Rapid Excavation Research Articles

Study on Safety Tunneling Technology of Secondary Outburst Elimination by CO2 Gas Fracturing in High-Outburst Coal Seam

The No. 3 coal seam in the Yuxi Coal Mine has a measured maximum gas content of 25.59 m3/t, along with a maximum gas pressure of 2.9 MPa, indicating its high risk to gas and outbursts. To mitigate outburst risks of the coal seam, the 1301 working face has been implemented with gas pre-drainage measures by grid boreholes from underlying roadways. After one year of extraction, it was confirmed that the gas content at all 33 test sites was below 8 m3/t, meeting the outburst prevention standards. However, during subsequent coal tunnel excavation, the gas desorption index K1 value frequently exceeded the standard, resulting in numerous occurrences of abnormal gas emission or small-scale outbursts. To tackle the challenges associated with safe excavation following the first-round regional outburst prevention measures, a research and industrial trial of CO2 gas fracturing (CO2-Frac) technology for secondary outburst prevention and rapid excavation was completed. The results show that the dual-hole and high-pressure (185 MPa) CO2-Frac considerably contributes to outburst prevention. K1 exceedances per hundred meters of tunnel excavations were from an average of 2.54 without CO2-Frac to an average of 0.28 after the new technology was implemented, leading to an eight-fold reduction. Additionally, the monthly excavation footage increased from an average of 81.64 m without CO2-Frac to an average of 162.42 m with CO2-Frac, resulting in a two-fold improvement. The dual-hole and high-pressure CO2-Frac is an advanced technology for safe and efficient excavation for secondary outburst elimination in highly outburst-prone coal seams in the Yuxi Coal Mine, with potential for widespread application in similar coal seam conditions.

Key technology of temporary support robot for rapid excavation of coal mine roadway

AbstractThe coal industry has long been troubled by the imbalance between mining and tunneling, and between excavating and support. The main cause of this problem is the inability to perform excavating and permanent support operations in parallel. Additionally, the limited space near the tunneling face hampers the efficiency of permanent support. Temporary support is an effective method to ensure the stability of the surrounding rock and expand the space for parallel operations between excavating and permanent support activities. This work provides a brief overview of the current research status on temporary support, emphasizing that the key to achieving safe, efficient, and rapid excavation lies in the development of temporary support robots. To meet the development needs of temporary support robots, three key technologies are proposed: the construction of a coupling model between the robot and the surrounding rock, spatial layout optimization of the rapid advancement system, and adaptive control of the robot. This work details the methods and approaches for constructing the coupling model, the elements of system spatial layout optimization, and the methods and strategies for the robot's adaptive control. Our team successfully tested the shield robot system at Xiaobaodang Mining Company, verifying the feasibility of these key technologies.

Characterization of gas hydrate generation in SDS-R141b compounding static system

Characterization of gas hydrate generation in SDS-R141b compounding static system

Experimental Study on Gas Drainage Through Long-distance Bedding Directional Borehole

In order to solve the problem of gas exceeding the limit in the No.3 coal seam excavation face of Huoerxinhe coalmine, the gas outburst control measure was adopted to pre-evacuate the gas by the long-distance bedding directional borehole. The results show that after 25 days of gas drainage by long-distance bedding directional borehole, the gas content of test point decreased from 13.81m3/t to 7.81m3/t, and the gas pre-pumping rate was about 43.30%. The driving speed of the main transport roadway was 1.48 times that of the traditional ordinary drilling drainage measures, and the tunneling efficiency indicators had not exceeded the standard. Through the application of this measure, it is confirmed that the long-distance bedding directional borehole can effectively reduce the drilling hole construction amount and increase the gas extraction rate, and effectively eliminate the danger of protruding, and realize the safe and rapid excavation of the coal mine roadway.

