HomeMy WebLinkAboutBLD2009-00161 GEO TECH •
Slope Stability Calculations (Simplified Bishop's Method of Circles)
/ 30'
i
90 ft �- Rotational Failure AUG 1 9 2009
Plane L_Not t+c�scale(nrrs)I .J !
Alpha=11.3 deg + _
\ (25%slope)
1. Compute factor of safety(FS)against sliding-Static Case(Ref "Stability Charts for Uniform Slopes"by
Radoslaw L. Michalowski, FASCE) - "Journal of Geotechnical and Geoenvironmental Engineering",April 2002.
From Figure 3"Stability charts for uniform slopes"the following parameters are known for native coarse silty sands
with some gravels(SW-SG):
c(cohesion)=200 psf, gamma(insitu unit density)= 141 pcf, H(height of slope)=90 ft,
phi(internal friction angle)=29 deg, then
c/[gamma x H x tan(phi)]=200/(141 x 90 x tan 29)=0.0284
Then for a 11.3 deg(25%)slope from Fig. 3:
FS/tan(phi)=FS/tan(29)=5.3 or, FS=Factor of Safety Against Sliding= 2.938>1.500 OKAY
2. Compute factor of safety(FS)against sliding-Quasi-Static(Seismic)Case(Ref: "Stability Charts for Uniform Slopes"
by Radoslaw L. Michalowski, FASCE) - "Journal of Geotechnical and Geoenvironmental Engineering",April 2002.
From Figure 4"Stability charts for uniform slopes"the following parameters are known for native coarse silty sands
with some gravels(SW-SG):
c(cohesion)=200 psf, gamma(insitu unit density)= 141 pcf, H(height of slope)=90 ft,
phi(internal friction angle)=29 deg, then
c/[gamma x H x tan(phi)]=200/(141 x 90 x tan 29)=0.0284
Then for a 11.3 deg slope(25%)slope from Fig.4 for a quasi-static analysis coefficient of 0.1:
F/tan(29)=3.8 or FS=Factor of Safety=2.106
For a quasi-static analysis coefficient of 0.2:
F/tan(29)=3.6 or FS=Factor of Safety= 1.996
As a result,for a quasi static analysis coefficient of 0.15,the Factor of Safety,FS=(2.106+1.996)/2=2.051> 1.100 OKAY
Slope Stability Analysis for 2-car Garage w/ADU
located at 6834 Oak Bay Road, Port Ludlow,WA 98365 Prepared by: Morta Engineering&Testing PLLC,1018 E.Wishkah St,Aberdeen,WA 98520
(parcel#821 051 016) (360)289-0958, (800)590-0958,(360)289-9682 fax,Smorta@AOL.com
Prepared for:Larry Rick, 6834 Oak Bay Road April 16,2008
Port Ludlow,WA 98365,(206)377-9143 cell Rev: Aug.15,2009 1 Site Visit:Fri.8-14-2009 Sheet 2 of 3
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Geotechnical Engineering Report for 2-car Garage Prepared by: MET,PLLC(Norte Engineering and Testing,PLLC) o
at 6834 Oak Bay Road, Port Ludlow,WA 98365 1018 E.Wshkah St,Aberdeen,WA 98520 c
(Parcel#821 051 016, Case#ZON07-00002) (800)590-0958,(360)289-9682 fax, Smorta@AOL.com ! ..
Prepared for: Lary Rick,6834 Oak Bay Road
Port Ludlow,WA 98365,(360)437-9792 May 6,2008 Site Visit:Fri.8 14-'09 Page 3 of 3
Rev:8-15-2009
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Updated Geotechnical Engineering Report for Garage Prepared by: MET,PLLC(Morta Engineering and Testing,PLLC)
at 6834 Oak Bay Road, Port Ludlow,WA 98365-9410 1018 E.Wishkah St.,Aberdeen,WA 98520 Scale 1"=50'
(Parcel#821 051 01 6,Case#ZONo7-00002) (800)590-0958,(360)289-9682 fax, Smorta@AOL.corn
Prepared for: Larry Rick,6834 Oak Bay Road,Port Ludlow,WA April 16,2008 0' 10' 20' 30'40' 50' 60' 70' 80'90'100'
98365,(360)437-9792 res, (206)377-9143 cell Rev:Aug.15,2009 Site Visit on Fri.8-14'09 Page 1 of 3