Roof Collapse Research Articles

Study on Arching Mechanism of Bridge Pile Foundation: Taking the Shiyangtai No.1 Bridge as an Example

The structure of a bridge has certain peculiarities, and its pile foundations are susceptible to uplift or settlement deformation due to various factors. This can result in bridge deck cracking, structural instability, tilting, and even irreversible damage, which significantly impacts the bridge’s stability and driving safety. This study focuses on the Shiyangtai No.1 Bridge and aims to investigate the factors that cause abnormal rise and fall deformations of bridge pile foundations. The study combines macro and micro analysis, physical characteristic testing of the overlying soil under the bridge pile foundation, and numerical simulation of the bridge pile foundation in the goaf. The study discusses in-depth the formation mechanism of the abnormal uplift of some pile foundations of the Shiyangtai No.1 Bridge based on the analysis of the factors influencing the abnormal rise and fall deformation of the bridge pile foundations at home and abroad. The expansive soil beneath the pile foundation is weak, and the force generated by the water expansion is insufficient to cause the pile foundation to rise to 309 mm. The results indicate that the pile foundation of the bridge is not affected by the expansion characteristics of the overlying soil. The collapse of the goaf roof generates double lateral thrust from the accumulation body at the bottom of the goaf and the upper collapse arch. This causes staggered bending uplift of the sandstone soil layer, resulting in upward squeezing pressure that causes the bridge pile foundation to rise. Therefore, the coal mining area is the main factor influencing the abnormal uplift of the pile foundation of the Shiyangtai No.1 Bridge.

Damage degradation law of mechanical properties of sandstone under different water-rich states

Safety is the primary guarantee for achieving coal mine production. The degree of water in the overlying rock of the coal seam has a significant impact on the mechanical strength of the rock, which can lead to subsidence, roof collapse, and rock burst in the mining area. Therefore, it is important to study the law of water-rich damage and deterioration of coal seam overlying rock, as well as the characteristics of bursting liability to prevent and control mining disasters. This paper aims to investigate the change in compressive strength, elastic modulus, and bursting liability of coal measure strata under different water content and their relationship with lithology, particle size, pore characteristics, and mineral characteristics. We carried out uniaxial compression tests on drilled and prepared samples of coal measure strata in the east of Ordos City. We also monitored the acoustic emission characteristics of the rock failure process under different water content. The results demonstrate that, in the dry state, the compressive strength of siltstone >fine sandstone >medium sandstone >coarse sandstone. As the water content increases, the rock transitions from brittle to plastic, and the compressive strength, elastic modulus, and bursting liability gradually decrease. The stress-strain curve changes from a single peak to bimodal and multimodal, and the active degree of acoustic emission events decreases, especially the low-value ringing count. Calcareous cementation, clay minerals, and chlorite exhibit strong softening properties when subjected to water, while the grain skeleton (comprising quartz, feldspar, mica) and siliceous cementation displays weak softening properties in such conditions. The most significant is the mechanical strength deterioration of siltstone containing a clay matrix. The research findings can provide reference and theoretical support for safe mining practices in coal mines.

Failure mechanism and strengthening countermeasures of end-anchored cable free section under combined tension and shear

As an effective and economical reinforcement method, end anchorage cables are widely used for roadway support in coal mines. The failure of the free section of the end-anchored cable (FSEC) under the combined action of tension and shear is a key factor inducing roof collapse accidents in coal mine roadways. Based on cable bolt tensile and shear test results, this paper aims to reveal the failure mechanism of the FSEC under tension and shear by establishing a mechanical model of the interaction between the cable bolt and jointed rock mass. The results show that the axial and shear force coupling in the FSEC increases because of the joint plane shear action. The FSEC is subject to tensile–shear failure when the axial and shear forces meet the tensile–shear composite yield condition at the inflection point of the sheared cable bolt. The steel strands of the cable bolt experience and transmit shear force through the contact point, resulting in an uneven distribution of shear stress in the cable bolt cross-section, directly causing the FSEC’s local failure. Strengthening countermeasures are proposed using a high-strength slotted steel pipe to protect the cable bolt under shear, and a strengthening device has also been designed. Experimental results obtained in the laboratory have revealed that the strengthening device does not only effectively enhance the cable bolt’s shear capacity by increasing its shear strength and changing the shear transfer mode, but also significantly improves the cable bolt’s comprehensive performance. This study elucidated the failure mechanism of the FSEC and provides a practical and convenient method for increasing the shear strength of an end-anchorage cable system and enhancing roadway stability.

