Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 4 SOIL SETTLEMENT
4.3.1 Normally Consolidated Soils
The settlement of a geotechnical feature or a structure resting on n layers of normally consolidated
soils (p c = p o) can be computed from Figure 4.3 where n is the number of layers into which the
consolidating layer is divided:
c c
n
S c = ∑i H o log p f
10 (4.4)
1+e 0 p o
Figure 4.3 Typical Consolidation Curve for Normally Consolidated Soil
The final effective vertical stress is computed by adding the stress change due to the applied load
to the initial vertical effective stress. The total settlement will be the sum of the compressions of
the n layers of soil.
4.3.2 Overconsolidated (Preconsolidated) Soils
For overconsolidated clay, i.e., OCR >1, the soils could have in the past subjected to a greater
stress than exists now. It maybe due to many factors including erosion of the weight of the natural
soil deosit, removal of the weight of a previously placed fill or structures, etc.
As a result of preconsolidation, the field state of stress will reside on the initially flat portion of the
e-log p curve. Figure 4.4 illustrates the case where a load increment, ∆p, is added so that the final
stress, p f . For this condition, the settlements for the case of n layers of overconsolidated soils will
be computed by summing the settlements computed from each subdivided compressible layer
within the zone of influence.
c c
n
S = ∑i (c r log p c
10 + c c log p f
10 )
1+e 0 p o
p c
March 2009 4-5