Underground Roadways Research Articles

Analysis on the Shear Stress Propagation Mechanism in the Rock Reinforcement System

Rock reinforcement is significant in maintaining the stability of excavated structures, such as tunnels and underground roadways. However, shear failure in the rock reinforcement system, especially the shear failure at the rock reinforcement bolt surface, induces a threat to the rock reinforcement system. To reveal the shear stress (SS) propagation mechanism in the rock reinforcement system, this article conducted a literature review. First, the investigation approaches that were used by previous researchers to study the SS propagation were summarized. The advantages and disadvantages of experimental tests, analytical simulation, and numerical simulation were compared and analyzed. Then, the SS propagation process in the rock reinforcement system was presented. Two typical SS propagation modes were explained. More attention was given to the SS propagation mode in which the maximum SS propagates from the external end of rock reinforcement bolts to the internal end of rock reinforcement bolts. After that, a discussion section was given. In the discussion section, the significance of the SS propagation was further emphasized. Moreover, the limitations in the analytical simulation and numerical simulation were indicated. It is concluded that when studying the SS propagation mechanism of rock reinforcement bolts, combining experimental tests, analytical simulation, and numerical simulation is a better choice. This study is beneficial for revealing the SS propagation mechanism of the rock reinforcement system.

Modeling of Floor Heave in Underground Roadways in Dry and Waterlogged Conditions

Floor heaving is a phenomenon that occurs in almost all mining roadways and tunnels. It can restrain the advance of the heading face or cause serious problems during roadway use. The highest levels of floor uplifting are observed in coal mines, which can reduce the output or even stop it altogether. The floor heaving intensity depends on the rock type, the stress in the rock mass, and rocks’ mechanical properties. Floor deformation develops when the secondary state of stress is formed around the working, and it is much higher and more dynamic in the case of waterlogged rocks. The presence of water increases the floor’s propensity to heave, especially clay rocks, such as claystones or mudstones, if they include water-absorbed minerals. In this paper, we present a new modeling methodology for roadway floor heave. The modeling covers a dry floor condition in which the parameters of the Hoek-Brown failure criterion are gradually lowered over time, and a waterlogged floor condition, in which the strength and strain parameters of the rocks are gradually reduced in line with their progressive saturation. In the second case, the claystone floor’s geomechanical parameters were investigated, and the rocks were subjected to water for up to 24 h. The results of the numerical simulation were compared with the in situ measurements of convergence and floor heave in the same coal mines from which the rock samples were collected. The consistency between the numerical simulations and the underground measurements reached 90–99%.

Dissipative structure suppression as a way to increase the sustainable improvement of the frame support bearing capacity

Introduction. A yield frame support is a basic means of providing the underground roadways’ stability in the deep mines operating in the hard ground control condition when the ratio of the ground pressure to the unconfined strength of surrounding rock mass exceeds 0.33. The operators adjust the nominal bearing capacity of the frames at 0.55 of their maximum or peak resistance Fmax because the frames operate in a dry friction mode spontaneously generating oscillation, which causes variation of the resistance in the range from 0.1 up to 0.9 of Fmax . Aim/tasks. We intended to reduce the dynamic oscillation of the support resistance that allows for increasing their bearing capacity. Methodology. We used a computer simulation by FLA3D model, indoor testing of the frames, and actual measurements in an underground coal mine. Results. We revealed a specific behavior of the frame support that reduced the limit of the bearing capacity by 45%. During yielding, the frames generate dissipative structures (DS) that become apparent due to the dynamic nature of stick-slip friction following the yielding process. We demonstrated that DS control and especially its suppression provides a sustainable increase in the frame bearing capacity. Conclusions. Improvement of the yield frames design and especially their clamps are the prospective way to control DS and provide sustainable enhancement of the frame bearing capacity.

