Shear strength of grouted clay: comparison of triaxial tests to direct shear tests

Slurry-soil interface direct shear (IDS) tests and the triaxial compression (TC) tests are currently used to determine the shear strength of grouted soil. However, many previous studies focused on sandy soils, and limited attention has been paid to clayey soil. This study introduces two grouting test methods designed to fabricate the grouted clay specimen suitable for TC and IDS testing. A group of grouting orthogonal tests is designed, and the shear strength parameters are calculated and compared based on the Mohr-Coulomb (MC) criterion. Findings showed that outcomes obtained from the IDS test are unreliable. The test results showed that the shear strength obtained from IDS test yields more serious deviations and lower MC criterion fitness. The test also showed that shear strength parameters under IDS test are unreliable compared with TC tests. Additionally, the cohesion measured by the IDS test was always larger than that associated with the TC test, which is caused by the extension of the shear surface in the shearing process according to the failure pattern. The overestimation of shear strength in the case of the IDS test decreased the predicted surface settlement, as proved by numerical simulations. The conclusions indicate that using TC tests to obtain accurate shear strengths of grouted clay is crucial for predicting the soil deformation and developing rational construction schemes.