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CIEM5740 Computer Methods for Slope Engineering

Assignment 2

(Due: 11:00 pm, Friday 18 Oct 2024, submitted online)

Q1 (50 Marks) Please derive the expression of factor of safety for an infinite slope (with effective strength parameters c' and f') for a case of seepage parallel to the slope surface. You may wish to refer to Chapter 6 of the book by Duncan and Wright (2005) (uploaded in CANVAS → Modules→ Reading materials→CIEM5740-Reading-DW-Book-chpt6.pdf).

Q2 (50 Marks) The following case study involving a failure in fissured over-consolidated clay slope was reported by Henkel and Skempton in 1954 (Henkel, D.J. and A.W. Skempton, 1954. "A landslide at Jackfield, Shropshire, in an over-consolidated clay", Geotechnique, 5:2:131-137). The failure occurred in 1952 in Jackfield, Shropshire, England. The slope profile is shown in Figure 1. The failure was a translational slide where the average depth to the failure plane was 17 ft. The ground water table was very near or at the surface. The peak strength parameters of the over-consolidated clay are: cohesion, c'= 220 psf and friction angle, φ'= 25°. The saturated unit weight of the soil is 145 pcf. (1) Please perform a simple infinite slope analysis with seepage parallel to the slope to determine the factor of safety. Based on your results what can you conclude on the use of the peak strength parameters in long-term stability investigation of overconsolidated clays. (2) Please try to use SLOPE/W to verify your result in (1). Hint: you may use “fully specified slip surface” method to define the actual failure surface. Also please choose the correct unit in SLOPE/W.

Figure 1 Profile of the Jackfield slope, Shropshire, England