138 Ground improvement by deep vibratory methods
With known parameters for the above expressions, the consolidation time
t can be calculated for different degrees of consolidation of the composite
layer of soil and stone columns. In practice, it is helpful to remember that
horizontal drainage is dominant in this scenario. Not only is the length of
the flow path within an infinite stone column pattern in radial direction very
often considerably shorter than in the vertical direction, but also horizontal
Impervious
boundaries
U v = f (T v )
h
k v
k h
Stone
column
d/2
d e /2
U r = f (T r , )
d
d e
Figure 4.21 Vertical and radial drainage flow characteristics.
0.001
0.2
0.4
0.6
0.8
1.0
0.01
Time factor T r , T v
0.1
1
1 0
Degree of consolidation U
v , U
r
0.3
0.5
0.7
0.9
0.1
0.0
v = Vertical flow
d e /d = 5
d e /d = 3
d e /d = 10
v
10
5
3
Figure 4.22 Time factors T v and T r for vertical and radial seepage flow. (Based on Terzaghi
and Peck, Die Bodenmechanik in der Baupraxis. Springer-Verlag, Berlin,
Germany, 1961 and Barron, Transactions of ASCE, 113(2346), 718–742, 1948.)