Ismet Canbulat

A Fractal Model for the Shear Behaviour of Large-Scale Opened Rock Joints

This paper presents a joint constitutive model that represents the shear behaviour of a large-scale opened rock joint. Evaluation of the degree of opening is made by considering the ratio between the joint wall aperture and the joint amplitude. Scale dependence of the surface roughness is investigated by approximating a natural joint profile to a fractal curve patterned in self-affinity. Developed scaling laws show the slopes of critical waviness and critical unevenness tend to flatten with increased sampling length. Geometrical examination of four 400-mm joint profiles agrees well with the suggested formulations involving multi-order asperities and fractal descriptors. Additionally, a fractal-based formulation is proposed to estimate the peak shear displacements of rock joints at varying scales, which shows a good correlation with experimental data taken from the literature. Parameters involved in the constitutive law can be acquired by inspecting roughness features of sampled rock joints. Thus, the model can be implemented in numerical software for the stability analysis of the rock mass with opened joints.

Improved roadway roof support design for Anglo American Metallurgical Coal’s underground operations

Abstract In order to ensure the stability of roadways, Anglo American Metallurgical Coal (AAMC) has developed a roof support design methodology that integrates analytical, numerical and empirical modelling through an integrated design methodology. This methodology currently is based on a deterministic approach. However, an improved methodology, based on a stochastic modelling technique, has also been developed and is being evaluated for various roof support design practices. The main advantage of this methodology is that the final design is based on the probability distributions of input parameters, thus the outcome is based on a distribution of factors of safety. This methodology has been evaluated at AAMC operations for the designs of roof support in critical areas and offers and improved method for determining the roof support requirements. A demonstration of the application of this methodology for the design of install road roof support at Moranbah North Mine is presented in this paper.

A Numerical Study on Dilation of a Saw-Toothed Rock Joint Under Direct Shear

The roughness of a rock joint gives rise to the phenomenon of dilatancy. Numerous studies have been conducted to examine their dilation behaviour partly due to its importance as a stabilising effect. While previous researchers have improved the understanding of dilation behaviour and identified important parameters affecting the magnitude of dilation during shear, there is still a lack of quantification of the method for predicting the dilation angle. This paper describes a systematic parametric study to investigate the effect of relative normal stress and geometric properties on the dilation of a saw-toothed rock joint by using a distinct element method code with Voronoi tessellation. The applicability of the numerical model was assessed by calibration with a series of standard laboratory tests. The simulation results indicate that the magnitude of relative normal stress plays the most important role among parameters and quantify how much those parameters affect the dilation behaviour during shear. The findings of this study, presented in a normalised relation, can be employed when dilation values need to be determined in rock engineering practice.

Underground coal mine layout selection using analytical hierarchy process

Abstract One of the most critical and complicated steps in mine planning is the selection of a suitable layout based on geological, geographical, geotechnical and economical parameters. These parameters influence the choice of different layouts of coal mine workings and normally examined on the basis of experience gained in the coalfields. The wide ranging combinations of geological, geotechnical and mining conditions make the selection of the optimum design and layout for a particular situation a difficult task. Variations in these parameters result in multiple feasible mine layouts; where each layout entails some inherent problems and the optimal layout is the one that offers the least problems. These variations in designs result in complex multi-decision situations that cannot be solved by a simple technique. This study applies the analytical hierarchy process in selection of the most viable panel orientation for a longwall operation. A back analysis of this technique was conducted at a mine located in Central Queensland, Australia. The geological and geotechnical aspects of the mine resulted in variations in the recommended panel orientations. Three different mine layouts with variable geological and geotechnical impacts were evaluated and the optimum mine layout was determined. This study also challenged the viability of the results obtained by performing a consistency check at every critical stage of the project.

Environmental influence on mesh corrosion in underground coal mines

Abstract The effect of corrosion on different steel mesh types was examined in a Controlled Mine Environment laboratory which recreated underground mine environmental conditions. Corrosion rates of mesh at different testing conditions were calculated and weld strengths of the corroded mesh were examined. Mesh specimens in ‘dry’ conditions had no significant corrosion effects over 12 weeks. However, ‘wet-dry cycle’ mesh specimens exhibited significant corrosion rapidly, with estimated corrosion rates of around 0.01 mm/yr for galvanised mesh, whether sprayed once or three times daily, 0.70 mm/yr for three times daily sprayed black mesh and 0.48 mm/yr for once daily sprayed black mesh. The mesh corrosion mechanism was dramatically changed by wet-dry cycle. The results are indicative of the behaviour of installed mesh.

Numerical analysis on mining-induced fracture development around river valleys

ABSTRACT This paper presents a detailed study of the mechanisms contributing to fracture development around river valleys associated with mining operations. Due to the geology and geomorphology of the Southern Coalfield of New South Wales, Australia, non-conventional subsidence effects usually occur. The influences associated with valley closure and upsidence are principally tensile and shear fracturing/cracking of the river and underlying strata, which act as underground flow paths for surface water. This paper explicitly simulates the mining-induced fracture development around the valley structure, utilising a distinct element method modelling technique with Voronoi tessellation. The fracture propagations within intact rock as well as along existing discontinuities are simulated in this study. It is demonstrated that the presence of natural geological discontinuities and the mining-induced stress field play an important role in determining the extent and pattern of fracture propagation. Analysis of the mining-induced explicit fracturing system in the vicinity of valley provides an improved understanding of the near-surface hydrological cycle and enables effective remediation of the mining-induced adverse impacts on river valleys.

Applicability of a joint constitutive model: correlation with field observations

Abstract 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.