900 PACIFIC AVE WOMEN AND CHILDREN PAVILLION 2018-01-02 MF Import

i i IProvidence Famity Services Center 9-91M-12723-0 t August 25. 1999 P�8 ' S.0 SLOPE STABILITY ANALYSIS In order to establish an appropriate setback from the ravine slope for uGliGes,pavements,and other I features at the project site,we analyzed the slope stability under seiected conditions. The following sections describe our method of analysis and present our results. � 5_1 Mathod of Analvsis � Slope stability analyses rypically involve five basic slope parameters: (1)bocation and shape of the potential failure surface, ;2) intemal friction angle of the various soiis, (3)oohesion cf the various I soils, (4) densiry of the various soiis, and (5) location of the piezometric groundwater surface. Unfortunately, few of these parameters are accurately known at the start of an analysis. Instead, these parameters usually musl be esGmated, interpreted, and/or assumed on tha basis of visual I observations, field testing, laboratory testing, empirical correlations, and experienoe with similar � soil rypes. I Once all five parameters have been tentatively established,the critical slip surtace and assoaated safety factor of a given slope can be calculated. A"critical slip surface"is deftned as the most likely surface along which a soil mass will slide, and a"safe.y factor" is defined as the ratio oi tlie sum ( of all moments resisting slope movement versus the sum of ail moments tending to cause slope movement. ConseG��ntly,a slope that possesses a safety factor of 1.0 is on the verge of sliding, I whereas a slope with a safety factor greater than 1.0 has some resistance to sliding. Acoording to standard geotechnical engineering practice, a static safety factor of 1.5 and a seismic safety factor of 1.1 are considered the conservative minimum vaiues for most slopes, but 1.2 and 1.0, Irespectively, are often regarded as acceptable values. Slope stability conditions for the project site were analyzed by means of Bishop's Simplified Methbd � of Slices, which utilizes a limit-equilibrium technique. All calculations were performed by means of the computer program SLOPE-W. This program utilizes topographic, soil, and groundwater information input by the user to determine the most critical slip surface for a variety of geometries. The enclosed Geologic Cross-Section E-E'(Figure 7) i�lustrates the ravine slope geometry,and Table 4 lists our conservatively estimated values of intemal friction angle, cohesion, and densiry I for each soil layer. We also eiected to analyze the existing slope using a piezometric level be'(nv the ravine bottom, to simulate the groundwater conditions at the time of our fieid explorations. 8y convention, seismic stability conditions are analyzed by applying a horizontal acceleratlon equal � to one-half of the appropriate peak ground acceleration. Based on a peak bedrock acceleration I of 0.28g for the site, we utilized a design value of 0.14g. � i I � 5�woRDVAoc�ss Prqens�seankn2awsn.'.�Aco�nsm�vro.,emce Moso-M�woa �.� I