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Home My WebLink AboutSlope Analysis for BLD2004-00770 - BLD Engineering / Geo-tech Reports - 5/20/2001 August 23,2004 Page# 1 of 1 GEOTECHNICAL TESTING LABORATORY SEAN DOYLE PO Box 2598 BELFAIR, WA98528 RECEIVED CMG 2 BELFAlk OFFICE Re: pole barn 421 Cutlass Way Belfair, WA Gentlemen: This letter is written to confirm that we did a slope analysis on the property at 411 Cutlass Way and found the slope conditions on the two properties to be very similar. It is our opinion that no further geotechnical study will be needed for construction of the above referenced pole barn. Thank you for this opportunity to be of service to you. If you have any questions, or if we can be of any further assistance please call on us at (360) 754-4612. Respectfully Submitted, GEOTECHNICAL TESTING LABORATORY �0 0j Was a Harold Parks �� EnpnesringGeo�ogyw, Engineering Geologist 0 827 9d t1e0�0 HAROLD PARKS � a 10011 Blomberg Street SW,Olympia,WA 98512 Do y RECEIVED N, 2 8 2004 426 W! CEDAR ST. Slope Stability Investigation au�k 311 NE Cutlass ` Apes Belfair, WA Prepared for Stephen Johnson,Inc. by Geotechnical Testing Lab Olympia, WA May 20, 2001 GEOTECI-INICAL TESTING LABORATORY STEPHEN JOHNSON,INC. P.O. BOX 488 BELFAIR,WA 98528 Re: Slope stability &setback analysis 311 NE Cutlass Court Belfair,WA Gentlemen: As per your request, we have conducted a slope stability investigation for a home located on the above referenced property. The result of this investigation, together with our recommendations, are to be found in the following report. The site is located in Mason County, Washington. SUBSURFACE EXPLORATION PROGRAM The subsurface exploration program consisted of a site reconnaissance and a review of information from our files of similar,work performed in this area. The slope was observed by our geologist, who studied the soils exposed at the site. The soil criteria shown on the slope profile were confirmed on the geological maps. SITE CONDITIONS The proposed home is to be located at the highest point of the lot on a leveled area to the west of the main access street. No excessive erosion or deep seated instability was observed. Under the surface,the soil was found to be a dense sandy gravel. The vegetation consists of grasses and trees indigenous to the northwest. The slope is bare of vegetation except for a few Fir trees. GEOLOGIC CONDITIONS The geology of the area as mapped by the Coastal Zone Atlas of Mason County Vol. 9 is Vashon Till (Qvt) characterized by Pleistocene silt deposits of sands, silty sands, and pebbly sands commonly bedded. It may contain large erratics with gravel lenses. The lower slopes are composed of a Vashon recessional outwash(Qvr). These are the youngest member of the Vashon Drift, consisting mainly of sandy and gravely meltwater or ablation deposits which have not been compacted by.the continental ice sheet. The native soils can be considered to be at or near their natural angle of repose, and the factor of safety for most of the slope is near unity in the unsaturated condition. HYDROLOGIC CONDITIONS The lot slopes to the west and all surface runoff discharges to well established drainage ways that ultimately run south and to the Hood Canal. Runoff from the roof and/or parking areas will not pose significant problems due to the high porosity of the native soils. SLOPE STABILILTY MODELING& ANALYSIS The site was modeled using a slope program and we have included a profile of the model later in this report. The native soils were modeled using 124 lbs/ft3 unit weight with an assumed phi angle of 33' in their cemented state. 