Mechanical behavior of sands treated by microbially induced carbonate precipitation

The mechanical behavior of sands treated using microbially induced carbonate precipitation (MICP) has been investigated at the macroscale and the microscale. Triaxial and confined compression tests with embedded shear and compression wave (S-wave and P-wave) sensors were conducted on two MICP-treated sands, Ottawa 50=70 and 20=30 silica sands. Triaxial compression tests were conducted at three different confining pressures (25, 50, and 100 kPa). Tests were also performed at calcium chloride (CaCl₂) concentrations of 0.1 and 0.3 M, resulting in specimens with average calcium carbonate (CaCO₃) content ranging from 1.5 to 2.5% for the 50=70 sand and from 1 to 1.6% for the 20=30 sand. In contrast to previous research, the results of triaxial tests presented in this paper show an increase of the soil strength even at 1% calcium carbonate content. After the tests, samples taken from the specimens were utilized to measure the CaCO₃ content and to perform analysis using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The SEM and EDS images were used to assess the morphology and spatial distributions of CaCO₃ at the microscale.