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

Chapter 4 SOIL SETTLEMENT
Mesri et al (1994) proposed correlating the secondary compression index, C , with the compression
index, C c , at the same vertical effective stress of a soil. He found that the C /C c ration is the
constant for a soil deposit (see Table 4.2).
The time at which secondary consolidation is assumed to commence is not well defined. A
pragmatic approach is to assume that the secondary consolidation settlement commences when
95% of the primary consolidation is reached (Terzaghi et al, 1991).
Table 4.2 Values of C /Cc for Geotechnical Materials
Material
Granular soil
Shale and mudstone
Inorganic clays and silts
Organic clays and silts
Peat and muskeg
(Source: Mesri et al [24])
C /Cc
0.02 ± 0.01
0.03 ± 0.01
0.04 ± 0.01
0.05 ± 0.01
0.01 ± 0.01
4.6 DIFFERENTIAL SETTLEMENT
Damage in structures due to settlement may be classified under 3 categories:
a) Architectural damage such as cracking in wall partitions and plaster
b) Structural damage where the structural integrity are affected and
c) Functional damage where the function of the structure may be impaired.
Figure 4.8 The Building was built partly on filled and partly on original ground, which resulted in
cracks due to excessive differential settlement
Normally, uniform settlement will not give rise to damage. It is the differential settlement that has
to be controlled. However, differential settlement is difficult to estimate due especially to the nonhomogeneity
in the ground, and the large variations in the loadings between different supporting
members. Figure 4.8 illustrates the appearance of crack due to differential settlement in a building.
The limit of allowable settlement may be better expressed in terms of angular distortion, θ is
θ =δ / L (4.11)
4-10 March 2009