Papers by Keyword: Rock Joints

Abstract: Quantitative estimation of scale effect is a complex problem which contained many uncertainties and should be solved using probability calculus and statistical approach. This paper aims to derive the structural factor according statistical strength theory involving discontinuity surface conditions account to estimate the design rock mass strength. A short review of scale effect estimation techniques based on statistical strength theory is given. A new method of structural factor evaluation is proposed. This technique allows accounting discontinuity conditions by changing the variation of tested specimen random sample. A function that describes the decreasing of strength due to poor discontinuity surface quality is introduced to correct the initial and central statistical moments of strength random distribution. The evaluation of the joints condition function based on analysis of the results of uniaxial compressive strength tests and petrographic structure of specimens is shown. Improving the statistical approach of structural factor evaluating increase the accuracy of the rock mass strength assessment and allow avoiding costly modifications of the mining excavation support design. A case of rock mass strength estimation under conditions of coal mine “Komsomolets Donbassa” according to proposed statistical method is studied.

Abstract: The non-uniformity feature of rock joints’ surface profiles is the main influencing factor of the sampling representativeness. In order to analyze the sampling representativeness of rock joints statistically, the joint roughness coefficient (JRC) of 18 pieces of natural slate rock structural plane samples with size from 100mm to 1000mm were measured. The results show that it is necessary to evaluate the representativeness of rock joints in engineering practice due to the large non-uniformity of JRC. The total variation of JRC for different measurement sections, sizes and samples indicates that the sampling representativeness can be evaluated by the average value and the distribution probability of JRC; moreover, the sampling representativeness should be considered the statistical law evaluation of JRC for the concrete size and sample, and offered the accurate standard in changing range.

Abstract: Cyclic loads are commonly encountered in geotechnical engineering; however most constitutive models do not account for the effect that such loads can have on the mechanical behaviour of soils and rocks. This work is concerned with the behaviour of jointed rock and, as the overall mechanical behaviour of jointed rock is usually dominated by the mechanical behaviour of the joints, it is focused on the behaviour of rock joints under cyclic loads. In particular, an extension of the existed constitutive model for cyclically loaded rock joints is presented. Variations of rock joint stiffness in both the normal and the shear directions of loading due to surface degradation are taken into account. The degradation of asperities of first and second order is considered, while a new relation is proposed for the joint stiffness in the normal direction during unloading. Numerical simulation results show good agreement of model predictions with existing experimental results.

Abstract: The purpose of this paper is to study the shear behavior of rock specimens containing joints with various distribution forms. Two sets of specimens are simulated by the rock failure process analysis code (RFPA2D). The friction-sliding failure pattern occurs with the lower undulation angle specimen, and the failure pattern turns to be tensile-shear failure mode gradually with the increase of undulation angle. The specimen possesses the highest peak shear load when the undulation angle is about 30º. And joint rock shear character also deteriorates with the increase of weak interlayer thickness. In the intermittent joint model, the unified connection ratio specimen’s peak shear load increases with rock bridge amount, and the multi-joint mode is beneficial to keep rock mass shear stiffness. This study comes to meaningful results to the expansion of joint rock strength evolution law with various joint distribution forms.

Abstract: In order to study the strength and deformation properties of rock joint under different shear velocities, normal stresses and undulation angles, series testes are conducted by a RMT-150C testing machines with artificial concrete rock joint samples in the present paper. Base on the experimental results, it can be found that the peak shear strengths decrease with the increment of shear velocity, and the decreasing rates tend to decrease with the increasing shear velocity. The shear strength of rock joints increase with the increasing undulation angles, and linearly increase with the increment of normal stress. It is also indicated that the shear stiffness increase with the increasing normal stress, undulation angle as well as the shear velocity with a decreasing tendency.

Abstract: Based on the field geology survey data, the probability distribution function of joint aperture was analyzed and the availability of the fitting data was verified. The joint aperture data observed the previous fitted function can be generated in the process of joint simulation. The seepage of rock mass is proportional to the third power of joint’s aperture. It is much more reasonable and feasible to analyze the permeability tensor of rock mass with the previous generated data. At the same time, the method comprehensively considered the effect of joint’s orientation, aperture, scale and their distribution.