Theory,technology and application of grouted bolting in soft rock roadways of deep coal mines

The grouted bolt,combining rock bolting with grouting techniques,provides an effective solution for controlling the surrounding rock in deep soft rock and fractured roadways.It has been extensively applied in numerous deep mining areas characterized by soft rock roadways,where it has demonstrated remarkable control results.This article systematically explores the evolution of grouted bolting,covering its theoretical foundations,design methods,materials,construction processes,monitoring measures,and methods for assessing its effectiveness.The overview encompassed several key elements,delving into anchoring theory and grouting reinforcement theory.The new principle of high pretensioned high-pressure splitting grouted bolting collaborative active control is introduced.A fresh method for dynamic information design is also highlighted.The discussion touches on both conventional grouting rock bolts and cable bolts,as well as innovative grouted rock bolts and cables characterized by their high pretension,strength,and sealing hole pressure.An examination of the merits and demerits of standard inorganic and organic grouting materials versus the new inorganic–organic composite materials,including their specific application conditions,was conducted.Additionally,the article presents various methods and instruments to assess the support effect of grouting rock bolts,cable bolts,and grouting reinforcement.Furthermore,it provides a foundation for understanding the factors influencing decisions on grouted bolting timing,the sequence of grouting,the pressure applied,the volume of grout used,and the strategic arrangement of grouted rock bolts and cable bolts.The application of the high pretensioned high-pressure splitting grouted bolting collaborative control technology in a typical kilometer-deep soft rock mine in China—the soft coal seam and soft rock roadway in the Kouzidong coal mine,Huainan coal mining area,was introduced.Finally,the existing problems in grouted bolting control technology for deep soft rock roadways are analyzed,and the future development trend of grouted bolting control technology is anticipated.

Numerical simulation and experimental research of surrounding rock deformation of floor roadway under short-distance coal seam group combined mining

According to the influence of the combination of short-distance coal seam group on mining roadway, using numerical simulation software FLAG2D to draw the abutment pressure distribution ahead the working face and the area of influence in fully-mechanized mining conditions, the variation rules of surrounding rock supporting pressure of floor roadway and the deformation rules were summarized. GYS-300 anchor dynamometer was used to measure the roadway surface displacement, and the conclusions of numerical simulation were verified.

Stability analysis of longwall top-coal caving face in extra-thick coal seams based on an innovative numerical hydraulic support model

The relationship between support and surrounding rock is of great significance to the control of surrounding rock in mining process.In view of the fact that most of the existing numerical simulation methods construct virtual elements and stress servo control to approximately replace the hydraulic support problem,this paper establishes a new numerical model of hydraulic support with the same working characteristics as the actual hydraulic support by integrating numerical simulation software Rhino,Griddle and FLAC3D,which can realize the simulation of different working conditions.Based on this model,the influence mechanism of the supporting strength of hydraulic support on surrounding rock stress regulation and coal stability in front of the top coal caving face in extra thick coal seam were researched.Firstly,under different support intensity,the abutment pressure of the bearing coal and the coal in front of it presents the “three-stage”evolution characteristics.The influence range of support intensity is 15%–30%.Secondly,1.5 MPa is the upper limit of impact that the support strength can have on the front coal failure area.Thirdly,within a displacement range of 2.76 m from the coal wall,a support strength of1.5 MPa provides optimal control of the horizontal displacement of the coal.

Surrounding rock control of gob-side entry driving with narrow coal pillar and roadway side sealing technology in Yangliu Coal Mine

Gob-side entry driving can increase coal recovery ratio, and it is implied in many coal mines. Based on geological condition of 10416 working face tailentry in Yangliu Coal Mine, the surrounding rock deformation characteristics of gob-side entry driving with narrow coal pillar is analysed, reasonable size of coal pillar and reasonable roadway excavation time after mining are achieved. Surrounding rock control technology and effective roadway side sealing technology are proposed and are taken into field practice. The results showed that a safer and more efficient mining of working face can be achieved. In addition, results of this paper also have important theoretical significance and valuable reference for surrounding rock control technology of gob-side entry driving with narrow coal pillar under special geological condition.

