Mixing Quality

The goal of binder–soil mixing processes is often to produce a treated mass which is uniform in terms of strength and stiffness. In general, however, chemically stabilised soil mass invariably has a certain degree of non-uniformity. The parameters which are typically used to quantify the departure from a perfectly uniform mix are the coefficient of variation and the scale of fluctuation. Such non-uniformity typically arises from two sources. Firstly, the in situ soil may be non-uniform. Spatial variation in soil strength has been widely studied (e.g. Phoon and Kulhawy 1999 ; Kim 2005 ). However, Liu et al. (2019) noted that the strength of in situ soil is not readily correlated to the stiffness and strength of the soil after treatment, since the soil would have been remoulded and admixed with binders. Instead, they proposed that a more appropriate parameter for characterising spatial variation within a layer of deposited soft clay to be improved is the in situ water content. For instance, Liu et al.’s (2019) data from the Marina Bay Financial Centre site appears to show higher water content in the mid-layer of the soft clay, which is consistent with the fact that the soil is still consolidating. This is also correlated to the variation in strength of the cement-treated clay.