Small strain stiffness degradation of MICP-treated sand and silt

Microbially Induced Carbonate Precipitation (MICP) can significantly improve the mechanical properties of soils through cementation between grains. The last two decades of research have demonstrated that MICP increases the stiffness and shear strength of geomaterials, as well as reducing their hydraulic conductivity and liquefaction potential. However, few studies have focused on the effects of MICP on the cyclic and dynamic behavior of soils, which is of fundamental importance in earthquake-prone countries. For instance, it is unclear whether medium-intensity earthquakes can totally or partially destroy MICP cementation, causing the material to lose the improvement of its properties long before a significant seismic event occurs. This paper presents a study of the cyclic behavior of two types of soils treated with MICP. The main objective is to evaluate the shear modulus degradation of MICP-treated soil and define the range of cyclic strain amplitude in which bio-cementation is effective in improving soil dynamic properties. Silty sand and silty tailings are tested through combined Resonant Column and Torsional Shear tests. Modulus degradation curves and damping are compared with untreated material. It was found that silty sand reaches a strain threshold where the effect of bio-cementation is lost, whereas in silty tailings the effect is maintained at all applied strain amplitudes.