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 boundary of sample close to the specimen holders and propagated inside the intact materials. In order to discover the reason of observed failure mechanism in experiments, the direct shear test was simulated using PFC2D. Results of numerical models showed that the gap zone size between the upper and lower specimen holders has a significant effect on the shear mechanism. For the high gap size, stresses concentrate at the vicinity of the tips of specimen holders and result in generation and propagation of tensile cracks inside the intact material. However, by reducing the gap size, stresses are concentrated on asperities, and damage of specimen at its boundary is not observed. Results of this paper show that understanding the shear mechanism of rock joints is an essential step prior to interpreting the results of direct shear tests.
Abstract In this paper, the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches. PFC2D was used for numerical simulations, in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes, the damage process is simulated. The joint interfaces were simulated by a newly developed modified s...
#1M. Bahaaddini(UNSW: University of New South Wales)H-Index: 9
#2Paul C. Hagan(UNSW: University of New South Wales)H-Index: 16
Last. Bruce Hebblewhite(UNSW: University of New South Wales)H-Index: 19
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This paper aims to study the shear behaviour of rock joints in a direct shear test using the particle flow code PFC2D. In this numerical approach, the intact rock is simulated by densely packed circular particles that are bonded together at their contact points; joint surfaces can be explicitly simulated using the modified smooth joint (SJ) model. In the modified SJ model for simulation of direct shear test, micro-scale slip surfaces (smooth joint contacts) are applied at contacts between the pa...
#1M. Bahaaddini(UNSW: University of New South Wales)H-Index: 9
#2Paul C. Hagan(UNSW: University of New South Wales)H-Index: 16
Last. Bruce Hebblewhite(UNSW: University of New South Wales)H-Index: 19
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Abstract A large number of studies have been carried out to investigate the effect of scale on the shear behaviour of rock joints. However, the nature of scale dependency of rock joints is still unknown and remains an ongoing debate. This paper investigates the effect of joint length on the shear behaviour of rough rock joints using PFC2D. In this numerical approach, the intact material is simulated by a dense packing of bonded particles and the joint is represented by micro-scale slip surfaces ...
Different failure modes during fracture shearing have been introduced including dilation, sliding, asperity cut-off and degradation. Several laboratory studies have reported the complexity of these failure modes during shear tests performed under either constant normal load (CNL) or constant normal stiffness (CNS) conditions. This paper is concerned with the mechanical behaviour of synthetic fractures during direct shear tests using a modified shear cell and related numerical simulation studies....
#1M. Bahaaddini(UNSW: University of New South Wales)H-Index: 9
#2G. Sharrock(UNSW: University of New South Wales)H-Index: 3
Last. Bruce Hebblewhite(UNSW: University of New South Wales)H-Index: 19
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Abstract In this paper, the shear behaviour of rock joints are numerically simulated using the discrete element code PFC2D. In PFC, the intact rock is represented by an assembly of separate particles bonded together where the damage process is represented by the breakage of these bonds. Traditionally, joints have been modelled in PFC by removing the bonds between particles. This approach however is not able to reproduce the sliding behaviour of joints and also results in an unrealistic increase ...
#1M. Bahaaddini(UNSW: University of New South Wales)H-Index: 9
#2G. Sharrock(UNSW: University of New South Wales)H-Index: 3
Last. Bruce Hebblewhite(UNSW: University of New South Wales)H-Index: 19
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The strength and deformability of rock masses transected by non-persistent joints are controlled by complex interactions of joints and intact rock bridges. The emergence of synthetic rock mass (SRM) numerical modelling offers a promising approach to the analysis of rock masses, but has not been rigorously compared with actual physical experiments. In this work, SRM modelling by the discrete element software PFC3D is used to investigate the effect of geometric parameters of joints on the rock mas...
#2Jae-Joon Song(SNU: Seoul National University)H-Index: 13
Abstract A numerical method to determine the contact areas of a rock joint under normal and shear loads is proposed. The method requires only three-dimensional surface coordinates at the initial stage before shearing, while some disparate materials are inserted between the joint surfaces or particular equipments are adopted for measurement of the contact areas during the test in other conventional methods. The joint surface is modeled as a group of triangular planes, and the contact condition of...
