Roof Stability Research Articles

Research on Support Technology for Unstable Roof Roadway Under Abandoned Roadways in Ultra-Thick Coal Seam

Due to the impact of disordered mining activities in previous years, numerous abandoned roadways exist in the second mining district of the 13# coal seam in Chejiazhuang Coal Mine. The stability of the new roadway roof was analyzed under various distributions of abandoned roadways above. It was determined that the ultimate stable thickness of the coal layer between the new and abandoned roadways is 4.0 m. When the thickness between the two is less than 4.0 m, the roof becomes unstable after excavation, posing a risk of collapse. Advanced grouting reinforcement is required to enhance roof stability before installing U-shaped steel arches. Mechanical experiments were conducted on the polymer grouting consolidation of fractured coal, showing a significant increase in residual strength compared to intact coal. Furthermore, the uniaxial compressive strength of the polymer grouting consolidation partially recovered. On average, the consolidation coefficient and recovery coefficient were 5.28 and 85.51%, respectively. Grouting increased the ductility of the fractured surrounding rock, enhancing its resistance to deformation and plasticity. A polymer grouting consolidation technology for supporting fractured surrounding rock under the unstable roof of abandoned roadways is proposed, along with the design of corresponding support schemes and parameters. Monitoring the results of mine pressure indicated that the surrounding rock remained stable after roadway excavation, validating the effectiveness of the support schemes and parameters.

Roof stability analysis model of super-long fully mechanized working face and its application

The strata behavior of a fully mechanized working face is obviously different from that of a short working face after the dip length of the coal face is lengthened. In view of the characteristics of high frequency, high peak value and large range of weighting in super-long working faces, a mechanical analysis model based on elastic foundation beam theory was established according to the bearing characteristics of hydraulic support and immediate roof. The results show that the roof deflection is positively correlated with the working face length, and with the increase of the working face length, the roof deflection in more areas has a larger value and it gradually changes from a single peak to multiple peaks. The roof stability decreases with the in-crease of the working face length and the decrease of length-thickness ratio. The research results are verified in working faces of different lengths in Buertai Coal Mine, and the phenomena of roof caving in different regions and asynchronous weighting in the face are explained. This study at-tempts to provide a theoretical basis for the roof treatment of super-long working faces.

Stability analysis of the false roof made of cemented tailings backfill in deep mine: A case study

The overall stability of cemented tailings backfill (CTB) false roof, as an important support structure in the quarry, is of great significance for realizing the safe recovery of the ore body. This paper aims at the practical problem of ore body mining under the condition of deep broken rock mass. By analyzing the typical process characteristics of underhand cut-and-fill mining method, the dangerous mechanical state of CTB false roof is determined, and the CTB false roof strength model based on the maximum tensile stress failure criterion and deep mining coefficient is established. Based on the measured load value of CTB false roof, the minimum required strength of CTB false roof is obtained. Through the performance tests of CTB under different proportioning schemes, the mechanical strength of CTB false roof (UTS：0.43MPa, UCS：6.22MPa) is designed，the proportioning parameters of CTB with "high strength, high fluidity, quick setting and low cost" are put forward. Finally, based on FLAC3D numerical simulation and field monitoring, the stability of CTB false roof with recommended ratio parameters is analyzed. The results show that the CTB false roof has not been violently displaced and destabilized in the process of service ore body mining, has good strength reserve, and is able to provide a safe workspace for mining, verifies the reliability and reasonableness of the CTB false roof proportioning parameter, and provides a new way for the study of false roof stability.

An exploration of improving stability of gob-side entry retained with graded and zoned pressure relief technology: a case study

To address the issues of uncertain pressure relief effectiveness and poor control of surrounding rock caused by the composite nature of the roof strata in the gob-side entry retained (GER), as well as significant changes in strata’s thickness and stability differences, this study focuses on the airway of the panel 3113 N in Longtan Coal Mine. Through field detection, theoretical analysis, and on-site applications, a stable mechanical model of the hard roof strata is established, elucidating the factors influencing fracture and instability in composite roof strata. The results indicate that roof stability of the GER depends on the position and ultimate load-bearing capacity of the hard roof strata, which in turn affects roof pressure relief effectiveness. Based on this, a roof classification method centered on “hard rock strata position and bearing capacity” is proposed. The retained roadway roof is categorized into four levels: Grade I (stable), Grade II (moderately stable), Grade III (unstable), and Grade IV (extremely unstable). Specific pressure relief methods, key parameters, roof control measures, and slope reinforcement methods are provided for each level of roof, forming a graded and zoned pressure relief technology for GER with composite roof. This approach emphasizes strong support and roof control, reinforced roadway sides, and precise roof cracking as core strategies. Field application results demonstrate that this graded and zoned pressure relief technology performs well, effectively maintaining stability of the surrounding rock in retained roadways.

