StatementA 12-m high rock slope has been excavated at aface angle of 60°. The rock in which this cut hasbeen made contains persistent bedding planes thatdip at an angle of 35° into the excavation. The4.35-m deep tension crack is 4 m behind the crest,and is filled with water to a height of 3 m abovethe sliding surface (Figure 6.15). The strengthparameters of the sliding surface are as follows:Cohesion, c = 25 kPaFriction angle, d = 37°The unit weight of the rock is 26 kN/m³, and theunit weight of the water is 9.81 kN/m³.RequiredAssuming that a plane slope failure is the mostlikely type of instability, analyze the followingstability conditions.H=12mTIRSTRIT₁=60°4m➜TRINIT TIKITRIT TINTZ=4.35 mp=35° Zw=3mFigure 6.15 Plane failure geometry for ExampleProblem 6.1.Factor of safety calculations(a) Calculate the factor of safety of the slope forthe conditions given in Figure 6.15.(b) Determine the factor of safety if the tensioncrack were completely filled with water dueto run-off collecting on the crest of the slope.(c) Determine the factor of safety if the slopewere completely drained.(d)Determine the factor of safety if the cohesionwere to be reduced to zero due to excessivevibrations from nearby blasting operations,assuming that the slope was still completelydrained.(e) Determine whether the 4.35-m deep tensioncrack is the critical depth (use Figure 6.6).Slope reinforcement using rock bolts(a) It is proposed that the drained slope withzero cohesion be reinforced by installing ten-sioned rock bolts anchored into sound rockbeneath the sliding plane. If the rock bolts areinstalled at right angles to the sliding plane,that is, T = 55°, and the total load on theanchors per lineal meter of slope is 400 kN,calculate the factor of safety.(b) Calculate the factor of safety if the bolts areinstalled at a flatter angle so that the T isdecreased from 55° to 20°.(c) If the working load for each bolt is 250 kN,suggest a bolt layout, that is, the number ofbolts per vertical row, and the horizontal and

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Factor of safety calculations (b) (a) Calculate the factor of safety of the slope for the conditions given in Figure 6.15. Determine the factor of safety if the tension crack were completely filled with water due to run-off collecting on the crest of the slope. Determine the factor of safety if the slope were completely drained. (c) (d) Determine the factor of safety if the cohesion were to be reduced to zero due to excessive vibrations from nearby blasting operations, assuming that the slope was still completely drained. (e) Determine whether the 4.35-m deep tension crack is the critical depth (use Figure 6.6). Slope reinforcement using rock bolts (a) It is proposed that the drained slope with zero cohesion be reinforced by installing ten- sioned rock bolts anchored into sound rock beneath the sliding plane. If the rock bolts are installed at right angles to the sliding plane, that is, T = 55°, and the total load on the anchors per lineal meter of slope is 400 kN, calculate the factor of safety. (b) Calculate the factor of safety if the bolts are installed at a flatter angle so that the T is decreased from 55° to 20°. (c) If the working load for each bolt is 250 kN, suggest a bolt layout, that is, the number of bolts per vertical row, and the horizontal and

9th Edition

ISBN:9781305970939

Author:Braja M. Das, Khaled Sobhan

Publisher:Braja M. Das, Khaled Sobhan

Chapter14: Lateral Earth Pressure: Curved Failure Surface

Section: Chapter Questions

Problem 14.3P