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Failure and deformation characteristics of shale under true triaxial stress loading and unloading under water retention and seepage

Citation

Zhang, Dongming (2022), Failure and deformation characteristics of shale under true triaxial stress loading and unloading under water retention and seepage, Dryad, Dataset, https://doi.org/10.5061/dryad.msbcc2g19

Abstract

A multifunctional true triaxial fluid-structure coupling system was used to conduct water retention and seepage tests of shale under true triaxial loading and unloading stress paths. The stress-strain evolution law of shale specimens under different experimental conditions was obtained, and the corresponding deformation and strength law was analyzed. The evolution law and failure characteristics of cracks in shale were obtained by CT scanning images before and after the experiment. The results show that under the condition of water retention, the volumetric strain of shale specimen increases first, then decreases and finally continues to increase with the increase of deviational stress, indicating that the volumetric change has experienced a process of compaction-expansion-compacting. The partial stress-maximum horizontal strain curve of the sample increases first and then decreases, while the deformation of the sample in the direction of intermediate principal stress shows the characteristics of repeated compression and expansion. In the seepage test, the permeability - maximum horizontal strain curve can be divided into two parts before and after fracture according to the deviant stress - maximum horizontal strain curve. Before fracture, the compression velocity of the specimen in the loading direction exceeds the expansion velocity in the unloading direction, resulting in a decrease in volume and a decrease in permeability. With the increase of deviatoric stress, cracks occur inside the particles and continue to spread from the tip until the cracks break through the shale specimen. In this process, the pore fissure area increases and the permeability of the sample increases rapidly. In terms of fracture evolution, for the water-retaining test, dense tensile and shear cracks appear on the failure plane perpendicular to the direction of maximum and minimum principal stress, and complex shear fracture network appears on the failure plane perpendicular to the direction of intermediate principal stress. For the seepage test, heavy shear failure occurs throughout the original fracture of the sample. With the increase of the penetration depth, the crack shape on the failure surface perpendicular to the direction of intermediate principal stress gradually changes from single type to complex type.

Funding

Scientific Research Foundation of State Key Lab of Coal Mine Disaster Dynamics and Control, Award: 2011DA105287-zd201804