Geoscience Reference
In-Depth Information
Table 6.4
General ground improvement methods for soft ground (
after
Sin, 2003)
Type of
treatment
Advantages/
disadvantages
Technical input
Piled
embankment
Instead of consolidating the soft compressible layer, it acts
as a structure and transfers all of the embankment load to
the tip of the piles. Nominal post-construction settlement.
Expensive/minimum
post-construction
settlement
Prefabricated
vertical
drain
(PVD)
Suitable and economical method to consolidate the soft
compressible layer. Nevertheless, progress of embankment
construction is slow due to the time taken to increase the
undrained shear strength being much longer.
Cheap/long
construction period
Stone
column
(SC)
Close spacing of SC expedites consolidation of soft
compressible layers. Compaction of stone will be a
difficulty due to the low undrained shear strength
(
<
15 kNm
−
2
) and lack of confinement strength.
Expensive, potential
for column bulging
effect
Total
replacement
(R/R)
With proper compaction of backfilling material,
post-construction settlement can be kept to a minimum.
Disposal of unsuitable material will be a great
concern. Replacement ratio is 100%.
Construction problem
due to high ground
water, disposal site
due to environmental
restraint
6.13 CHOICE OF CONSTRUCTION METHODS
As mentioned before, buildings on peat are often constructed on piles. But for line
structures like roads, the choice of construction method is a matter of finding optimal
solutions between economic and technical factors, available construction time and the
target performance standards. Undoubtedly construction in this difficult terrain is not
easy, but with better understanding it can be more manageable.
In evaluating the effectiveness of the various construction techniques, many
variables need to be considered. These include:
•
Effectiveness of the methods
•
Availability of materials and equipments
•
Cost of materials
•
Construction time
•
Post construction maintenance
•
Environmental effects
Table 6.4 presents a review of the ground improvement techniques applicable for
general soft soils.
McManus
et al.
(1997) recommended the following options when constructing on
peat, depending on the thickness of the deposits:
•
Removal and replacement when the thickness of the deposit is
≤
3m.
•
When the thickness of the deposit is more than 3mbut less than 10m, the following
options may be considered: preloading, stage construction with vertical and sand
drains, lightweight fills and surface mattresses.
