Partitioning Control Mechanism and Engineering Practice of Rebuilding Bearing Arch in Surrounding Rock under High Ground Stress

The mining of coal seam has a significant influence on the stability of the roadway near it, especially under the condition of high ground stress. To study the control mechanism of the surrounding rock under the influence of high ground stress, a general idea for the partition control of the rebuilding bearing arch (RBA) was proposed in this paper. Based on the basic mechanical performance test of the bearing arch, this paper built a mechanical model of the RBA based on Protodyakonov’s pressure arch theory, analyzed the influence of the strength of the bearing arch on the surrounding rock failure, and obtained the ultimate thickness of the bearing arch failure under high ground stress. The results show that the RBA’s damage is closely related to the overburden load and RBA’s thickness. The tensile stress and shear stress of RBA increase linearly with the overburden load increase and increase sharply with the load-bearing arch’s thickness, showing a nonlinear relationship. To maintain the surrounding rock’s stability, it is necessary to ensure that the RBA’s thickness is within a specific range. The results are applied to the Wantian coal mine. The theoretically determined load-bearing thickness is 10 m, which can effectively control the surrounding rock deformation and significantly reduce the roadway’s repair rate

Analysis of Mathematical Model for Migration Law of Radon in Underground Multilayer Strata

This paper summarized the separation process of radon based on its geophysical-chemical properties. Taking into account the geological conditions of mining, the mathematical model of radon migration in underground multilayer strata (UMS) was established to investigate the distribution law of radon concentration in UMS. It was found that the distribution of radon concentration in UMS is affected by both the properties of the strata and the depth of cover and the radon concentration law varies at different depths even in the same layer stratum. At last, in order to validate the derivation result of the mathematical model of radon migration in UMS, the actual measured values (AMV) and the calculated values (CV) were compared further. As a result, the CV was found to be approximately equal to the AMV with deviation values (DV) less than 5%, which indicates that the derivation result of the mathematical model of radon migration in UMS is correct

Optimization of drilling parameters for coal seam gas extraction considering fluid–solid coupling and field application

Abstract Affect gas extraction efficiency to find out the optimum well location parameters, based on the gray correlation analysis of borehole diameter, borehole spacing, and extraction pressure three boreholes parameters that influence efficiency of gas extraction from the design of orthogonal experiment, using COMSOL simulate the effective radius of extraction under different experiments, and the effective radius of extraction for optimizing index quantitative gas extraction efficiency. The results showed that: factors affecting the gas extraction efficiency of the correlation between high and low aperture drilling, borehole spacing, and extraction from extraction negative pressure, it is concluded that the influence parameters of optimal layout parameter values, respectively, borehole diameter 8 cm and 3 m borehole spacing, extraction pressure 50 kPa, combined with the numerical simulation analysis using the optimal layout of gas drilling extraction from about 30 days. The decrease in gas pressure is about 45%, which basically meets the extraction standard, and the decreasing trend of gas pressure is obviously slowed down when the extraction time is longer than 30 days. The engineering experiment is carried out in the 9306 transport lane of a mine in Guizhou Province, and the results are basically consistent with the simulation results, which verify the rationality of the gray correlation analysis method to optimize the drilling parameters, and provide a theoretical basis for the optimization of drilling parameters

Mechanism of Secondary Breakage in the Overlying Strata during Repetitious Mining of an Ultrathick Coal Seam in Design Stage

When designing the mining of an ultrathick coal seam, the laws governing movement in the overlying strata during mining are a fundamental issue based on which several problems are addressed, including determining the mining method and the roadway arrangement, controlling the surrounding strata, and selecting the devices. The present paper considers possible problems related to strata overlying a large mining space subjected to repeated disturbances during the mining of an ultrathick coal seam, including repeatedly broken strata and the existence or inexistence of the structure. The BM coal seam in the No. 2 coal mine of the Dajing mining area in the East Junggar coalfield is studied. Physical simulations are performed on the movements of the overlying strata during slicing mining of the ultrathick coal seam, revealing the new feature of “break-joint stability-instability-secondary breakage” in the overlying strata. Mechanical models are constructed of the secondary breakage of the overlying strata blocks under both static and impact loading, and mechanical criteria are proposed for such breakage. Based on the research findings, methods for controlling the surrounding strata during slicing mining of an ultrathick coal seam are proposed, including increasing the mining rate and designing reasonable heights for the slicing mining

Analysis on the Influence Degree of Deformation Control Factors of Deep-Buried Roadway’s Fractured Surrounding Rock Using Orthogonal Design

