Analysis on Influence Factors of Roadway Instability in High-Stress, Steeply Inclined Extra-Thick Coal Seam

In order to solve the problem of roadway support safety in coal mining under high stress conditions and to improve safe and efficient production in coal mines, the control countermeasures of the surrounding rock stability and the optimization scheme of support are put forward and the model and numerical simulation of roadway bolt support system are established. Based on bolt support theory and instability mechanism of the coal rock dynamic system, this paper puts forward the evaluation of support effect and the optimization parameters of bolt support, and the scheme of mine pressure monitoring and the corresponding support optimization system are established. The roof fall accident and the bolt and cable of support have been broken in the Wudong coal mine, the phenomenon of bolt pulling out in the roadway. The causes of roof fall are analyzed and the solutions are put forth, judging the influence of different factors on roadway support. In view of the roof fall accident in the North Lane of the east wing of the +575 level 43 #coal seam in the north mining area of the Wudong coal mine, the cause analysis and support suggestions are made. And, according to the performance of the bolting material and anchoring agent, the laboratory theoretical research was carried out. Through the experiment, it is concluded that the FRP bolt with a diameter not less than 27 mm is the first choice for the side support of the working face in the mining roadway, then ribbed steel bolt with a diameter not less than 20 mm for the nonworking face, and the length of the anchor rod not less than the range of the loose circle. Therefore, full-length anchoring should be carried out in roadway support, the anchorage length of the anchor cable should be increased, and the integrity of the roof should be improved, so as to reduce the amount of roadway roof separation and improve the support effect.

Securing the quality of mesh weld joints in bolt support through robotized operation

Stabile strength properties of the mesh weld joints is one of the key factors in ensuring the required load-bearing capacity of the bolt support as a whole. In accordance with the basic principles of the statistical process control concept, the best quality is ensured by the production process that has the minimum variability of the results. To identify the initial parameters of the control charts used to monitor the stability of the process, the strength properties of the mesh weld joints were studied for manual, contact and robotic welding in the conditions of OKS LLC. Robotic welding is made using the ABB robotic complex consisting of three manipulators, two of which are designed to execute the movement of the welding arc and one to displace the mesh into and out of the welding zone. It is shown that the distribution of welding strength values in robotic welding is characterized with the lowest value of sample standard deviation. It was found that robotic welding was the only method among those investigated that ensured the values of additional samples to fall within the initially set range in the control charts.

Numerical Simulation Study on the Influence of Mine Earthquake on the Bolt Stress

Mine earthquake, as an underground disaster that occurs frequently, has a great impact on coal mine roadway and support. The stability analysis of the bolt support in roadway under different mine earthquake magnitudes is a key issue to be solved urgently in mining fields. This paper attempted to simulate the occurrence state of mine earthquake with explosive blasting process and verified it with actual coal mine microseismic monitoring data. ANSYS/LSDYNA software was used to analyze the impact of magnitude and location of mine earthquake hypocenter on the stability of bolt support and the dynamic stress characteristics of bolt. The results showed that with the increase in source energy of mine earthquake, the damage location of bolt mainly appears in the front of bolt and the loading position has no obvious change, but there is stress wave superposition effect, which deepens the damage of bolt. The bolts in the middle of the lane and the middle of the roof are greatly affected, so the support strength should be strengthened in these places. In addition, this paper compared the safety factor of bolt and the supporting effect of different schemes from three aspects such as roof subsidence, axial stress of bolt, and safety factor of bolt and then put forward a more economical and effective supporting scheme.

Effect of Foundation Pit With Different Support and Excavation Methods on Adjacent Buried Hydrogen Pipe

Support and excavation methods have a great effect on the supporting role of the foundation pit. To investigate the effect of foundation pit with different support and excavation methods on adjacent buried hydrogen pipe, a pipe–soil coupling model was established. Deformation, strain, and stress of the pipe near the foundation pit with different support and excavation methods were analyzed. The results show that stress concentration appears on the upper and lower surfaces of the middle part of the pipe after the foundation pit excavation. The high stress areas on the upper and lower surfaces are distributed symmetrically about the pipe center. Upper surface of the pipe's middle section is pressed and the lower surface is pulled, but the strain distribution of the pipe at the pit edge is opposite. Vertical displacement of the pipe is bigger than its horizontal displacement. The underground continuous wall as the most common support structure can effectively reduce the pipe deformation. Supporting methods have different effects on buried pipe's mechanical behavior. Lateral reinforcement, inner support, and bolt support can effectively reduce the pipe deformation, but the mitigating effect of lateral reinforcement is less than inner support and bolt support. The pipe is also affected by time and space of the foundation pit excavation. The slope excavation can greatly reduce the pipe deformation, but the effects of island excavation and basin excavation are not obvious. Those results can provide references for pipe safety assessment and protection.