Geological characteristics of coal mines in the Zagros basin of Iran: Unveiling rock mechanical properties and time-dependent behavior

The Zagros Basin in southwestern Iran is a significant source of coal, with numerous coal mines operating in the region. Ensuring the stability of coal mines is crucial for safe and efficient mining operations. This study investigates the time-varying response of rocks and roof resistance in coal mines in the Zagros Mountains using a novel approach that combines numerical simulation, relaxation testing, and rock displacement studies. The results show that rocks exhibit significant time-dependent behavior, with changes in rock mechanical properties over time. A comprehensive viscoelastic-plastic model is developed to accurately describe the time-varying strain-softening response of rocks and simulate laboratory tests. The model integrates the Burgers and strain-softening models, simulating stress relaxation curves and rock displacement over time. The study reveals that the rock mass displays significant nonlinear behavior, with changes in rock mechanical properties over time. The findings of this study highlight the importance of considering the time-varying response of rocks and roof resistance in coal mine stability analysis. The results provide valuable insights into the time-dependent behavior of rock mass in coal mines in Iran, which can inform mining practices and mitigate potential hazards. Results in this study can contribute to developing strategies for improving roof stability and reducing the likelihood of roof collapses.

Analysis of roof stability in ultra-large LNG storage tanks based on field measurements

ABSTRACT To ensure an accurate assessment of the stability of the steel roof during construction of ultra-large LNG storage tanks, real-time monitoring throughout the entire concrete roof pouring process of the world's largest 270,000 cubic meter LNG storage tank was implemented. A computational model for the stability of the steel roof during construction course was established, and the influence of time interval between pours, the holding pressure, and the volume of concrete poured on the stability of the steel roof were studied. The results show that the stability of the steel roof can be enhanced significantly by increasing the time interval between pours within the first eight days after each pouring. Increasing the holding pressure can improve the stability of the steel roof, with more significant effects observed when the time interval between pours is shorter. The volume of concrete poured plays a critical role in structural stability.

Unraveling time-dependent roof stability dynamics in Iran's coal mines through laboratory-based rock displacement testing

Roof stability is a critical concern in coal mines, as the potential for roof collapse poses a significant risk to miners' safety and productivity. Roof stability is heavily influenced by the time-dependent properties of the rock mass above the workings. This study uses rock displacement testing to examine the effect of time-dependent properties on roof stability and resistance reduction in coal mines in Iran. The study employed laboratory-based rock displacement tests on samples collected from coal mines in Iran, subjected to varying stress levels over time, to simulate the gradual deterioration of rock mass strength in underground mining conditions. The samples were monitored for displacement under these conditions to quantify the reduction in roof resistance over time and assess its effect on roof stability. The study found that areas with high stress at equilibrium gradually fail with time, and the stress transfers from the failure zone into deeper solid rock. The results demonstrate that varying viscous parameters can lead to different relaxation behaviors and stress distribution. Furthermore, incorporating strength degradation into numerical simulation can capture the failure under creep conditions and improve the accuracy of predicting time-dependent roof failure. This research aims to enhance safety measures and reduce the risk of collapses by investigating the time-dependent properties of roof stability through rock displacement testing in Iran's coal mines. The study's innovative approach uses numerical simulation based on the viscoelastic-plastic model to simulate the time-dependent behavior of the rock and incorporate strength degradation into the simulation. The results provide valuable insights into the time-dependent behavior of rock mass in coal mines in Iran and contribute to developing strategies for improving roof stability and lessening the chance of roof collapses. The instantaneous elastic strain was 4.35 × 10–4, and creep simulation was activated to run for a time equivalent to 2 × 106 s.

