Synthetic Rock Mass Approach Research Articles

Damage Evolution and Integrity Assessment of Jointed Rock Mass Based on Synthetic Rock Mass Approach

The integrity coefficient Kv of bed rock is one of the important approaches to evaluate the stability of engineering rock mass, but this parameter is difficult in frequent field tests. The integrity coefficient is the quantitative index for evaluating the complete deformation of rock mass, while the damage variable represents the level of damage of the jointed rock mass, and both have similar physical meanings and represent the degree of deterioration of surrounding rock. Damage variables and damage constitutive models were constructed based on Weibull distribution damage model and Synthetic Rock Mass (SRM) model. The relationship between damage variables and numerical calculation and damage constitutive curves of different weathered granite rocks in Hongtuzhang tunnel was calculated. A new method for evaluating integrity coefficient of rock mass is proposed.

Examining the Effect of Natural Fractures on Stone Mine Pillar Strength Through Synthetic Rock Mass Approach

Examining the Effect of Natural Fractures on Stone Mine Pillar Strength Through Synthetic Rock Mass Approach

Application of a synthetic rock mass approach to the simulation of blasting-induced crack propagation and coalescence in deep fractured rock

Application of a synthetic rock mass approach to the simulation of blasting-induced crack propagation and coalescence in deep fractured rock

Synthetic Rock Mass Modelling and Geotechnical Mapping: An Open Pit Mine Case Study in Anisotropic Rock

ABSTRACT Most pit boundaries at Sishen Mine in South Africa consist of Banded Iron Formation (BIF), which exhibits anisotropic behaviour on a rock mass scale. A generally applicable approach is to apply Synthetic Rock Mass (SRM) modelling to characterise rock mass anisotropy. To characterise the rock mass for slope stability analysis, the persistence of bedding planes is very important. Subsequently, a sensitivity analysis on the effect that bedding persistence has on rock mass strength, was performed. Results indicate that bedding plane sizes less than the sample dimensions, produce higher strengths due to the influence of rock bridges. SRM modelling therefore demonstrates that persistence is a critical factor in rock mass strength analysis and subsequent slope stability analyses. The definition of SRMs is completely reliant on data provided by high quality, bench-scale structural mapping. The importance of geotechnical mapping is discussed, as it is currently the only way to accurately determine persistence. The Sishen study is a case in point that geotechnical mapping remains an essential function to obtain the appropriate rock mass characteristics for slope design. Routine mapping exercises, performed by well-trained geotechnical engineers, will therefore remain critical to acquire the necessary input parameters to advance the cutting edge SRM approach.

Improving DFN-geomechanical model integration using a novel automated approach

In the past decade, numerical modelling has been increasingly used for simulating the mechanical behavior of naturally fractured rock masses. The synthetic rock mass approach often adopted has three main components: data collection and characterisation; discrete fracture network (DFN) modelling; and finally, geomechanical modelling to simulate rock mass behaviour. The focus of this paper is the integration of the DFN with geomechanical models, with emphasis on the numerical aspects of embedding rather complex 2D fracture networks within a finite element mesh. A new method is introduced that simplifies fracture networks, while maintaining important fracture properties such as orientation, connectivity, and intensity. The resulting finite element mesh is of sufficient quality to both improve computational time and eliminate spurious results that may be associated with the presence of highly distorted elements. The proposed method uses a web-based code with two integral components (DFNAnalyzer and DFNCleaner) that analyse the properties of the original fracture network, and then perform simplifications to ensure an acceptable (user defined) mesh quality is achieved.

Characterisation of confinement effect on jointed rock pillars using a Synthetic Rock Mass approach

SummaryConfinement effect on jointed rock pillars is numerically characterised in this research using a Synthetic Rock Mass (SRM) approach. The SRM is an integrated model incorporating a discrete fracture network within a Particle Flow Code 3D particle assembly. In this paper, the confinement effect on a 3D jointed pillar SRM model is investigated in a series of simulations, including biaxial compression tests and true and conventional triaxial compression tests. The numerical results suggest that the applied confining stresses generally result in higher pillar strengths and ductile post‐peak responses. More brittle post‐peak behaviour is simulated in the biaxial and true triaxial tests when the pillar is confined by a high stress in one lateral direction and by a zero/low stress in the other lateral direction. This phenomenon is attributed to significant lateral pillar dilation in the less confined direction. Detailed pillar failure modes are monitored in the uniaxial and triaxial tests. Axial splitting fractures and long shear zones cutting through the pillar are simulated when the pillar is able to dilate in the direction of least confinement. Localised shearing along joints and failed rock blocks is the dominant failure mode when the pillar dilation is resisted by the applied confining stresses. The pillar remains relatively intact with limited cracking in the pillar core in the highly confined triaxial tests. Copyright © 2016 John Wiley & Sons, Ltd.

