Crack coalescence in rock-like specimens with two dissimilar layers and pre-existing double parallel joints under uniaxial compression

Experimental investigation on hydraulic fracturing of granite specimens with double flaws based on DIC

A uniaxial compression test was conducted with a servo loading apparatus to study the failure of a rock-like specimen with a pre-existing single flaw. The evolution of cracks was monitored with digital image correlation technology and simulated with the expanded distinct element method based on the strain strength criterion. The concentration and evolution of the principal strain field were found to be consistent with the initiation, propagation, and coalescence of cracks. As the inclination angle increased, the position of the maximum principal strain concentration changed from within the flaw to the flaw tips, and the distribution of the horizontal displacement field changed from symmetric to antisymmetric. The initiation stress and peak strength were affected by the inclination angle; they were minimum when the inclination angle was 60°. As the inclination angle increased, the failure mode of the specimens transformed from mostly tensile failure to mostly shear failure.

Failure characteristics of rock-like materials with single flaws under uniaxial compression

Experimental and numerical study on the interaction between holes and fissures in rock-like materials under uniaxial compression

Changes in Microstructure and Mechanical Properties of Low-Permeability Coal Induced by Pulsating Nitrogen Fatigue Fracturing Tests

The cracks in a rock tend to initiate, propagate, and coalesce under loading. Based on the digital image correlation (DIC) method, uniaxial compression tests are carried out on rock-like specimens with various arrangements of two parallel cracks. The full-field strain and failure features of the rock-like materials are observed and analysis by a self-developed code. Two process zones are defined according to the differences between the shear strain field and the tensile strain field: a shear process zone and a tensile process zone. The following results are obtained in this study. (1) Three coalescence modes can be observed using the DIC method: a shear coalescence mode, a tensile coalescence mode, and a mixed coalescence mode. (2) At the microscopic level, the bridge angle and crack arrangement affect the formation of the process zone; at the macroscopic level, they determine the crack propagation path and the failure mode. (3) The peak strength of the rock-like specimen is related to the crack inclination angle and the bridge angle. (4) Numerical modeling by the expanded distinct element method and the strain strength criterion simulates the different coalescence modes of the experimental study efficiently.

Cracking Processes and Coalescence Modes in Rock-Like Specimens with Two Parallel Pre-existing Cracks

The artificial fracturing technique under coupled hydro-mechanical effects is widely used in many rock engineering. Therefore, the study on the fracturing behaviors and mechanical properties of hydro-mechanical coupled cracks is very crucial. In this study, a series of fracturing tests were conducted on the cylinder gypsum specimens with single pre-existing cracks using triaxial compression loading system. Water pressure was applied inside the pre-existing cracks and led to the specimen failure with external compression loading. A new type of cracks, namely horizontal coupled cracks (HCC), were found in some specimens. Macroscopic observations reveal that HCC, which were mainly caused by the hydraulic pressure, were different from any tensile wing cracks, shear secondary cracks, or shear anti-wing cracks. Subsequently, a microscopic study was performed using scanning electron microscope (SEM), the outcomes suggest that: (1) Shear fracturing zones (SFZ) and tensile fracturing zones (TFZ) under coupled hydro-mechanical effects displayed distinct characteristics on orientations, length, and independence of gypsum grains; and (2) the HCC were tensile cracks when they just initiated from outer tips of pre-existing cracks. While tensile stress made major contribution to the specimen failure during the whole fracturing processes, the HCC became tensile and shear mixed cracks when the specimen was about to fail.

Experimental Study on the Fracturing Behaviors and Mechanical Properties of Cracks under Coupled Hydro-Mechanical Effects in Rock-like Specimens

The invention relates to a true triaxial hydraulic coupling test device for realizing visualization based on a biaxial rheometer, thereby carrying out hydraulic coupling testing on a marble sample with front and rear surfaces having centers with penetrating cracks in a front-rear communication manner. The true triaxial hydraulic coupling test device comprises two modified polycarbonate plates thatare in a mutual butt joint manner to form square sealed inner space and a biaxial rheometer loading assembly for applying pressures on a marble sample in four directions. The marble sample is arranged in the sealed inner space; and the biaxial rheometer loading assembly applies pressures on the marble sample by the modified polycarbonate plates.. Compared with the prior art, the true triaxial hydraulic coupling test device has advantages of true three-axis loading, visual operation, and the like.

Yimeng Zhou

Papers

Cracking Processes and Coalescence Modes in Rock-Like Specimens with Two Parallel Pre-existing Cracks

Experimental investigation on hydraulic fracturing of granite specimens with double flaws based on DIC

Failure characteristics of rock-like materials with single flaws under uniaxial compression

Experimental Study on the Fracturing Behaviors and Mechanical Properties of Cracks under Coupled Hydro-Mechanical Effects in Rock-like Specimens

True triaxial hydraulic coupling test device for realizing visualization based on biaxial rheometer