Coalescence of offset rock joints under biaxial loading

Abstract

Crack coalescence in rock masses was studied by performing a series of biaxial compresion tests on specimens made of rock-like material. Specimens of size 63.5 · 27.9 · 20.3 cm, made of 72% silica sand, 16% cement (Type I) and 12% water by weight were tested. The joint inclination angle was maintained at 45°, while the offset angle i.e. angle between the plane of the joint and the line that connects the two inner tips of the joints, was changed from 0°to 90°with an increment of 15°. Three levels of lateral stress were used; 0.35 MPa, 0.7 MPa and 1.5 MPa on each sample. HP data acquisition system was used to record the data for each sample. In each sample, four LVDTs were fixed to measure the axial and lateral displacement along the sample. The failure mechanisms were monitored by eye inspection and a magnifier to detect crack initiation and propagation. For each test, the failure surfaces were investigated to determine the characteristics of each surface. Wing cracks initiated at the tip of the joint for the low confining stress applied, while at higher confining stresses wing cracks also initiated at the middle of the joint. Secondary cracks initiated at the tip of the joint due to shear stress. Three modes of failure took place due to coalescence of the secondary and wing cracks. The bridge inclination was the main variable that controlled the mode of failure. For bridge inclination of 0°, the coalescence occured due to shear failure and for bridge inclination of 90°the coalescence occurred due to tensile failure while for the other bridge inclinations coalescence occured due to mixed tensile and shear failure.

Injection‐Induced Propagation and Coalescence of Preexisting Fractures in Granite Under Triaxial Stress

“…In the literature, different terminologies have been used to describe the discontinuities in rocks or rock‐like materials created by sawcut, water jet cut, or other methods (molding, etc. ), such as silts (e.g., Brace & Bombolakis, ; Nemat‐Nasser & Horii, ), slots (e.g., Petit & Barquins, ; Thomas & Pollard, ), cracks (e.g., Ashby & Hallam, ; Hoek & Bieniawski, ; Nemat‐Nasser & Horii, ), flaws (e.g., Brace, ; Lee & Jeon, ; Wong & Einstein, ), faults (e.g., Sobolev, ), joints (e.g., Liu et al, ; Mughieda & Karasneh, ), and fractures (e.g., Bobet & Einstein, ; Misra et al, ; Reyes & Einstein, ; Shen et al, ). In this paper, from the perspective of reservoir geomechanics, we use the term fracture to represent the preexisting discontinuity in the granite sample and use the term crack to indicate the new macrofractures initiated and propagated from the preexisting fracture(s).…”

Crack Initiation, Propagation, and Failure Characteristics of Jointed Rock or Rock‐Like Specimens: A Review

“…e tests showed wing cracks appeared under unconfined and slightly confined compressive loads and disappeared entirely at high confining stresses. Mughieda and Advances in Civil Engineering Karasneh [61] investigated the coalescence mode between cracks through a series of biaxial compression tests on rocklike specimens. e dimensions (height × width × thickness) of each specimen are 63.5 × 27.9 × 20.3 cm ( Figure 11).…”

Study on the fracture behavior of prefabricated fissures granite based on DIC and laser scanning techniques

“…Specifically, the selected test materials can be divided into surrounding rocks in actual engineering projects and specimens made of a similar material with prefabricated fissures. The types of prefabricated fissures and the spatial arrangement of the prefabricated fissures in the specimens can be classified as combination of prefabricated fissures and holes, 8,9 prefabricated fissures, 10–15 nonparallel prefabricated fissures, 16–20 prefabricated fissures with different inclination angles, 21,22 and so forth. Relevant research results have analyzed crack growth from various aspects by using various methods.…”