Laserfiche WebLink
Providence Family Services Center 9-91 M-12723-0 <br /> � Augusl 25, 1999 P�9 <br /> TABLE 4 <br /> ESTIMATED PROPERTIES OF ON-SITE SOILS FOR STABILITY ANALYSIS <br /> Soil Type Density Cohesion Inbrnal F�iction <br /> (pc� (ps� Angle <br /> (degreas) <br /> Medium-Dense Weathered Till 115 0 32 <br /> Ve Dense Glaciai Till 135 250 35 <br /> 5.2 Results of Analvsis <br /> IUtilizing the aforementioned values oi intemal friction angle, cohesion, density, and piezometric <br /> elevation, we calculated the safery factors associated with numerous slip surfaces, inGuding <br /> I circular and non-circular shapes. We subsequently found that the minimum safety factors <br /> correspond with a shallow slide that originates about 10 to 12 feet behind the slope brink. This <br /> sliding mode represents failure within the weathered till layer and indicates that the soil becorties <br /> ( more slide-resistant with depth; that is, deep-seated slope movements involving the giacial till <br /> deposit are highly unlikely. Appendix C of this report contains diagrams illustrating the various <br /> failure geometries. Our analyses yieided minimum safety factors of 1.21 and 1.26 under static <br /> I conditions, and safety factors of 0.97 and 0.98 under seismic conditions. Table 5 summarizes <br /> these anaiytical result�. <br /> � All of the static safety factors derived From our stability analysis meet or exceed the aforementioned <br /> acceptable minimum value, whereas two of the seismic safety factors are slightly below the <br /> acceptable minimum desired value. The latter results indicate that slope failure is possible during <br /> { a fairly strong earthquake (with an acceleration of 0.28 or higher). However, �uch a failure wouid <br /> � not necessarily be a totai collapse of the soil mass involved; rather, it might be only a subsidence <br /> of several inches or several feet. Furthermore, the results indicate that such a failure would <br /> Iprobably invo!ve only the soil within about 10 to 12 horizontal feet of the slope brink. <br /> � TABLE 5 <br /> CALCULATED SAFETY FACTORS FOR SELECTED SLIDE CONDITIONS <br /> ( Sliding Sliding Static Saismfc <br /> Depth Mode Safety Factor Safety Factor <br /> Shallow-seated Circular 1.21 0•97 i <br /> IShallow-seated Non-Circular 1.26 0.98 I <br /> Dee -seated Circular 1.53 1.22 � <br /> I (, <br /> I5�WOROPROC�99 PrqKu�SealUe�17000s�iP2]RoO�nspmPm�nOence HOIp�Rp1 wpa �� <br /> I <br />