Instability mechanism of mining roadway passing through fault at different angles in kilometre-deep mine and control measures of roof cutting and NPR cables

The angle α between the fault strike and the axial direction of the roadway produces different damage characteristics. In this paper, the research methodology includes theoretical analyses, numerical simulations and field experiments in the context of the Daqiang coal mine located in Shenyang, China. The stability control countermeasure of "pre-splitting cutting roof + NPR anchor cable"(PSCR-NPR) is simultaneously proposed. According to the different deformation characteristics of the roadway, the faults are innovatively classified into three types, with α of type I being 0°-30°, α of type II being 30°-60°, and α of type III being 60°-90°. The full-cycle stress evolution paths during mining roadway traverses across different types of faults are investigated by numerical simulation. Different pinch angles α lead to high stress concentration areas at different locations in the surrounding rock. The non-uniform stress field formed in the shallow surrounding rock is an important reason for the instability of the roadway. The pre-cracked cut top shifted the high stress region to the deep rock mass and formed a low stress region in the shallow rock mass. The high prestressing NPR anchor cable transforms the non-uniform stress field of the shallow surrounding rock into a uniform stress field. PSCR-NPR is applied in the fault-through roadway of Daqiang mine. The low stress area of the surrounding rock was enlarged by 3-7 times, and the cumulative convergence was reduced by 45%-50%. It provides a reference for the stability control of the deep fault-through mining roadway.

Enhancing Evolutionary Algorithms With Pattern Mining for Sparse Large-Scale Multi-Objective Optimization Problems

Sparse large-scale multi-objective optimization problems(SLMOPs)are common in science and engineering.However,the large-scale problem represents the high dimensionality of the decision space,requiring algorithms to traverse vast expanse with limited computational resources.Furthermore,in the context of sparse,most variables in Pareto optimal solutions are zero,making it difficult for algorithms to identify non-zero variables efficiently.This paper is dedicated to addressing the challenges posed by SLMOPs.To start,we introduce innovative objective functions customized to mine maximum and minimum candidate sets.This substantial enhancement dramatically improves the efficacy of frequent pattern mining.In this way,selecting candidate sets is no longer based on the quantity of nonzero variables they contain but on a higher proportion of nonzero variables within specific dimensions.Additionally,we unveil a novel approach to association rule mining,which delves into the intricate relationships between non-zero variables.This novel methodology aids in identifying sparse distributions that can potentially expedite reductions in the objective function value.We extensively tested our algorithm across eight benchmark problems and four real-world SLMOPs.The results demonstrate that our approach achieves competitive solutions across various challenges.

Numerical and theoretical study of large-scale failure of strata overlying sublevel caving mines with steeply dipping discontinuities

The deformation and fracture evolution mechanisms of the strata overlying mines mined using sublevel caving were studied via numerical simulations.Moreover,an expression for the normal force acting on the side face of a steeply dipping superimposed cantilever beam in the surrounding rock was deduced based on limit equilibrium theory.The results show the following:(1)surface displacement above metal mines with steeply dipping discontinuities shows significant step characteristics,and(2)the behavior of the strata as they fail exhibits superimposition characteristics.Generally,failure first occurs in certain superimposed strata slightly far from the goaf.Subsequently,with the constant downward excavation of the orebody,the superimposed strata become damaged both upwards away from and downwards toward the goaf.This process continues until the deep part of the steeply dipping superimposed strata forms a large-scale deep fracture plane that connects with the goaf.The deep fracture plane generally makes an angle of 12°-20°with the normal to the steeply dipping discontinuities.The effect of the constant outward transfer of strata movement due to the constant outward failure of the superimposed strata in the metal mines with steeply dipping discontinuities causes the scope of the strata movement in these mines to be larger than expected.The strata in the metal mines with steeply dipping discontinuities mainly show flexural toppling failure.However,the steeply dipping structural strata near the goaf mainly exhibit shear slipping failure,in which case the mechanical model used to describe them can be simplified by treating them as steeply dipping superimposed cantilever beams.By taking the steeply dipping superimposed cantilever beam that first experiences failure as the key stratum,the failure scope of the strata(and criteria for the stability of metal mines with steeply dipping discontinuities mined using sublevel caving)can be obtained via iterative computations from the key stratum,moving downward toward and upwards away from the goaf.

