Wetting effects and strength degradation of swelling shale evaluated from multistage triaxial test

Abstract

The multistage triaxial compression test was mainly utilized in this research to investigate the degradation in the strength of swelling shale under different wetting conditions. Shale samples were tested in four different conditions: (1) under their natural moisture content denoted as intact, and after soaking in, (2) water, (3) polymer solution, and (4) bentonite solution, separately. The experimental results showed that a considerable decrease in the shale’s strength was noted after soaking in water and the lubricant fluids (LFs). The polymer solution caused the least decrease in the strength compared to other fluids. Strength envelopes of the tested shale were constructed for intact and soaked states. These envelopes showed fair agreement between the single stage and the multistage triaxial compression test results, indicating suitability of the multistage triaxial compression test for the tested swelling shale.