Civil Engineering Reference
In-Depth Information
The term Cam clay was coined by the Cambridge research workers because the
river in Cambridge is called the Cam. Do not misunderstand this. You cannot go to
Cambridge and dig up any Cam clay; it is simply the name of a theoretical model or
a set of equations. The status of Cam clay is like the status of elasticity. You cannot
find any elasticity anywhere; what you can find is steel or copper which behave in a
way very like the theory of elasticity, at least over small strains. In the same way you
cannot find any Cam clay; what you can find are reconstituted (and some intact) soils
that behave in a way very like the theoretical model called Cam clay.
12.3 State boundary surface for ordinary Cam clay
The basic equation for the state boundary surface for ordinary Cam clay is
ln
p
−
−
q
Mp
+
λ
λ
−
κ
v
λ
−
κ
=
1
(12.1)
The basic parameters
M
,
have been described in earlier chapters. They are
all material parameters and depend only on the nature of the soil grains.
This equation defines the state boundary surface shown in Fig. 12.1. The surface
meets the
v
λ
,
κ
and
p
plane along the isotropic normal compression line where
q
:
=
0 and
ln
p
and hence, substituting in Eq. (12.1),
v
=
N
−
λ
N
−
=
λ
−
κ
(12.2)
The curves shown in Fig. 12.1 are constant volume sections and undrained stress
paths. The equation for an undrained stress path can be obtained from Eq. (12.1) with
Figure 12.1
State boundary surface for ordinary Cam clay.
