' BASALT ,t Not to Scale GeoResources, LLC Geology Map 5007 Pacific Highway East, Suite 20 Single-Family Residence Fife, Washington 98424 131 Shore Drive Phone: 253-896-1011 Jefferson County, Washington Fax: 253-896-2633 DocID:Lindal.Rembaugh.GM March 2009 Figure 4 . - ' • • f• 40-ir I'11\, ` .1 rs'. ,Maple _,.o _Alder___ �� f _ Spruce y a Hemlock *; r 2. k ---- _Cad,_.__ i� - �r ! v Y _ 3. __For _., 4 T. • e5. ps+A4:Ca°p q�& ,11 a � Approximate Site Location SIoDe Suability Stable � i, ,R [�� L Intermediate Unstable IM Unstable Recent Landslide MAR 2 4 20'33 It, Unstable Old Landslide `N Modified JEFFERSON CHk'rFY Dcr R 'Wtt. 1 Not to Scale GeoResources, LLC Coastal Zone Atlas 5007 Pacific Highway East, Suite 20 Single-Family Residence Fife,Washington 98424 131 Shore Drive Phone: 253-896-1011 Fax: 253-896-2633 Jefferson County, Washington DocID:Lindal.Rembaugh.CZA March 2009 Figure 5 , , , (J) 0 I> r M ,-. 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