Q1. [30 Marks]
Table 1 gives data from a standard shearbox (direct shear) test on a sample of 125g of dry sand. The initial dimensions of the sample were 60mm×60mm on plan ×20mm in height. The test was carried out at a constant normal effective stress of 50kPa. Take the specific gravity of the soil grains Gs=2.65. Plot graphs of
(a) shear stress τ against shear strain γ;
(b) volumetric strain εvol against shear strain γ;
(c) specific volume υ against shear strain γ .
(d) Comment on these graphs and estimate the peak and critical state effective angles of friction of the soil.
Table 1: Shearbox Data
|
Relative horizontal displacement x (mm)
|
Upward vertical movement of shearbox
lid y (mm)
|
Shear stress τ (kPa)
|
|
0
|
0
|
0
|
|
0.02
|
0.002
|
19
|
|
0.04
|
0.008
|
34
|
|
0.06
|
0.016
|
43
|
|
0.08
|
0.026
|
47
|
|
0.20
|
0.064
|
56
|
|
0.32
|
0.128
|
51
|
|
0.48
|
0.192
|
46
|
|
0.64
|
0.256
|
41
|
|
0.80
|
0.288
|
37
|
|
0.96
|
0.320
|
34
|
|
1.12
|
0.321
|
33
|
Q2. [40 Marks]
Table 2 gives data from consolidated-undrained triaxial compression tests on three samples of a particular type of clay. Explaining your reasoning, identify the peak and the critical state strengths in terms of friction angle for each test. Why is it not possible to identify a critical state strength in test 3? On one diagram, plot the Mohr circles of stress at the peak strength for all three tests, and sketch in the peak strength failure envelope. On a separate diagram, plot the Mohr circles of stress at the critical state for tests 1 and 2, and estimate the critical ' state strength φcric .
Table 2: Triaxial test data
Q3. [30 Marks]
Using your own words, outline the procedure/steps (using bullet points) for performing the conventional consolidated-drained test for a saturated clay-type soil sample. Word limit: 1000.