Kinetics of microfine cement filtration during constant rate permeation through sands
Permeation grouting is a cost-effective ground improvement technique that involves the injection of grout into the voids of geological material to improve the engineering properties by reducing the permeability and/or increasing the strength. Permeation grouting can be performed with either cementitious suspensions or chemical solutions. However, over the last several decades, cementitious suspensions have become popular for permeation grouting due to their cost-effectiveness, finer particle size distribution, and minimal impact on the environment. Nevertheless, the particulate nature of the microfine cement increases the susceptibility to filtration: a phenomenon that reduces the penetration performance of the grout and the uniformity of the delivered cement through the injected length of the soil material. The penetrability of a cementitious grout suspension is highly dependent on the stability and the filtration tendency of the cementitious grout, while the filtration of cement particles in the voids of the soil material is dependent on both the grain size distribution of the porous medium and the rheological properties of the grout itself. The research in this thesis consisted of various permeation grouting experiments constructed with a poorly graded mortar sand at variable lengths and permeated with four different grout mixes: two microfine cement grouts at water to cement (w:c) ratios of 2:1 and 3:1 and two microfine cement grouts at w:c ratios of 2:1 and 3:1 with 2 percent by weight of superplasticizer. During the permeation, the pressure buildup at the bottom of the sand columns was measured and the effluent was collected to determine the cement concentration of the grout with time for the duration of the permeation. After permeation, the sand columns were de-constructed and samples were taken to measure the cement distribution, in terms of w:c ratios, along the height of the column. The results of this research highlight the impacts that the stability and the filtration tendency of cementitious grouts, with and without superplasticizer, have on the pressure buildup at the bottom of a soil column, the cement concentration outflow for the duration of permeation, and the cement distribution along the injected length of a soil column.