Effects of calcium carbonate on hydro-mechanical properties of bentonite

¹ Department of Civil Engineering, Shanghai University, Shanghai 200444, China
² B-Z Geotechnical Co. Ltd., Nanjing, Jiangsu 210096, China
³ Institute of Geotechnical Engineering, Southeast University, Nanjing, Jiangsu 210096, China

^* Corresponding author’s e-mail: qinaifang@shu.edu.cn

Abstract

To simulate characteristic changes of the bentonite mixing with CaCO₃ crystals that precipitate from groundwater around the high-level radioactive waste repositories, different amounts of CaCO₃ powders were mixed in the bentonite. In this study, four series of bentonite/CaCO₃ mixtures were prepared with different contents of CaCO₃ powders. A series of swelling, compression and direct shear tests were conducted on the bentonite/CaCO₃ samples using deionized water. Terzaghi consolidation theory was adopted to compute the hydraulic conductivity of bentonite/CaCO₃ mixtures. The results demonstrated that the final swelling strain decreased with increasing vertical stress and the content of CaCO₃ powders. The compression index decreased slightly with increasing CaCO₃ content. It was found that as the CaCO₃ content increased, the hydraulic conductivity of bentonite/CaCO₃ mixtures decreased. There was a peak point in the shear strength of unsaturated samples with the differences of the CaCO₃ content. The cohesion of unsaturated samples increased first and then decreased, but saturated samples presented the opposite character. It could be seen from the scanning electron micrograph that the existence of CaCO₃ powders filled pores of bentonite/CaCO₃ mixtures and made the structure denser.