Numerical Optimization of Drilling Parameters for Gas Predrainage and Excavating-Drainage Collaboration on Roadway Head

In order to improve efficiency of gas drainage, the reasonable layout parameters for borehole on roadway head are investigated. Assuming that the coal mass has a dual pore structure with fractures and pores, a multiphysical field coupling mathematical model is proposed for gas drainage. The governing equations of gas adsorption, seepage, and diffusion are considered. The process of gas preextraction and excavating-extraction collaboration on roadway heading face in 2606 haulage roadway of Zhangcun mine is modeled by finite element (FE) method. The effects of gas drainage under different drilling arrangements are analyzed. The results show that the fastest decreasing rate of gas content occurs at the beginning of drainage, and decreasing rate of gas content tends to be stable in the later stage. After removing the predraining on roadway head, the gas content at the center of coal wall on the roadway heading face will rebound. The included angle between the borehole and the roadway middle line determines the spatial area of gas drainage. Too small included angle will reduce the area of gas content reduction, while too large included angle will result in a blind area on both sides of the roadway. The change in borehole spacing affects the decreasing rate of gas content in the rock and coal around the roadway. Large spacing may cause an inadequate decreasing rate in the middle of the roadway, while small spacing may cause an inadequate decreasing rate in both sides of the roadway. In the field application, the pure gas flow and gas concentration of drainage show a downward trend in whole. The gas concentration decreased from 13.2% to 10.8%, and the pure gas flow decreased from 10.6 m3/min to 8.15 m3/min. Research achievements can provide a basis for gas drainage in underground roadway.

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.

Development and Application of Thermal Insulation Material for Underground Roadway with High Ground Temperature

Development and Application of Thermal Insulation Material for Underground Roadway with High Ground Temperature

Research on a hydraulic manipulator arm of an automatic bottom laying robot for underground roadway in coal mine

This paper studies a robot with rapid bottoming technology that integrates the transportation, installation and removal of bottoming modules, and rapid road surface leveling. It is driven by explosion-proof diesel and is used for new application equipment with fine operation ability in high-risk environment of coal mine roadway. Research on the integrated design of equipment and research on automation control technology to realize the safe and rapid construction of the bottom laying module, so as to realize the automation of module laying and achieve efficient and safe laying of modules.

Discussion on Roof Support Technology of Underground Roadway Excavation in Coal Mine

Discussion on Roof Support Technology of Underground Roadway Excavation in Coal Mine

Experimental investigation of damage evolution and failure criterion on hollow cylindrical rock samples with different bore diameters

The roadway direction is often parallel to the direction of the maximum principal stress for the structure arrangement of underground roadway. To study the instability mechanism of roadway under the maximum principal stress, a series of uniaxial compression acoustic emission (AE) experiments were carried out on hollow red sandstone and granite rock samples with different bore diameters. The test results suggest that the oblique shear or X-shaped shear failure occurs in hollow rock samples, and the failure process is accompanied by a sudden jump in accumulative energy of AE signals, at the same time, the ringing count arrived at peak value. The increase in bore diameter haves contributed to the decline of ringing count and accumulative energy. A statistical damage constitutive model of Weibull distribution was established for hollow rock samples. On the basis of optimizing the damage variable, a damage constitutive model based on AE ringing count was obtained, which can better describe the damage state and stress state of rock samples. The AE accumulative energy was selected as the state variable, and the failure criterion model was finished based on the cusp catastrophe theory to estimate the rock sample failure. The judgment results show that the failure moment of rock sample is accurately included in the judgment time interval. This research can provide reference and technical support for the stability control and monitoring of underground engineering roadways.

Experimental study on resin-anchored bolt concentricity including a device for more consistent bolt centering

The bolts not being coaxial with the boreholes they are installed in is a common problem during roof bolting in tunnels and underground roadways. This paper uses theoretical analysis and laboratory experiments to analyze the influence of noncoaxial bolt on resin-anchored and to find an effective solution for eccentric bolt. After analyzing the stress distributions along the resin–rock interface (the R-R interface), we found that when the bolt is eccentric, the shear stress distribution at the interface is not uniform. The shear stress at the R-R interface closer the bolt is higher and this causes the bond at the R-R interface to fail more easily, which reduces the anchoring performance. The strength of bolts anchored with different degrees of eccentricity was analyzed using pullout tests. The test results show that bolt concentricity is positively correlated with both the anchoring strength and the energy absorption capacity. This indicates that an eccentric bolt will weaken the anchoring quality of bolt. To solve the eccentric bolt problem while taking the mechanics of bolt installation into account, a bolt radial limiting device (BRLD) has been designed. Laboratory experimental results show that the BRLD can effectively ensure the concentricity of a bolt. This research has explained why bolts that are not centered decrease the anchoring strength of resin. It also provides an economical and convenient method for ensuring that bolts are installed concentricity to improve anchoring system performance.

