Experimental study on the influence mechanism of clay particles on the microbial treatment of granite residual soil

Abstract

The content of clay particles has a key influence on the physical and mechanical properties of microbial solidified granite residual soil. Microbial-induced calcite precipitation (MICP) treatment method of “mixing + grouting” was used to prepare microbial solidified granite residual soil samples with different clay contents and to explore the influence of clay content on the reinforcement effect of microbial solidified granite residual soil. A series of direct shear tests, disintegration tests, and microscopic observation tests was conducted to quantitatively analyze the influence of clay content on the shear strength and disintegration resistance of microbial solidified granite residual soil. The conclusions are summarized as follows: the shear strength and disintegration resistance of granite residual soils solidified by MICP treatment were remarkably improved, with the shear strength increasing by 9%∼16% when the clay content varied from 10%∼40%. The internal friction angle of the granite residual soil with different clay contents increased and then decreased with the increase in clay content. The cohesion of the microbial solidified granite residual soil increased with the increase in clay content, and the internal friction angle reached a minimum of 20% clay content (17.27°), which is 31.85% lower than that of 0% clay content (25.34°). The cohesion of the microbial solidified granite residual soil reached a maximum of 40% clay content (39.54 kPa), which is 8.69 times higher than that of 0% clay content (4.55 kPa). The MICP treatment technology is capable of effectively improving the shear strength and disintegration resistance of granite residual soils. The MICP treated process produces calcium carbonate precipitates that link the sand particles and fill the pores between the soil particles, increasing the number of larger agglomerates in the granite residual soil, which is the essential reason for the improvement in the softening and disintegration of the granite residual soil when exposed to water.