An Examination of the Effect of Chemically Induced Damage on the Monotonic and Cyclic Shearing Behavior of Biocemented Sands

Microbially induced calcite precipitation is a biomediated soil improvement method that can improve the engineering properties of granular soils. Although improvements in soil engineering behaviors afforded by biocementation have been extensively characterized, there remains limited understanding of the anticipated long-term engineering behavior of biocemented soils following progressive chemical damage that may be experienced following initial applications. In this study, 10 direct simple shear tests were performed to investigate the effect of chemically induced damage on the drained monotonic and undrained cyclic shearing behaviors of biocemented loose Ottawa F-65 sand. All specimens were either uncemented, biocemented to different cementation levels corresponding to shear wave velocity increases (ΔV_s) between 150 and 500 m/s, or biocemented to a ΔV_s near 250 or 500 m/s and then subjected to degradation injections, which induced chemical damage and achieved ΔV_s reductions of either 100 or 200 m/s. For all specimens, V_s and soil calcium carbonate content measurements were performed to assess improvement magnitudes, cementation uniformity, and evaluate magnitudes of chemically induced damage. As expected, increases in biocementation levels as captured by V_s increases were shown to progressively improve drained monotonic and undrained cyclic shearing behaviors. Following chemically induced damage, however, behavioral improvements were largely retained and were found to be consistent with the nondegraded biocemented specimens on the basis of similar V_s values. The performed tests provide the first examination of the expected long-term engineering behaviors of biocemented sands and yield new understandings regarding the anticipated impacts of chemical damage on behaviors relevant to subsurface liquefaction mitigation applications and other geotechnical use cases.