Effects of shearing direction on shear behaviour of rock joints (original) (raw)
Related papers
The Effect of Asperity Inclination and Orientation on the Shear Behavior of Rock Joints
Geotechnical Testing Journal, 2013
This study investigates the effect of asperity inclination angle and asperity orientation on the shear behavior of rock joints under 3 constant normal loading conditions. The effects of these two rock joint characteristics were investigated by creating artificial rock joints having a 4 regular pattern of triangular asperities that were oriented at different angles in the plane of shear. Large-scale direct shear tests were conducted 5 over a range of normal stresses, on 0.30 Â 0.30 m gypsum blocks containing well-mated joints with different asperity orientation and inclination 6 angle characteristics. Experimental results illustrate the importance of considering both the asperity orientation with respect to the loading direction 7 and the applied normal stress when predicting the shear behavior of rock joints. In general, higher normal stresses increased the stiffness of the 8 rock joints in shearing, while a reduction in the shear strength of the rock joints was observed when increasing the asperity orientation angle. The 9 dilation curves indicated the occurrence of both dilation and lateral displacement during shearing. Two different techniques are used to quantify 10 the condition of the joint surfaces: the first approach utilizes the concept of fractal dimension, and the second utilizes the concept of potential con-11 tact area. These approaches can be applied in a useful fashion within the framework of existing shear failure criterion for oriented rock joints.
Assessing the Shear Behavior of Oriented Rock Joints under Constant Normal Loading Conditions
Geo-Congress 2014 Technical Papers, 2014
This paper presents results from a series of constant normal load direct shear tests on artificially created rock joints, in an attempt to quantify the effects of different factors that contribute to the shear strength along "ideal" rock joints. Particular focus is given to the effect of asperity orientation with respect to the direction of shearing. In many historical rock joint shear strength criteria, the effect of a joint's roughness on the joint shear strength is described based on analysis of only a single profile in the direction of shearing. More recent studies have observed that the distribution of sheared area on a joint surface during shear is significantly affected by the location and distribution of the three-dimensional contact area of the joint surfaces, and results can vary with changes in the asperity inclination angle, the direction of shear, and the applied normal stresses. Results from the current study indicate that the asperity orientation angle has a significant influence on the relative contribution of the contact surface area to the shear strength of a rock joint. In joints with oriented asperities, a combination of vertical displacement (dilatancy) and lateral displacement during shearing was observed. The lateral displacement resulted in a reduction in the magnitude of observed shear-induced dilation of the joint, as well as a reduction in the strength of the joints against the induced shear load. Finally, an alternate approach for describing the shear behavior of oriented rock joints was used to characterize the impact of asperity orientation with respect to the direction of shear on the shear behavior of the rock joint.
This paper describes the role of mobilized asperity angles in shear behaviour of weak rock joints based on the results of direct shear tests using roughness profiles in 1mm intervals. Matched joint sets of plaster casts, which simulate Barton’s typical joint roughness profiles, are created for the tests. In order to simulate accurate asperities with the same intervals, special moulds are produced by a 3D printing technique. Based on the measured compressive strength of the plaster casts, the direct shear tests are performed under low normal stress conditions. The interpretation of the test data demonstrates a parameter which is the relationship between the mean values of mobilized asperity angles in damaged areas to the asperity component of Barton’s shear strength criterion. In low normal stress conditions, Baton’s criterion, combined with the proposed parameter, shows high correlation with the test results. This indicates that the shear behaviour of joints is governed by the partly mobilized asperities in low normal stress conditions. As a result, the parameter has a linear relationship with the joint roughness coefficients according to the normal stresses and the compressive strength of the plaster materials. As the parameter is obtained from the asperity angles estimated by 1mm intervals, this can correlate with measured roughness profiles obtained by manual or remote sensing methods.
Shear strength of rock joints under constant normal loading conditions
2019
The variation of shear strength of rock joints under constant normal loading conditions was studied. Three dimensional printing technology was incorporated to produce moulds of rock joints. Rock joints samples with three different roughness values were cast using concrete with uniaxial compressive strength of 20 MPa. Samples were sheared using a direct shear testing machine for normal stress values ranging from 0.25 to 0.7 MPa. In addition, effects of shear rate on shear strength properties of rock joints were experimentally investigated. It was found that the shear strength of rock joints is a function of normal stress, joint roughness and shear rate values. In addition, it was shown that three dimensional printing technology is a useful tool to replicate real rock joints.
