Roof Stability Research Articles

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.

Study on Active Support Parameters for Surrounding Rock with Ultra-Large Span Open-Off Cut in Thick Coal Seam

In order to effectively control the stability of surrounding rock in ultra-large span open-off cuts by employing the techniques of support strength theory calculations and analogical application methods, two sets of rational support schemes were proposed, and the optimal design of active support parameters in thick coal seams with ultra-large span open-off cuts was explored by using theoretical analysis, numerical simulation, and field experiments. The results demonstrated that the span is one of the key factors influencing the stability of the roadway roof, exhibiting an inverse quadratic relationship with the peak stress borne by the roadway roof. By utilizing the pre-stressing force of anchor cables and support strength formulas, two sets of active support schemes for controlling the surrounding rock in thick coal seams with ultra-large span open-off cuts were established, and an optimized support scheme was obtained through numerical simulation. These findings provide references and guidance for related mining engineering under actual conditions in mines.

Optimum design parameters for a venturi-shaped roof to maximize the performance of building-integrated wind turbines

Venturi-shaped roofs provide advantageous wind conditions for efficiently operating building-integrated wind turbines without losing usable floor area. Despite these advantages, venturi-shaped roofs have been sparsely adopted for buildings due to the lack of understanding of their optimum designs to maximize the performance of building-integrated wind turbines. For the first time in literature, this study investigated four design parameters: support structure, corner modification, tunnel shape, and wind turbine arrangement to estimate the optimum venturi-shaped roof design by conducting Computational Fluid Dynamics (CFD) simulations. The results revealed the advantages of shorter support structures with convex and concave shapes at upwind and downwind ends, creating high wind speeds with low turbulence intensities. Corner modifications to the tunnel's entrance and exit are vital to suppress flow separation at the tunnel's entrance and uniform distributions of wind speed and pressure. This study recommends aerodynamic tunnel shapes that follow a non-uniform rational B-spline (NURBS) to accelerate wind without increasing turbulence intensities. The optimum design parameters performed better in normal and oblique wind directions, confirming their universal applicability. This study proposes integrating all optimum design parameters into a venturi-shaped roof design to alleviate the adverse effects of support structures, which are essential for a stable roof design.

Feasibility analysis on the utilization of TWH-caverns with sediment space for gas storage: A case study of Sanshui salt mine

Underground salt cavern (USC) has emerged as an optimal location for large-scale energy storage, encompassing oil, gas, hydrogen, carbon dioxide, and compressed air energy storage (CAES), owing to its inherent advantages of substantial capacity, stability, and hermeticity. However, most salt mines in China are characterized by a relatively thin salt layer thickness, a large number of interlayers and low salt layers grade. Consequently, a substantial proportion of the cavernous space resulting from water solution mining becomes progressively covered by insoluble sediment. Herein, the feasibility of gas storage in two butted-well horizontal (TWH) caverns with sediments, located within the Sanshui salt mine in Guangdong Province, China, is comprehensively analyzed through engineering investigation, physical model experimentation, numerical simulation, and theoretical analysis. Firstly, a theoretical model was developed to calculate the volume of caverns based on salt grade (soluble content). Secondly, a joint physical model experiment and numerical simulation were conducted to obtain the most probable shape of the process for forming water-soluble caverns. Moreover, a novel technology was proposed to utilize sediment space for gas storage in TWH-caverns. Ultimately, the support pressure of surrounding rock was determined by using the passive earth pressure theory, and subsequently, an assessment of cavern stability was conducted. Here, the numerical simulation results demonstrated that in the absence of sediment space utilization, there was a limited capacity for gas storage, resulting in significant deformation of the surrounding rock and an increased level of roof instability. On the contrary, sediment can provide structural support to the surrounding rock, thus increasing its stability (the plastic zone expansion was reduced from 1600 % (0.3 σz), 1345 % (0.35 σz) and 1297 % (0.4 σz) to 109 %, 87 % and 78 %, respectively) and enhancing the capacity for gas storage. Accordingly, this study provides valuable guidance for the assessment of gas storage in low-grade salt sedimentary environments, as well as for the design of gas injection and brine discharge, and stability evaluations.

Roof Stability of Underground Limestone Mining with Stratified Joints during Excavation Process

Roof Stability of Underground Limestone Mining with Stratified Joints during Excavation Process

Roof stability analysis of cylindrical tunnels in hard soil/soft rock with reduced tension strength

Three-dimensional roof stability analyses of cylindrical tunnel segments limited along the tunnel direction were performed based on the modified Mohr–Coulomb failure criterion with reduced tensile strength. A wedge-shaped region of the classical Mohr–Coulomb envelope, where unrealistic tensile and shear strengths are predicted, is truncated by a Mohr circle associated with the true tensile strength. This revised failure criterion with partial nonlinearity allows geomaterials deep into the roof to deform with large velocity gradients under the normality plastic flow rule, observed in field investigations. Using the kinematic approach of limit analysis, rigorous bounds for three quantitative stability measures–stability number, factor of safety, and supporting pressure–were calculated. The roof failure mechanism adopted is relatively elaborate, involving three-dimensional geometry intersecting with a cylindrical tunnel segment; thus, an efficient approach was presented for tunnels with long length constraints. With respect to extremely short tunnel lengths, a modified roof failure mechanism with distinct ridges was proposed. The factor of safety with accommodation of the nonlinear pressure dependency was estimated by a consistent procedure associated with a reduced elliptic failure criterion. The results show that roof stability distinctly depends on the magnitude of the true tensile strength, internal friction angle, and length constraint.