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Home My WebLink About802341001 Geotech Assessment~n,~Ao1- ooooy s Epolo - v o yRlc GEOTECHNICAL ASSESSMENT Prepared For Cecelia Goodnow December 26, 2007 For the Property Described as Tax # 802341001, 445 Elkhorn Ridge Road Section 34, Township 28 North, Range 2 West, W.M. Jefferson County, Washington Prepared by NTI ENGINEERING &SURVEYING, INC. 717 S. Peabody Street Port Angeles, Washington 98362 Phone 360-452-8491 Fax 360-452-8498 Web Site www.nti4u.com E-mail info@nti4u.com FEB 2 5 2008 JEffEfl$ON COUNTY DCD r "~/ 7 '~ ~ NTI ENGINEERING &SURVEYING 717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362 Engineers ^ Land Surveyors ^ Geologists Construction Inspection ^ Materials Testing ... j (360) 452-8491 1-800-654-5545 FAX 452-8498 E www.nfi4u.com - al :info ..nti4u.com December 26, 2007 Cecelia Goodnow 12620 Manzanita Road NE Bainbridge Island, WA 98110 Subject: Geotechnical Assessment for Tax # 802341001, 445 Elkhorn Ridge Road Located in Section 34, Township 28 North, Range 2 West, W.M., Jefferson County, WA Dear Mrs. Goodnow: Background At your request, NTI Engineering & Surveying, Inc. (NTI) completed a geotechnical assessment of the above referenced property consisting of research of available literature and geologic maps of the area, and a site visit on December 14, 2007 for visual observations. This assessment was in response to the property being listed as a "Moderate Landslide Hazard" area by the Jefferson County Department of Community Development. It is our understanding that you plan to construct a single family residence and associated infrastructure on the property. Site Description The subject property is located at 445 Elkhorn Ridge Road off of Elkhorn Lane and Lords Lake Loop Road north of Quilcene (Figure 1}. The hilly property is bounded on all sides by wooded rural property designated as forest land, with residences on some of the adjoining parcels (Figures 2 & 3). Existing improvements to the property include a driveway and nearby utilities. A homesite and drainfield location has been selected (Figures 2 & 3}. The property is situated on the south end of a ridge that runs in anorth-south direction. The property slopes down towards the west, south and east. There is a knoll on top of the ridge at the south side of the property which has been selected as the desired homesite. The property has been logged in the past and is currently vegetated with young trees and brush. No springs or seeps were observed in the vicinity of the homesite, and no evidence of past landslide activity was observed. Many rock outcrops are visible in the area. ~.~ ~Xa„ #_ ~i ~~ °ma"~a^« 3 d t ~T7 ~' `~} i ~,~, r )2 !'L. _ +~ , S+' r ~. ~^+ .„~S>° t~, ~ , ~ ~~ i ~; Figure 1 ~~,`_, f ~~~ lla ll FEB 2 5 2U~8 ~EEEENSUNCOUNIY DCD Figure 2 ~~~ Figure 3 FEB 2 5 2006 JEFFE850N000N~4 DCD Site Geology The Department of Ecology's "Geology and Ground-Water Resources of Eastern Jefferson County, Washington" maps the soil in the area of the property as Sedimentary rocks, undifferentiated (Ts}. This unit consists of mudstone, siltstone, sandstone, and conglomerate. According to the Soil Survey of Jefferson County Area, Washington (United States Department of Agriculture, 1975), the subject property and vicinity is mapped as Rock Land (Rk). This unit is described as predominantly sandstone conglomerate, sandstone and basalt. Visual observations made at the site were generally consistent with the above descriptions. The visible outcrops were composed of conglomerate and it appears that the entire ridge is composed of rock with shallow areas of residual and colluvial soil (Photo 1). Photo 1: View of slope showing exposed moss covered bedrock ~, "' \`, P~~~ ~--~ FEB 2 S 208 JEffERSON C~UNiV DCG Conclusions and Recommendations The subject property appears grossly stable and the project seems feasible from a geotechnical perspective. Based upon our assessment of the property, it is our opinion that the hillside does not represent a landslide hazard. We recommend that footings be founded in the bedrock. For footings founded in soil on slopes greaterthan 18.5° (33.3%), we recommend that building foundations complywith Section 1805.3.1 & 3.2 of the International Building Code (IBC) which deals with footings on or adjacent to slopes. That text and related illustration can be found in the appendix of this report. Limitations This report has been prepared for your exclusive use in conjunction with the above referenced project. The report has not been prepared for use by others or for other locations. Others may use it only with the expressed written permission of the Engineer. Within the limits of scope, schedule and budget, this report was prepared in general accordance with accepted professional engineering and geological principles and practices in this or similar localities at the time the report was prepared. