Comparison and Correction of Multistage Triaxial Tests to Single Stage Triaxial Test for the Rock Mechanical Testing

In this work, we investigate the relationship between two test protocols; the Single Stage Triaxial (SST) is where a constant confining stress is applied and the axial stress is raised until the sample fails. This is compared to the Multistage Triaxial (MST) test, where the sample is loaded to the point of positive dilatency (PPD) then unloaded to low deviatoric stress, the confining stress raised and the procedure repeated. We have performed these measurements for several different types of rocks (Shale, Sandstone, and Chalk) and compared the results in terms of Young’s modulus, Poisson’s ratio, stiffness, friction angle, and cohesion. We provide a detailed discussion of the techniques and measurements required to correct the MST results to those obtained from SST protocol. A single correction factor is found to relate the MST results to the SST. Future work is proposed to further develop the measured parameters from these two test protocols.