Improvement of Shear Strength Parameters on Clay Shale Using Calcite Precipitation Method

Abstract Clay shale, known for its expansive and weathered characteristics, poses challenges in construction when exposed. The calcite precipitation method offers a viable solution to bolster load-bearing capacity and counteract potential soil expansion while ensuring reversible changes. This study aims to evaluate improvements in the shear strength parameters of clay shale through the calcite precipitation method. The research involved soil properties tests, hydrolysis rate and precipitation ratio analyses, and direct shear tests on both saturated and dry soil specimens. Results showed clay shale samples with PL, LL, and PI values of 41.60%, 21.97%, and 19.62%, respectively, categorizing them as low to medium plasticity clayey soils (CL). The optimal treatment concentration was determined at 20 g/L soybean concentration with a precipitation ratio of 93%. In treated-saturated conditions, cohesion (c′) increased from 4.10 kPa to 12.07 kPa, and the internal friction angle (φ′) rose from 0.54° to 2.87°. Remarkable enhancements were observed in treated-dry samples, with c′ increasing from 7.53 kPa to 183.84 kPa, and φ′ rising from 2.31° to 19.25°. The SCU-CP method effectively improved the properties of dry clay shale.