Stability control measures for roof cutting and NPR supporting of mining roadways in fault areas of kilometre-deep coal mine

The study focuses on the stability control measures for mining roadways in fault zones of deep mines,using Daqiang Coal Mine as a case study.The control system under consideration,referred to as"pre-splitting cutting roof+NPR anchor cable"(PSCR-NPR),is subjected to scrutiny through theoretical analysis,numerical modelling,and field trials.Furthermore,a comprehensive analysis is undertaken to evaluate the stability control mechanism of this particular technology.The study provides evidence that the utilization of deep-hole directional energy-concentrated blasting facilitates the attainment of directional roof cutting in roadways.The aforementioned procedure leads to the formation of a uniform structural surface on the roof of the roadway and causes modifications in the surrounding geological formation.The examination of the lateral abutment pressure and shear stress distribution,both prior to and subsequent to roof cutting,indicates that the implementation of pre-splitting techniques leads to a noteworthy reduction in pressure.The proposition of incorporating the safety factor Q for roof cutting height is suggested as a method to augment comprehension of the pressure relief phenomenon in the field of engineering.The analysis of numerical simulation has indicated that the optimal pressure relief effect of a mining roadway in a fault area is attained when the value of Q is 1.8.The NPR anchor cable exhibits noteworthy characteristics,including a high level of prestress,continuous resistance,and substantial deformation.After the excavation of the roadway,a notable reduction in radial stress occurs,leading to the reinstatement of the three-phase stress state in the surrounding rock.This restoration is attributed to the substantial prestress exerted on the radial stress.The termination point of the NPR anchor cable is strategically positioned within a stable rock formation,allowing for the utilization of the mechanical characteristics of the deep stable rock mass.This positioning serves to improve the load-bearing capacity of the surrounding rock.The mining roadway within the fault region of Daqiang Coal Mine is outfitted with the PSCR-NPR technology.The drop in shear stress experienced by the rock surrounding the roadway is estimated to be around 30%,whilst the low-stress region of the mining roadway extends by a factor of approximately 5.5.The magnitude of surface displacement convergence experiences a decrease of approximately 45%-50%.The study’s findings provide useful insights regarding the stable of mining roadway in characterized by fault zones.

Evaluation of roof cutting by directionally single cracking technique in automatic roadway formation for thick coal seam mining

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery,reduce roadway excavation and improve mining safety.In this method,roof cutting is the key process for stress relief,which significantly affects the stability of the formed roadway.This paper presents a directionally single cracking(DSC)technique for roof cutting with considerations of rock properties.The mechanism of the DSC technique was investi-gated by explicit finite element analyses.The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment.On this basis,the optimized DSC technique was tested in the field.The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock,thus,achieve directionally single cracking on the roadway roof.The DsC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway.Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.

Study on ascending mining roadway layout of close distance coal seams in deep mine

To solve the problems appeared in mining process of No.2 seam, the ascending stress-releasing mining method was adopted. Studying on the reasonable layout of actual mining roadway in upper coal seams is the precondition of successful ascending mining. By using ＂device of leak measuring by blocking up double ends＂, it detected the height of overburden water flowing fractured zone originated from sub-coal seams mining. Thus it proved that the actual mining roadway of No.2 upper ascending seam was located in the smooth sagging zone. On the basis of analyzing the stress-releasing effect of sub-coal seams mining to upper coal seams by using RFPA software, it analyzed the stability of up-face coal seams and the reasonable location of starting cut in up-face coal seams. It also analyzed the reasonable gateway location in upper coal seams, which ensured the crossheading in upper coal seams out of the effect of sub-coal work face mining by using theory of underground pressure. Meanwhile, the reasonable pillars dimensions in upper coal seams by building the structure mechanics model of stope were researched. It can make the roadway driven along next goaf to be located in low stress zone, and be beneficial to keeping roads stable owing to less stress of surrounding rock. Finally, it tested the rationality of the layout method of roads in upper coal seams by engineering field measurement in 3221 working face.

Support technologies for deep and complex roadways in underground coal mines:a review

Based on geological and mining characteristics,coal mine roadways under complex conditions were divided into five types,for each type the deformation and damage characteristics of rocks surrounding roadways were analyzed.The recent developments of roadway support technologies were introduced abroad,based on the experiences of supports for deep and complex roadways from Germany,the United States and Australia.The history and achievements of roadway support technologies in China were detailed,including rock bolting,steel supports,grouting reinforcement and combined supports.Four typical support and reinforcement case studies were analyzed,including a high stressed roadway 1,000 m below the surface,a roadway surrounded by severely weak and broken rocks,a chamber surrounded by weak and broken rocks,and a roadway with very soft and swelling rocks.Based on studies and practices in many years,rock bolting has become the mainstream roadway support form in China coal mines,and steel supports,grouting reinforcement and combined supports have also been applied at proper occasions,which have provided reliable technical measures for the safe and high effective construction and mining of underground coal mines.

