Experimental investigation on strength and failure behavior of carbonate rocks under multistage triaxial compression

Conventional or single stage triaxial compression experiments for obtaining failure envelope of rocks require several specimens to be tested under different confining pressures. As a replacement, multistage triaxial tests using one specimen have been employed in experimental rock mechanics for situations where preparing several specimens is difficult or expensive. The results obtained by the multistage triaxial test may deviate from those obtained by the single stage. However it is believed that using multistage triaxial test can decrease the cost and time and the obtained results are still reliable due to less variability in the rock properties. Several methods have been proposed for conducting multistage triaxial test including ISRM suggested method and a modified version of the ISRM method proposed by Crawford and Wylie. The results of this study demonstrate that both multistage methods give reasonable results. However, the modified method provides closer results to the single stage, because the specimen is subjected to less damage. As the number of the loading stages rises, both ISRM and the modified version provide lower strength parameters comparing to the single stage.