Shear Behaviour of Rock Joints
2000
This title covers the fundamental properties of rock joints, the method of laboratory testing of rock joints, and shear strength assessment under different loading conditions. This work is intended as a reference text for students and practitioners in mining and rock engineering.
EVALUATION OF SHEAR STRENGTH OF MODEL ROCK JOINTS BY EXPERIMENTAL STUDY
In this paper, variation of the shear strength of artificial rock joints under constant normal loading condition is studied. Idealised joint surfaces were prepared using a developed molding method with special mortar and shear tests were performed on these samples under CNL conditions. Different levels of normal load and shear displacement were applied on the samples to study joint behaviour before and during considerable relative shear displacement. Nine types of saw-tooth joints have been selected for simplicity of modelling to quantify the effect of CNL conditions on joint shear behaviour. It was found that the shear strength of joints is related to rate of shear displacement, joint roughness (varying joint asperity angles) and applied normal stress condition. Finally, based on the experimental results and observations made of sheared joint samples, a new peak shear strength envelope is proposed to model sawtooth type joints tested under CNL conditions.
Experimental study of shear behavior of rock joints under constant normal stiffness conditions
International Journal of Rock Mechanics and Mining Sciences, 1997
The shear behavior of synthetic soft rock joints (regular saw-tooth) was investigated in the laboratory under constant normal stiffness condition (CNS). A large-scale shear apparatus was designed and constructed which can test joints under both constant normal load (CNL) and CNS conditions. It is observed that CNL condition overestimates joint dilation compared to CNS condition and thereby, underestimates the peak shear stress of joints. Plot of shear stress against normal stress shows that a bilinear shear strength envelope is suitable for soft rock joints subjected to CNL conditions, while linear or bilinear envelopes are acceptable for CNS testing depending on the asperity angles. The shear behavior of infilled joints was also investigated under CNS conditions, and it was found that a very small thickness of bentonite infill reduced the shear strength significantly. The shear strength of joints almost approached that of pure infill, when the infill thickness to asperity height ratio reached 1.60.
LABORATORY MODELLING OF ROCK JOINTS UNDER SHEAR AND CONSTANT NORMAL LOADING
In this paper, the shear behaviour of artificial rock joints under constant normal loading conditions is studied. Idealised joint surfaces were prepared using a developed molding method with special mortar and shear tests were performed on these samples under CNL conditions. Different levels of normal load and shear displacement were applied on the samples to study the shear behaviour of sawtooth shaped joints before and during considerable relative shear displacement. Nine types of saw-tooth joints have been selected for simplicity of modelling to quantify the effect of CNL conditions on joint shear behaviour. It was found that the shear strength of joints is related to rate of shear displacement, joint roughness and applied normal stress condition. Finally, based on the experimental investigations and observations made of sheared joint samples, four conceptual models of shear stress-shear displacements have been developed. These four models summarize the entire experimental results based on elastic, dilation and residual zone defined along the shear displacement axis. The findings of this study expand current state of knowledge of joint shear strength which may be of significance for further research and for understanding the shear behaviour of rock joints for a stability analysis of the designed structures in surface and underground rock engineering.
2014
Shear behaviour of infilled rock joints under cyclic loading and constant normal stiffness conditions were studied. The experiments were carried out in a cyclic loading direct shear apparatus. The laboratory studies were conducted using saw tooth shaped asperities cast in high strength gypsum plaster. Two types of triangular asperities inclined at 9.5° (Type I) and 18.5° (Type II) from the shearing direction were considered for testing. Clayey sand (75% fine sand and 25% Kaolinite) at initial moisture content of 12.5% was selected as the infill material. Profile of shear planes and strength envelopes for different conditions of infill thickness to asperity height ratio, initial normal stress, and initial asperity angle were investigated.
Evaluation of shear strength of rock joints subjected to cyclic loading
Soil Dynamics and Earthquake Engineering, 2003
Variation of the shear strength of rock joints due to cyclic loadings is studied in the present paper. Identical joint surfaces were prepared using a developed moulding method with special mortar and shear tests were performed on these samples under both static and cyclic loading conditions. Different levels of shear displacement were applied on the samples to study joint behaviour before and during considerable relative shear displacement. It was found that the shear strength of joints is related to rate of displacement (shearing velocity), number of loading cycles and stress amplitude. Finally, based on the experimental results, mathematical models were developed for evaluation of shear strength in cyclic loading conditions.