Mingzhong Gao

Elliptical fracture network modeling with validation in Datong Mine, China

Roof-coal recovery rate and the performance of gas extraction are essentially controlled by the fractures within coal-rock mass. Thus, it is important to generate the accurate fracture network ahead of mining face. In this study, ten boreholes located differently from the 8212 working face of Tashan Mine in Datong coal mining group, China, were drilled. With the help of borehole video instruments, the location, orientation of each fracture and the fracture number of different intersection type on each borehole wall were mapped with the advancing of mining face. These data were analyzed using the Matlab Toolbox RJNS3D and Dips to determine structural homogeneity zone, to find the number of fracture sets that exist in the coal-rock mass, volume density frequency for each set and the probability distributions of orientation, fracture size in 3-D. Sampling biases associated with orientation, spacing were corrected during the process. The constructed fracture networks were validated by comparing the observed mean spacing along normal vector of mean orientation for each set and the predict value on similar scanlines.

Lessons Learnt from Measurements of Vertical Pressure at a Top Coal Mining Face at Datong Tashan Mines, China

Mining mechanics usually refers to the movement of overburden rocks and stress redistribution induced by mining effects, especially during the evolution of abutment pressure at a mining face (Xie et al. 2011). The characteristic of the stress field at a mining face serves as an important foundation for achieving roof safety and preventing excess gas (Suchowerska et al. 2013; Yang et al. 2011a). The mining effect may cause coal rocks to fracture, causing coal methane to escape from the fractured rock into the mining face, resulting in the exceedance of safety limits for gas. This is especially relevant under intensive mining conditions (Yang et al. 2011b; Li et al. 2006; Wang et al. 2012). Therefore, the study of mining mechanics is of great importance in achieving the safe and efficient coal mining. Many specific studies have been conducted to investigate stress redistribution, strata deformation, strata failure and fluid flow of coal seams (Islam and Shinjo 2009; Yang et al. 2014). However, these studies only focused on mining mechanics induced by mining advances, and neglected local mining effects, such as coal caving processes used for top coal caving method. In this manuscript, a field test and analytical analysis were conducted. A combination of global and local mining mechanics was consequently proposed for the top coal caving. Based on the real-time pressure monitoring of single props and hydraulic supports at a top coal mining face, intensive factors of pressure were adopted to provide a quantitative description of the mining mechanics.

History, advancements, and perspective of biological research in deep-underground laboratories: A brief review

The world is entering a new era of exploring and exploiting the deep-underground space. With humans poised to reach historical depths in the use of the deep Earth, it is essential to understand the effect of the deep-underground environment on the health of humans and other living organisms. This article outlines the history and development of biological research conducted in deep-underground laboratories and provides insight into future areas of investigation. Many deep-underground laboratories have investigated the effects of reduced cosmic ray muons flux, searching for rare events such as proton decay, dark matter particles, or neutrino interactions, but few have focused on the influence of the environmental factors in the deep-underground on living organisms. Some studies revealed that prokaryote and eukaryote cells maintained in low levels of background radiation exhibited an stress response, which manifested as changes in cell growth, enzyme activity, and sensitivity to factors that cause genetic damage; however, the underlying mechanisms are unclear. There remains an urgent need to understand the detrimental and beneficial biological effects of low background radiation and other factors in the deep-underground on humans and other organisms. Consequently, a multidisciplinary approach to medical research in the deep-underground has been proposed, creating a new discipline, deep-underground medicine, and representing a historical milestone for exploring the deep Earth and in medical research.

Derivation and application of an analytical rock displacement solution on rectangular cavern wall using the inverse mapping method

Rectangular caverns are increasingly used in underground engineering projects, the failure mechanism of rectangular cavern wall rock is significantly different as a result of the cross-sectional shape and variations in wall stress distributions. However, the conventional computational method always results in a long-winded computational process and multiple displacement solutions of internal rectangular wall rock. This paper uses a Laurent series complex method to obtain a mapping function expression based on complex variable function theory and conformal transformation. This method is combined with the Schwarz-Christoffel method to calculate the mapping function coefficient and to determine the rectangular cavern wall rock deformation. With regard to the inverse mapping concept, the mapping relation between the polar coordinate system within plane ς and a corresponding unique plane coordinate point inside the cavern wall rock is discussed. The disadvantage of multiple solutions when mapping from the plane to the polar coordinate system is addressed. This theoretical formula is used to calculate wall rock boundary deformation and displacement field nephograms inside the wall rock for a given cavern height and width. A comparison with ANSYS numerical software results suggests that the theoretical solution and numerical solution exhibit identical trends, thereby demonstrating the method’s validity. This method greatly improves the computing accuracy and reduces the difficulty in solving for cavern boundary and internal wall rock displacements. The proposed method provides a theoretical guide for controlling cavern wall rock deformation failure.

The Effect of Excavation Disturbance on Rockburst Trigger under Different Horizontal Geostress

Rockburst is one kind of dynamic geological disaster, and the influencing factors are complicated and diversified. Among which the high geostress is the major external cause, the hard brittle rock mass is the major internal cause, and excavation disturbance is the major incentive. The initial horizontal geostress in the surrounding rock significantly affects distribution of secondary stress after excavation, which is closely related to rockburst occurrences. Therefore it is necessary to study the excavation disturbance on rockburst trigger under different horizontal geostress. To accomplish the research goal, the underground powerhouse at Pubugou hydropower station in Sichuan Province, China was taken as an example. The numerical model was set up to simulate the actual excavation steps and predict rockburst intensity based on stress criterion. The analysis indicated that the potential hazard of rockburst increased with the rise of horizontal geostress. When horizontal geostress was more dominant, rockburst usually happened on the roof and bottom of cavern; when vertical geostress was more dominant, rockburst usually happened on the side wall of cavern. Specially, when the ratio of horizontal geostress to vertical geostress was greater than 1.7, we should seriously pay attention to the effect of excavation disturbance on rockburst trigger and take proper measures to prevent and control rockburst.