Civil Engineering Reference
In-Depth Information
9.4
Stresses due to Pre-loading and Subsequent Unloading
Increased horizontal in-situ stresses may also arise as a result of high overburden pres-
sure due to sediments or due to an ice load acting over long periods. These stresses may
persist over a geologic timescale, even if the formations above had been eroded away.
The origin of such horizontal stresses due to geological pre-loading and subsequent
unloading was described by Wittke (1990) in a qualitative manner. Figure 9.8 shows an
element e of clay originally located at the ground surface that is subsequently loaded by
an overburden increasing with time due to sedimentation. The clay is then consolidated
by the load of overburden and continuously converted into a claystone. This process is
called “diagenetic consolidation”.
Figure 9.8
Development of increased horizontal stress in a clay due to diagenetic consolidation and
erosion (Wittke 1990)
When a layer of thickness t
1
is sedimented, the clay element e is subjected to the vertical
stress
σ
V1
=
γ
S
⋅
t
1,
(9.12)
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