Large-scale model tests of biogrouting for sand and rock

Biogrouting as a new method for ground improvement or seepage control has been developed and extensively studied in recent years. Most studies have focused on lab bench, small-diameter sand column tests. To simulate in situ conditions more closely, biogrouting tests on two 1 m3 models were carried out. One was for pure silica sand and another was for rock blocks filled with sand. A significant reduction in permeability and an increase in shear strength were achieved in both model tests after ten rounds of biogrout treatment. The mechanical characteristics of the biologically cemented sand were studied using samples cored from the 1 m3 model. The distribution of the calcium carbonate content and the shear strength within the 1 m3 model was studied. Correlations between the unconfined compressive strength and the permeability of the cemented sand and the calcium carbonate content were established. Suggestions of methods to improve the uniformity of the biogrouting treatment are made in this paper.