Response Of Jointed Rock Mass Research Articles

Model experiment on dynamic behavior of jointed rock mass under blasting at high-stress conditions

The blasting response of jointed rock mass under high-stress conditions is studied in a laboratory experiment using model specimens. The crack initiation mode and initiation angle at the joint are analyzed, as well as the stress intensity factor and crack velocity. The blasting stress wave increases the stress concentration at the joint which promotes crack initiation and propagation. The dynamic behavior of the crack can be divided into two stages – the initiation stage and the propagation stage. The theoretical criterion based on the minimum strain energy density factor can well predict and explain the crack initiation behavior under blasting loading. The high-stress condition enhances the degree of shear failure of the crack initiation at the joint, which has significant effects on the dynamic behavior of subsequent crack propagation and leads to larger crack initiation angles.

Applicability of a joint constitutive model: correlation with field observations

This paper presents the results of numerical studies that illustrate the performance of a new joint constitutive model developed for the stability analysis of large-scale jointed rock masses. The joint model features the reduction of stiffness and strength due to joint initial opening and scale effect, which has been demonstrated by performing a series of direct shear tests. The study thus focuses on the model’s applicability to field-scale rock joints. The movement of a real rock slope is first investigated numerically where the mechanical behaviour of joints is represented by the Mohr–Coulomb model and the proposed joint model. The slope is appraised to be much less stable by the simulation using the developed joint model, which agrees more with the qualitative observation on the site. The response of jointed rock masses to excavation is also examined by simulating two underground rock structures where the mechanical behaviour of joints obeys the developed model in the numerical modelling. Predictions from numerical simulations are in good agreement with field monitoring data surrounding the caverns. Thus, the new joint constitutive law can be utilised to evaluate the stability of large-scale rock structures with sufficient capability.

Distinct Element Modeling of the Effect of Joint Persistence on Dynamic Fracturing of Jointed Rock Masses

Rock masses consist of intact rock and discontinuities such as faults, joints and bedding planes. The presence of such discontinuities in rock masses dominates the response of jointed rock masses to static and dynamic loading. These structural weak planes seriously hinder and affect the propagation of stress waves in rock mass. The joints parameters such as persistence, orientation, distribution patterns, spacing and filling material have a significant effect on the response of rock masses against wave propagation. In most studies of blast induced wave propagation in jointed rock mass, it is assumed that joints are continuous. In many situations the rock mass consists of non-continuous joints and rock bridges. Rock bridges and discontinuous joints have a different effect on wave and fracture propagation in a blasting operation. With regard to complexities associated with rock blasting in particular in jointed media, numerical tools are viable alternatives for rock blasting analysis. In this study the DEM methods was employed to investigate the effects of rock bridges on the wave propagation process. A plain strain 2D scenario was assumed and a single blasthole explosion was simulated. Three models with different jointing orientation patterns including jointing pattern parallel to free face, perpendicular to free face and orientated at 45 degree with respect to free face were analyzed numerically to investigate rock mass fracturing while blast wave propagation. The discontinuous joints were considered to be filled with weak materials (open joints) and rock bridges are composed of intact rock. In order to allow material plastic failure, a Mohr-Coulomb material model was used. The analysis results show that the stress concentration at the rock bridge location leads to excessive fracturing. This effect is more visible at the free face where the stress wave reflection occurs. Moreover, the obtained results show that the pattern and orientation of non-continuous joint system has a pronounced effect on rock fragmentation.

Wave and fracture propagation in continuum and faulted rock masses: distinct element modeling

In this study, to investigate the dynamic fracture mechanism of blast-induced fracturing of rock mass around a blasthoe, two-dimensional (2D) distinct element method was used. The dynamic stresses, material status, and velocity vectors are shown to investigate rock mass failure subjected to blast load. On the other hand, rock masses consist of intact rock and discontinuities such as faults, joints, and bedding planes. The presence of such discontinuities in rock masses dominates the response of jointed rock masses to static and dynamic loading. This paper focuses on the effect of fault orientation on dynamic fracturing of rock mass. In order to investigate the effect of faults on dynamic fracturing of rock mass, a numerical simulation was conducted. The two-dimensional (2D) distinct element code was used to simulate the effect of a fault on rock failure and stress distribution through the rock mass due to blast wave propagation. The blast loading history was calculated using analytical method and was applied to the blasthole walls. Accordingly, the interaction of explosive energy transferred to the rock mass from the blasthole was examined as a function of distance to the fault plane. A Mohr–Coulomb material model was used for host rock to allow for plastic failure calculations. The study can be divided in two parts: firstly, surface blast and secondly, underground blast. The conducted numerical study describes the role of fault in blasting in a qualitative manner. On the other hand, a free-face boundary was considered as a common blast operation which is conducted in surface mining. In second part, blast was modeled in underground operations at presence of in situ stresses. The results in such areas showed predominant effect of pre-stresses as well as fault orientation on fracture propagation.

A new method for stochastic calculation of the mechanical response of jointed rock masses

A new method for stochastic calculation of the mechanical response of jointed rock masses

Strength and Deformational Behaviour of a Jointed Rock Mass

An assessment of the strength and deformational response of jointed rock masses is an essential requirement in the site selection, design and successful execution of Civil and Mining Engineering projects. A quick estimate of these properties for preliminary evaluation of alternate sites, will reduce considerable expenditures for field tests. An attempt has been made in the present study to develop a link between strength and deformability of jointed block masses with the properties of intact specimens, obtained from simple laboratory tests, taking into account the influence of the properties of the joints. Extensive experimentation has been carried out on large specimens of jointed block masses under uniaxial compression. The model material represents a low strength rock. Various joint configurations were introduced to achieve the most common modes of failure occurring in nature. A coefficient called Joint Factor has been used to account for the weakness brought into the intact rock by jointing. Methods of computing the Joint Factor for various modes of failure of a jointed mass in an unconfined state have been established. The effect of Joint Factor on strength and tangent modulus of the mass has been studied and the values have been correlated with those of intact rock. Guidelines for assessing probable modes of failure of a jointed mass will enable one to estimate the relevant strength and tangent modulus of the mass.