Stability of Underground Coal Mine Roadway Excavated in Soft Rock Mass

This paper studies the stability and ground behavior of the main roadway excavated in a soft rock mass at PT Gerbang Daya Mandiri (GDM) underground coal mine in Indonesia. The stability and ground behavior of the main roadway under various geological and excavation conditions was analyzed and discussed through numerical simulations and field measurement data. Based on the results, it is found that the mechanical conditions of claystone and the geological conditions of the roof have an obvious impact on the stability of the main roadway. The large roof displacement of the roadway occurs when the roadway is excavated in the deteriorated claystone, whereas the small roof displacement occurs when the roadway excavation is made in the undeteriorated claystone and when the coal layer is present in the roof. Under undeteriorated conditions of claystone, the small failure zone and displacement of the roadway occur. The current support system using the steel arch SS400 is effective to control the roadway stability. As the claystone has deteriorated due to groundwater, the failure zone and displacement expand considerably, and the roadway stability decreases significantly. The use of the current support system (steel arch SS400) is difficult to control the stability of the main roadway. Under this situation, a stronger steel arch SS540 is recommended to apply. Furthermore, the presence of a coal layer during the excavation considerably improves the stability of the main roadway. Compared with the roadway excavated in claystone only, the displacement decreases significantly. In addition, by leaving a thicker coal layer in the roof, a better stability condition of the roadway can be achieved.

Impact of the water evaporation on the heat and moisture transfer in a high-temperature underground roadway

As the underground engineering proceeds to a greater depth, the thermal stresses resulted from high-temperature surrounding rock become a major challenge for the deep construction and safe operation. Understanding of the characteristics of heat and moisture transfer in a roadway is critically required to assist in predicting and improving the thermal environment in the underground. The present work developed a fully coupled model capable of simulating the non-isothermal flow inside the roadway and heat transfer in surrounding rock together with moisture transfer driven by water evaporation. And the proposed model has been validated with the field test data and reasonable agreement was achieved. Comparing the models with or without water evaporation, it is discovered that ignoring latent heat will cause a serious deviation in air temperature prediction. Examining the critical factors on the effect of heat and mass transfer in the roadway is found that dehumidifying the initial airflow or increasing ventilation speed can effectively promote the latent heat release and reduce the temperature of airflow and surrounding rock. And this effect is greater significant for the higher temperature roadway. The present study can provide a robust theoretical basis and foundation for heat hazard control in underground engineering.

Numerical Analysis of the Effect of Heterogeneity on Underground Roadway Stability under Dynamic Loads

With the increasing depth of coal mining and expanding mining scale, the rocks surrounding deep roadways are in a complex mechanical condition of frequent dynamic disturbance. The heterogeneity has an important influence on rock mass failure under dynamic loads. Therefore, it is necessary to study the deformation and failure of heterogeneous roadway under dynamic load. In this paper, the effect of heterogeneity on stability of roadway under static and different dynamic loads is studied. According to the results, the effect of rock mass heterogeneity on the deformation and failure of surrounding rock varies with different degrees of heterogeneity. Under static loading conditions, the stability of roadway is negatively correlated with the degree of heterogeneity of the rock mass. Under dynamic loading conditions, the change of heterogeneity degree has significant influence on the stability of surrounding rock. With the increase in dynamic load strength, the change in variation difference in the average value of roof sag, stress distribution, and plastic zone caused by variations in heterogeneity will increase. This study contributes to understanding the deformation and failure characteristics of heterogeneous roadways under dynamic loads and can be used to analyze heterogeneous roadways under dynamic loads.

