Self-Harddeningng Slurry Filtration and the End of the API Test Dead End

By comparison to the management of bentonite trenching slurries where the use of the standard API filtration test is common QC practice, in the case of self-hardening trenching slurries (SHS), the API filtration test is rarely used or specified and for good reasons. Nevertheless, filter cakes resulting from loss of makeup water through the side walls of the trench do form and are many times thicker than those of a pure bentonite slurry. The standard API filtration apparatus is simply inadequate for self-hardening slurries. A modified apparatus operating at pressures corresponding to actual hydrostatic heads, and during realistic durations corresponding to actual trenching construction sequence is required and is available. The magnitude of filter cakes is determined for a variety of SHS formulations at a specific pressure. Increased concentration of solids from the basic SHS formula at the top of the cake to the interface with the ground is given as a variation of density and moisture content. The effect of suspended solids of a working SHS is given in parallel to base pure SHS. A discussion on the role of SHS filter cakes in SHS cutoff wall design is provided as well future directions of research to follow.