Roof stability analysis for a shallow-buried cylindrical tunnel in Hoek-Brown rock strata

Roof stability of shallow-buried cylindrical tunnels in rock strata following the generalized Hoek-Brown criterion (GHB) is analyzed in this work. Based on the limit analysis method, a three-dimensional (3D) shallow-buried collapse mechanism for tunnel roofs is developed to derive various stability measures. Optimization codes are programmed to capture the optimal stability measure solutions. The effects of the 3D geometric characteristics, the rock mass strength parameters, and the buried depth on tunnel roof stability are investigated by a parametric analysis. The critical buried depth ratios corresponding to the transition between the shallow-buried and deep-buried tunnel roof collapse mechanisms are also presented. Thereafter a series of stability charts of the required supporting pressure and the factor of safety (FoS) is proposed for design purposes. This study provides a theoretical basis for design and engineering of tunnels with limited buried depth.

Study on Variation Law of Ground Pressure before and after Hard Roof Fracturing

Hard roof has the characteristics of small fracture development, good structural integrity and strong integrity, and the hanging roof area is large during mining, which seriously threatens the safety production of working face.Based on the characteristics of hard roof such as high strength, large thickness and difficulty in self-caving, directional drilling hydraulic fracturing is adopted to destroy the structural stability of hard roof and make it reach an ideal fracture form. At the same time, the variation law of strata behavior in working face before and after fracturing of hard roof is explored.The results show that:①During the normal weighting period of hard roof working face, the support pressure of working face is generally small, but when the hard roof is broken, it will cause the phenomenon of strong weighting in working face, which threatens safe production;②Hydraulic fracturing leads to secondary development of primary fractures in hard roof and continuous diffusion in the form of fracture network, which destroys the original bearing structure of hard roof and forces hard roof to collapse ahead of time;③Thirdly, comparing the weighting law of working face before and after fracturing, it is found that after pressure relief, the initial weighting step of working face decreases by 50.8 m, which is 56.4% year-on-year, and the average periodic weighting step decreases by 3.7 m, which is 21.4% year-on-year. After pressure relief, there is no strong strata behavior in working face, and hydraulic fracturing achieves the expected effect.

Assessing prestressed anchor cable support as ore pillar alternatives in stope span expansion: A case study

In large diameter long-hole (LDL) stopes, ore pillars are often set up in the rock drilling chamber to expand the span. However, after the ore pillars are blasted along with the stope, the stability of the roof is difficult to control, and collapse often occurs. This study introduced the idea of employing PAC support technology to replace the traditional ore pillar support and conducted site investigations, theoretical analysis, numerical simulations, and field tests to develop a technology for expanding the span of LDL stope based on prestressed anchor cable (PAC) support. Following a detailed investigation of pillar-supported LDL stope roof collapse events and geological conditions, a mechanical model for the stress arch considering the lateral stress coefficient was developed combining the failure characteristics and deep conditions, and the inverse relationship between the lateral coefficient of ground stress and the height of the stress arch above the opening was determined. Numerical simulation results demonstrate that the elliptical parabolic stress arch mechanical model has been verified, and PAC effectively controls roof stability, as evidenced by displacement and plastic zone response. Field tests were carried out utilizing PAC support, and monitoring results affirm the PAC support system's efficacy in stabilizing the roof. Using PAC to replace ore pillars resulted in a remarkable 29.8 % improvement in blast hole drilling efficiency and reduced ore dilution rate within the stope from 22.3 % to 14.2 %. This study serves as a reference for addressing analogous challenges in other mining operations.

Three‐dimensional stability analysis for a deep‐buried tunnel roof considering soil stratum strength nonlinearity

AbstractA three‐dimensional (3D) collapse mechanism was employed in this work to investigate the roof stability of deep‐buried cylindrical tunnels in soil considering strength nonlinearity. Based on the kinematic approach of limit analysis, three tunnel roof stability measures, namely, the stability number, the required support pressure, and the factor of safety solutions were derived to provide quantitative indicators for evaluating tunnel roof stability. Optimal upper bound solutions for these measures were obtained through optimization. Subsequently, the effects of soil strength nonlinearity and 3D geometry characteristics on roof stability and the profiles of collapsing blocks were investigated: The increase in the nonlinear coefficient m and the tensile strength σt, as well as the decrease in the initial cohesion c0, will lead to a deterioration in the stability of the tunnel roof, and also result in a larger range of collapse blocks of the tunnel roof. A 3D stability analysis of the tunnel roof can provide more reasonable stability estimates than a 2D stability analysis. When the length‐to‐radius ratio L/R → ∞, the 2D solution results.