Ensemble learning model on Artificial Neural Network - Backpropagation (ANN-BP) architecture for coal pillar stability classification

Pillars are important structural units used to ensure mining safety in underground hard rock mines. Unstable pillars can significantly increase worker safety hazards and sudden roof collapse. Therefore, precise predictions regarding the stability of underground pillars are required. One common index that is often used to assess pillar stability is the Safety Factor (SF). Unfortunately, such crisp boundaries in pillar stability assessment using SF are unreliable. This paper presents a novel application of Artificial Neural Network-Backpropagation (ANN-BP) and Deep Ensemble Learning for pillar stability classification. There are three types of ANN-BP used for the classification of pillar stability distinguished by their activation functions: ANN-BP ReLU, ANN-BP ELU, and ANN-BP GELU. These three activation functions were chosen because they can solve the vanishing gradient problem in ANN-BP. In addition, a Deep Ensemble Learning process was carried out on these three types of ANN-BP to reduce the prediction variance and improve the classification results. This study also presents two labeling alternatives for pillar stability by considering its suitability with the SF. Thus, pillar stability is expanded into four categories: failed with a suitable safety factor, intact with a suitable safety factor, failed without a suitable safety factor, and intact without a suitable safety factor. There are five features used for each model: pillar width, mining height, bord width, depth to floor, and ratio. In constructing the model, the initial dataset is divided into training data, validation data, and testing data. In this case, four type of proportions are used. For training-testing division the proportions are: 80 % : 20 %, 70 % : 30 %, for training-validation-testing division the proportions are: 80 % : 10 % : 10 %, 70 % : 15 % : 15 %. Average accuracy, F1-score, and F2-score from 10 trials were used as performance indicators for each model. The results showed that the ANN-BP model with Ensemble Learning could improve ANN-BP performance with an average accuracy 86.48 % and an F2-score 96.35 % for the category of failed with a suitable safety factor.

Fire Resistance Performances of Composite Roofs According to Application and Non-Application of Purlin

This study evaluates the risks of roof collapse for three types of roofs designed for 1-h fire resistance performance: a roof system with a purlin, a roof system without a purlin, and a unit roofing system without a purlin. The roof system with the purlin and the unit roofing system satisfied 1-h fire resistance performance, however, the roof system without the purlin did not. It was determined that the roof systems with and without purlin were at risk of casualties owing to the rapid increases in deformations after 30 min in the fire experimental test. The maximum deformation of the unit roofing system was larger than that of the other systems. However, because the deformation over time showed a linear behavior, the risk of collapse owing to the rapid increase in deformation was considered to be the lowest.

Design of Integrated Electrical Installations with Solar Panel in Muhammadiyah Ibtidaiyah Madrasah Building in Jurangono, Gemantar Village, Mondokan-Sragen

The Muhammadiyah Mondokan Branch Manager has a business charity in the field of education at the Elementary School level or often known as MI Muhammadiyah (MIM). MIM Gemantar was founded in 1978 with a basic education level. In carrying out its activities, MIM Gemantar is under the auspices of the Ministry of Religion. Accredited B on November 9, 2017. MIM Gemantar has the most apprehensive building conditions compared to the other four MIMs in Mondokan. On Monday, according to the news from Jateng, inews.id, it was reported that the roof of MI Muhammadiyah Gemantar had collapsed, resulting in the head of the school office and 2 students being injured. The incident of the collapse of the classroom roof occurred during teaching and learning activities or KBM taking place on Monday, January 9 2023 around 08.15 WIB. For the past four months, students from three classes have been assigned to one room. The room whose roof collapsed was used by three classes due to the small number of students, namely grades II, IV and VI. The purpose of this research is to design an integrated electrical installation with solar panels in the MIM Gemantar building which will be renovated. This has several benefits, including as a form of utilizing renewable energy and also as a learning medium for 4th year students with the theme of renewable energy. The method of this activity is for the team to obtain a floor plan of the building to be built, then carry out a design which is as simple as the implementation process, it is easy to update capacity, draw a single line and plan a budget. Currently the MIM Gemantar Mondokan Sragen building has finished building 4 classrooms, so it still requires the construction of 2 more classrooms. The source of electricity for the electrical installation of the 4 classroom buildings all use electrical energy from PLN. In the future, if funds are available and the manager wants the installation of solar panels, then only add according to the design results of a single line electrical installation that is integrated with solar panels on-grid (can be done in stages of 200 Wp, 400 Wp, even up to 1,000 Wp). The capacity of solar panels does not have to match the planned capacity, meaning that this capacity can be carried out in stages according to the conditions of the funds provided.