Failure mechanism and stability identification of surrounding rock for soft-rock tunnels using long-footage rapid excavation method

Faced with the increasing development trend of extra-long traffic tunnels in western China, adopting the long-footage rapid construction method in soft-rock strata is the key to improving construction efficiency. Therefore, exploring the method for the stability identification of soft-rock tunnels suitable for long-footage rapid construction is of great practical engineering significance. A comprehensive identification method for the surrounding rock stability of soft-rock tunnels under rapid construction was proposed by combining the upper-bound limit analysis method and the safety factor method. This method was applied to analyze the progressive deterioration mechanism of surrounding rock stability under different geological environments and excavation footages. Finally, based on the tunnel engineering that crosses the carbonaceous slate stratum, the physical and mechanical parameters of the surrounding rock were calibrated by monitoring the mechanical behavior of the support structure. Moreover, the applicability of this method in engineering practice was analyzed. The results show that the safety factor expressed by the ratio of dissipated power to external force power can form a one-to-one mapping relationship between the instability trace and the safety factor. Thereby, the correlation equation between the safety factor and the in-situ stress is established. The proposed comprehensive identification method can determine whether the surrounding rock has experienced sliding instability along the yield surface and whether it has experienced collapse caused by overall loose and fractured instability. After adopting the long-footage rapid construction method and strengthening the support structure, the haunch convergence only increases by 11.1%, and the vault settlement decreases by 9.3%. These data verify the engineering applicability of this method.

Collaborative optimization of driving support technology in the W3233 working face return airway

Deep-shaft mining in roadway stress concentration, difficult control of the surrounding rock, and mining imbalance affect mining efficiency in coal mines. The mechanical parameters and crack development law of roadway surrounding rock were studied by laboratory experiments. The mechanical model was established by the method of theoretical analysis, the maximum empty roof distance was deduced, and two support schemes were designed. Through the numerical simulation method, the support scheme was compared and analyzed, the deformation rule of roadway surrounding rock, the optimization of roadway support parameters and the application of hysteresis technology are studied. The effect of different support schemes was verified by three-dimensional similar simulation experiments. The practical engineering verification showed that the construction time of each support circle was reduced by approximately 1 h, and the work was completed 60 days earlier. The research showed that the optimal support scheme was support scheme 1 (7 bolts with 800 mm × 1000 mm spacing between the roof, 10 bolts with 800 mm × 1000 mm spacing between the two sides, and 2 × 1 × 2 cables with 1600 mm × 2000 mm spacing between the roof). Support scheme 1 was applied to the engineering site to control the deformation of surrounding rock at 80 mm, and the deformation was less than the original support scheme. The construction was completed in advance under the hysteresis process, and the support efficiency and operation safety were improved. The results revealed the mechanism of surrounding rock control and proved the effectiveness of digging support synergy. This optimization plan serves as a reference for studying roadway support in rapid excavation and provides theoretical support for safe and efficient coal roadway mining.

Development and Optimization of Traction System for Heavy Engineering Machinery

The traction system of heavy equipment is a key part of the heavy engineering machinery and the traction ability of the heavy engineering machinery have high requirements for the overload capacity, reliability, maintainability, cost, and other aspects of the walking part. With the development of electrohydraulic technology, the traction technology of heavy equipment has also been continuously improved and the driving mode of the traction part has also developed from hydraulic driving to AC variable frequency driving. Engineering machinery is early generally driven by a fuel engine through a transmission shaft, gearbox, drive axle, and wheel reducer to complete the equipment. Heavy truck, bulldozer, tunneling machines, anchor excavators and shuttle trucks are commonly used heavy equipment in mechanized mining and rapid excavation of mines. Their traction performance plays a crucial role in improving the efficiency of working face excavation. This paper introduces the traction system of heavy equipment and compares the hydraulic drive system and electric traction drive system for them. The design scheme of the electric control system and the traction converter system is analyzed and a optimization scheme of the traction converter system is proposed. The optimized frequency converter adopts a modular assembly structure, which is convenient for installation, debugging, and after-sales service. Field application shows that the optimized frequency conversion system improves production efficiency and reduces failure rate.

