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HomeMy WebLinkAbout935100008 Geotech Assessment (1998)ALLEN L. HART ENGINEERING GEOLOGIST (253) 752-8963 1720 N. Oakes Tacoma, Washington 98406-7524 February 19,1998 RUssell Ferguson 20245 Viking Way Poulsbo, Washington 98370 Re: Report-Provision of subsurface soil information; 851 Thorndyke Road, Port Ludlow, Jefferson County, Washington. Parcel 935100008 S-T-R: 09-27-01 E. Project number 980104 This report presents a summary of subsurface soil information developed for the referenced site. The scope of the services provided was outlined in my proposal to dated January 23, 1998. Authorization to proceed with the subsurface exploration was received on January 30, 1998, and the fieldwork was completed on February 10, 1998. SUBSURFACE INVESTIGATION PROGRAM The subsurface conditions of the site were evaluated by excavating and logging soils encountered in one soil exploration boring, completing a reconnaissance of the site and adjacent areas, reviewing soil boring logs from the adjacent lot to the north of the study site, and reviewing information in my files. The boring location is shown on the attached Site Plan, Figure 1. The bodng location and field exploration work was specified by Jim Levey of Art Anderson Associates, your project geotechnical engineer. As originally conceived two bodngs to a maximum depth of 20 feet were planned with the b0dng on the slide scarp reaching a minimum elevation of 454 feet. However, following discussions with Mr. Levey at the time of the fieldwork, the bodng on the slide scarp below the house was deleted due to safety concerns. The remaining bodng was extended to a depth of 38 feet (elevation 446+/-), the maximum depth reachable with the available equipment, to obtain the desired subsurface information. - The boring was made using a small, highly portable drill dg, supplied by CN Ddlling of Seattle, Washington. The soil bodng was extended to a depth of 38 feet with soil samples obtained at the intervals shown on the bodng log. Soils exposed in the bodng were examined and logged by the Russet~ Ferguson/Report-$ubsurface soff inforrnab'on; 85f Thomdyke Road, Port Ludlow, Washington February 19, 1998 Page 2 Project 980104 engineering geologist. Standard Penetration Test (SPT) samplers were used to obtain soil samples for evaluation and determine N-values for the materials encountered. The N-value is evaluated using a SPT sampler ddven 18 inches using a 140 pound hammer free-falling 30 inches. The N-value is the number of blows required to ddve the sampler the last foot. In the bodngs the N-value was used as an indication of the of the relative soil density. The soil strata encountered are shown on the attached bodng log, Figures 2 and 3. The soil strata shown on the log were observed at spot locations. Actual subsoil conditions and thicknesses may vary between the bodng locations or as expOsed in excavations or slope exposures. Upon completion the boring was sealed and backfilled in accordance with Washington State .. Department of Ecology regulationsl Elevations referenced in this report are based on the topography shown on the drawing by Art Anderson Associates titled "Ferguson Slope Repair, 851 Thomdyke Road, South Point, Washington- Site Plan", dated September 4, 1997. This drawing provides a base for the attached Figure 1. SITE AND SUBSURFACE CONDITIONS The subject property is located on the east side of Thomdyke Road just north of the intersection of Thorndyke Road and Finch Lane in Jefferson County. The existing residence is located approximately 90 feet back from the street with the landslide study area located neady directly east of the home. The slide width approximates the width of the house and the top of the slide scarp is generally within 10 to 15 feet of the house foundations. Measured slope angles on the scarp at the head of the slide range from about 45 degrees to 70 degrees with some sections approaching vertical. Measured slope angles on the body of the slide range from less than 30 degrees to on the order of 45 degrees. To the south of the landslide area where slopes appear not to have been disturbed (slopes to the north have recently slide) slope angles generally range from near 30 degrees to about 43 degrees. The slide itself appears to have occurred pdmadly as a shallow, face-type failure, removing primarily the weathered and root loosened materials to a depth of about five to eight feet. It appears that there was minimal involvement of the dense to very dense slope core soils. Although some raveling, spalling and minor sloughing is occurring from the scarp around the landslide area, at the time of my fieldwork there were no indications of larger, potentially deeper-seated slides on the property. Russell Fergusoru'Report-Subsurface SOl7 information; 851 Thomdyke Road, Port Ludlow, Washington February 19, 1998 Page 3 Project 980104 As exposed on the bodng, it appears that the east side of the residence is underlain by about 2.5 feet of loose sand fill which ovedies about three feet of loose matedal ranging in composition from silty sand to sand and silt with occasional to scattered gravels. In general appearance this silty material looks like a Weathered glacial till. Below the till-like'soils are gray-brown to gray, dense to very dense sands which extend to beyond the bottom of the bodng. Generally the soils found in this bodng are similar to those described on soil logs for two bodngs made