Experimental optimization of microbially induced calcite precipitation (Micp) for contact erosion control in earth dams

Abstract

Microbial Induced Calcite Precipitation (MICP) is a bio-mediated soil improvement technique which is low-cost, low-maintenance and non-disruptive to wild life and aesthetics. It holds the potential for simultaneously retaining the hydraulic conductivity, increasing the shear resistance and preferentially cementing the interface between coarse and fine particles. Previous studies have shown that, unlike other biocementation works—such as liquefaction control and railroad embankment stabilisation—the shear strength increase necessary on interfaces vulnerable to contact erosion in earth dams is very low, requiring different optimal MICP treatment formulations to be explored. The study presented herein focuses on MICP treatment across the boundary between a fine sand and a coarse sand in the context of one-dimensional flow column experiments. Treatment optimisation is evaluated by varying important parameters including formulations of chemical amendments, and the particle size distribution of the fine grained fraction. Subsequently, a procedure is developed for measuring the calcite bond shear strength using an Erosion Function Apparatus (EFA), whereby an undisturbed MICP treated specimen is slowly protruded into a flume and eroded by surface-parallel flow. Measurements of the surface movement of the eroding sample are made with a laser reflecting on the soil surface in the flume. The progress of erosion can hence be monitored as the flow velocity is increased. Results open up new interesting perspectives on the treatment scheme needed for MICP implementation for contact erosion control in dams.