The numerical simulation of rapid excavation technologies under the combined form of hydraulic fracturing and drill-and-blast method

With the aim of the drilling and blasting in underground space, there are problems of poor tunnel formation, large crushing and loosening area, difficult support, low driving efficiency, and special geological conditions that are not suitable for drilling and blasting. According to the fracturing and blasting theory and auxiliary hole effect, a combined hydraulic fracturing and drilling blasting tunneling technology was proposed in this research. Establish a rock breaking model, and according to the mechanism of swelling and breaking, the rock breaking efficiency and effect of swelling and breaking, the number of drill holes and the arrangement of drill holes affect the rock breaking performance; the traditional drilling and blasting method used the change of dynamic pressure and vibration velocity to judge the propagation and attenuation process of blasting vibration, as well as the range of damage area. The ANSYS LS-DYNA, a numerical simulation software, was used to determine the position and size of the top facing holes, the optimal spacing of fracturing holes, blasting holes and auxiliary holes. The static load applied to the arc part can effectively reduce the crushing area, the crack area and the elastic area. The lower rectangular part is arranged with the auxiliary holes reasonably to inhibit the propagation of the blasting shock wave, slow down the development of the fracture, guide the extension direction of the crack, and reduce the damage range of the three areas, avoid low efficiency of deep hole blasting, and judge the practicability and operability of this method based on the timeliness of each stage of excavation. The combined pressing and blasting method with the high-efficiency and short-distance, multi-frequency and high-efficiency excavation effectively controlled the shape of the upper area of the roadway, which contributes to reducing the damage area of the surrounding rock, developing a safe working environment, decreasing the maintenance cost of the roadway in the later stage, and providing a innovative way for the development of underground space in the future.

3C-3D tunnel seismic reverse time migration imaging: A case study of Pearl River Delta Water Resources Allocation Project

In recent years, tunnel boring machines (TBMs) have been widely used because of their fast construction speed and economical benefits, and the need to obtain geological information ahead of the tunnel to ensure the TBM tunnel construction safety has also arisen. Faced with the complex geological environment, seismic forward-prospecting is the primary method for predicting the unfavorable geological structure in front of the tunnel face. As a crucial step in seismic forward-prospecting method, migration can image geological characteristics and help learn the distribution of unfavorable geology. To achieve all-round imaging of unfavorable geology, we suggested a three-component (3C) three-dimensional (3D) tunnel seismic reverse time migration imaging method. The acoustic wave equation is employed for the forward and backward wavefield extrapolation after the P/S-wave separation to eliminate the imaging artifacts from severe converted waves in tunnels. GPU parallelization is used to accelerate the calculation to further adapt to the rapid excavation of TBMs. The proposed method is validated in two typical numerical models, especially for 3C seismic data that provides all-round geological information to achieve enhanced imaging energy and artifact reduction, which demonstrates the significance of 3C seismic data to migration imaging. This case study was conducted in the Pearl River Delta Water Resources Allocation Project in Guangdong Province, China. The reliability of 3C3D tunnel seismic reverse time migration imaging in field tunnel engineering was investigated. Two consecutive detections were performed, and then the spatial positions of faults and fractures in front of the tunnel face were accurately judged by the combination of the two imaging results. Based on the detection results, the excavation rate was slowed down and the tunnel lining support was increased. The TBM then successfully passed through the risk areas. This case study can serve as a reference for other tunnels with similar concerns regarding the necessity of 3C seismic data and consecutive detections.

Comparative experimental investigation on true triaxial double-sided fast unloading rockburst and biaxial compression under high stress

To explore the effect of rapid excavation unloading under high pressure on delayed rockburst, a true triaxial double-sided rapid unloading rockburst experiment and a biaxial compression failure experiment without unloading were carried out. The results show that the rapid unloading of excavation before the occurrence of rockburst will cause unloading damage, and the axial strain, acoustic emission (AE) count, and AE energy will suddenly increase at the unloading point. The AE source shows that the rapid unloading produces many tensile cracks, mainly distributed near the free surface. The axial peak stress of the rockburst and the stored strain energy before failure are higher than those of biaxial compression, so the ejection velocity of free surface fragments is also higher at failure.

