Chapter 15, Problem 15.20P

### Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939

Chapter
Section

### Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939
Textbook Problem

# A cut slope was excavated in a saturated clay with a slope angle β = 57° with the horizontal. Slope failure occurred when the cut reached a depth of 8 m. Previous soil explorations showed that a rock layer was located at a depth of 12 m below the ground surface. Assuming an undrained condition and that γsat = 19 kN/m3: a. Determine the undrained cohesion of the clay (Figure 15.12). b. What was the nature of the critical circle? c. With reference to the top of the slope, at what distance did the surface of the sliding intersect the bottom of the excavation?

(a)

To determine

Find the undrained cohesion cu of the clay.

Explanation

Given information:

The inclination angle β is 57°.

The saturated unit weight γsat of clay is 19kN/m3.

The depth Hcr of cut takes place is 8.0 m.

The depth of rock layer located below the ground surface is 12 m.

Calculation:

Determine the depth function D using the relation.

D=DepthofrocklayerlocatedbelowthegroundsurfaceDepthofcut

Substitute 12 m for depth of rock layer located below the ground surface and 8.0 m for depth of cut.

D=128=1.5

Refer Figure 15

(b)

To determine

Find the nature of the critical circle.

(c)

To determine

Find the distance that the surface of sliding intersects the bottom of the excavation.

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