It is a complex issue to select the support structure parameters for a deep-buried roadway with fractured surrounding rock; especially when the support structure parameters need to be adjusted, the influence degree of support structure parameters on roadway deformation needs to be determined. The deformation of deep-buried roadway’s fractured surrounding rock development was investigated using multi-index orthoplan in this paper. According to the coal mine field investigation, support structure’s failure often occurs, and some need to be repaired many times. Through the roadway surrounding rock drilling, it was found that the stress of the surrounding rock was relieved, resulting in the cavity and separation of the stratum layer. The two sidewalls’ development and roof fractures are mainly tangential, and the original rock state appears only beyond 6.3∼8.2 m. The length of bolts, the row distance between bolts, the length of cables, and the row distance of U-shaped steel were selected as control factors in the multi-index orthogonal design, and roadway’s deformation values were taken as the test indexes. According to the orthoplan, nine numerical simulation schemes were designed, and FLAC3D was used for establishment. The range analysis method was used to analyze the test results. The results show that the control factors’ influence order on the total deformation of the roadway is as follows: row spacing between U-shaped steel > bolt length > cable length > row spacing between bolts, the influence order on the deformation of the roadway floor is as follows: row spacing between U-shaped steel > row spacing between bolts > bolt length > cable length, same as the left sidewall and right sidewall, and the influence order on the roadway roof’s deformation is as follows: row spacing between U-shaped steel > bolt length = cable length > row spacing between bolts, which provide a reference for the support design of deep-buried roadways with fractured surrounding rock, especially the adjustment of the supporting structure

A Novel Comprehensive Detection Method for the Dynamic Characteristics of Coalface Overburden: A Case Study in China

Accurate and efficient acquisition of information about the dynamic characteristics of coalface overburden can provide an important theoretical basis for green mining in coal producing regions in western China. In this study, a novel method for comprehensively detecting the dynamic behavior of coalface overburden is proposed in order to address deficiencies of the existing detection methods. The new method combines surface radon measurement, overburden borehole imaging, and underground pressure observation into a comprehensive detection technology system, resulting in spatial and temporal integration of surface, overburden, and underground detection. To examine the feasibility of the proposed method, a field experiment was carried out at #1103 coalface in the Suancigou Coal Mine, which is operated by the Inner Mongolia Yitai Coal Co. Ltd. The results of the three approaches are largely consistent and they complement one another. But it must be pointed out that this method needs to be further improved by more field experiments. Based on the experimental results, a technique for forced caving by presplit blasting of the overburden was developed and then implemented to #1103 coalface. The practical use of the technique led to good results: it effectively prevented roof-associated accidents by controlling the first weighting step to about 82 m, contributing to safe and efficient mining; coal production was expected to increase about 126 kilotons

Experimental Study on Deformation Characteristics of Gangue Backfill Zone under the Condition of Natural Water in Deep Mines

To address the problem of surface subsidence caused by the compression of filling gangue in deep mines, a layered compaction test was designed based on the zonation of the failure of the overburden in the goaf and layered property of the filling gangue. The deformation characteristics of filling gangue in natural and water-bearing states were obtained. The deformation of filling gangue during the 0~100 kN loading stage was an approximately positive S-type, which reflects the relative “advancement” in terms of deformation. The filling gangue deformation in the 100~500 kN loading stage was an approximately inverted S-type, which reflects the relative “lag” in terms of deformation. In a natural state, the load-time curves of the dead load stage were consistent. Under a water-bearing condition, the load-time curve for the dead load stage had apparent “step” characteristics and presented a special phenomenon of displacement rebound. Under gradient loading, the strain showed an exponential growth model, and energy dissipation showed a logarithmic growth model. Under a natural state, the energy dissipation showed consistently increasing distribution patterns, while the energy dissipation showed a normal distribution model under the water-bearing state

Evolution Characteristics of Overburden Strata Structure for Ultra-Thick Coal Seam Multi-Layer Mining in Xinjiang East Junggar Basin

The efficient and safe extraction of ultra-thick coal seam in the Xinjiang East Junggar Basin has been a major focus in the future of mining in China. This paper systematically studied the overburden strata fracturing process and the structure evolution characteristics based on a typical ultra-thick coal seam condition in Xinjiang, using both physical and numerical modeling studies. The interactions between shields and the roof strata were also examined, from the perspective of ground support. The results indicated that roof structure was mainly in the form of voussoir beam at the early mining stage, where overburden stability was affected by the rock mass properties and mining parameters. The support load mainly included top coal and immediate roof gravity load and the load caused by main roof rotary consolidation. As a result of mining disturbance and strata movement, the overlying strata re-fractured in the later mining stage. The roof structure changed from beam to arch gradually and propagates upwards with the increase of multi-layer mining times. The support load was mainly the gravity load of the friable rock mass within compression arch. The results will provide a guideline for the improvement of roof stability under similar mining conditions in Xinjiang

Experimental Study on Deformation Characteristics of Gangue Backfill Zone under the Condition of Natural Water in Deep Mines

To address the problem of surface subsidence caused by the compression of filling gangue in deep mines, a layered compaction test was designed based on the zonation of the failure of the overburden in the goaf and layered property of the filling gangue. The deformation characteristics of filling gangue in natural and water-bearing states were obtained. The deformation of filling gangue during the 0~100 kN loading stage was an approximately positive S-type, which reflects the relative “advancement” in terms of deformation. The filling gangue deformation in the 100~500 kN loading stage was an approximately inverted S-type, which reflects the relative “lag” in terms of deformation. In a natural state, the load-time curves of the dead load stage were consistent. Under a water-bearing condition, the load-time curve for the dead load stage had apparent “step” characteristics and presented a special phenomenon of displacement rebound. Under gradient loading, the strain showed an exponential growth model, and energy dissipation showed a logarithmic growth model. Under a natural state, the energy dissipation showed consistently increasing distribution patterns, while the energy dissipation showed a normal distribution model under the water-bearing state