# Effect of Methane Adsorption on Mechanical Performance of Coal
## 1 Introduction  
With increasing mining activities, underground mining is reaching deeper levels, which are settled on geological environments different from shallow coal mines [1]. Disturbance of land by mining breaks the stress and gas pressure equilibrium of the original rock in the coal reservoir. During the process of tunneling, large mining spaces along the goal result in a significantly high pressure on the working face and surrounding rock of the roadway [2, 3]. As the surrounding rock is simultaneously affected by the lateral support pressure of the adjacent working face [4, 5], the pressure of the surrounding rock can increase to values up to 10 times more than those of the original rock stress [6, 7, 8]. Additionally, the stored gas can also present different gusher states. This phenomenon inevitably leads to the movement, deformation, and even destruction of gas-containing coal rock strata [9, 10], thus promoting the occurrence of coal mine power disasters, such as rock burst and coal and gas outbursts [11], posing a serious threat to coal mine workers. In order to eliminate potential dangers and effectively prevent the occurrence of coal mine power disasters, it is necessary to understand the laws of deformation and failure in gas-containing coal rocks. It is particularly important to study the mechanical properties of gas-containing raw coal under high stress environments [12, 13].  
The mechanical behavior of gas-containing coal rock under constant triaxial stress conditions have been thoroughly investigated. [PERSON] et al. [14] analyzed strength variationand elastic modulus in gas media by measuring the triaxial compressive strength and deformation of more than 200 gas-containing coal samples with an in-house triaxial experimental device. [PERSON] et al. [15] applied a triaxial experiment to anthracite samples containing high amounts of gas to investigate the effects of axial pressure and lateral pressure on coal deformation and coal seam permeability. [PERSON] et al. [16] performed triaxial compression experiments at different confining and gas pressures to investigate energy consumption and the seepage characteristics of coal samples during the compression process. By using the intrinsic time plasticity theory, [PERSON] et al. [17] established a constitutive relationship for the intrinsic time of gas-containing coal. In addition, some scholars have studied the effects of geological conditions [18; 19], temperature [20; 21], different loading and unloading conditions [22; 23], effective confining pressure [24; 25], and waste characterization [26] on the performance of gas-bearing coal.  
As shown herein, previous researchers have mostly studied the triaxial compression mechanisms in coal rock containing gas under varying condition of stress, gas pressure, and temperature. However, there are few reports on the mechanical behavior of high-rank coal and medium-rank coal under high stress environments. By using the original coal samples obtained in the Qujing mining area, we applied three-dimensional stress to study changes in mechanical properties of raw coal containing methane at different effective confining pressures and methane pressures. The study presented herein provides a valuable reference for deep coal seam mining for the prevention and control of coal and gas disasters, especially during the application of deep coal seam fracturing technology in surface coalbed projects.