Stability of longwall face adjacent to gateroads

Longwall is the widely used mining method in the word and in Vietnam due to the high production and high level of safety. To maintain production as scheduled, the stability of a longwall face is of great importance, especially at areas adjacent to gateroads where ground pressure is strongly concentrated. This paper presents a study on the stability of longwall faces adjacent to gateroads under medium and hard-to-cave roofs. By using theoretical and field measurement methods, the authors conclude that in such geological conditions, the ground pressure at face adjacent to gateroads increases and decreases cyclically. At the study site, the ground pressure fluctuates in the range of 20÷26 MPa, and the piston chainage changes in the range of 0.6÷0.9 m. The face stability is closely related to ground pressure and roof stability. The study demonstrates that the face area near tailgate appears to be less stable compared to that near maingate, and initial signs of roof weighting can occur. The paper’s results serve as fundamental science assisting mining engineers in better identifying longwall face stability, from which effective prevention and remedy measures can be developed.

Excavation compensation and bolt support for a deep mine drift

To overcome large deformation of deep phosphate rock roadways and pillar damage, a new type of constant-resistance large-deformation negative Poisson's ratio (NPR) bolt that can withstand a high pre-stress of at least 130 KN was developed. In the conducted tests, the amount of deformation was 200–2000 mm, the breaking force reached 350 KN, and a high constant-resistance pre-stress was maintained during the deformation process. A stress compensation theory of phosphate rock excavation based on NPR bolts is proposed together with a balance system for bolt compensation of the time-space effect and high NPR pre-stress. Traditional split-set rock bolts are unable to maintain the stability of roadway roofs and pillars. To verify the support effect of the proposed bolt, field tests were conducted using both the proposed NPR bolts and split-set rock bolts as support systems on the same mining face. In addition, the stress compensation mechanism of roadway mining was simulated using the particle flow code in three dimensions (PFC3D)-fast Lagrangian analysis of continua (FLAC3D) particle-flow coupling numerical model. On-site monitoring and numerical simulations showed that the NPR excavation compensation support scheme effectively improves the stress state of the bolts and reduces the deformation of the surrounding rock. Compared to the original support scheme, the final deformation of the surrounding rock was reduced by approximately 70%. These results significantly contribute to domestic and foreign research on phosphate-rock NPR compensation support technology, theoretical systems, and engineering practices, and further promote technological innovation in the phosphate rock mining industry.

Contribution of Individual Support Components to Roof Stability in a Longwall Gateroad

Contribution of Individual Support Components to Roof Stability in a Longwall Gateroad

Experiment Study on the Mechanical Behavior and Acoustic Emission Response of Thick and Hard Sandstone Roof in Xinjiang Mining Area

One of the primary threats to coal mine safety production is the sudden extensive fracturing and collapse of thick and hard roof strata. A range of uniaxial compression experiments with acoustic emission (AE) monitoring was performed for studying the mechanical properties and crack evolution of thick and hard roof sandstone specimens. AE temporal response analysis revealed that the damage process of thick and hard roof sandstone specimens exhibited distinct stages. Additionally, AE event localization indicated that microcracks within the thick and hard roof sandstone specimens propagated from the ends to the middle of the specimens during the loading process, eventually leading to severe failure. The b-value analysis demonstrated that during the early loading stage, the scale of internal microcracks within the thick and hard roof sandstone specimens gradually decreased with the optimization of the load-bearing structure. In the later loading stage, the scale of microcracks increased with the deterioration of the load-bearing structure. Furthermore, RA–AF analysis revealed that the specimens experienced combined tensile–shear failure, primarily dominated by tensile failure throughout. The AE characteristics observed during the deformation of thick and hard sandstone can provide references for the monitoring of roof stability and early warning of potential disasters in thick and hard sandstone conditions.

