Cyclic Degradation of Weakly Cemented Soil and Artificial Bedding Plane in Cyclic Ring Shear Test

Cyclic degradation is a common phenomenon in the engineering practice of soil dynamics. In the literature, numerous earthquake-induced landslides occurred in slopes of naturally cemented soil or having a pre-existing shear surface. However, the cyclic degradation of naturally cemented soil and soil containing bedding planes needs to be sufficiently clarified, especially in the cyclic ring shear test. This study aims to elucidate the cyclic degradation of cemented soil and artificial bedding planes that simulate the actual slip surfaces using consolidation-constant volume cyclic loading ring shear apparatus. Accordingly, a small content of cement was added to kaolin clay to model the naturally cemented soil. The combined specimens of two halves were employed to simulate the bedding planes. The cyclic ring shear tests were conducted on four types of samples, including two normal samples (0% cement, 2% cement) and two combined samples (2% + 0% cement; 2% + 2% cement) under various test conditions to investigate the effects of normal stress, shear-torque amplitude, and overconsolidation ratio (OCR) on the cyclic degradation. The test results showed that the cyclic degradation parameter of all samples decreased with the increase in normal stress from 98 to 294 kPa, shear-torque amplitude from 30 to 90 kPa, and OCR from 1 to 4. The research results also indicated the significant role of cementation bonding in cyclic degradation behavior. Accordingly, the cyclic degradation of 2% cement sample is highly sensitive to the increase in normal stress levels, shear-torque amplitudes, and OCR.