This paper proposes a novel understanding of the mechanisms of coal and gas outbursts based on static-dynamic coupling loading and effective stress theory. Previous mechanisms of coal and gas outburst have a problem in describing the failure process of coal. Static-dynamic coupling loading is required to fully understand the development process of coal and gas outburst. The effective stress theory is also introduced to analyze the coal and gas outburst due to its similarity with that of sand vibrating liquefaction. Our results show that coal experiences deformation of shear compression instead of dilatancy in the development process of coal and gas outburst. Furthermore, coal not only absorbs in-situ stress, but also endures dynamic loading. In particular, the measured data suggests that when approaching the dangerous region of coal and gas outburst, coal seam gas pressure significantly rises with increasing compressive deformation of coal seam. These results validate our proposal. Additionally, a physical-mechanics model is established to realize quantitative analysis of the mechanism of coal and gas outburst.
Nowadays, a comprehensive action hypothesis (Xo?ot, 1966, and Bufan, 1985) has been widely used in the study of mechanisms of coal and gas outbursts, which is regarded as comprehensive action results of in-situ stress, physical and mechanics properties of coal, and coal seam gas pressure. Under the guidance of comprehensive action hypothesis, great attention has been paid to describe the mechanics failure mechanisms of coal and gas outbursts from different aspects (Zhemin, 1982. Zhongcheng, 1987. Shinin, 1990. Mengtao, 1991. Chenglin and Bin, 1995. Shaolin, 1999. Deyong, 2003. Qianting, 2008). Mechanics basis of these mechanisms is mainly derived from traditional rock mechanics. These mechanisms have provided a powerful theoretical guideline for the prediction and prevention in coal and gas outbursts. However, based on traditional rock mechanics, dilatancy cannot explain the rise of coal seam gas pressure during coal and gas outburst which has been observed at site. Actually, coal not only absorbs in-situ stress, but also endures dynamic loading which is not taken into consideration in the traditional rock mechanics. Coal and gas outburst always occurs in the region which contains tectonic coal. However, mechanics properties of tectonic coal under static-dynamic coupling loading have not been investigated yet. Additionally, we find that coal and gas outburst has a similarity with sand vibrating liquefaction, as they are both about granular element under staticdynamic coupling loading. Therefore, this paper proposes a novel mechanism of coal and gas outbursts based on effective stress theory and static-dynamic coupling loading theory. Our work includes theoretical analysis, site validation, and model establishment.