Assessment of dynamic characteristics of bio-cemented sand considering microbially induced calcite precipitation treatment.

Abstract

Enhancement of dynamic characteristics of sand through bio-cementation is one of the prospective ground improvement techniques for sustainable development considering seismic loading scenarios. Microbially induced calcite precipitation (MICP) has already been established as an efficient and low-cost and sustainable bio-cementation technique. In the present study, engineering characteristics of poorly graded standard Ennore sand of India have been improved through the bio-cementation effects of Sporosarcina pasteurii bacteria using the MICP technique. Microstructure images obtained through scanning electron microscope and crystalline form of minerals present obtained through X-ray diffraction analyses are presented for the bio-cemented sand. Finally, dynamic characteristics of the bio-cemented sand are investigated through strain-controlled unconsolidated undrained cyclic triaxial testing varying the shear strain range from 0.3 to 1.5% with 1.0-Hz frequency. Variations of shear modulus and damping ratio of bio-cemented sand with shear strain are reported considering treatment durations of 7 and 14 days with treatment intervals of 12 and 24 h, respectively. It is observed that the improvement in shear modulus of bio-cemented sand for lesser strain rate approximately ranges from 37% to more than 80% compared to untreated sand. Furthermore, for strain higher than 1.0%, the margin of improvement varies from 50 to 70%. Moreover, the damping of bio-cemented sand was found to be lesser than untreated sand, and the variation is more significant for the higher number of loading cycles. This study is helpful in the assessment of dynamic characteristics of bio-cemented sand specifically applicable to seismic design.