Influencing Factors of Disturbance Effects of Blasting and Driving of Deep Mine Roadway Groups

The development and application of roadway group layout methods in coal mines have become more common and the mutual disturbance of blasting and driving of roadway groups has also become more prominent at depth. To improve the stability of rock mass surrounding roadways, we performed a systematic study on the factors that influence blasting and driving disturbances of adjacent roadways in deep mine roadway groups. We use the dynamic analysis module in FLAC3D to obtain the influence laws of three factors on the disturbance effects of adjacent roadways, namely, excavation methods, layer position changes of the roadway group, and whether or not bolt support is applied in the first roadway. Blasting strongly influences the surrounding roadway and increased horizontal distance can effectively reduce the disturbance effects of blasting and driving between adjacent roadways compared with increased vertical distance. Bolt support of the first excavated roadway enhances the roadway integrity and better stabilizes the rock structure surrounding the roadway. Industrial tests were carried out on three uphill roadways in the Gubei no. 1 mine (6-2). The monitoring results show that the movement of the roof and floor of the floor uphill return wind roadway is larger than that on the two sides. There is no notable change in the deformation speed of the surrounding rock in the floor return air roadway, but the deformation speed of the uphill conveyor belt roadway changes significantly. The results show that when the blasting excavation of a deep mine roadway group is more than five times the tunnel spacing, the increased horizontal distance effectively reduces the disturbance effects of excavation between adjacent roadways, which is consistent with the simulation results.

Bearing Characteristics of Surrounding Rock of Deep Mining Roadway with Full and End Bolt Anchorages: A Comparative Numerical and Experimental Study

The support strength of surrounding rock in deep mining roadways can be significantly improved by replacing the end bolt anchorage with a full one. The support effects of both types of anchorage and the axial stress distribution characteristics in anchored bolt bodies were assessed via the indoor pull-out test, simulated via the FLAC3D software, and verified by field measurements. The stability and variation patterns of the axial force, as well as the evolution law of bearing characteristics of surrounding rock, were analyzed. The results indicate that the polymorphic deformations of deep mining roadway surrounding rock and the bolt support body interact synchronously. The axial force evolution trend in bolt bodies with end anchorage revealed by field tests was consistent with the laboratory test results, in contrast to that of full anchorage. Although stress distribution laws in both sides of the mining roadway were the same for both types of anchorage, the vertical stress peak and damage range of full-anchored surrounding rock slightly exceeded those of the end-anchored one. The anchored area bearing a higher load alleviated the stress concentration of the surrounding rock. Since the deformations in fully and end anchored surrounding rocks increased gradually and sharply, respectively, the full anchorage is more conducive to deformation moving control of deep mining roadway surrounding rock. The research results can provide theoretical guidance for the design and construction of deep mining roadway bolt support.

Research on the Large Deformation Prediction Model and Supporting Measures of Soft Rock Tunnel

The weak surrounding rock has the characteristics of easy softening, poor integrity, low mechanical strength, etc., which makes it easy to induce different degrees of deformation and damage under excavation disturbance and then seriously affects the stability of the tunnel. Carrying out soft rock tunnel deformation prediction research and designing the supporting structure according to the predicted value is of great significance to engineering construction and design. Based on the grey theory, the large deformation of the vault, shoulder, and waist of the soft rock tunnel are predicted, and then the specific bolt support is designed in the maximum predicted value (Smax·R) area. The control effects of different bolts, spacing (d), length (L) on the maximum displacement (Smax·M), and maximum stress (σmax·M) the surrounding rock are analyzed by numerical simulation. Results show that the gray model has high prediction accuracy, the best prediction time is one week, and the maximum error is only 2.99%; with the decrease in d, resin bolt support has a significant supporting effect compared with mortar bolt support, with Smax.M and σmax·M reduced by 64.38% and 10.35%, respectively; as the L of bolt increases, compared with the mortar bolt support, the resin bolt support has a more obvious restraining effect on the surrounding rock deformation, and Smax·M and σmax·M are reduced by 28.20% and 10.00%, respectively; when 4.5 m < L < 6.0 m and 0.6 m < d < 0.7 m, resin bolt support should be adopted; in other ranges, mortar bolt support or resin bolt support has a less significant difference in controlling surrounding rock deformation.

Sensitivity Analysis and Experimental Verification of Bolt Support Parameters Based on Orthogonal Experiment

This paper presents a unified supporting parameter optimization procedure for the coupled bolt-rock systems by using the orthogonal experimental methods. Convergence of surrounding rock surface and deformations in the rock are taken as the objective functions for the stability of the surrounding rock of the roadway. The key support parameters of the bolt are considered as input variables. The simulation software FLAC3D is employed to develop the mechanical model for the coupled bolt-rock system and the objective functions of the coupled system are therefore obtained in the software. Combining the variance and multivariate linear regression analysis, an approach is derived to investigate the sensitivity of the support parameters to the objective functions. The corresponding support parameters are then optimized. The 15106 working of a practical mine in Yangquan is taken as an example. According to the similar simulation theory, corresponding simulation experiments are performed. Thus, the proposed method is validated and its robust performance for optimization of supporting parameters of the bolt is also demonstrated. The method provides a theoretical basis for the determination of bolt support parameters for mining roadway in a fully mechanized mining face.