Curve forming prediction of coal mine roadway based on RBF interpolation.

Underground roadway excavation is a complex process, especially roadway curved excavation. In addition, the rationality of the design of coal mine roadway excavation scheme directly affects the speed of roadway excavation. The more reasonable the scheme design, the more conducive to rapid excavation. In order to avoid the influence of invalid construction on the efficiency of roadway excavation, this paper studies the forming of roadway bend. Based on the analysis of the tunneling process of the roadway curve, the mathematical model of the roadway curve is established. Taking the turning radius of the roadway curve as the evaluation index, the influence of various factors on the roadway curve excavation is analyzed. The research shows that the radius of the roadway curve increases with the increase of the feed rate, the working space position of the roadheader and the required width of the roadway, and decreases with the increase of the working space angle. Then, combined with the advantages of KNN algorithm, an interpolation model for calculating the radius of the curve is established based on RBF algorithm, and the radius of the tunnel curve is reconstructed and predicted. It provides a basis for the rational design of the construction process of the roadway bend and a reliable numerical algorithm for the design of the radius of the roadway bend. It also provides a theoretical basis for improving the efficiency of high roadway excavation in coal mines.

Characteristics of Roof Collapse of Mining Tunnels in the Fault Fracture Zone and Distribution of the Boundary Force of the Accumulation Body

Under the influence of coal mining, the gravel in mining tunnel sections of a fault fracture zone is prone to collapse, and the collapse accumulation body will block the tunnel, which has a very adverse influence on the safety production of coal mining and the evacuation of personnel after underground disasters. The macroscopic and mechanical characteristics of the collapse accumulation body have been studied extensively in previous works. The purpose of this paper is to provide theoretical support and reference for the rapid excavation of the tunnel blocked by the collapse accumulation body in the fault fracture zone. Taking the fault fracture zone in the tunnel as the research background, the physical characteristics and boundary mechanical characteristics of the collapse accumulation body in the fault fracture zone are studied by the method of combining on-site investigation and theoretical analysis. The results show that the force acting on the boundary on both sides of the accumulation body is passive resistance from the side wall, which is derived from the slip effect of the accumulation body slope. Similarly, the unstable boundary of the fault fracture zone caused by tunnel instability is elliptical, and the overlying load of the rescue channel to be excavated in the accumulation body is limited. On the basis of the collapse instability dimensions of the broken zone of the tunnel surrounding the rock, the calculation formulas of the height of the accumulation body and the horizontal force at the boundary were established, respectively, under two conditions of whether the collapse space was filled, and whether the curve relationship between the distribution of the horizontal force at the boundary of the accumulation body and the buried depth in the accumulation body was obtained.

Design of a Highly Adaptable Advance Support for a Deep, Fully Mechanized Roadway and Analysis of Its Support Performance

Considering the harsh environment of deep, fully mechanized working faces and the acutely imbalanced time distribution among excavation, support and anchoring, this paper designed a new type of highly adaptable advance support for fully mechanized roadways that boasts high adaptability, great support strength and a large working space. Firstly, the structure composition and working principle of the advance support were introduced. The structures and mechanical characteristics were then emphatically discussed. Subsequently, with the geological conditions of the 8224-machine roadway in the XT Coal Mine taken as an example, the loads of the advance support were obtained and then imported into the Ansys software to obtain the stress distribution and displacement distribution of the whole advance support and its parts through calculation. Based on the distribution, the stress and strain of the advance support were analyzed. The simulation results are as follows: Under various working conditions, the maximum displacement of the advance support was 4.5 mm, which is negligible compared to the overall size of the support; the maximum stress was 72.8 MPa, which is lower than the yield strength of the material (235 MPa). Therefore, the designed support can bear the pressure from the surrounding rock in the mine. Moreover, the roof beam, which is a weak link in the support, deserves more attention in subsequent engineering designs. This method conduces to not only parallel operations of excavation, support and anchoring, but also to rapid excavation and the safe production of roadways, providing fresh ideas for the advance support for fully mechanized roadways.

