Sand Bonded with Calcite Precipitation under Cyclic Simple Shear

Previous studies have shown that ureolysis driven calcite precipitate improves the behavior of granular soil under unidirectional principal loads. However, the behavior of these improved soils can be very different under dynamic loading conditions. This study aims to understand the behavior of bio-cemented sand under cyclic simple shear tests. Calcite was precipitated by inducing urease enzyme rich bacteria in clean fine sands (particle size<425 μm). Improvement in the cyclic resistance of sand was assessed through cyclic-direct simple shear (CDSS) tests. Samples were prepared by dry pluviation method in a stainless steel column of 71 mm diameter and 20 mm height, with an opening on the top and bottom cover. Bacterial suspension was injected in to the saturated soil sample followed by cementation solution containing equimolar mixture of urea and calcium chloride solutions. Load controlled cyclic tests were conducted on the above treated samples. The samples were then tested under constant volume, which helped co-relate the vertical stress change to its excess pore water pressure. The sample failed when shear strains exceeded 3.75 % or when the pore pressure ratio reached unity. Shear strains governed the failure in most samples. The test results showed that the cyclic resistance increased and the pore pressure ratio decreased with the increase in precipitation.