In this study, the shear behavior of discontinuities possessing two different rock wall types with distinct separate compressive strengths was investigated. The designed profiles consisted of regular artificial joints molded by five types of plaster mortars, each representing a distinct uniaxial compressive strength. The compressive strengths of plaster specimens ranged from 5.9 to 19.5 MPa. These specimens were molded considering a regular triangular asperity profile and were designed so as to ...
Different failure modes during fracture shearing have been introduced including normal dilation or sliding, asperity cut-off and degradation. Attempts have been made to study these mechanisms using analytical, experimental and numerical methods. However, the majority of the existing models simplify the problem, which leads to unrealistic results. With this in mind, the aim of this paper is to simulate the mechanical behaviour of synthetic and rock fracture profiles during direct shear tests by u...
#1Weinan Wang(CUMT: China University of Mining and Technology)H-Index: 1
#2Qiangling Yao(CUMT: China University of Mining and Technology)H-Index: 9
Last. Qiang Xu(CUMT: China University of Mining and Technology)H-Index: 2
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To study the weakening mechanism of the shear characteristics of water-bearing rock joints, four types of artificial saw-tooth joints (including tooth inclination angles of 0°, 15°, 30° and 45°) were prepared in sandstone with four moisture content (0%, 1.55%, 3.1% and 4.65%). This work adopted the non-destructive water intrusion, X-ray diffraction (XRD), acoustic emission (AE) and direct shear tests to mainly investigate the water and inclination angle-induced changes in shear mechanical proper...
#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...
This study takes the rock masses in the dam foundation of a sluice gate of the Datengxia Hydropower Station in China as a case study to determine the geometrical and mechanical representative volume elements (RVEs) considering the special natures of rock masses (inhomogeneity and anisotropy). 3D fracture networks are generated on the basis of fracture data in the field and then used in this study for RVE determination. The representative parameters for RVE determination are selected and presente...
In this study, five groups of numerical models with different conditions were established by using PFC2D (particle flow code) to simulate the direct shear tests of noncoplanar nonthrough jointed rock mass. It is proved that normal stress and shear rate, as well as the connectivity rate, relief angle, and inclination angle of joints, have significant influence on the strength characteristics, number of cracks, and the stress of the rock mass according to measurement taken at five different measur...
#1Yuan Zhao(CSU: Central South University)H-Index: 5
#2Guoyan Zhao(CSU: Central South University)H-Index: 7
Last. Xin Cai(CSU: Central South University)H-Index: 19
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Abstract Acoustic emission (AE) and moment tensor simulation with discrete element method (DEM) have been proven to be an effective method to analyse the failure mechanism of rock. The ratio (R) of isotropic and deviatoric components of moment tensor is often used to distinguish the failure mechanism of AE events. However, the critical value of R to distinguish different failure mechanism has not been strictly verified, and the method to evaluate the fracture mechanism of macrocrack qualitativel...
Last. H. R. Mansouri(SBUK: Shahid Bahonar University of Kerman)H-Index: 17
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AbstractThe mechanical behaviour of intact rock materials is controlled by properties of grains and cementation (bonding) between grains. In the particle flow code (PFC), three main bonding approac...
#2Kourosh Shahriar(AUT: Amirkabir University of Technology)H-Index: 24
Last. Kaveh Ahangari(IAU: Islamic Azad University)H-Index: 12
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Rock failure mechanism is one of the most important issues in rock mechanics engineering which plays a key role in the stability analysis of various structures. Therefore, different failure criteria have been proposed to understand the failure mechanism of rocks. One of the most commonly used rock failure criteria is the Hoek-Brown criterion, in which there is a parameter called mi, which is very important to the response provided by this criterion. Due to the importance of conducting extensive ...
Despite their frequent natural occurrence and engineering encounter, heterogeneous rock joints (rock joints with different lithological characters on both sides of the joint surface) have been studied much less systematically. To study the shear behavior and failure mechanism of bolted heterogeneous rock joints, laboratory tests were performed on the heterogeneous rock joints having different joint roughness coefficients (JRC) under different anchorage conditions. The results indicate that shear...
Last. Jianbo Zhu(SZU: Shenzhen University)H-Index: 25
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Abstract Understanding the shear behaviour of rough joints is of great significance for dealing with rock engineering problems. In many cases, rock joints are often subjected to dynamic loadings, which are usually caused by explosions, impacts or earthquakes, etc. Until now, the dynamic shear characteristics of rock joints have not been well understood. In the present study, we investigate joint shear behaviour at different shear rates and develop a rate-dependent constitutive model of rough joi...
