Civil Engineering Reference
In-Depth Information
(i) Determine the value of the pore pressure coefficient B and state whether or not the
soil was saturated.
(ii) Plot the variation of deviator stress with strain.
(iii) Plot the variation of the pore pressure coefficient A with strain.
Solution:
(i)
∆
∆
σ
3
u
a
120
300
B
=
=
=
0 4
.
The soil was partially saturated as B was less than 1.0.
A
A
B
Strain (%)
Δ
u
d
(
Δ
σ
1
−
Δ
σ
3
)
A
30
200
2.5
30
200
=
.
0 15
0.375
5.0
30
420
0.071
0.178
7.5
0
620
0
0
10.0
−
40
750
−
0.053
−
0.132
15.0
−
110
900
−
0.122
−
0.304
20.0
−
180
950
−
0.188
−
0.470
Fig. 4.28
Example
4.9.
4.11 The triaxial extension test
In the normal triaxial test the soil sample is subjected to an all-around water pressure and fails under an
increasing axial load. This is known as a compression test in which
σ
1
>
σ
2
=
σ
3
.
When the cohesive intercept, c
′
, is equal to zero, as is the case for drained granular soils, silts and
normally consolidated clays, then the relevant form of the Mohr-Coulomb equation is:
′
−
′
=
′
′
+
′
′
σ
σ
σ
sin
φ
σ
sin
φ
1
3
1
3
