Abstract Frictional behaviour of joints/faults is of great importance in many geo-engineering applications across different scales. It is known that the joint surface roughness is one of the critical parameters controlling the frictional behaviour of rock joints. While nominal normal and shear stresses acting across the joint asperities are calculated based on overall shearing area, the actual normal and shear stresses can be much greater due to smaller actual contact area. The actual contact area on the other hand is known to be related to the joint surface roughness. In order to investigate the effect of contact area on the shear behaviour of rock joints, an extensive set of direct shear experiments at different normal stresses on dry and saturated shale, limestone and sandstone tensile joints were undertaken. To compare the frictional properties of natural and artificial samples, synthetic samples were also fabricated, and their frictional properties were evaluated. Results of this study revealed that the predominant parameter controlling the frictional strength is the actual contact area. While the common models in predicting the shear strength of rock joints were unable to fit the experimental data based on nominal contact area, the results based on actual contact area fit the measured values accurately. In addition, it was observed that when the actual contact area is considered, Mohr-Coulomb criterion is sufficient to fit the experimental data irrespective of the rock type, joint surface roughness or whether dry or saturated. This highlights that the Mohr-Coulomb criterion can appropriately predict the frictional strength if the actual contact area can be estimated. More importantly, the results showed that the surface roughness cannot dictate the shear behaviour of rock joints without considering the actual contact area.
The success of a hydraulic fracturing (HF) operation is strongly dependent on brittleness of the formation. Several models based on mechanical testing, mineral composition, and sonic log data have been proposed to quantify the brittleness of formations known as brittleness index (BI). The limitations of these conventional BI models, in particular, the consistency and applicability at field scale with the complex in situ conditions are poorly understood. We therefore developed a novel BI model ba...
Abstract Coupled geomechanics-fluid flow constitutive models are generally developed based on macro-(core) scale observations such as stress-strain responses, fluid pressure and temperature often without in-depth knowledge of the micro-scale phenomena. Recent addition of direct micro-scale imaging capability for triaxial or direct shear systems has enabled the identification of micro-scale phenomena during failure process using techniques such as 3D X-ray computed tomography. These X-ray transpa...
#1Zhen Wang(Nanjing University of Science and Technology)H-Index: 109
#1Zhen Wang(Nanjing University of Science and Technology)H-Index: 1
Last. Xiao Wang(SEU: Southeast University)H-Index: 1
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Abstract Stress relaxation is an important time-dependent behavior of rock mass. To investigate the stress relaxation behavior and the influence of stress history and surface morphology on the stress relaxation of rock discontinuity, iso-stress cyclic relaxation tests and shear stress relaxation tests with loading–unloading stress histories were conducted on artificial rock discontinuity samples and natural rock discontinuity samples. The characteristics of the stress relaxation curve with diffe...
A new generation of Hoek cells was designed and built to conduct triaxial testing on rock-like materials. The new design has the advantages of both conventional Hoek cells (e.g., minimal preparation and setup time) and conventional triaxial systems (e.g., on specimen radial deformation measurement), and it is capable of measuring the permeability at a controlled temperature. This quick release triaxial cell is robust, fast, and cost efficient and can be used for high pressure–high temperature ex...
#2Chuangzhou Wu(CUMT: China University of Mining and Technology)H-Index: 1
Last. Dongqiao Liu(CUMT: China University of Mining and Technology)H-Index: 1
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Abstract The time-dependent behavior of rock joints, specifically creep and stress relaxation, govern the long-term stability of underground structures, but have not been fully understood. The effect of asperity degradation on the time-dependent behavior of rock joints is investigated in this test. Triangular synthetic rock joints with four asperity angles (θ = 0°, 10°, 30° and 45°) are tested for creep and stress relaxation. It is revealed that the failure mode of a rock joint during creep and ...
#1M. Bahaaddini(UNSW: University of New South Wales)H-Index: 9
The common method for determination of the mechanical properties of the rock joints is the direct shear test. This paper aims to study the effect of boundary condition on the results of direct shear tests. Experimental studies undertaken in this research showed that the peak shear strength is mostly overestimated. This problem is more pronounced for steep asperities and under high normal stresses. Investigation of the failure mode of these samples showed that tensile cracks are generated at the ...
Abstract Frictional behaviour of rocks from the initial stage of loading to final shear displacement along the formed shear plane has been widely investigated in the past. However the effect of sample size on such frictional behaviour has not attracted much attention. This is mainly related to the limitations in rock testing facilities as well as the complex mechanisms involved in sample-size dependent frictional behaviour of rocks. In this study, a suite of advanced triaxial experiments was per...
Total rock porosity is a key parameter in a wide range of disciplines from petroleum to civil and mining engineering. Porosity is particularly important in petroleum engineering applications, e.g., from estimation of hydrocarbon in place to prediction of geomechanical properties. Conventional techniques used to measure the total porosity, i.e., mercury intrusion, nitrogen physisorption, focused ion beam–scanning electron microscopy (FIB–SEM), nuclear magnetic resonance (NMR) spectroscopy, gas po...
#2M. Bahaaddini(SBUK: Shahid Bahonar University of Kerman)H-Index: 9
Last. Hamid Roshan(UNSW: University of New South Wales)H-Index: 21
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Abstract null null The role of surface geometry and its evolution during shearing process on the hydromechanical behaviour of rock discontinuities has long remained an open question for geologist. During the shearing process, only a fraction of discontinuity is in contact and the actual stresses on these contacts are considerably greater than nominal stresses. However, measuring the contact area during shearing process has been a significant experimental challenge due to difficulties in detectio...
As a common geological structure, rock joints have a great influence on the mechanical properties and stability of rock mass engineering. The shear constitutive model of the rock joint and its calculation methods have played an important role in theoretical and experimental research. Most of the existing elastic–plastic shear constitutive models of the rock joint are simplified to linear form or only considering hardening behavior, while the shear test results show that the post-peak nonlinear s...
The effects of grain size and different multi-stage shearing techniques on shear strength along discontinuities were analyzed in this study. Laboratory direct shear tests were carried out on plaster mortar with maximum grain sizes of 0.5 mm and 1.0 mm. All specimen surfaces were essentially similar, copied from the same natural, Hungarian coarse-grained sandstone joint with a low joint roughness coefficient (JRC = 8). Tests within two different normal stress ranges (σn = 0.25–0.5 and 0.5–1.5 MPa...