Vibro compaction of granular soils 73
The primary effect of the shaking of saturated sand is the generation of
excess pore water pressure with settlement occurring as it dissipates. The
time for the settlement to develop depends on the length of the drainage
path and the permeability of the sand. In highly permeable sand, it may
occur immediately, but in less permeable sand only after many hours.
It has been found that volume deformation decreases with increasing density of the sand and decreasing induced strain. Accordingly, the volumetric
strain ε v in saturated sand developing after liquefaction as proposed by
Tokimatsu and Seed (1987) is presented in Figure 3.29 as a function of the
CSR and corrected normalized SPT blow count (N 1 ) 60 . The abscissa uses a
conversion between relative density D r and SPT N-values proposed by the
same researchers, which is based upon an empirical expression which G.
Meyerhof had presented in 1957 as follows:
D
N
r
0
21
0.7
= ⋅
′ +
σ
(3.18)
with the effective overburden pressure ′
σ 0 in kg/cm 2 (1 kg/cm 2 = 100 kPa).
10
0
0.3
0.2
0.1
0.5
0.4
0.6
0.0
M = 7.5
Volumetric strain (%)
10 5 4 3
2
1 0.5
0.2
0.1
CSR
47
67
80
90
0
Relative density D r (%)
(N 1 ) 60
20
30
40
50
Figure 3.29 Relationship between CSR, (N 1 ) 60 , and volumetric strain in saturated sand.
(Redrawn from Tokimatsu, K. and Seed, H.B., J. Geotech. Eng., ASCE, 113,
861, 1987.)