Stress distribution rule of roadway affected by overhead mining in gently inclined coal seams group

In light of the severe deformation and destruction of the district raise tunnel in the mining area at the northern part of the Lubanshan colliery, by the theoretic analysis and numerical simulation, both the mining stress distribution in seams group and the deformation and destruction mechanism of floor district raise were investigated. The results show that, at the maximum vertical distance of 40 m, the abutment stress has an influence on the recovery of 2# and 3# coal seam and 8# coal seam at distance of 30 m. As a result, the recovery of 8# is rather than those of 2# or 3# coal seam, which contributes to the deformation and destruction of the district raise surrounding rock. The major factors affecting the abutment stress include the mining depth, mining height, residual gob space, adjacent working faces and short spacing coal seam recovery.

Prediction of upper limit position of bedding separation overlying a coal roadway within an extra-thick coal seam

Failure of the surrounding rock around a roadway induced by roof separation is one major type of underground roof-fall accidents.This failure can especially be commonly-seen in a bottom-driven roadway within an extra-thick coal seam("bottom-driven roadway"is used throughout for ease of reference),containing weak partings in their roof coal seams.To determine the upper limit position of the roof interlayer separation is the primary premise for roof control.In this study,a mechanical model for predicting the interlayer separation overlying a bottom-driven roadway within an extra-thick coal seam was established and used to deduce the vertical stress,and length,of the elastic,and plastic zones in the rock strata above the wall of the roadway as well as the formulae for calculating the deflection in different regions of rock strata under bearing stress.Also,an approach was proposed,calculating the stratum load,deflection,and limiting span of the upper limit position of the interlayer separation in a thick coal seam.Based on the key strata control theory and its influence of bedding separation,a set of methods judging the upper limit position of the roof interlayer separation were constructed.In addition,the theoretical prediction and field monitoring for the upper limit position of interlayer separation were conducted in a typical roadway.The results obtained by these two methods are consistent,indicating that the methods proposed are conducive to improving roof control in a thick coal seam.

Prediction and control of rock burst of coal seam contacting gas in deep mining

By analyzing the characteristics and the production mechanism of rock burstthat goes with abnormal gas emission in deep coal seams,the essential method of eliminatingabnormal gas emission by eliminating the occurrence of rock burst or depressingthe magnitude of rock burst was considered.The No.237 working face was selected asthe typical working face contacting gas in deep mining;aimed at this working face,a systemof rock burst prediction and control for coal seam contacting gas in deep mining wasestablished.This system includes three parts:① regional prediction of rock burst hazardbefore mining,② local prediction of rock burst hazard during mining,and ③ rock burstcontrol.

Research on space-time coupling action laws of anchor-cable strengthening supporting for rock roadway in deep coal mine

In order to obtain space-time coupling relationship of anchor-cable to improve supporting effect for deep coal mine rock roadway, FLAC3D was used to investigate into mechanical characteristics of the roadway whose crosssection shape was vertical wall and semi-circular arch when the roadway was supported by bolts and metal mesh. The results show that the extent of stress concentrations, the range failure zone, and the deformation at the roof center and two spandrels of roadway are greater than those at other positions, except at the floor. The reasonable positions of anchor-cable supporting are the roof center and two spandrels of roadway. The anchor-cable should be installed at good time with bolts supporting after roadway driving be- cause it can improve the stress states of deep surrounding rock around the roadway and control the roadway deformation effec- tively. The engineering practice has proven that the sustained deformation of deep surrounding rocks is effectively controlled when the anchor-cable supporting is adopted at reasonable positions of the roadway at good time.

Layout and support design of a coal roadway in ultra-close multiple-seams

A roadway within ultra-close multiple-seams(RUCMSs) is one of the most difficult supported coal roadways to deal with in underground coal mines. This is usually due to the unknown stress distributions, improper roadway layout, and unreasonable support parameters. In order to solve this support problem and effectively save RUCMSs from frequent and abrupt disasters(such as serious deformation of the surrounding rock, roof cave ins, and coal side collapse), a comprehensive method is adopted here which includes theoretical analysis, numerical simulation, and field monitoring. A mechanical model was constructed to determine the stress distribution in the coal pillar after two sides of a longwall panel had been mined. Based on this model, the horizontal, vertical, and tangential stress equations for the plane below the floor of the upper-left coal pillar were deduced. In addition, a typical coal mine(the Jinggonger colliery, located in Shuozhou city, Shanxi province, China) with an average distance between its 9# and 11# coal seams of less than 8.0 was chosen to conduct research on the proper layout and reasonable support required for a typical coal roadway located within coal seam 11#. Using FLAC3D(Fast Lagrangian Analysis of Continua in 3-Dimensions) numerical software, eight schemes were designed with different horizontal distances(d) between the center lines of the coal pillar and the roadway in the lower coal seam(RLCS). The simulations and detailed analysis indicate that the proper distances required are between 22.5 and 27.5 m. A total of 20 simulation schemes were used to investigate the factors influencing the support provided by the key bolts(bolt length, spacing, distance between two rows, installation angle, and pre-tightening force). The results were analyzed and used to determine reasonable values for the support parameters. Field results show that the stability and strength of the RLCS can be effectively safeguarded using a combination of researched stress distribution characteristics, proper layout of the RLCS, and correct support parameters.