on the property to the north. Soils exposed in the slide scarp are generally similar to those found in the boring at a similar depth/elevation except that between aboUt elevation 460 and 455 (drilling depth: 24 to 29 feet) there are several half to one and a half inch thick silt and clay layers which were not found in samples from _ the bodng. ' In general the soils exposed in the bodngs on this and the adjacent property and exposed in the Slope appear similar to those described on vadous maps of the area. Most of the soils encountered in the boring were found to range from moist to very moist with the wetness of the near surface soils being attributed rainfall pdor to and dudng the time of our fieldwork. No ground water Was encountered dudng ddlling and no water accumulated in the uncased, open hole following removal of the auger. However, water seepage was noted from the scarp face south of the boring approximately between elevation 460 and 455 feet. This seepage zone appears to be localized and confined to the southern half of the slide scarp at the indicated elevation. REPORT LIMITATIONS This report has been prepared for the exclusive use of Russell Ferguson and his agents for use in planning the proposed resupport of the residence and landslide repairs.' The scope of work for this project is limited to the provision of subsurface soil information based on the field exploration work specified by Mr. Jim Levey. The provision of specific geotechnical design recommendations is beyond the scope of this study. The soil conditions described in this report and the'conclusions contained~in . this report are provided for this specific site only and should not be expanded for use on adjacent properties without additional exploration and review of those sites by this firm. The report conclusions and interpretations should not be construed as a warranty of the subsurface conditions. There are possible variations in subsurface conditions. Allen L. Hart Engineering Geolog_ ist ('253) 752-8963 Russell Ferguson/Report-Subsurface solT informatJon; 851 Thomdyke Road, Port Ludl~w, Washington Project 980104 February ~19, 1998 Page 4 NOTE: Although I have explored subsurface conditions as part of this study, I have not conducted analytical laboratory testing of any samples obtained, have not evaluated the site for the potential presence of contaminated soil, and have not evaluated or addressed ground water conditions or concems except as noted in this report. The. owner and the contractor should make themselves aware of and become familiar with applicable local, state, and federal safety regulations, including current OSHA excavation and trench safety standards.. Construction site safety generally is the sole responsibility of the contractor. The contractor shall also be solely responsible for the means, method, techniques, sequences, and operations of construction operations. The firm, Allen L. Hart, Engineering Geologist is providing the preceding information and recommendations solely as a service to Russell Ferguson. Under no circumstances should the provision of this information or recommendations be construed to mean that' the firm Allen L. Hart, Engineering Geologist is assuming responsibility for construction site safety or the contractor's activities; such responsibility is not implied and should not be inferred. Within the limitations of scope, schedule, and budget for this WOrk, it is warranted that the work has been done in accordance with generally accepted practices followed in this area at the time this is report was made. No other warranty, expressed or implied is made. . Should you have any questions or concerns which have not been addressed, or if we may be of additional assistance, please call. Allen L. Hart, CPG, RG/EG Engineering Geologist cc: Jim Levey, Art Anderson Associates Allen L. Hart Engineering Geologist (253) 752-8963 / ~ ~2, 76 , ~ , , , ~ ~o. ~ lw ' ~ ~~ "-- ~ O0 ~ '~~5/ ~JO~/~~ ~ - ~, '_~  .;:.. . · '_ -~_ x ~ ' ~~~ ~ ' ' ' ~ . / / / ~Ye. ' , ~ _,~ /'~e~ __ , . ~ ~ ~ ~ / "~o~ ~. : ..- ~ ~: ~ ~ F:R~SON ~LOP~ R:PAIE I/,~I ART ANDERSON ~ ~ = ~.~ . o ~o ? ~ 651 7HORNDYKE ~D .~~~ A S S O C I A T E S ~ ~ ~ ~ m 148 FIRST STREET BREMERTON, WA 98337 ~' 5 IT ~ ' PLAN e~ MARION STREET(206i 622-6221SEATTLE' WA 98104 ,,, Hollow stem auger SHEET 1 OF 2 ~ SAMPLING METHODISI' Standard penetration test (SPT) with 140 lb S U R F A C E E L E V A T I O N ' 484+/. hammer, 30 inch drop D A T U M: Assumed, see Figure 1 · BLOW .COUN¥ ~ ~ MATERIAL TEST · WA'I ER coNTENT ,% u. ,.. tn o,_ otn t~ !c30 DESCRIPTION .RESULTS , , Brown to gray, loose, silty SAND, wet. (Fill) ! occasional to scattered gravel, very moist. '~ _- (Looks somewhat like a weathered ' Gray-brown to gray, dense, gravelly SAND to SAND with some gravel and varying silt to ~ SAND, very moist to moist. Fine SAND with silt --10 10- ., I -15 ~ 15-- - Gray, very dense, SAND, very moist to moist. - 20 -20 - _ '2sI I- 25- - 1 i I i i ! ! , , ! , -- 30 ' , LOG OF BORING Allen L. Hart Engineering Geologist (253) 752-8963 Figure 2 i , ~DRILLING METHOD' BORING DESIGNATION' B-l(continued) SHEET'2 OF 2 SAMPLING METHOOISi' SURFACE ELEVATION' DATUM' · BLOW .COUNT / ~ ~ MATERIAL TEST · WA1 ER CONTENT % '~ ~" DESCRIPTION RESULTS _ ~ e ~ ~ Gray, ve~ dense, SAND, moisL --35 35-- ,, Boring terminated at 38.0 feet. -- 40 O- No fr~ ground water observed in boring. -- -- : _ I , --~ {3- , , LOG OF BORING Allen L. Hart Engineering Geologist (253) 752-8963 Fig ute 3