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

Chapter 8 GROUND IMPROVEMENT
Figure 8.13 Relationship of F(n) and D/dw
Figure 8.13 shows the relationship of F(n) to D/d w for the ideal case. Within a typical range of D/d w ,
F(n) ranges from approximately 2 to 3.
The theory of consolidation with radial drainage assumes that the soil is drained by a vertical drain
with circular section. The radial consolidation equations include the drain diameter, d. A band shape
PVD drain must therefore be assigned as “equivalent diameter”, d w. For design purposes, it is
reasonable to calculate the equivalent diameter as:-
where,
d w = (2(a+b)/π) (8.5)
a
b
= width of the band – shaped drain cross section
= thickness of a band-shaped drain cross section
Equation A8.5 can be further simplified to
d w = (a + b) /2 (8.6)
8A-4 March 2009