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January 15, 2008 <br />FOS = <br />4.4 Analysis Results <br />tan (actual friction angle) <br />tan( friction angle at failure) <br />Page 30 <br />(Eqn. 8) <br />The results of the analysis are summarized in Table 5. The most relevant case for <br />recommending maximum spoil pile heights is Case #4c for the average bedding dip of 13° and <br />Case #5c for the steepest bedding of 25°. Only results from these two cases are presented here. <br /> Table 5. Summary of Results for Cases Analyzed <br /> Slope Fill Height Spoil <br /> (H:V)/ above Q- Bedding Bedding Spoil Friction at <br /> Angle Floor at Toe Dip Friction Cohesion Lim of Equi Safety <br />Case (°) (ft) (°) (°) (psf) (°) Factor <br />4a 1.3/37.6 205 13 5 0 51 Unstable <br />4b 1.3/37.6 137 13 5 0 46 Unstable <br />4c 1.3/37.6 68 13 5 0 38 1.07 <br />5a 1.3/37.6 50 25 15 0 55 Unstable <br />5b 1.3/37.6 40 25 15 5 47 Unstable <br />5c 1.3/37.6 30 25 15 50 38 1.07 <br />*Depth from Ground to Q-Floor is 217 ft <br />Case #4c had a spoil slope face of 37.6° (1.3H:1 V) and a spoil pile height of 68 ft above <br />the toe. The groundwater table was assumed 1 ft above the weak Q-Floor mudstone to represent <br />saturated mudstone but drained spoils. The initial spoil strength parameters were 0 = 55°, C = 0, <br />Tf= 0. The initial peak bedding plane strength, was assumed to be Oi = 15° for the Q-Floor <br />mudstone. <br />The equilibrium state was computed assuming no groundwater effects: drained, <br />unsaturated conditions. The groundwater table was then introduced and the mass density below <br />the phreatic surface was adjusted to simulate saturated conditions and the model rerun to <br />equilibrium. The Q-Floor mudstone strength was then reduced to a residual strength condition <br />(0j = 5°) to represent long-term softening of the Q-Floor on the inclined bedding. The limit of <br />equilibrium state was reached when the spoil friction was reduced to 38°. <br />Contours of velocity, shown in Figure 18, illustrate the unstable area of the spoil pile. <br />The gray area has low velocities which are considered negligible. The model is not in an <br />equilibrium state and, thus, the slope is considered unstable under these conditions. The failure <br />mode is indicated by a circular slip mechanism in the spoil pile; not unstable slip along bedding. <br />The case with the next increment of spoils added had higher velocities and also did not come to <br />an equilibrium condition at spoil friction above 40°. The safety factor for this case of 68 ft of <br />spoils is FOS =1.07. <br />Agapito Associates, Inc.