A 25-m high rock cut with a face angle of 60° has been excavated in a massive, very weak volcanic tuff. A tension crack has opened behind the crest and it is likely that the slope is on the point of failure, that is, the factor of safety is approx imately 1.0. The friction angle of the material is estimated to be 35°, its density is 25kN / (m ^ 3) and the position of the water table is shown on the sketch of the slope (Figure 4). The rock contains no continuous joints dipping out of the face, and the most likely type of failure mode is circular failure. Required- (a) Carry out a back analysis of the failure to determine the limiting value of the cohesion when the factor of safety is 1.0. (b) Using the strength parameters calculated in (a), determine the factor of safety for a completely drained slope. Would drainage of the slope be a feasible method of stabilization? (c) Using the ground water level shown in Figure 4 and the strength parameters calculated in (a), calculate the reduction in slope height, that is, amount of unloading of the slope crest required to increase the factor of safety to 1.3. (d) For the slope geometry and ground water level shown in Figure 4, find the coordin ates of the center of the critical circle and the position of the critical tension crack.
Q9.1 -
A 25-m high rock cut with a face angle of 60° has been excavated in a massive, very weak volcanic tuff. A tension crack has opened behind the crest and it is likely that the slope is on the point of failure, that is, the factor of safety is approx imately 1.0. The friction angle of the material is estimated to be 35°, its density is 25kN / (m ^ 3) and the position of the water table is shown on the sketch of the slope (Figure 4). The rock contains no continuous joints dipping out of the face, and the most likely type of failure mode is circular failure.
Required-
(a) Carry out a back analysis of the failure to determine the limiting value of the cohesion when the factor of safety is 1.0.
(b) Using the strength parameters calculated in (a), determine the factor of safety for a completely drained slope. Would drainage of the slope be a feasible method of stabilization?
(c) Using the ground water level shown in Figure 4 and the strength parameters calculated in (a), calculate the reduction in slope height, that is, amount of unloading of the slope crest required to increase the factor of safety to 1.3.
(d) For the slope geometry and ground water level shown in Figure 4, find the coordin ates of the center of the critical circle and the position of the critical tension crack.
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