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.
It is one of the important safety problems in the process of mining shallow coal seams in western China that the rock mass affected by mining stress breaks and forms a penetrating fracture, leading to a sand burst in the working face. The self-developed test system is used to carry out the experimental study on the flow characteristics of Aeolian sand in fractures. The research work is focused on the influence of several parameters, such as the thickness of the Aeolian sand layer, the fracture opening, and the fracture dip angle on the velocity of sand particles in fractures. The results show the following: (1) The influence of fracture opening and fracture angle on sand burst rate is much greater than that of sand thickness. No matter what the fracture angle and fracture opening value are, the influence weight of sand thickness on sand burst rate is almost zero. (2) When other conditions are unchanged, with the increase of fracture dip angle, the sand burst rate increases significantly, and the relationship between the sand burst rate and the fracture dip angle is exponential. (3) The influence weight of fracture opening is the largest. With the increase of fracture opening, the sand burst rate increases logarithmically. Finally, according to the test results, the relation equation which can simultaneously describe the influence of fracture opening and fracture inclination on the rate of the sand burst is fitted. This study can provide a theoretical basis and scientific guidance for the prevention and control of coal mine sand inrush disasters caused by roof cracking in western coal mines.
The definition of design load with walking crowd excitation on these slender structures is a significant problem to human-induced vibration. To capture the characteristics of walking crowd loads, this article researches both the ground reaction force and ground reaction moment for 36 healthy adults. Firstly, a oscillate system modeling walking leg is used to build a governing equation, which further transformed into the discrete state space. Then the Kalman method is applied to filter the noises for the measured ground reaction force, which can well remove the noises hiding in the measured signals. In addition, the Fourier series are used to model the ground reaction force and ground reaction moment, and the first six corresponding coefficients are obtained and analyzed. This work comprehensively explores the excitation force and moment from walking pedestrian feet. The result of this study provides the reference of load design for these slender structures such as footbridges, grandstands, or stations under crowd excitation.
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