A hybrid PSO-ANFIS model for predicting unstable zones in underground roadways

The problem of roof failure in underground coal mines is responsible for many fatalities, injuries, downtimes, and delays in production planning. Currently, the support systems in underground roadways are mainly designed based on the miners’ experience or, at worst, on trial and error. Nonetheless, the excessive roof displacements may lead to undesirable instabilities that have adverse effects on the mining operations. The uncontrolled roof failures are the major cause of calamitous consequences in Tabas underground coal mine, northeast of Iran, which brought about many disasters in recent years, from the threat of personnel’s safety to the postponement of coal production. Therefore, this research aims at developing a hybrid neuro-fuzzy model to approximate the unknown nonlinear relationship between the maximum roof displacements (dmax) and geomechanical features at Tabas longwall mine. After designing several hybrid models, the Particle Swarm Optimization (PSO) algorithm could significantly improve the performance of the Adaptive Neuro-Fuzzy Inference System (ANFIS). The results of three hybrid neuro-fuzzy models show that the optimization process in PSO is superior in comparison with Genetic Algorithm (GA) and Simulated Annealing (SA). According to the results, the determination coefficients (R2) between the measured and predicted values of dmax for PSO-ANFIS, SA-ANFIS, GA-ANFIS, and ANFIS were respectively obtained as 0.944, 0.907, 0.882, and 0.887. The associated error indicated that the PSO-ANFIS model could yield the best performance when encountered with unseen data. Compared to the ANFIS, the PSO-ANFIS model demonstrated an increase of about 6% in R2, and a decrease of about 34% in the Root Mean Square Error (RMSE). Therefore, our strategy in this research is to predict the dmax at first, and then to establish two milestones as 33% of the dmax for timely installing standing support systems, and 66% of the dmax for announcing an alarm threshold in potentially unstable zones. This may be useful to derive a reasonable judgment for predicting the unstable zones, and implementing preventive measures ahead of time in longwall roadways.

Experimental Study on Creep Behavior and Crack Evolution of Stratified Structural Sandstone under Segmental Constant Load

The hazards induced by stratified rock mass creep are still one of the major problems that threaten the safety of underground engineering. This paper takes safe construction of underground roadway in Urumqi mining area as the research background. In this study, we mainly adopted rock mechanics experiments to accomplish the research on creep behavior and crack evolution of stratified structural sandstone. Creep deformation characteristics of stratified structural sandstone under different load were revealed; also, we analyzed the reason why a part of rock samples failed but others were not under the same load. Creep behavior and crack evolution of rock samples without stratified structure have significant randomness. The crack evolution and failure characteristics of stratified structural rock samples were mainly manifested as failure along and cutting through structural plane and their combined forms. Creep strain, creep duration, and creep rate of rock samples with stratified structure had a nonlinear relationship with applied load, such as exponential function or logarithmic function. Understanding the evolutionary relationship between the above parameters and load provides a basis for obtaining the creep behavior of stratified rock mass under different load conditions.

Compound-mode crack propagation law of PMMA semicircular-arch roadway specimens under impact loading

An underground roadway usually contains defects of various types, and when the roadway is subjected to external loading, the locations of those defects influence the roadway by differing degrees. In this study, to study how the locations of defects affect crack propagation in a roadway, specimens with tunnel-type voids were made using polymethyl methacrylate, and the stress wave produced by a bullet impacting an incident rod was used as the impact load. Meanwhile, the variations in crack speed, displacement, and dynamic stress intensity factor during crack propagation were obtained using an experimental system of digital laser dynamic caustics, and the commercial software ABAQUS was used for numerical simulations. From the experiments and numerical simulations, the crack propagation path was verified and the impact fracture behavior of a semicircular-arch roadway with different defect positions was presented. The results show that when the pre-fabricated crack is on the central axis of the sample, the crack propagation is purely mode I; when the pre-fabricated crack is 5 mm from the central axis, the crack propagation alternates between mode I and a mixture of modes I and II; when the pre-fabricated crack is at the edge of the semicircular-arch roadway, the crack propagation follows the I–II mixed mode.

Seismic Response Analysis of Deep Underground Roadways and Coal Pillars under the Influence of the Adjacent Goaf

In this work, a numerical study is conducted on the seismic response of deep-buried roadways in coal mines under the influence of goafs, and a 3D numerical model of the seismic response simulation of deep-buried roadways is established using the coupling model of the finite difference method and the distinct element method. This model simulates the seismic response of different coal pillar widths and the seismic conditions of the deep-buried roadways under the influence of the adjacent goafs. The deformation, stress distribution, and plastic area distribution of roadways and coal pillars are systematically studied, and the situations under the static load and the roadways, which are not affected by the goafs, are compared and analyzed. A reasonable width of the coal pillar is proposed on the basis of the stability of the roadway and the coal pillars. In the end, suggestions for the reasonable setting of coal pillars under seismic load are provided.

