1. Introduction
With the progressive increase in the intensity of coal resources, shallow coal resources are becoming rare, and most of the mines are mined in deep areas in order to improve the sustainability of the coal industry [
1,
2,
3,
4,
5]. The surrounding rock is shattered and loose, with extensive damage and cracked joints, as a result of numerous variables such as geo-stress, dynamic pressure, and geological structure [
6]. Fractured roadway excavation, the complicated stress environment with asymmetrical distribution, and an evident increase in in-situ ground stress would produce strength deterioration and secondary stress concentration distribution on the surrounding rock [
7]. Deep roadways are plagued by a variety of issues, such as asymmetrically high ground stress and various lithologies, making it difficult to pinpoint the sources of structural instability and adopt effective management techniques [
8,
9,
10].
Figure 1 depicts geological data from asymmetrical structural fractures along roadways, including sandstone and mudstone [
11].
Scholars conducted extensive research on the deformation and failure mechanisms of soft rock roadways, as well as proposed and built roadway support technologies [
3,
5,
6,
12]. Yu et al. [
2] systematically studied the stability of deep-buried rocks through field investigation, laboratory analysis, theoretical derivation, and engineering applications. He et al. [
3] proposed that core scientific issues arising in deep underground projects are encountered with the conditions of “three-high and one-disturbance”, i.e., high in-situ stress, high temperature, high seepage pressure, and a strong mining disturbance, which form a complex geomechanical environment for deep engineering. Li et al. [
5] carried out a large-scale geomechanical model test to explore the surrounding rock deformation and failure mechanisms of such deep roadways. Yang et al. [
12] showed that shallow rock has a significant scale of tensile failure, which causes swelling and fracture surrounding the roadway. Significant floor heaving, side shrinkage, and roof sinking occur as a result of the primary support being weak and when there is no support on the floor. To support the ventilation roadway, a novel “bolt-cable-mesh-shotcrete + shell” combination support is suggested. Wang et al. [
13] demonstrated that roadway deformation is extensive with a wide damage range. The anchor bolts are frequently found in the severely fractured surrounding rock, the support potential is not utilized, the arch’s support strength is insufficient, and the post-bearing capacity is low; all of these mainly lead to the failure of the roadway bearing capacity and a concept of “high-strength, integrity, and pressure-relief” is proposed. Common supporting methods for shallow roadways are unlikely to extend to deep geological settings; thus, Kang et al. [
14] are looking at developing a new type of combined supporting system for weak floors in difficult geological environments. Li et al. [
15] provided a case study of the deformation failure mechanism and support technology for a deep roadway with soft rock mass and evaluates the modes, influencing factors, laws, and processes of deformation failure in the roadway based on comprehensive field research and numerical model analysis. Zhao et al. [
16] presented a technique that involves analyzing the failure features of roadways, as well as the microscopic fracture properties of the surrounding rock, using a digital drilling televiewer and three-dimensional laser scanning devices. Zuo et al. [
17] systematically investigated the Macro/Meso dynamic behavior of deep rock or coal–rock combined institutions under various loading conditions and developed a coupled grouting control technology for the surrounding rock, standard strength assistance in the deep roadway, and the corresponding velocity vector movement model of overlying strata. Shi [
18] proposed a systematic model of deformable block systems that represents an important solution for large displacement, large deformation, and failure computational methods, assuming that the forces acting on each block, whether from applied load or interaction with other blocks, assuage the equilibrium conditions. Chen et al. [
19] used insight into mechanics to evaluate the fracture and develop principles of floor mining fractures to reveal the coupling relationship between certain mining-induced fractures and theoretical stress and hydraulic pressure, and defined a model of fracture progression and connection structure for the deep floor discoloration based on a self-developed simulation test, especially for high floor water transients.
