The application of fractional calculus in the rheological problems has been widely accepted. In this study, the constitutive relationship of the generalized Kelvin model based on fractional calculus was studied, and the meshless method was introduced so as to derive a new meshless algorithm formula based on the fractional calculus of the generalized Kelvin model. By using the MTS815.02 hydraulic servo rock mechanics test system, the creep test of mudstones is carried out, and the related data of the creep process were obtained. Based on the generalized Kelvin model of fractional calculus, the related creep parameters of the argillaceous sandstone under compression were fitted. The results showed that the solution of the generalized Kelvin model based on fractional calculus was greatly consistent with the numerical method solution. Meanwhile, the meshless algorithm based on fractional calculus had a favorable stability and accuracy.

In the western region of China, coal mining activities are prone to induce water and sand inrush disasters, which seriously threaten the safe production of the coal resources. In this paper, an experimental device was designed to simulate the process of water and sand inrush, and then, the control factors of the disasters in the broken rock mass in the goaf were investigated. Also, the seepage fracture channels in the broken rock mass were simplified by using the 3D printing technology, and the effects of fracture aperture and angle on the seepage characteristics of water-sand mixtures were analyzed. The experimental results showed that the porosity and skeleton structure of the broken rock mass were the key factors to control the water and sand inrush disasters. The smaller the initial porosity of the broken rock mass, the weaker its permeability, and the less probable to form a dominant channel for the water and sand inrush disasters. Conversely, the broken rock mass structure with larger size gradation was more likely to form the permeable channels, and the quality of the sand inrush was greater. In addition, it was also found that the angle of the fractures within the broken rock mass affected the seepage characteristics of water-sand mixture, and the permeability showed an exponential relationship with the fracture angle. Meanwhile, as the fracture aperture increased, the fracture angle generated greater influence on the permeability. Finally, we proposed the water and sand inrush prevention and control technology based on the experiment results. The results of this study can provide a reference for the control of water and sand inrush disasters in western China.

When the mountain tunnel projects passing through the complex formation with coal, it happened along with disaster accidents such as gas outburst, gas combustion, and gas explosion. These disasters should seriously threaten the safety and life of the construction personnel and affect the normal operation of the tunnel construction. Ventilation is the most effective means to control gas, fire, dust, heat, and other disasters. To study the effects of different ventilation modes in highway gas tunnels, Fluent software was used to simulate forced ventilation, exhaust ventilation, and mixed ventilation in a high gas tunnel of a highway in Hunan. The distribution law of the airflow velocity and gas concentration of these three ventilation modes were obtained to determine the optimal ventilation system. It was shown that vortex zones of different ranges formed in the tunnel for all three ventilation modes, and the gas concentration was higher in the vortex zone than in other regions. Mixed ventilation of them is superior to the other two modes, showing the best ventilation effect with regard to airflow velocity and gas concentration.

In the reuse stage of a gob-side entry retaining, failure of the structure and stability of the main roof have a significant effect on the safety of the advanced support and ventilation space at the working face. In this study, field investigation, theoretical analysis, and industrial experimentation were performed to analyse the fracture characteristics and formation process of the gob-side entry retaining roof during the reuse period. A dynamic-equilibrium mechanical model of the main roof structure is presented and the formation mechanisms of different types of short cantilever rock beam structures are clarified. The following major conclusions are drawn: (1) Three types of short cantilever rock beam structures occur in the main roof of a gob-side entry retaining during the reuse period, namely, the short cantilever-articulated rock beam structure, short cantilever step rock beam (type I) structure, and short cantilever step rock beam (type II) structure. (2) The stability criterion for these three short cantilever rock beam structures was also determined; that is, when the sliding instability coefficient K1, the short cantilever-articulated rock beam structure will form, and when the sliding instability coefficient K<1, the short cantilever step rock beam (type I or II) will form. (3) The governing law for the thicknesses of the main roof, immediate roof, and coal seam of the short cantilever rock beam structure was clarified; namely, the K-value gradually increases with increases in the thickness of the coal seam, drops sharply and then decreases gradually with increases in the thickness of the main roof, and decreases slowly with increases in the thickness of the immediate roof. The research results were validated at the gob-side entry retaining project in the Huainan mining area and have theoretical significance and reference value for roadway support projects with similar conditions.

This study investigates water-sand bursting disasters associated with fractured rock that affect safe mining in the mining areas of Western China. A broken rock water-sand seepage rheological test device was developed, and rheological tests were conducted on multiple groups of broken rock samples with single-stage axial loading and different load levels. When the rheology of each group of broken rock samples was stable, water-sand mixed fluid was injected into the samples at a certain pressure gradient to conduct water-sand seepage tests on broken rock masses. It was found that when the porosity of a fractured rock mass is within a certain range, the water-sand mixed fluid does not completely pass through the fractured rock mass and some sand particles are filtered by the fractured rock sample. There is an exponential relationship between the sand breaking ability and the sand filtration ability of fractured rock and its initial porosity, and the permeability of fractured rock decreases by a certain extent after sand filtration. However, for different load levels, when the flow through a fractured rock mass tends to be stable, the final porosity of the fractured rock mass decreases exponentially with axial compression. Based on the classical Kelvin rheological model and the basic theory of fractional calculus, a new fractional rheological model has been proposed and the rheological parameters under different load levels were fitted to the model. The new fractional rheological model is better able to describe the rheological characteristics of broken mudstone.

To address the large deformation of the surrounding rock of deep gob-side entry retaining under high stress, lithological characteristics of the surrounding rock and failure model of support body and their evolutionary processes are analyzed through field investigation and theoretical analysis. Failure mechanisms of surrounding rock and the technology to control it are studied systematically. The results show that the causes of the large deformation of the surrounding rock are weak thick mudstones with softening property and water absorption behavior, as well as its fragmentation, dilatancy, and long-term creep during strong disturbance and highly centralized stress states. The cross-section shape of the roadway after deformation and failure of the surrounding rock is obviously asymmetric in both the horizontal and vertical directions. Since the original system supporting the surrounding rock is unable to completely bear the load, each part of the supporting system is destroyed one after the other. The failure sequences of the surrounding rock are as follows: (1) roadway roof fracture in the filling area, (2) filling body fracture under eccentric load, (3) rapid subsidence of the roadway roof, and (4) external crack drum and rib spalling at the solid coal side. Due to this failure sequence, the entire surrounding rock becomes unstable. A partitioned coupling support and a quaternity control technology to support the surrounding rock are proposed, in which the roof of the filling area plays a key role. The technology can improve the overall stability of gob-side entry retaining, prevent support structure instability caused by local failure of the surrounding rock, and ensure the safety and smoothness of roadways.