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stresses become low and the sample fails. For states A, B and C characteristic
values are elaborated in the Table 7.3. Fig 7.10 is typical for loose to medium
dense sand. In very loose sand pore pressure build-up can continue all the way to
the stress origin, in which case liquefaction occurs. Draw the circles of Mohr for
state A, B and C.
Application 7.3
The immediate settlement of a saturated soft soil layer being subjected to a fill
on top is practically zero, but not at the edges of the fill (Fig 7.8). Why is that?
Application 7.4
Consider application 7.1. How much must the groundwater level rise to create a
critical situation (slope instability), according to the laboratory measurements? If
the rain has an intensity of 5 cm/day, how long should it rain to reach the critical
rise? Data provided: porosity
n
= 0.4, vertical permeability
k
v
= 0.08 m/day.
Application 7.5
If the circle of Mohr touches the failure envelope, the direction of the critical
shear plane can be determined. In Fig 7.2 a stress state (circle of Mohr) is given.
What are the directions of the critical shear plane (angles in degrees relative to the
x-axis)?
Application 7.6
At a given depth in soil the active soil state is defined by a vertical soil stress of
75 kPa and a horizontal stress 15 kPa. The cohesion is 15 kPa. What is the
corresponding friction angle and what is the maximum possible horizontal stress
(passive state)? Hint: Use a graphical approach.
Application 7.7
Given
c
= 15 kPa,
= 35°, Skempton's pore pressure parameter
A
= 1 (soft
normally consolidated clay), Skempton's pore pressure parameter
B
= 1 (saturated
soil), isotropic consolidation pressure
p
0
'
= 100 kPa.
- Draw a graph of the total and effective stress path (tsp resp esp) during
undrained triaxial compression.
- Estimate the undrained strength
c
u
.
- With
B
= 0, repeat in a new graph.
- Comment on the influence of
B
on
c
u
.
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