Deformation Behavior Of Sandstone Research Articles

Dynamic Deformation and Failure Characteristics of Deep Underground Coal Measures Sandstone: The Influence of Accumulated Damage

Understanding accumulated damage effects is essential when undertaking deep underground rock engineering, as complex in situ environments and intense engineering disturbances realistically affect the physical and mechanical properties of rocks. Accumulated damage mainly causes the extension of micro-cracks and the sprouting of specific defects in the rocks, altering the microstructural parameters. In this investigation, loading and unloading tests were used to simulate the damage states of the deep underground coal measures sandstone. The accumulated damage factor was formed by combining the P-wave and energy damage variables. The effect of accumulated damage on the bearing capacity and deformation behavior of sandstone was particularly pronounced after experiencing impact loading. The experimental results demonstrate that the accumulated damage factor can depict the initial damage state of sandstone as well as the subsequent dynamic and progressive damage. There is a mutually governing effect between accumulated damage and strain rate. In contrast, accumulated damage significantly extends the range of strain rates, which is fed back into the dynamic uniaxial compressive strength of the sandstone. There is a negative correlation between dynamic fracture energy and accumulated damage, which strongly agrees with the sandstone’s deformation mechanism. The combination of accumulated damage and impact loads can be used to assess the long-term safety of deep underground rock engineering.

Damage evolution of sandstone based on acoustic emission under different seepage conditions

The stability and safety of rock mass in underground constructions are influenced by the damage processes of cracks evolution caused by the excavation under coupled hydro-mechanical loading conditions. In this paper, to understand the crack development and damage evolution of sandstone under different seepage conditions, a series of triaxial compression tests with acoustic emission under different water pressures (5, 10, 15 MPa) are carried out. The stress-strain behavior, crack stress thresholds, failure mode, AE characteristics and micromechanical mechanisms are analyzed and discussed. The experimental results demonstrate that the crack stress thresholds and the mechanical property of studied sandstone decrease with the increase of water pressure. Moreover, the water pressure has an important influence on and deformation behavior of sandstone, for instance, the elastic modulus and deformation modulus decreased when the water pressure increased. Based on the result of accumulated ring counts, the damage evolution of sandstone gradually increased with increasing water pressure. Finally, the micro-structural evolution under the coupling effects of water pressure and applied stress is discussed. The obtained results can be used to identify the initiation and propagation of studied sandstone in the engineering applications.

Effect of confining pressure on mechanics and deformation behavior of sandstone containing a single inclined joint

The mechanics behaviors, failure modes and acoustic emission characteristics of rectangular green sandstone specimens containing a single joint with various inclination degree under different confining pressure have been determined in this article. The samples were tested over a confining pressure range of 0 to 40 MPa, and the inclination of the joint was varied between 0° and 50°. The test results indicated that: Mohr–Coulomb criterion is fit to peak strength of intact samples and residual strength of jointed samples with 40°. But the peak strength of jointed sample with 40° increases nonlinearly with confining pressure, which can be fitted by Hoek–Brown criterion. And the confining pressure has a reduction effect on anisotropy for jointed rock. When the inclination angle was less than 40°, the joint has a small negative influence on the strength and deformation of the jointed sample, as the inclination angle increased from 40° to 50°, a drop decrease in peak strength and Young’s modulus can be observed. The failure modes can be classified into T-mode, S-mode and SD-mode. Finally, the evolution laws of AE count for green sandstone specimens has been discussed.