52nd U.S. Rock Mechanics/Geomechanics Symposium,
2018. American Rock Mechanics Association
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ABSTRACT: The growing global population is leading to reduced space and a need for more resources. This is causing engineered structures to be designed within rock masses at greater depths, and subjected to significant thermo-mechanical loading. Numerous hydro-thermo-mechanical in-situ experiments, including block tests and heated plate load tests have demonstrated the effects of temperature on discontinuity mechanics at a large scale. In this study we propose two methodologies for the multi-stage testing of discontinuity shear strength at incremental temperatures under triaxial conditions. The two methodologies result in different thermomechanical behavior of the specimens. If deformation of the specimen is constrained during heating, no change in residual shear strength of the discontinuity is seen, however, if the specimen is unloaded and free to deform under thermal loading, it displays reduced shear strength upon reloading. This preliminary data has potential implications for the design of engineered structures in these elevated thermo-mechanical environments.
Advancements in engineering capability have led to structures being designed within rock masses at greater depths, where they are expected to withstand not just greater stresses, but also elevated temperatures. The thermal loading of a rock mass can occur due to the geothermal gradient in the cases of deep tunneling, mining and geothermal heat production, or due to the heat generation from high-level radioactive waste in a geological disposal facility.
Rock masses are heterogeneous and discontinuous. Under applied stresses, the mechanical behavior and strength of a rock mass is commonly controlled by the behavior and strength of the discontinuities (Hoek, 1983). Discontinuities vary widely in terms of their origin (joints, bedding, foliation, faults, shear zones etc.) and associated physical characteristics. Characterizing their mechanical properties under different conditions is therefore paramount to understanding the behavior of a rock mass under these conditions. Numerous hydrothermo-mechanical in-situ experiments, including block tests and heated plate load tests have explored the effects of temperature on discontinuity mechanics at a large scale and shown modifications in the mechanical behavior of discontinuities at these elevated conditions (Cramer and Kim, 1986; Hardin et al., 1981; Zimmerman et al., 1985). However there have been no small scale studies to understand the mechanics of individual discontinuities under these loading conditions.
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