Cement mixedclaySoft Clay collected from construction sites and sentto Tanah Merah Staging Ground (TMSG) are inherently very low in strength, andare widespread in coastal regions such as Singapore. More than 80% of the earthreceived by TMSG is Soft Clay, hence there is a need to optimise the use of clayand reduce the usage of sand for reclamation. One of the ground improvementschemes that has been adapted is using cement or lime for chemicalstabilization. Cement is used more in the Asia region not only due to itsrelative abundance and lower cost, but it is also more effective (Lorenzo andBergado, 2004).
The lower the water content of the clay, the greater thestrength improvement, thus a dryer mix proportion is often desired for higherstrength gains. However, mixing the clay in a dryer condition creates theproblem of homogeneity and workability that affects the efficiency of mixingand therefore the improvement (Tan, et al., 2002; Quiroga, et al.
, 2017). A cementand water content must be selected for the mixture to have sufficient strengthgain, and the ability to be mixed efficiently and have adequate workability.Filter CakeFormationThe initial loss of water from the geotextile tube iscontrolled by the pore size of the geotextile tube, but thereafter, theformation of a filter cake occurs around the geotextile tube. The filter cakeis formed during the initial stages of dewatering as fine particles are trappedin the geotextile and forms a bridge at the geotextile surface.
As theparticles accumulate, they form a new filtration system. However, studiesgoverning the change in geometrical shape of the geotextile tube do not accountfor formation of the filter cake. It is found that after the filter cake hasformed, the dewatering rate is controlled by the filter cake properties ratherthan those of the geotextile (Maurer, 2011).DewateringEfficiencyThe function of a geotextile tube is to reduce the volume of water inthe 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 thetube, being filtered by the geotextile membrane. The initial rate of dewateringis quick and most apparent during the filling phase as compared to the drawdownphase and can be attributed to the formation of the filter cake, impeding theflow 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 theoutflow of water from this process is negligible compared to the suspension andsettling processes.