A hierarchical local-model tree for predicting roof displacement in longwall tailgates

An explicit challenge for mine productivity and personnel’s safety in mechanized underground mines is to envisage the uncontrolled roof displacements, usually occurred in underground roadways. For this purpose, support systems are to be installed to guarantee the proper functionality of underground structures during mining operations. Roof displacement is a reliable indicator to examine stability conditions of tunnels or roadways, which are driven in underground coal mines. In this research, a neuro-fuzzy-based method, namely hierarchical local model tree (HiLoMoT), was employed to predict the roof displacements and consequently indicate the unstable zones in a tailgate roadway. In this regard, the geomechanical and instrumentation information measured from a longwall panel at Tabas coal mine was employed to validate the developed HiLoMoT model. According to the results, the proposed HiLoMoT model could predict roof displacements in reasonable conformity when compared with measured ones. In order to examine the prediction capability of the HiLoMoT model, three indices of the coefficient of determination ( $$R^{2}$$ ), variance accounted for (VAF), and root mean square error (RMSE) were used. Introducing unseen test data, $$R^{2}$$ , VAF, and RMSE were, respectively, obtained as 0.952, 95.13, and 0.0193, which showed high goodness of fit and low error for the proposed model. In comparison with ANFIS as a common fuzzy-based model, HiLoMoT could predict the roof displacement by a nonlinear partitioning based on the incremental tree-construction, which improves the quality of the model without further iteration loops or trial and error. Therefore, the HiLoMoT model may be implemented as a new applicable tool for predicting roof displacements ahead of time in mechanized longwall mining.

The Elastoplastic Solutions of Deep Buried Roadway Based on the Generalized 3D Hoek-Brown Strength Criterion considering Strain-Softening Properties

The deep underground roadways are widely used in the mining industries at present, but the relevant theoretical bases are not fully understood. In this paper, the numerical solutions for strain-softening surrounding rock under the generalized three-dimensional (3D) Hoek-Brown (GZZ) strength criterion are developed incorporating the confinement-dependent characteristics of ψ and η ∗ and their influences on the stress and displacement of equivalent circular roadway. On the basic of a finite difference, method for the strain-softening model is proposed to consider the variation of ψ and η ∗ in analyzing the strain-softening behavior of rock masses. Combining the equilibrium equation and strength criterion, the stress conditions for each annulus are calculated analytically. The displacement for each step is obtained analytically by solving the differential equation through invoking flow rule and Hooke’s law. The accuracy of the proposed method is verified through the comparison between the results and the previous studies. The effect of intermediate principal stress of GZZ strength criterion is considered; the rationality of the proposed method is verified by two aspects. First, by comparing with the two-dimensional narrow and generalized H-B strength criterion, the advantage of GZZ strength criterion that considers the effect intermediate main stress is highlighted. On the other hand, compared with the three-dimensional linear D-P criterion, the advantage of GZZ strength criterion in the theoretical research of deep underground roadway in coal mine is highlighted. The results show that the strain-softening of the surrounding rock in the plastic zone of the roadway can reduce the pressure of the surrounding rock, but it will greatly increase its deformation. In the high field stress areas, the strain-softening of surrounding rock is the key reason for the destruction of the roadway. It is suggested that in the design and calculation of the support system of the roadway, the strain-softening characteristics of the surrounding rock should be considered, which is very important to avoid large deformation and damage of roadway.

Dynamic Monitoring Technology of Air Quantity in Mine Ventilation System Based on Optimum Location of Wind Speed Sensors

To improve the accuracy and reduce the disturbance during the monitoring, the index system and the mathematic model of optimal wind speed sensors’ location are established using the variable fuzzy theory. Then the adjustment analysis of redundant wind speed sensor measurement and the standard deviation filter method are put forward. Then, the dynamic monitoring technology in mine ventilation network is formed and the automatic monitoring system of air quantity in mine ventilation network is established. The application in a complex ventilation network shows that, this method only needs 10 wind speed sensors (7 must install points and 3 redundant install points) to obtain the air quantity of 19 branches. And it can achieve the dynamic monitoring in the underground roadway, which provides an important basic data for management decisions in mine ventilation network.