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

Chapter 8 GROUND IMPROVEMENT
each pass, the craters are either levelled with a dozer or filled with
granular fill material before the
next pass of energy
is applied. Figure 8.10 shows the schematic of the dynamic compaction process.
Figure 8.10 Dynamic Compaction
All of the energy is
applied from
existing grade and the
degree of improvement is a function of the
energy applied i.e.,
the mass of the tamper, the drop height, the grid spacing
and the number of
drops at each grid point location.
The application of
dynamic compaction shall take into consideration the noise and vibration
disturbances to the surrounding. Excessive vibration
may cause
distresses to the neigbouring
structures.
In situ test such as SPT, CPT or Piezocone can be used during and after completion of dynamic
compaction to verify whether the desiredd improvement has not
been achieved. If necessary,
additional energy could be applied to further improve
the densification and improvement of the
ground.
8.2.7
Some
Additional
Considerations
a) The selection of ground improvement methods is subjected to the following
criterions:-
i) Cost effectiveness of the treatment method as
compared to the overall project cost
ii) The availability of the
treatment method in the country
iii)
Types of soil to be treated
iv)
Long term
and differential settlement requirements for the
structures
b) The
construction rate of the earthworks is usually faster than the dissipation of pore water
pressure (especially in low permeability
clay soil). The initially high excess pore water pressure
developed in the ground due to rapid construction will reduce the effectivee strength of the soil
and
may lead to ground instability. However, the excess pore pressure will slowly dissipate with
time, thus increases the effective stresss of the soil which eventually increases the stability of the
ground. Hence,
total stresss analysis with undrainedd condition, which is usually the most critical
condition, is used in the design of ground treatment.
8-10
March 2009