Roadway failure and support in a coal seam underlying a previously mined coal seam

The influence of an upper,mined coal seam on the stability of rock surrounding a roadway in a lower coal seam is examined.The technical problems of roadway control are discussed based on the geological conditions existing in the Liyazhuang Mine No.2 coal seam.The stress distribution and floor failure in the lower works after mining the upper coal is studied through numerical simulations.The failure mechanism of the roof and walls of a roadway located in the lower coal seam is described.The predicted deformation and failure of the roadway for different distances between the two coal seams are used to design two ways of supporting the lower structure.One is a combined support consisting of anchors with a joist steel tent and a combined anchor truss.A field test of the design was performed to good effect.The results have significance for the design of supports for roadways located in similar conditions.

Experimental investigation on behaviors of bolt-supported rock strata surrounding an entry in large dip coal seam

In order to investigate the behaviors and stability of rock strata surrounding an entry with bolt supporting in large dip coal seams (LDCSs) dipping from 25° to 45°, a self-developed rotatable experimental frame for similar material simulation test was used to build the model with the dip of 30°, based on analyses of geological and technological conditions in Huainan mine area, Anhui, China. The strata behaviors, such as extracting- and mining-induced stresses development, deformation and failure modes, were synthetically integrated during working face advancing. Results show that the development characteristics of mining-induced stress and deformation are asymmetrical in the roadway. The strata behaviors are totally different in different sections of the roadway. Because of asymmetrically geometrical structure influenced by increasing dip, strata dislocating, rock falling and breaking occur in roof. Then, squeezing, collapsing and caving of coal happen in upper- and lower-rib due to shearing action caused by asymmetrical roof bending and dislocating. Owing to the absence of supporting, floor heaving is very violent and usually the zone of floor heaving develops from the lower-rib to upper-rib. Engineering practices show that, due to the asymmetrical characteristics of rock pressure and roadway configuration, it is more difficult to implement bolt supporting system to control rock stability of roadways in LDCSs. The upper-rib and roof of entries are the key sections. Consequently, it is reliable to use asymmetrical bolt-mesh-cable supporting system to control rock stability of roadways based on the asymmetrical characteristics of roadway configuration and strata behaviors.

Relationship between joint development in rock and coal seams in the southeastern margin of the Ordos basin

To predict joint development characteristics of coal seams, joint characteristics of rock seams from 88field stations were observed and comparisons were made between joint characteristics of coal and rock seams at 10 coal outcrops. Additionally, detailed joint measurements of underground coal seams were taken at two coal mines. This study investigated the effects of seam thickness, lithology, and structure on joint development and established the relationship between joint development of coal and rock seams, which allowed predictions of predominant joint densities for the No.5 coal seam in the southeastern margin of the Ordos basin. The results show that outcrop and underground coal seams exhibit the same joint systems as rock seams. The joints are mainly upright. Predominant joints strike 55° on average, followed by joints striking 320°. The joint density of the coal seam is 18.7–22.5 times that of the sandstone seam at the same thickness. The predominant joint density of the No.5 coal seam, controlled by the structure, is 4–20 joints per meter. Joint densities exhibit high values at intersecting areas of faults and folds and decrease values in structurally stable areas. The permeability increases exponentially with increasing density of the predominant joints.