10011 Blomberg Street SW,Olympia, WA 98512 Phone#:(206)7544612 Fax#: (206)7544848 GEOTECHNICAL TESTING LABORATORY We have calculated the slope and have found no indication of deep seated instability there. Slope 1 is a profile of the natural slope to the west. Sectional failure may occur under saturated conditions. The slope stability is mapped by the Coastal Zone Atlas of Mason County Vol. 9 as "stable". Sloughing in this area will not impact the home because of the distance from the home to the western slope. Our study also indicates that the slope is stable. IMPACT ANALYSIS We do not anticipate that the proposed project will have any off-site impact. HISTORY OF LANDSLIDE ACTIVITY Landslide activity has not occurred historically on the subject property. However occasional sloughing does occur during periods of heavy precipitation along the North Shore Road over a mile from this site and under different hydrologic and geologic conditions. OPINION OF POTENTIAL STABILITY Potential for instability is minimal. Potential for minor erosion is probable since all vegetation has been removed from the site. To correct this annoyance,the bare ground should be seeded with grass or straw. HILLSIDE FOUNDATIONS (DAYLIGHT DIMENSION) Structures built on sloping sites offer a number of potential problems. Fig. I illustrates a basic consideration for what is called the"daylight" dimension, which is the horizontal distance from the bottom of the footing to the adjacent ground surface. Many building codes require a minimum distance for this dimension in order to assure some safety against the pushing out of the footing in the downslope direction. Logically, the limit for this distance depends on the type of soil and the angle of the slope of the ground surface. For low slope angles, a reasonable daylight dimension is assured simply because of the usual requirements for the minimum depth of the bottom of the footing below the surface in a vertical direction. As the slope increases, the daylight dimension is less assured and should be limited to some minimum distance. A setback of 8 feet from the horizontal intersect of the slope will provide the critical exposure necessary. (see Fig. 1) A common problem with hillside construction is that shown in Fig. 2, where recontouring of the construction site results in a portion of the building being placed on some significant depth of fill. If possible, all of the footings should be carried down to a depth below the fill. If structural fill is used and placed with reasonable compaction, it may be possible to rest the footings in the fill, provided that this is done only with inspection and supervision by a qualified soils consultant. RECOMMENDATIONS All material excavated from the site cannot be dumped on site without adequate subgrade preparation at the spoils location and proper fencing and runoff controls. All spoils soil must be compacted to 90% MDD (maximum dry density)as per ASTM D-1557 and protected from erosion. 10011 Blomberg Street SW,Olympia, WA 98512 Phone#:(206)7544612 Fax#: (206)7544848 GEOTECIINICAL TESTING LABORATORY The conclusions and recommendations in this report are based on our interpretation of the site conditions as they presently exist, anticipated future construction activities, and the expectation that our exploratory efforts adequately define the subsurface conditions throughout the site. In the event that the scope or location of the project should change, or subsurface conditions different from those encountered during our study be observed or suspected, we should be advised. At that time, a review of the changed conditions will be made and alternative or remedial recommendations given as requested. Thank your for this opportunity to be of service to you. If you have any questions concerning this report, please contact us at (360)754-4612. Respecfully submitted, GEOTEC�IFIND ICAL TESTING LAB Harold Parks, Engineering Geologist r � ■ n1. 10011 Blomberg Street SW,Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206)754A848 G EOTECHNICAL TESTING LABORATORY VICINITY MAP , a NYC 300 S� l O ` O g N ry h j C� i 106 _ 300 ezn Stars Pa fb'nt h t s HOW cafrel 10011 Blomberg Street SW, Olympia, WA 98512 GEOT CHNI E CAL TESTING LABORATORY TOPOGRAPHIC MAP ■ no t t -I`�.N, t ' hk r' •r� is s.s S .t.