Study on the Long-Distance Gas Pre-Drainage Technology in the Heading Face by Directional Long Borehole

Gas control in the heading face of a coal roadway is an important and difficult point in coal mining in China. On the basis of analyzing the disadvantages of high gas control cost and long drainage period in the existing mine heading face, a long-distance pre-drainage method of long-distance drilling is proposed to control the gas in the heading face so as to improve the tunneling speed. Applied to the engineering geological conditions of Changcun coal mine, the technology is studied in detail. First, a gas migration model considering permeability changing with time is established, and the model is put into the numerical simulation software to study the variation law of permeability and gas pressure under the conditions of single borehole and multi-borehole drainage. The results show that with the increase of drainage time, the permeability around the borehole increases gradually, the gas pressure decreases gradually, and the permeability at the borehole boundary increases the most, reaching 1.2 times the initial permeability. In the process of multi-borehole drainage, there will be mutual influence between boreholes, but with the increase of borehole spacing, the degree of this influence gradually decreases. Second, according to the results of numerical simulation, a reasonable gas drainage scheme is designed and applied in the field. The field application shows that the technology has a good gas drainage effect, the gas drainage concentration and flow are at a high level for a long time, the drilling cuttings quantity is always lower than the critical value, and the excavation length of roadway increases by more than 50 m per month. These results indicate that this technology is a promising method to realize the safe and rapid excavation of a mine coal roadway.

Instability mechanism and coupling support technology of full section strong convergence roadway with a depth of 1350 m

The nonlinear stability control of surrounding rock with large deformation is the key issue in realizing rapid excavation of deep soft rock roadway. Combined with various research methods, this paper deeply analyzes the characteristics of instability. Through the modified Drucker-Praeger criterion, the mechanism of roadway instability under the coupling actions of multiple factors is studied, and the control strategy of deep soft rock roadway is given. On this basis, the combined support scheme is optimized and verified by simulation, test and field application. The results show that: (1) Long aging, strong rheology and full section are the basic characteristics of deep soft rock roadway convergence. High resistance and yield are the inherent requirements of nonlinear large deformation roadway support. (2) The asymmetric support of roof and floor violates the objective law that the floor heave of deep soft rock roadway is larger. (3) Roadway instability is the result of comprehensive action of internal and external factors, which reflects the gradual deterioration process of the rock mass. The purpose of the support is to effectively improve the bearing capacity of the surrounding rock and avoid this process. (4) It is an effective measure to improve the support efficiency and an important way to realize the stability control of nonlinear large deformation roadway by combine the parts organically and coordinate their bearing performance.

Influence of Yield Pillar Width on Coal Mine Roadway Stability in Western China: A Case Study

Roadway excavation technology in underground coal mines has an important impact on mining efficiency and production safety. High-efficiency and rapid excavation of underground roadways in coal mines are important means to improve the production efficiency of coal mines. To tackle the problems of instability of roadway and support difficulties, the tail entry of panel 3105 in Mataihao Mine was used as the case study. The methods of underground investigation, theoretical analysis, and FLAC3D numerical simulation were used to analyze the stability of the surrounding rock under different yield pillar widths. Through the stress field, displacement field, and plastic zone of roadway surrounding rock, the stability of the rock surrounding the roadway under different yield pillar widths (4 m, 6 m, and 8 m) was analyzed. The results show that, with the increase in the yield pillar width, the plastic zone failure and displacement of the roadway surrounding rock are mainly manifested in the narrow pillar rib, seam rib, roof, and floor. The plastic zone distribution changes slightly; the roadway displacement exhibits basic symmetry. The vertical stress and the displacement of the two sides increase with the increase in the yield pillar width, and the roof displacement and the ratio of tensile failure of the surrounding rock decrease with the increase in the yield pillar width. According to the dynamic evolution law of the rock surrounding the roadway along the goaf side, the effect of the yield pillar size is revealed, and a reasonable yield pillar width is determined. When the yield pillar width is 6 m, the plastic zone failure of the surrounding rock and the displacement of the two sides of the roof are the most balanced among the three schemes. This provides a reference for the selection of the narrow yield pillar size in coal mines under the same geological conditions.