Application of Synthetic Rock Mass modeling to veined core-size samples

Rock masses of the primary copper ore at the El Teniente mine fail mainly through the infill of preexisting veins during the caving processes, especially through those composed of less than 35% hard minerals (quartz and pyrite). In this study, the Synthetic Rock Mass (SRM) approach is used to reproduce the results of ten uniaxial compression tests on veined core-size samples of El Teniente Mafic Complex (CMET) lithology, from El Teniente mine, Codelco-Chile. At the scale of the tested samples it is observed that veins composed mostly of quartz dominate the failure process. The developed methodology considers generating a deterministic Discrete Fracture Network (DFN) based on the veins mapped at the surface of each core sample. Then, the micro-parameters of the Bonded Particle Model (BPM) are calibrated to represent the macro-parameters of the average block of intact rock within all samples. Next, the micro-parameters of the Smooth-Joint Contact Model (SJCM), which represent the mechanical properties of veins, are calibrated to reproduce the stress–strain curves and the failure modes of the veined core-size samples measured during the laboratory tests. Results show that the SRM approach is able to reproduce the behavior of the veined rock samples under uniaxial loading conditions. The strength and stiffness of veins, as well as the vein network, have an important impact on the deformability and global strength of the synthetic samples. Contrary to what was observed in the laboratory tests, synthetic samples failed mainly through weak veins. This result is expected in the modeling given that anhydrite veins are considered weaker than quartz veins. Further research is required to completely understand the impact of veins on the behavior of rock masses.

Convergence of synthetic rock mass modelling and the Hoek–Brown strength criterion

Synthetic rock mass modelling is based on estimating the mass scale properties of rock directly from properties of the intact material and observed jointing geometry and strength. This technique explicitly represents characteristics of the rock mass that are implicit in the widely applied, empirical Hoek–Brown strength criterion. We demonstrate here that the two approaches converge in mass strength and the strength envelope when the necessary conditions for the empirical method are satisfied. However, the synthetic rock mass approach is advantageous whenever the necessary conditions of the empirical method are not satisfied. As an example, we use the synthetic rock mass method to describe an anisotropic strength envelope for a rock mass with four independent joint sets, where the orientation-specific strength has a significant impact on rock mass stability. In addition we show that rock mass strength is controlled strongly by joint persistence and the resultant connectivity of discontinuities, and only weakly by joint density and intensity.

Experimental and Numerical Investigations into the Strength of Intact Veined Rock

In this paper, the authors report on a series of laboratory and numerical modelling experiments aiming to quantify the behaviour of intact veined rock. Five controlled triaxial compression experiments were conducted on intact veined specimens of mafic intrusive complex andesite (CMET) from the El Teniente mine. The experiments demonstrated that veins controlled the fracturing and resulting peak strengths of the specimens. High-quality experimental data made possible the development of numerical experiments using a 3D Particle Flow Code and the synthetic rock mass (SRM) methodology. The numerical experiments demonstrated that the SRM approach could be successful for modelling the behaviour of veined rock. Greater value was gained by coupling the results of high-quality laboratory tests to comprehensive numerical models.

Numerical investigation of the scale effect and anisotropy in the strength and deformability of coal

The decrease in strength and stiffness of coal with increase in specimen size has long been recognized as scale effect. In this study, a synthetic rock mass (SRM) approach has been used to investigate this scale effect and the anisotropy of coal. A discrete fracture network (DFN) for the coal was created and then embedded into bonded-particle models to form a range of varying size of SRM coal specimens. Unconfined compression tests on the SRM specimens showed that the SRM approach is capable of quantitatively reproducing the dependency of the strength and stiffness on the size of the coal specimens. The strength and stiffness anisotropy of coal can also be reproduced. The numerical results are shown to be in good agreement with published laboratory and field test results.

The synthetic rock mass approach for jointed rock mass modelling

This paper describes synthetic rock mass (SRM) modeling, a new approach for simulating the mechanical behavior of jointed rock mass. This technique uses the bonded particle model for rock to represent intact material and the smooth-joint contact model (SJM) to represent the in situ joint network. The macroscopic behavior of an SRM sample depends on both the creation of new fractures through intact material and slip/opening of pre-existing joints. SRM samples containing thousands of non-persistent joints can be submitted to standard laboratory tests (UCS, triaxial loading, and direct tension tests) or tested under a non-trivial stress path representative of the stresses induced during the engineering activity under study. Output from the SRM methodology includes pre-peak properties (modulus, damage threshold, peak strength, etc.) and post-peak properties (brittleness, dilation angle, residual strength, fragmentation, etc.). Of particular interest is the ability to obtain predictions of rock mass scale effects, anisotropy, and brittleness, properties that cannot be obtained using empirical methods of property estimation. This paper presents the theoretical background of the SRM approach along with some example applications.

Empirical and numerical approaches for geomechanical characterization of coal seam reservoirs

Abstract The effects of fractures or joints on geomechanical properties of coal when transitioning from small samples to larger field scales have long been recognized. Two geomechanical characterization methodologies for of a coal seam for reservoir engineering are presented which attempt to account for these scale effect. The first is a well established empirical rock mass classification method, the Geological Strength Index (GSI). The second is a newly developed numerical technique, termed the Synthetic Rock Mass (SRM). GSI was developed to empirically account for the influence of rock joint density and joint surface conditions on the behaviour of the rock mass. The established GSI to strength and deformation theories are reviewed and an approach to account for joint stiffness based on the minimum confining stress is presented. The SRM approach to jointed rock mass geomechanical characterization is a numerical modeling technique which combines the Bonded Particle Model for rock and Discrete Fracture Network simulation. The intact or matrix of the SRM is calibrated to laboratory data, the DFN inserted creating a numerical representation of the rock mass which can then be tested at any scale. In each case, the approaches attempt to geomechanically characterize (strength, modulus, etc) the large scale behaviour of the coal seam, where the properties can then be used for continuum type simulation (reservoir simulation, borehole stability, etc).