Civil Engineering Reference
In-Depth Information
the embankment is constructed, (b) immediately after it is completed and (c) after a
very long time are:
(a) Before construction of the embankment:
•
in the clay:
σ
=
γ
z
=
20
×
2
=
40 kPa
z
u
=
γ
w
h
w
=
10
×
2
=
20 kPa
σ
z
=
σ
z
−
u
=
40
−
20
=
20 kPa
•
in the sand:
σ
=
γ
z
=
20
×
5
=
100 kPa
z
u
=
γ
w
h
w
=
10
×
5
=
50 kPa
σ
z
=
σ
−
u
=
100
−
50
=
50 kPa
z
(b)
Immediately after construction of the embankment the sand is drained so
the pore pressure remains constant. The embankment is wide so there are
no horizontal strains, the clay is undrained and the effective stresses remain
unchanged:
•
in the clay:
σ
=
γ
z
=
(4
×
15)
+
(2
×
20)
=
100 kPa
z
σ
z
=
20 kPa, as in (a)
−
σ
z
=
u
=
σ
100
−
20
=
80 kPa
z
•
in the sand:
σ
=
γ
z
=
(4
×
15)
+
(20
×
5)
=
160 kPa
z
u
=
50 kPa
σ
z
=
σ
−
u
=
160
−
50
=
110 kPa
z
(c) After a very long time the excess pore pressures in the clay will have dissi-
pated to the steady state conditions corresponding to the water table at original
