53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: Surface instability of residual soil slope due to erosion is one of the widespread issues all over the world. Bio-cementation is a novel soil improvement method, wherein urease-producing bacteria or urease enzyme can be used to bind sand particles through calcite formation, enhancing the engineering properties of soil. This research work aims to assess the feasibility of bio-cementation technique as a potential alternative for surface stabilization of the slopes. A residual slope soil (Hokkaido, Japan) was instrumented in bench-scale slope for solidification test at the laboratory. Native ureolytic bacteria was enriched under optimum environmental conditions and injected to percolate through slope surface, followed by number of injections of cementation solution. The results indicated that relatively a stiff layer/ crust (6∼9 MPa) with the thickness ranging from 3-4 cm is found along the slope surface. However, the UCS values decreased with the depth of the slope. The hydraulic conductivity of the slope soil reduced from 1.9×10−2 cm/s to 1.85×10−3 cm/s (by 90%) due to the cementation, which could inhibit the excess infiltration of rainwater and enhance the surface runoff.
Studies by several investigators have demonstrated that residual soil slope failures can be attributed to several factors such as climatic conditions, geological features, soil characteristics, topography, vegetation level and/ or combination of the above (Rahardjo et al., 2005; Morbidelli et al., 2018; Zhang et al., 2018). Residual soils are generally unsaturated, and most of the failures in residual soil slopes occurs during or soon after the heavy rainfall (Rahardjo et al., 2005). Rainfall results infiltration and surface runoff in a slope structure. Infiltration of rainwater into the slope is governed by rainfall intensity and soil infiltrability (Oh and Vanapalli, 2010). The rate of infiltration is relatively high in the early stages of rainfall and decreases with the time; and once the surface zone reached its saturated state, the ponding or runoff starts occurring over the slope surface.
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