Civil Engineering Reference
In-Depth Information
The cross-sectional area of the box was 3600 mm
2
and the test was carried out in a fully
instrumented shear box apparatus.
Determine the strength parameters of the soil in terms of effective stress.
Solution:
The plot of load transducer readings against strain is shown in Fig.
4.13a
. From this plot,
the maximum readings for normal loads of 0.2, 0.4 and 0.8 kN were 138, 237 and 417 kN.
For this particular case, the maximum readings could obviously have been obtained
directly from the tabulated results, but viewing the plots is sometimes useful to dem-
onstrate whether one of the sets of readings differs from the other two.
The shear stress at each maximum load reading is calculated.
Normal load (kN)
Normal stress (kPa)
Shear force (N)
Shear stress (kPa)
0 2 10
3600
.
×
6
0 138 10
3600
.
×
6
0.2
=
56
138
=
38
0.4
111
237
66
0.8
222
417
116
The plot of shear stress to normal stress is given in Fig.
4.13b
.
The effective stress envelope is obtained by drawing a straight line through the three
points. The strength parameters are:
φ
′
=
25°; c
′
=
13 kPa.
Fig. 4.13
Example
4.3.