Study on the Theory and Method on Identification of the Mobile Block in the Face-Contacted Blocks Structure in Rocks Between Coal Seams to Mine the Left-over Coal Above the Gob

In mining the left-over coal above the gob,stope wall rock of mining area have hard limestone.through field observation,the face-contacted block structure was found in rocks between coal seams to mine the left-over coal above the gob.In order to probe into the movement law of rock strata and strata control measures,it is very important to identify the mobile block in face-contacted block structure of rocks between coal seams.This paper relies on the thought of block theory to establish appropriate parameter matrix and figure out its discrimination matrix in view of the fact that the block in face-contacted block structure has high intensity and stiffness,the

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 Supporting of Seam Roadways in Deeply Inclined Coal Seams

Based on the present problems of the support method of gateways in complex surrounding rock in steeply inclined seams, this paper discusses the support selection of lasting gateways in steeply inclined seams, and evaluates the support effects. It draws the conclusion that the support of bolt-mesh-anchor is the most effective support of this sort of gateways by using scale model simulation in lab and practice application.The support effects of practice application are satisfactory. It will give a beneficial reference to other analogical mine and has an extensive application prospect.

Stability analysis and control technology of gob‑side entry retaining with double roadways by flling with high‑water material in gently inclined coal seam

To ameliorate the defects of insufcient support resistance of traditional roadside flling bodies for gob-side entry retaining(GER),overcome the inability to adapt to the deformation of surrounding rock,and isolate the goaf efectively,a new type of high-water material as a roadside flling body for GER technology with double roadways was proposed.The instability analysis and control technology of GER with double roadways by flling high-water material into a gently inclined coal seam were studied.The basic mechanical properties of the new high-water material were investigated through laboratory experiments,and their main advantages were identifed.The reasonable width of the roadside flling wall of a high-water material was obtained by combining ground pressure observation and theoretical calculations.The distribution characteristics of the stress and plastic zone of surrounding rock of GER after being stabilized by the disturbance of the working face were studied using numerical simulations,and the failure range of GER by flling with high-water material was revealed.Based on this,a coupling control technology of anchor cables and bolts+single props+metal mesh+anchor bolts is proposed.Through the coupling methods of arranging borehole peeping and observing the convergences of surrounding rock,the results demonstrate that GER with double roadways by flling with a 1.8-m-wide high-water material has a good control efect.The above research will play an active role in promoting the application of high-water materials in GER roadside flling.

Controlling Effects of Surrounding Rock to Coal Seam Gas Occurrence

Surrounding rock of coal seam was one of the important factors to gas occurrence. The coal seam gas occurrence was studied by the index of roof strata thickness or sand content rate;we found that there were certain shortcomings. In order to reasonably evaluate the influence of coal seam surrounding rock on gas occurrence in Panji mining area, we quantitatively evaluated the effect of coal seam surrounding rock on gas occurrence by influence coefficient of roof strata thickness, and built six mathematical models of the variational gas content in the mining area which is divided into six gas geological units. The results shows that the coal seam gas content is mainly influenced by 20 mroof strata in each gas geological unit, the gas content presents the tendency of increase, and with the influence coefficient of strata thickness increases, they exist a significant linear relationship.

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.

Mechanics analysis on the conditions of rock burst occurrence in the coal mass of roadway rib

According to the rock burst features occurred in the coal mass of roadway rib in one mine,the mechanics model of coal mass and roof structure system along the edge of goaf was founded to analyze the stress of roof rock layer,so the subside curve of roof rock layer was deduced.Furthermore,the stability of coal and rock system were analyzed,the critical load and critical resistance zone were used to judge the danger degree of rock burst occurrence.The influence of coal mass strength,brittleness degree,coal seam thickness,roof thickness,suspending length,equivalent shear module on the critical load, critical resistance zone was confirmed.So the rock burst occurrence conditions of coal mass in roadway rib mainly depend on mining depth,coal seam thickness and hard roof and floor,which are decided by the above studies,and successfully applied in prediction and prevention of rock burst in this mine.

Study on mechanism and practice of surrounding rock control of high stress coal roadway

The mechanical principle and surrounding rock deformation feature of highstress coal roadway was analyzed.The condition of stress balance of the kind of theroadway was put forward.The surrounding rock control principle and supporting techniqueof high stress coal roadway were discussed.It was very important to control early daysdeformation of coal sides.The supporting strength is should increased,so the strengthloss of coal sides is decreased.The range of plastic fluid zone is reduced.The abovemention-ned principle is applied in industrial test,and the new supporting technique is ap-plied successfully.