Guangzhi Yin

A New Experimental Apparatus for Coal and Gas Outburst Simulation

Instantaneous coal and gas outbursts are dynamic underground mining phenomena in which coal and gas are suddenly and violently ejected from a coal face (Shepherd et al. 1981). Since March 22, 1843, when the first recorded coal and gas outburst happened in the Isaac mine, Zeroual coalfield, France (Lama and Bodziony 1998), experts have conducted extensive investigations on these outbursts. However, understanding and predicting such a disaster has achieved only limited progress in the intervening years (Chen 2011). Field data of coal and gas outbursts are rarely captured; thus, experts from different countries have worked on mathematical models or explored the mechanisms for coal and gas outbursts (Litwiniszyn 1985; He and Zhou 1994; Frid 1997; Beamish and Crosdale 1998; Valliappan and Zhang 1999; Li 2001; Cao et al. 2001, 2003; Alexeev et al. 2004; Xu et al. 2006; Aguado and Nicieza 2007; Wold et al. 2008; Zhang and Lowndes 2010; Chen 2011; Xue et al. 2011). For example, a porous rock is composed of a skeleton and pores. Its skeleton is made up of solid particles and its pores form a system of capillaries filled with gaseous substances. This model of a porous medium suggests a domino effect that leads to a catastrophic failure, or outburst, of the coal. The occurrence of an outburst depends on the local stress state, gas content, and physicomechanical properties of the coal. Such models or mechanisms lack sufficient experimental evidence. Coal and gas outbursts are so devastating that field trials are almost impossible. An alternative is to simulate the dynamic phenomenon of a coal and gas outburst in the laboratory with a specially designed apparatus. Some efforts have been made to develop an experimental apparatus for coal and gas outburst simulations (Meng et al. 1996; Guo et al. 2000; Cai 2004). However, their designs for the apparatus had some limitations, such as using small coal samples and simulating only horizontal coal seams. A key limitation is that all outburst caverns are manually opened. These limitations may significantly affect the experimental results. For instance, a smaller coal sample may have a greater boundary effect. Outburst accidents occur more frequently in dip coal seams, especially in rock cross-cut coal uncovering, which refers to the excavation process of rock cutting just before the exposure of the coal seam. Manually opening the outburst cavern may be too slow. This may reduce the intensity of coal and gas outbursts in the tests. In addition, the current apparatus cannot simulate the local concentration of stress in front of the coal face because it can only apply a uniformly distributed load on coal samples through a single loading plate. Finally, the current apparatus cannot simulate gas infiltration from the entire cross-section because the coal samples only have a single inflatable hole. & Changbao Jiang jcb@cqu.edu.cn

Development of a New Direct Shear Testing Device for Investigating Rock Failure

Rock failure is commonly induced by compressive and shear coupled loading. The process and mechanism of rock deformation and failure under compressive–shear loading conditions are important to the study of rock engineering and stability (Cai and Liu 2009). Direct shear tests are widely used in geotechnical engineering to investigate rock mechanics and the rock failure process. To date, numerous shear box devices to evaluate rock mechanics and a variety of engineering applications have been proposed (Kim et al. 2012; Gomez et al. 2008; Jiang et al. 2004; Suits et al. 2008; Shrivastava 2013; Konietzky et al. 2012). However, much previous research focuses primarily on the mechanical characteristics of rock. As external loading increases, cracks grow and join with neighboring cracks, inducing stress redistribution and localized stress concentration, which influence the strength and failure behavior of rock masses (Lajtai 1974). Therefore, the mechanism of crack growth and coalescence in rock masses remain a fundamental problem in rock mechanics and engineering practices (Yang et al. 2013). In this study, a new device (Fig. 1) designed to test direct shear is developed and tested on sandstone with a constant normal load. A CCD camera and stereomicroscope were employed to record crack fractures of specimen surfaces, and rock damage was recorded by acoustic emission monitoring system. During the shearing process, AE signal changes were found to indicate crack initiation and propagation on the surface of specimens. Micro-cracks were observed on the specimen surfaces, including different genesis tension cracks, shear cracks and rock bridges. Crack growth both along and through particles was clearly observed.

A Novel Large-Scale Multifunctional Apparatus to Study the Disaster Dynamics and Gas Flow Mechanism in Coal Mines

China is the world’s leading producer and consumer of coal, and more than 70% of the coal deposits in China have relatively high coalbed methane (CBM) contents (Xu et al. 2017). CBM is a major hazard in coal mine production because it can pose a serious risk of disaster (e.g., coal and gas outburst, hereinafter referred to as outburst) (Karacan et al. 2011), and CBM extraction is an effective method for reducing the disaster risk (Liu et al. 2016). Thus, many apparatuses have been developed in recent years (Alexeev et al. 2004; Jessen et al. 2008; Ranjith and Perera 2011; Sobczyk 2014; Jiang et al. 2015; Yin et al. 2016; Li et al. 2016; Geng et al. 2017; Jin et al. 2018) that have significance for investigating the disaster dynamics and gas flow mechanism in coal mines. However, these apparatuses have several limitations: (1) the specimens used in the experiments have very small dimensions; thus, errors associated with the seepage field induced by boundary effects cannot be avoided; (2) their limited data acquisition channels hinder the study of the time–space evolution of the reservoir parameters in the coalbed; and (3) they have a single function, which is not conducive to performing different types of tests. To overcome these challenges, a novel large-scale multifunctional (LSMF) apparatus was developed. The newly developed LSMF apparatus can not only simulate outburst disasters but can also be used to conduct gas flow experiments (e.g., CBM drainage, carbon dioxide sequestration, and carbon dioxide-enhanced CBM recovery (CO2-ECBM)). This paper describes the design principles, structures, and key technologies of the LSMF apparatus, and an outburst example test was performed to validate its capability and reliability.