Research on Application of Rapid Excavation Support in Coal Mine

Research on Application of Rapid Excavation Support in Coal Mine

Prediction of TBM Operational Parameters Using an Integrated Data Mining Framework

Tunnel Boring Machine (TBM) is widely used in tunnel construction because of its high safety, less effect on surroundings and rapid excavation speed. However, its performance is highly dependent on the adjustment of operational parameters during tunnelling. In many cases, the project delays even the accidents take place due to the mis-operation of inexperienced drivers. To improve the adaptability of a TBM in complex geological conditions, this study proposes an integrated data mining framework to perform near real-time prediction of two operational parameters including thrust and torque. The integrated framework provides a set of data processing methods including data cleaning, partition of full tunnelling cycles, feature extracting and model establishment. These data mining methods were applied to analyse the in-situ data of a water conveyance project. The results showed that the proposed framework performed well in predicting those two parameters with the determination coefficient R2 all exceeding 0.9, which illustrated the feasibility of using the proposed framework to assist driving in TBM construction.

Performance of a Large-Scale Excavation by Bottom-Up Technique in Hangzhou Soft Clay

This paper studied the excavation of a foundation pit above a running subway tunnel in Hangzhou soft soil. The zoned excavation and top-down construction techniques were adopted to control the deformation caused by foundation pit excavation. The excavation was divided into four parts, named Zone A, B, C, and D. Zone A adopted temporary diagonal bracing, and the control effect of deformation was poor; it was cancelled and changed to rapid excavation and thicker cushion in Zones B, C, and D. During the whole construction process, the lateral displacement and settlement of the diaphragm wall, surrounding ground surface, and building settlement were monitored and analysed. The data showed that the lateral displacement of the diaphragm wall was effectively reduced by the zoned excavation technique, and the maximum lateral displacement value of the diaphragm wall in Zone A was the least; rapid excavation and reduced soil exposure time also could effectively control the deformation, and the lateral displacement of the diaphragm wall in Zone C is less than Zone B and Zone D. The ground settlement is strongly related to the lateral displacement of the diaphragm wall. In order to reduce the surrounding ground and building settlements, efforts should be made to reduce the wall lateral displacement.

Research and field application of ultra high pressure hydraulic cutting technology in Gaohe coal minethe title of your paper here

In order to improve the permeability of low permeability coal seam, improve the gas drainage efficiency of + 450m bedding boreholes in Gaohe mine, and ensure the safe and rapid excavation of + 450m level north wing air inlet roadway, ZGF-100 (a) type ultra-high pressure hydraulic slotting device suitable for the characteristics of 3 coal seam in Gaohe mine is developed. The feasibility and implementation scheme of high pressure water drilling and slotting integration technology are studied, and the slotting effect is preliminarily analyzed investigate. The research shows that the technology of using ultra-high pressure water to cut coal seam to cause cracks and increase permeability can effectively conduct the original cracks in the coal body, increase the gas drainage effect of boreholes along the seam, increase the drainage pure quantity by 1.8 ∼ 3.6 times, increase the effective drainage radius from 1.3m to 2.4m, and reduce the drilling engineering quantity by more than 50%. Hydraulic cutting technology can effectively improve the gas drainage efficiency of low permeability coal seam, which is worthy of promotion.