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. The observations, conclusions and recommendations presented in this report were based on ourvisual observations of the subject property at the time of our site visit; no laboratory tests were performed.. If you desire a more detailed analysis of your site,. you are encouraged to obtain such services. Soil and geologic conditions can vary significantly between test holes and/or surface outcrops. If there is a substantial lapse of time, conditions at the site have changed or appear different than those described in this report, we should be contacted and retained to evaluate the changed conditions and make modifications to our report if necessary. ,~,~i~ ., ~ r r Sincerely, NTI ENGINEERING & SURVEYING, David Hanna, P.E. Civil Engineer ~~~} 1V1V I' ~~ r~ ~o INC. ~ 23747 ~ `f'O ~~'GI3 TER~~~^~'~ I , ~ , b ANAL E ~Q~~ ~~~ CSC. Bill Pa on L.E.G. .. ~ ~ .. . ~ ., ~ . a ~ ~ ..~ . ~~~ Engineering Geologist ~:4.. B:IReportslGOCE0701.slope stability.34(28-2).Lords Lake Loop Rd.doc EXPIRES 8-25-09 APPENDIX FEB 2 5 2008 ~E~fEflSON COUN14 UCO SAILS AND FOUNDATIONS 1805.3 Footings on or adjacent to slopes. The placement of buildings and structures on or adjacent to slopes steeper than ane unit vertical in three units horizontal {33.3-percent slope) shall conform to Sections 1805.3.1 through 1805.3.5. 1$05.3.1 Building clearance from ascending slopes. In general, buildings below slopes shall be set a sufficient dis- tancefromthe slope to provide protection from slope drain- age, erosion and shallow failures. Except as provided for in Section 1805.3.5 and Figure 1805.3.1, the following criteria will be assumed to provide this protection. Where the exist- ing slope is steeper than one unit vertical in ane unit hori- zontal (100-percent slope), the toe of the slope shall be assumed to be at the intersection of a horizontal plane drawn from the top of the foundation and a plane drawn tangent to the slope at an angle of 45 degrees (0.79 rod} to thk~ horizon- tal. Where a retaining wall is constructed at the sae of the slope, the height of the slope shall be measured from the top of the wall to the top of the slope. 1805.3.2 Footing setback from descending slope sur- face. Footings on or adjacent to slope surfaces shall be founded in firm material with an embedment and set back from the slope surface sufficient to provide vertical and lat- eralsupport for the footing without detrimental settlement. Except as provided for in Section 1805.3,5 and Figure 1805.3.1, the following setback is deemed adequate to meet the criteria. W here the slope is steeper than 1 unit ver- tical in 1 unit horizontal (1.00-percent slope}, the required setback shall be measured from an imaginary plane 4S degrees (0.79 rod) to the horizontal, projected upward from the toe of the slope. 1505.3.3 Pools. The setback between pools regulated by this code and slopes shall be equal. to one-half the building footing setback distance required by this section.. That por- tion of the pool wall within a horizontal distance of 7 feet (2134 nun} from the top of the slope shall be capable of sup- porting the water in the pool without soil support. 1$OS.3.41'ouudationelevation. Qngraded sites, the top of any exterior foundation shall extend above the elevation of the street gutter at point of discharge or the inlet of an approved drainage device a minimum of 1.2 inches (305 mmj plus 2 percent. Alternate elevations are permitted sub- ject to the approval of the building official, provided it can be demonstrated that required drainage to the point of dis- charge and away from the structure is provided at all loca- tions on the site. 1805.3.5 Alternate setback and clearance. Alternate set- backsand clearances are pemutted, subject to the approval of the building ofpicial. The building official is permitted to require an investigation and recommendation of a registered design professional to demonstrate that the intent of this sec- tion has been satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material. FACE OF FoortNc TOP of SLOPE ~~ :.... ., ...., FAGS OF E------r~- ............: ~/`sr~UCru~E TOE OF H/3 BUT NEED NOT H SLOPE EXGEED 40 FT, MAX. HJ2 BUT NEED NOT EXCEED f5 F? MAX. Far SI: E fact = 304.8 mm. FIGURE 1845.3.1 FOUNDATION CLEARANCES FROM SLOPES 2006 INTERNATIONAL BUILDING CODE' ~~~~~~~ FEB 2 5 2008 341 JEffERSONCOUNiYUCO