Roof filling control technology and application to mine roadway damage in small pit goaf

To recover coal resources that have been damaged by traditional mining methods and ensure stability of the lower roadway in a small pit goaf,the goaf area must be filled and reinforced.In this research,the 1202 working face of the Hanzui mine is considered as an example for classifying the roof of the mining tunnel under the small kiln destruction zone,the effect of the goaf on the roadway is determined based on the radio tunnel penetration method,a mechanical model to determine the roof filling control mechanism was established,and the duct foaming system and roof filling process were designed.The results show that the scope and degree of influence of the goaf on the mining lane are large,but safe tunneling can be ensured through the use of a steel shed and advanced grouting techniques.When the roof conditions are not similar,materials with different filling heights and filling strengths can be used to control the roof filling of the roadway.By combining field experience and laboratory tests,it was determined that a high-foaming material with a water-cement ratio of 1:0.6,a suitable high-foaming additive,and a water volume ratio of 1:30 is cost-efficient for filling and meets the filling strength requirements.Finally,the reliability of the proposed technology was verified by field experiments,which provide a reference for filling operations in similar mines.

Deformation and failure study of surrounding rocks of dynamic pressure roadways in deep mines

In order to understand the change rules of stress-displacement in surrounding rocks of dynamic pressure roadways in deep mines and to obtain a theoretical basis for analyses of roadway stability and designs of support, we established a coupling equation of adjacent rock strength, mining stress and supporting resistance on the basis of an elastic-plastic theory of mechanics. We obtained an analytical solution for stress and displacement distribution of elastic and plastic regions in surrounding rock of dy-namic pressure roadway.. Based on this theory, we have analyzed the changes in stress-displacement in elastic and plastic regions of surrounding rocks of dynamic pressure roadways in the Haizi Coal Mine. The results show that: 1) radial and tangential stress change violently within the first 4 m from the inner surface of a roadway after excavation; radial stress increases while tangential stress decreases within a range of about 6 m from the inner surface of the roadway as a function of q3; 2) radial and tangential stress increase with an increase in the mining pressure coefficient k; the increase in the rate of tangential stress is greater than that of ra-dial stress; 3) the radial displacement of the inner surface of roadways decreases with an increase in q3, provided that k remains unchanged.

Roadway layout for recycling residual coal pillar in room-and-pillar mining of thick coal seam

In the context of a room-and-pillar mining gob in Shanxi province in China,this paper numerically investigates the stress distribution and deformation rules of roadway surrounding rocks at various locations of residual coal pillars in room-and-pillar mining gobs using software FLAC3 D.It is found that the concentrated stress beneath coal pillars distributes in a shape of ellipse.A reasonable roadway layout is then proposed.In this design,it is indicated that roadways should be designed to avoid the supporting zones of pillars with increasing compression and take into account the roof falling and crushing in the upper gob.According to the surrounding rock deformation characteristics and mining roadway locations as well as the supporting principles of timely support,rock reinforcing,piecewise management and suiting local conditions,a new asymmetric shield supporting plan is proposed.The field surveying results show that this supporting plan can effectively control the roadway rock deformation,thus guarantee the safe and smooth construction of roadways.

De-stressed mining of multi-seams:Surrounding rock control during the mining of a roadway in the overlying protected seam

Surrounding rock control in the overlying protective coal seam is a challenging topic for de-stressed mining of multi-seamed coal.Current research findings on roadway control were used in the design of a physical model of a complex textured roof having a varying thickness.The model was used to study roadway instability and collapse caused by dynamic pressure.The results show that when the thickness of the roof exceeds the bolted depth the roadway security is least and the roof has the greatest possibility for collapse.Numerical simulations were also carried out to study stress redistribution before and after roadway excavation during underlying protective seam mining.The evolution of roadway displacement and fracture,as affected by support methods,has been well studied.A series of support principles and technologies for mining affected roadways has been proposed after demonstration of successful practical application in the Huainan Mines.These principles and technologies are of extended value to deep coal mining support in China.

