Shear strength behaviour of rock joint material influenced by different weathering grade (original) (raw)

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.

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.

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.

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.

Shear strength criteria for rock, rock joints, rockfill and rock masses: Problems and some solutions

Although many intact rock types can be very strong, a critical confining pressure can eventually be reached in triaxial testing, such that the Mohr shear strength envelope becomes horizontal. This critical state has recently been better defined, and correct curvature or correct deviation from linear Mohr-Coulomb (M-C) has finally been found. Standard shear testing procedures for rock joints, using multiple testing of the same sample, in case of insufficient samples, can be shown to exaggerate apparent cohesion. Even rough joints do not have any cohesion, but instead have very high friction angles at low stress, due to strong dilation. Rock masses, implying problems of large-scale interaction with engineering structures, may have both cohesive and frictional strength components. However, it is not correct to add these, following linear M-C or nonlinear Hoek-Brown (H-B) standard routines. Cohesion is broken at small strain, while friction is mobilized at larger strain and remains to the end of the shear deformation. The criterion 'c then n tan ϕ' should replace 'c plus n tan ϕ' for improved fit to reality. Transformation of principal stresses to a shear plane seems to ignore mobilized dilation, and caused great experimental difficulties until understood. There seems to be plenty of room for continued research, so that errors of judgement of the last 50 years can be corrected.

Effect of Cement Injection on Shear Behaviour of Jointed Rock based on Mohr-Coulomb Criterion

2019

Common problem in mining activity is instability caused by jointed rock mass. The strength of jointed rock masscan be increased by cement injection. An artificial rock sample made from dental plaster type of moldano tara isused in this study to evaluate the influence of cement injection to the strength of jointed rock sample. The roughnessof joint surface are obtained from the natural rock joints and divided into three groups of Joint RoughnessCoefficient (JRC) values based on Barton criteria. The injection materials are mixture of cement and water withthe ratio of water and cement of 4: 5 and 3: 2. This artificial samples are then subjected to direct shear tests. Thetest results are analyzed by Mohr-Coulomb criterion to obtain the cohesion and internal friction angle. It isrevealed that cohesion and internal friction angle increased for injected rock sample. The strength increase variesby JRC condition. For Sample with JRC value between 8-10, the study find that injection material ...

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.

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.

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.