►, � ' y,4� "�"�yam:�s4"•_S;'�y�i-��'•`ca�• . ��'J f.�� •wr,��s� � lli��.".��Yi'j� �� y��y -Yi`1�� ;.f. ter i t•s ti� .- :, 10011 Blomberg Street SW, Olympia,WA 98512 GE OTECHNICAL TESTING LABORATORY GEOLOGIC MAP i if l "•,!� j / �:-."� t. s 'XSIV$ of �� . t •,' Cone rr(i pp � � a i L f�l t� ; t 1 M U Dy Plum Pt Qdr 10011 Blomberg Street SW, Olympia, WA 98512 GEO TECHNICAL TESTING LABORATORY SLOPE STABILITY /\ J;W Qv .zij .." Wf f • & IR BE'lf'd. ut •o• •/i PA �Piur'n Pe Mud 12 ) tati 10011 Blomberg Street SW, Olympia, WA 98512 Steve Johnson 311 NE Cutlass Crt. ¢angle: 33.0° Unit Weight: 124 Critical Slope Angle,Saturated: 17.9° Horizontal Sectional Sectional Angle of Total Saturated Saturated Unsaturatec Unsaturated X Y Z Elevation Distance % Slope Factor Total Total Total Total Internal Factor Section Total Section Total Sectional Grid Station Elevation Change From Last Slope Angle of Safety Horisontal Change Slope Angle Friction of Safety P> P> (S> (1> Factor Line Point Feet Feet Ste.pt.(ft) P F Feet Feet % p ¢' F Critical Critical ¢ ¢ of Safety From To 1 0 175.00 0.00 0.00 0 0.0° n/e 0 0 0 0.01 16.5 e/a F Ste. Sta. 1 1 175.00 0.00 10.00 0.0% 0.0° n/e 10.00 0 0.0% 0.01 16.5 n/a Safe Safe Safe Safe n/o 0 1 1 2 175.00 0.00 10.00 0.0% 0.01 de 20.00 0 0.0% 0.0° 16.5 n/a Safe Safe Safe Safe n/a 0 2 1 3 175.00 0.00 10,00 0.0% 0.01 a/a 30.00 0 0.0% 0.0° 16.5 n/a Safe Safe Safe Safe n/a 0 3 1 4 174,00 1.00 10.00 10.0% 5.7° 2.% 40.00 1 2.5% 1.4° 16.5 11.85 Safe Safe Safe Safe 2.96 0 4 1 5 174.00 0.00 10.00 0.0% 0.0° Ida 50.00 1 2.0% 1.1° 16.5 14.81 Safe Safe Safe Safe 5.92 4 5 1 6 171.00 3.00 40.00 7.5% 4.3° 3.95 90.00 4 4.4% 2.5° 16.5 6.66 Safe Safe Safe Safe 3.95 0 6 1 7 171.00 0.00 15.00 0.0% 0.0° Ala 105.00 4 3.8% 2.2° 16.5 7.78 Safe Safe Safe Safe 5.43 6 7 1 8 166,00 5.00 50.00 10.0% 5.7° 2.% 155.00 9 5.8% 3.3° 16.5 5.10 Safe Safe Safe Safe 2.96 0 8 1 9 165.00 1.00 40.00 2.5% 1.4° 11.89 195.00 10 5.1% 2.9° 16.5 5.78 Safe Safe Safe Safe 4.44 8 9 1 10 160.00 5.00 18.00 27.8% 15.5° 1.07 213.00 15 7.0% 4.0° 16.5 4.21 Safe Safe Safe Safe 1.07 0 10 1 11 155.00 5.00 18.00 27.8°A 15.5° 1.07 231.00 20 8.7% 4.9° 16.5 3.42 Safe Safe Safe Safe 1.07 0 11 1 12 150.00 5.00 15.00 33.3% 18.4° 0.89 246.00 25 10.2% 5.8° 16.5 2.91 Yes Safe Safe Safe 0.89 0 12 1 13 145.00 5,00 18.00 27.8% 15.51 1.07 264.00 30 11.4% 6.5° 16.5 2.61 Safe Safe Safe Safe 0.98 12 13 1 14 140.00 5,00 21.00 23.8% 13.4° 1.24 285.00 35 12.3% 7.0° 16.5 2.41 Safe Safe Safe Safe 1.07 10 14 1 15 135.00 5.00 22.00 22.7% 12.8° 1.30 307.00 40 13.0% 7.4° 16.5 2.77 Safe Safe Safe we 1.11 10 15 1 16 130.00 5.00 22.00 22.7% 12.8° 1.30 329.00 45 13.7% 7.8° 16.5 2.17 Safe Safe Safe Safe 1.13 10 16 1 17 125.00 5.00 23.00 21.7% 12.3° 1.36 352.00 50 14.2% 8.1° 16.5 2.09 Safe Safe Safe Safe 1.16 10 17 1 18 125.00 0.00 54.00 0.0% 0.01 a/e 406.00 50 12.3% 7.0° 16.3 2.41 Safe .Safe Safe Safe 1.56 10 18 1 19 120.00 5.00 30.00 16.7% 9.5° 1.79 436.00 55 12.6% 7.2° 16.5 2.35 Safe Safe Safe Safe 1.59 10 19 1 20 120.00 0.00 30.00 0.0% 0.01 a/e 466.00 55 11.8% 6.7° 16.5 2.51 Safe Safe Safe Safe 1.78 10 20 Slope Profile 180,00 -- --- _... r ad 170.00 h m e s i t e ;. 180.00 --- ----. ----- r ---•---------- 150.00 .....-------------- - ... - •-- •---' i Etevatlon (feet) 140.00 --------.....------- ---- 130.00 --.. ------------ .__d..r-e.i .,f.i_e_l.d_..a.r9 110.00 -----------------`------•----------,- MAO 0 100 200 300 400 500 Horizontal Distance(Feet) GEOTECHNICAL TESTING LABORATORY SITE PLAN w � . UJ Sc�T�c Tow.k 6�A 3s' w rb o 10011 Blomberg Street SW, Olympia, WA 98512 G EOTECHNICAL TESTING LABORATORY daylight FIGURE, 1 Critic:ul exposure colidilion for a IiWslde'fvotlng. i if FIGURE 2 1'roblenis of foundations on graded liWslde sites. 10011 Blomberg.StrW SW,Olympia, WA 98512