The DEM represents rock masses as a collection of blocks that can be stiff or deformable, and an explicit solution technique is used [
20]. The blocks are permitted to behave as if they were continuum media, and the block and joint interactions are represented using Newton’s equations of motion. Unlike the finite difference method, this avoids the requirement for a huge stiffness matrix. Fairhurst et al. [
21] understood the advantages of the distinct element method for modeling non-continuous rock masses by comparative analysis of an excavation in a jointed rock mass developed by a finite difference method and a universal distinct element code model. Bai et al. [
22] utilized the discrete element method to simulate the failure of a laminated roof, focusing on the formation and stabilization of micro cracks and macroscopic cracks, including the growth of control mechanism stress and deformation in the laminated roof. Hamdi et al. [
23] utilized a mixed finite-discrete element method to model the entire 3D cracking procedure during traditional laboratory testing, including Brazilian tension and uniaxial compression strength. Srisharan et al. [
24] presented stability studies on two tunnels, a horseshoe-shaped and an inverted arch-shaped tunnel, in a deep coal mine in China using the DEM simulation model. The calibrated models were analyzed for different supported and unsupported cases to estimate the significance and adequacy of the current supports being used in the mine and to suggest possible optimization. Zang et al. [
8] presented a case study on the deformation failure behavior and support design of a deep roadway in the Tangyang mine by field tests and DEM simulations. Finally, a DEM simulation and a field experiment were conducted to evaluate the rationality of the proposed support scheme, and the results showed that the new support method could effectively control the surrounding rock. In a study by Li et al. [
25], DEM was carried out to further explore the deformation failure characteristics and factors influencing deep roadways with different engineering geological conditions.
Dongpang Mine (shown in
Figure 2a) in Xingtai City, Hebei Province, is currently mining at a level of +480. The #2 coal seam has a ground burial depth of approximately 580m. The coal and rock masses are impacted by high ground stress, high ground temperatures, and high permeability after deep mining. The mine track roadway in the 11 mining area (TR-11MA) was severely distorted throughout the service era and has undergone numerous repairs, but the control effect is not discernible. A large amount of the previous literature on the mechanism of deformation and failure of deep roadways and the research methods of control technology mainly focuses on in-site testing, theoretical models, and numerical simulations [
1,
19,
26]. However, few studies have focused on matching support strength and support structure (rock bolts and anchor cables axial force, length of anchorage agent, bolt pre-stress, and thickness of pallets). Furthermore, few systematic investigations on the failure characteristics of the surrounding rock have been conducted (thickness of the loose rock zone and fracture distribution characteristics of the surrounding rock), which is the motivation of this paper. Combining the above-mentioned site’s geological conditions, the method of field and numerical simulation is used to systematically study the failure characteristics of deep high-stress, analyze the stress field, crack field, and damage change characteristics of the deep high-stress main roadways affected by mining disturbances. Finally, corresponding control technologies were proposed for the repair and extension section of the main roadways, which reduces roadways repair times, improves the sustainability of development, and serves as a model for deformation control of similar deep high-stress roadways.
Therefore, the main objectives of this paper are:
- -
Geological conditions and field study on the deformation and failure characteristics of the deep high-stress main roadways;
- -
Numerical simulation study on deformation and failure mechanism of deep main roadways;
- -
To develop a basic control strategy of the reinforcement and repair technology of the deep main roadway in the Dongpang coal mine.
5. Conclusions
This study used a combination of field investigation and numerical simulation methodology to reveal the mechanism of abnormal deformation and failure characteristics of deep high-stress roadways induced by mining disturb. The following are the main conclusions:
The field study results demonstrate that the mechanism of deformation and failure of TR-11MA in the eastern panel mining disturbance. Moreover, the matching test of the support structure evidences the importance of the selection of supporting structure parameters.
The initiation, propagation, and coalescence of internal cracks were investigated throughout the formation process of the TR-11MA, which showed that the stress in the ribs wall of TR-11MA at period 2 is 23.3 MPa and 24.6 MPa, respectively.
The surrounding rock control parameters of the new extension section and the reinforcement repair section of TR-11MA are proposed, respectively, and the field application effect is significant, which provides a reference for the support design of the deep roadway and the sustainability of the development of a deep coal mine.