Reliability analysis on bolt support structure of coal roadway under the influence of mining

Based on the features of the serious deformation of coal roadway,many random variables of the mechanics of the surrounding rocks and the influence of mining, the reliability analysis model of the support structure of coal roadway under the influence of mining is established,and the calculating formulas of reliability of the support structure is obtained with the engineering structure reliability theory. And the reliability is calculated based on the method of Monte Carlo to the coal roadway which is exampled on the influence of mining or not. The relationship between support parameters and reliability, the mining influence coefficients and reliability is established, which provides theory foundations for the design of the coal roadway bolt support.

Joint Bearing Mechanism of Coal Pillar and Backfilling Body in Roadway Backfilling Mining Technology

In the traditional mining technology,the coal resources trapped beneath surface buildings,railways,and water bodies cannot be mined massively,thereby causing the lower coal recovery and dynamic disasters.In order to solve the aforementioned problems,the roadway backfilling mining technology is developed and the joint bearing mechanism of coal pillar and backfilling body is presented in this paper.The mechanical model of bearing system of coal pillar and backfilling body is established,by analyzing the basic characteristics of overlying strata deformation in roadway backfilling mining technology.According to the Ritz method in energy variation principle,the elastic solution expression of coal pillar deformation is deduced in roadway backfilling mining technology.Based on elastic-viscoelastic correspondence principle,combining with the burgers rheological constitutive model and Laplace transform theory,the viscoelastic solution expression of coal pillar deformation is obtained in roadway backfilling mining technology.By analyzing the compressive mechanical property of backfilling body,the time formula required for coal pillar and backfilling body to play the joint bearing function in roadway backfilling mining technology is obtained.The example analysis indicates that the time is 140 days.The results can be treated as an important basis for theoretical research and process design in roadway backfilling mining technology.

Rockburst mechanism and the law of energy accumulation and release in mining roadway: a case study

The rockburst dynamic disasters in the process of deep coal mining become more and more serious.Taking the rockburst occurred in the 23130 working face of Yuejin Coal Mine as the engineering background,we study the characteristics of mining stress feld around roadway,the plastic failure morphological characteristics of surrounding rock and the accumulation/release law of elastic energy before and after burst.An analysis model quantitatively describing the physical process of rockburst in the mining roadway is established,and the calculation method of dynamic release of elastic energy in the physical process of rockburst is educed.The mechanism of rockburst in mining roadway is revealed.The results show that an“L-shaped”stress concentration zone is formed within 100 m of the 23130 working face,and the principal stress ratio of the surrounding rock of the transportation roadway is 2.59–4.26.The change of the direction of the maximum principal stress has a signifcant efect on the burst appearance characteristics.The failure strength of diferent sections of the mining roadway is characterized by the elastic energy release value.With the increase of the working face distance,the elastic energy released by burst failure and the expansion variation of failure boundary radius show a nonlinear variation law that tends to decrease steadily after sharp fuctuation.The closer to the working face,the higher the burst risk.At a distance of 10 m from the working surface,the maximum principal stress reaches its maximum value.The butterfy-shaped failure system generated by the surrounding rock of the roadway has energy self-sustainability,and the elastic energy released by the sudden expansion of the butterfy leaf is enough to cause a burst damage of 1.9 magnitude.This work could provide theoretical support for the prediction and prevention of rockburst.

Deformation effect of lateral roof roadway in close coal seams after repeated mining

This paper analyzed the deformation mechanism in lateral roof roadway of the Ding Wu-3 roadway which was disturbed by repeated mining of close coal seams Wu-8 and Wu-10 in Pingdingshan No. 1 Mine. To determine the strata disturbance scope, the strata displacement angle was used to calculate the protection pillar width. A numerical model was built considering the field geological conditions. In simulation, the mining stress borderline was defined as the contour where the induced stress is 1.5 times of the original stress. Simulation results show the mining stress borderline of the lateral roadway extended 91.7 m outward after repeated mining. Then the original stress increased, deforming the road- way of interest. This deformation agreed with the in situ observations. Moreover, the strata displacement angle changed due to repeated mining. Therefore, reselection of the displacement angle was required to design the protective pillar width. Since a constant strata displacement angle was used in traditional design, the orooosed method was beneficial in field cases.

