Civil Engineering Reference
In-Depth Information
Exercises
Exercise 4.1
A soil sample is tested to failure in a drained triaxial test using a cell pressure of
200 kPa. The effective stress parameters of the soil are known to be
φ
′
=
29° and
c
′
=
0.
Determine the inclination of the plane of failure, with respect to the direction of
the major principal stress, and the magnitudes of the stresses that will act on this
plane. What is the maximum value of shear stress that will be induced in the soil?
Answer
Failure plane inclined at 30.5° to major principal stress.
Effective normal stress on failure plane
=
295 kPa.
Shear stress on failure plane
=
161 kPa.
Maximum shear stress
=
184 kPa.
Exercise 4.2
A soil has an effective angle of shearing resistance,
φ
′
, of 20° and an effective cohe-
sion, c
′
, of 20 kPa. What would you expect the value of the vertical stress to be at
failure if the soil is subjected to:
(a) a drained triaxial extension test with a cell pressure of 250 kPa?
(b) a drained triaxial compression test with the same cell pressure?
Answer
(a) 95 kPa,
(b) 567 kPa
Exercise 4.3
The readings below were taken during two shear box tests carried out on samples
of the same sand. In both cases the normal stress was 200 kPa.
Shear stress (kPa)
Horizontal
displacement (mm)
Test 1
Test 2
0
0
0
0.5
59
73
1.0
78
118
1.5
91
143
2.0
99
150
2.5
106
149
3.0
111
139
3.5
113
133
4.0
114
126
4.5
116
122
5.0
116
120
Draw the shear stress/displacement curves for the two tests, and determine the peak
and consant volume values of angle of shearing resistance.
Answer
φ
′
=
37°,
φ
′
=
30°
