Experimental study on disintegration of unsaturated red clay in Ca²⁺ solution environment

Guilin is a world-famous karst area characterized by a high concentration of Ca²⁺ in its groundwater. The disintegration of red clay plays a key role in the collapse of soil caves. In order to study the disintegration mechanisms of unsaturated red clay in Ca²⁺ solution, disintegration tests were conducted using a self-made disintegration apparatus. The soil samples are placed on the sieve plate of the disintegration apparatus, and a tensile meter records the real-time change of samples mass to calculate the disintegration rate. XRD analysis and filter paper method were employed to determine the mineral composition and matric suction of red clay, respectively. The results show that the matric suction decreases with increasing moisture content and increases with the void ratio. When the matric suction exceeds 965 kPa, disintegration is markedly intense, and the disintegration rate shows no significant correlation with Ca²⁺ concentration. When the matric suction is below than 965 kPa, the disintegration rate increases from 0.057 to 3.027 g/s with the increase of Ca²⁺ concentration. The disintegration of red clay with high matric suction is primarily attributed to the rapid ingress of water molecules and the compression of air due to matric suction, resulting in tensile stress. The disintegration of red clay with low matric suction is primarily caused by the reduction in the diffusion layer thickness of clay particles and the weakening of interparticle attraction due to Ca²⁺.