Monitoring and analysis of nonlinear dynamic damage of transport roadway supported by composite hard rock materials in Linglong Gold Mine

The study concentrates mainly on the development of failure process incomposite rock mass. By use of acoustic emission (AE), convergence inspection, pressure monitoring,level measurement techniques and the modem signal analysis technology, as well as scan electronmicroscopy (SEM) experiment, various aspects of nonlinear dynamic damage of composite rock masssurrounding the transport roadway in Linglong gold mine are discussed. According to the monitoringresults, the stability of the rock mass can be synthetically evaluated, and the intrinsic relationbetween the damage and the characteristic parameters of acoustic emission can be determined. Thelocation of the damage of rock mass can also be detected based on the acoustic emission couplemonitoring signals. Finally, the key factors which influence the stability of the transport roadwaysupported by composite hard rock materials are found out.

A NEW TECHNIQUE FOR ROADWAY DUST CONTROL IN SURFACE MINE

This paper describes a new technique for the roadway dust control in surface mine. In the method, the emulsified tar liquid with low concentration and the super water-absorbing resin are taken as dust adhesive and sprayed on the roadway. After doing a large number of in-situ experiments, the technique has shown its excellent characteristics on sticking dust, preventing water evaporation and reducing the combined cost of truck transportation.

Anchorage performance of large-diameter FRP bolts and their application in large deformation roadway

In underground coal mines, fibre reinforced polymer(FRP) bolt is ideal for mined rib reinforcements as it can prevent gas explosions caused by shearer frictional spark. With increasing mining depth, small diameter FRP bolts used in shallow underground mining cannot fulfil the rib support requirements. Under the engineering background of deep underground shortwall mining in Wudong coal mine, this paper systematically studies Φ27 mm FRP bolt support for large deformation coal rib. Specimens with a fan-shaped cross-section were used to enable the tensile testing of the bolt rod, the measured average tensile strength of the studied FRP bolt was(486.1 ± 9.6) MPa with a maximum elongation of 5.7%±0.6%.The shear strength of the bolt was measured as approximately 258 MPa using a self-made double shear testing apparatus. Based on the equivalent radial stiffness principle, a laboratory short encapsulation pullout test(SEPT) method for rib bolting has been developed undertaken consideration of the mechanical properties of the coal seam. Results showed that the average peak anchorage forces of the Φ27 mm FRP bolt and Φ20 mm steel rebar bolt were 108.4 and 66.4 k N, respectively, which were agreed with the theoretical calculations and field measurements. Based on theoretical analysis of the loading states of the bolt under site conditions, bolting method of full-length resin grouting was adopted to offset the weaknesses of the FRP bolt. Numerical method was employed to compare the bolting effect using Φ27 mm FRP bolts and steel rebar bolts. Large diameter FRP bolting was determined as the optimum rib support scheme to increase the productivity of the coal mine and to enhance the ground control capability for+425 level mining roadways. This study provides the laboratory testing design and theoretical prediction of large diameter FRP bolts used for rib support in large deformation roadways.

Experimental study on stability control technology of surrounding rock of deep roadways in coal mine

In order to solve effectively the problems of deep mining with safety and high efficiency, the multi- pie factors influencing the stability of deep rock roadway and technical problems are analyzed in the light of the severe situation of effective mining for deep coal resource, and the stability control methods for deep rock road- way are provided, which are based on the idea of combined support with separated steps and integral control of surrounding rock of deep rock roadway. The suggested methods were applied to a deep rock roadway with -648 m depth in Gubei coal mine of Huainan area. The field test was carried out and the in-situ monitoring was imple- mented, and the support scheme was optimized and adjusted to improve the stability of the surrounding rock of the roadway based on the feedback analysis. The results showed that the stability can be improved greatly by the provided control methods tbr deep roadway. The present methods lbr stability control of deep rock roadway can be used to other deep rock roadways with the similar conditions.

Numerical Study on Effect of Longwall Mining on Stability of Main Roadway under Weak Ground Conditions in Indonesia

The purpose of this research is to study the effect of longwall mining on the stability of main roadway in the underground coal mine. The PT GDM （Gerbang Daya Mandiri） underground coal mine in Indonesia, where the rocks are weak, was selected as a representative study site. To accomplish the objective of the research, the finite difference code software FLAC3D was used as a tool for the numerical simulations. The longwall mining of several panel and barrier pillar widths at various depths was simulated and discussed. Based on the simulation results, it indicates that the effect of coal panel extraction on the main roadway stability depends on the width of panel and barrier pillar. The greatest effect occurs when the large panel width and the small barrier pillar width are applied, whereas the smallest effect happens when the narrow panel width and the large barrier pillar width are adopted. In this paper, therefore, to maintain the stability of the main roadway with the aim of maximizing the coal recovery, the appropriate size of panel and barrier pillar width is proposed for each mining depth for this underground coal mine.