Soft Clay collected from construction sites and sent
to Tanah Merah Staging Ground (TMSG) are inherently very low in strength, and
are widespread in coastal regions such as Singapore. More than 80% of the earth
received by TMSG is Soft Clay, hence there is a need to optimise the use of clay
and reduce the usage of sand for reclamation. One of the ground improvement
schemes that has been adapted is using cement or lime for chemical
stabilization. Cement is used more in the Asia region not only due to its
relative abundance and lower cost, but it is also more effective (Lorenzo and
Bergado, 2004). The lower the water content of the clay, the greater the
strength improvement, thus a dryer mix proportion is often desired for higher
strength gains. However, mixing the clay in a dryer condition creates the
problem of homogeneity and workability that affects the efficiency of mixing
and therefore the improvement (Tan, et al., 2002; Quiroga, et al., 2017). A cement
and water content must be selected for the mixture to have sufficient strength
gain, and the ability to be mixed efficiently and have adequate workability.
The initial loss of water from the geotextile tube is
controlled by the pore size of the geotextile tube, but thereafter, the
formation of a filter cake occurs around the geotextile tube. The filter cake
is formed during the initial stages of dewatering as fine particles are trapped
in the geotextile and forms a bridge at the geotextile surface. As the
particles accumulate, they form a new filtration system. However, studies
governing the change in geometrical shape of the geotextile tube do not account
for formation of the filter cake. It is found that after the filter cake has
formed, the dewatering rate is controlled by the filter cake properties rather
than those of the geotextile (Maurer, 2011).
The function of a geotextile tube is to reduce the volume of water in
the pumped slurry in order to achieve a desired strength and solids content.
The geotextile tube undergoes four solids-water processes to occur within:
suspension, settling, deposition and consolidation (Yee and Lawson, 2012).
Figure 1: End of filling phases (Yee and Lawson, 2012)
During the filling stage, the effluent water starts to flow out of the
tube, being filtered by the geotextile membrane. The initial rate of dewatering
is quick and most apparent during the filling phase as compared to the drawdown
phase and can be attributed to the formation of the filter cake, impeding the
flow of the effluent out of the geotextile tube (Maurer, 2011; Yee, et al., 2012).
Further reduction of volume will be due to self-weight consolidation, and the
outflow of water from this process is negligible compared to the suspension and