Roof movement and instability fracture characteristics in shallow-buried thin coal seam conventional mining faces

The variation in the width of the mining face significantly affects the stability of the face, leading to potential roof fracturing and collapse. Additionally, strong mining pressure can manifest, severely impeding the safe production of coal mines. This study uses the No. 16705 conventional working face of Jinda Coal Mine as its engineering background to investigate the characteristics of roof strata movement and instability under conditions of variable-width mining in shallow-buried thin coal seams. First, the dynamic load of the roof strata is estimated based on the key strata theory. Next, a mechanical model of the immediate roof strata movement in the working face is established based on the theory of elastic thin plates, which has been used to reveal the impact of different dimensions of the overhanging plate structure and residual overhanging structures in the corner on roof movement and its associated fracture mechanics. The findings indicated that the maximum bending deformation, deformation moment, and bending stress all have an exponential function relationship with the roof width. Similarly, these metrics have an exponential function relationship with the overhanging span of the roof. In addition, these parameters all have a linear functional relationship with the size of the residual overhanging structures in the corner. Finally, the effect of roof instability on overlying pressure is analyzed, and both the initial fracture step length and cyclic movement fracture step length of the roof are estimated. These insights offer valuable scientific guidance and a theoretical foundation for analyzing the adaptability of load-bearing pillars pressure in thin coal seam mining faces, bearing significant relevance to safety production.

On the dynamic stability of tunnel roof in nonuniform rock/soils characterized by nonlinear Mohr envelope

This study proposes a pseudo-static procedure for investigating roof stability of deep-buried tunnels in non-uniform rock/soil surrounds, on the basis of a generalized nonlinear Mohr envelope and upper bound theorem. Non-uniformity of rock/soil surrounds is discretized to certain layers characterized by differing rock/soil properties. An effective collapse mechanism is constructed, satisfying an associated flow rule and the generalized Mohr envelope. After having computed the internal and external rates of work, the upper bound formulations including collapse profile, collapse height and width are derived based on work rate balance equation. FE modelling is simulated to verify the analytical solutions with and without considerations of vertical dynamic forces. Effects of corresponding parameters representing rock/soil properties and external forces are investigated to demonstrate the implication on tunnel roof stability, aiding to provide reference for design and engineering practice.

Study and application of deeply optimized neural network in roof stability evaluation

Study and application of deeply optimized neural network in roof stability evaluation

Influence on the roof stability of EMU induced by welding deformation

The EMU roof with a thin plate structure is prone to buckling deformation during welding, which will affect its stability. Due to the complex structure, large size, and many types of welded joints, it is an urgent problem to solve the influence of different joint shapes on welding deformation and buckling stability in one model. Based on the inherent strain-temperature loading method, the inherent strain data of four kinds of local joint butt, lap, fillet, and plug welding were accurately obtained through joint welding deformation verification. Then the welding deformation simulation and buckling stability analysis were conducted. The results indicate that plug welding will have minimal impact on roof deformation. The roof buckling deformation cannot occur under the original and 1.2 times heat input conditions are selected within the range of the actual given heat source parameters. Under the 1.5 times heat input condition, the roof buckling deformation occurs. The results provide technical support for the selection of the welding process and the roof stability study of the EMU.

Key Bearing Structure Instability Mechanism: A Case Study in Mining Under Close‐Distance Coal Pillar

This study is aimed at solving the issue of mining under the boundary coal pillar of the close‐distance coal seam that causes roof falling. This study established a new key bearing structure model for analyzing the structural instability mechanism when mining under the coal pillar at the working face by taking Shaping Coal Mine as an example. The purpose of this study is to analyze the formation process, load transfer mechanism, and two failure types of the key bearing structure using theoretical analysis and numerical simulation. Additionally, this study discussed the timing and method of roof control for different key bearing structure failure types. Research shows that the instability of the key bearing structure composed of the coal pillar, interlayer rock, and lower coal body is the important reason behind the roof falling. The instability types of key bearing structures include the coal pillar instability type and the cantilever beam instability type. The stability width of the interlayer rock cantilever beam and the coal pillar jointly ascertain the failure type of the key bearing structure. In the 9204 working face, the key bearing structure was destroyed when the coal pillar was 14 m wide, resulting in the roof stress being as high as 31.81 MPa. The stress drop phenomenon can be used as a boundary to divide the failure process of the key bearing structure into three stages. The pressure relief of the coal pillar and interlayer rock cantilever beam is an effective way to deal with this problem, and the coal pillar instability type needs to be pressure relieved earlier than the cantilever beam instability type. The research findings offer new insights into the roof stability control of mining under the coal pillar.