Insights into the Energy Sources of Bursts in Coal Mines and the Effective of Prevention and Control Measures - Mahdi Zoorabadi - Winton GalePublished Feb, 2018Coalburst is a general term, which is commonly used in the coal mining industry for the violent failures of coal in the ribs and face of roadways and panels in underground coalmines. Due to lack of interest in the industry to reveal the causing source of the event, or due to uncertainty about the source, they happily use this term. The term by its own does not reveal the source of the energy, which causes the event. There are three sources of energy that can cause a burst event in underground coalmines: 1) store elastic strain energy, 2) seismic events and 3) gas expansion energy. This paper presents the fundamentals about these sources of energies and discusses our known and unknown facts about the mechanisms. Additionally, it discusses the reliability and effectiveness of stress relief holes and gas exhaust holes as controlling measures to prevent burst events. Insights-into-the-Energy-Sources-of-Bursts-in-Coal-Mines-and-the-Effective-of-Prevention-and-Control-Measures-M.Zoorabadi-2018.pdf1.4 MB
Impact of bedding plane and laminations on softening zone around the roadways - 3D Numerical Assessment - Mahdi ZoorabadiPublished Feb, 2017When the distributed rock stress around the roadways exceeds the strength of the rock, the rock is failed and a softening zone is formed. Roof deformation developed in the roof and ribs of the roadways are highly controlled by the depth of softening zones. The rock failure process starts from a point ahead of the face and grows into the roof, floor and ribs by advancing roadway. The
maximum stress that can be transferred through the failed rocks would be equal to its residual confined strength. Therefore, rock stress is moved above failed zone and will create new failure zone if it is higher than the confined strength of rock at that depth. This process continues until the confined strength of the rock becomes higher than stress components. Bedding and lamination planes play a big role into the failure pathway of rocks around roadways. The thickness of softening zone is significantly influenced by the shear and tensile strength of bedding planes and laminations. This paper presents a 3D numerical assessment of the bedding and lamination planes impacts to the forming and extension of the softening zones. It highlights the requirements for better characterisation of bedding and lamination planes for reliable simulation of roadways. Impact-of-bedding-plane-and-laminations-on-softening-zone-around-the-roadways-3D-Numerical-Assessment-M.Zoorabadi-2017.pdf1.5 MB
Deformability Modulus of Jointed Rocks, Limitation of Empirical Methods and Introducing a New Analytical Approach-Mahdi-ZoorabadiPublished Feb, 2016Deformability modulus of jointed rocks is a key parameter for stability analysis of underground structures by numerical modelling techniques. Intact rock strength, rock mass blockiness (shape and size of rock blocks), surface condition of discontinuities (shear strength of discontinuities) and confining stress level are the key parameters controlling deformability of jointed rocks. Considering cost and limitation of field measurements to determine deformability modulus, empirical equations which were mostly developed based on rock mass classifications are too common in practice. All well-known empirical formulations dismissed the impact of stress on deformability modulus. Therefore, these equations result in the same value for a rock at different stress fields.
This paper discusses this issue in more detail and highlights shortcomings of existing formulations. Finally it presents an extension to analytical techniques to determine the deformability modulus of jointed rocks by a combination of the geometrical properties of discontinuities and elastic modulus of intact rock. In this extension, the effect of confining stress was incorporated in the formulation to improve its reliability. Deformability-Modulus-of-Jointed-Rocks-Limitation-of-Empirical-Methods-and-Introducing-a-New-Analytical-Approach-M.Zoorabadi-2016.pdf943 KB
Analytical Procedure to Estimate the Horizontal Anisotropy of Hydraulic Conductivity in Coal Seams - Winton Gale - Mahdi ZoorabadiPublished Feb, 2015The horizontal hydraulic conductivity anisotropy of coal seams is a controlling parameter for designing gas drainage boreholes. The ratio between the maximum and minimum horizontal hydraulic conductivity (RkH-kh) and the orientation of maximum horizontal conductivity defines this anisotropy in horizontal plane.
This paper presents a new analytical procedure based on the field stress data and geometrical properties of coal cleats to calculate these two parameters. The application of this procedure for a real case in Eastern of Australia resulted in an average ratio of 20.9 for RkH-kh and orientation of NE for maximum horizontal conductivity. The comparison between these results with the measured values validated the accuracy of proposed procedure to estimate the anisotropy of horizontal hydraulic conductivity of coal seams. Analytical-Procedure-to-Estimate-the-Horizontal-Anisotropy-of-Hydraulic-Conductivity-in-Coal-Seams-W.Gale-M.Zoorabadi-2015.pdf377 KB