Research on the impact and control techniques of gangue rib in hard roof

Blocking gangue support is a key link in gob-side entry retaining by roof cutting and pressure release (GERRC), and its stability is related to the success or failure of the retained roadways. Due to the severe dynamic pressure and high hardness of the gangue during hard roof collapse, serious bending and toppling instability of the section steel can easily occur. Since potential safety hazards exist in gangue ribs, the 1105 panel of the Qiuji Coal Mine is used as the engineering background, a mechanical model of gangue impact is constructed based on four forms of gangue motions, and the failure of a blocking gangue support structure under hard roof conditions is explored with ABAQUS software. The results indicate the following: (1) Section steel experiences transient bending by gangue impact, and will further bending failure or toppling instability occurs under roadway roof subsidence and gangue compression. (2) This impact causes the steel bar mesh to generate a significant transient lateral force, which couples with gangue compression, resulting in instability and slip of the section steel. To this end, three optimized components have been proposed, sliding yield I-steel, reinforced bolts and link components, and the optimal parameters are obtained. The results of the numerical simulation and field tests suggest that the new blocking gangue support structure has a good support effect, and the field deformation of the gangue rib is reduced by 86%. No failure of I-steel occurs with the new blocking gangue support structure. This study can provide a reference for the control of gangue ribs in GERRC under similar geological conditions.

Structural stability of lunar lava tubes with consideration of variable cross-section geometry

This paper provides detailed numerical analyses of lunar lava tubes stability, where for the first time variability in cross-section geometries is considered. A novel approach included a dedicated procedure for extracting characteristics needed for random geometry generation together with the demonstration of its usage. Stability analyses were performed with finite element limit analysis (FELA) which is found to be very effective for analyzing tens of thousands of realizations. The FELA method provides collapse geometries that were examined to constrain the relations between the collapse size extent and width of the lava tube. New findings on types and sizes of lunar lava tube roof collapses were obtained, and they are the first step toward making stability analysis more realistic for future human and robotic exploration of lunar lava tubes. The results allow us to constrain the approximate widths of the lunar tube beneath skylights to be 300 m, as observed for the assumed rock parameters. In addition, the probabilistically based analyses allow to show that thin roofs (< 10 m) are very unlikely to be stable for the tubes of a few hundred meters in width under lunar conditions, and that the gravity trigger failures are more probable on the Moon when considering variations in lava tube geometry than for the previously considered cases of elliptical and circular shapes.

Machine learning approach for the prediction of mining-induced stress in underground mines to mitigate ground control disasters and accidents

The bord and pillar method is commonly employed in Indian underground coal mines, and the extraction rate varies between 30 and 65%. During pillar extraction, pillars are subjected to severe stress conditions. Due to this, the natural state of stress equilibrium is disturbed, resulting in severe strata control problems leading to sudden, unpredictable failure such as a premature collapse of pillars, severe roof or side fall, and sometimes leading to serious/fatal injury or burial of machinery. This paper deals with the prediction of mining-induced stress during pillar extraction using Machine Learning (ML) techniques like Random Forest and Multilayer Perceptron. The various factors used for the formulation of the models for predicting the mining-induced stresses are Depth of the workings (H), Panel width/length (W/L), Pillar width/working height (w/h), Goaf length, and Area of extraction. This paper highlights the importance of operational parameters rather than geological parameters. The Correlation coefficient (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}$$\\end{document}) of mining-induced stresses for the case studies discussed in the paper is 0.85 for Random Forest and 0.76 for Multilayer Perceptron, which shows Random Forest results have a comparative edge over Multilayer perceptron. With this developed prediction models, the stress conditions of pillars can be predicted.Graphic abstract

Back analysis of a building collapse under snow and rain loads in a Mediterranean area

Abstract. At the end of February 2018 the Mediterranean area of Montpellier in France was struck by a significant snowfall that turned into an intense rain event caused by an exceptional atmospheric situation. This rain-on-snow event produced pronounced damage to many buildings of different types. In this study, we report a detailed back analysis of the roof collapse of a large building, namely Irstea Cévennes. Attention is paid to the dynamics of the climatic event, on the one hand, and the mechanical response of the metal roof structure to different snow and rain loads, on the other hand. The former aspect relies on multiple sources of information that provide reliable estimates of snow heights in the area before the rain came into play and substantially modified the load on the roof. The latter aspect relies on detailed finite-element simulations of the mechanical behavior of the roof structure in order to assess the pressure due to snow and rain loading, which could theoretically lead to failure. By combining the two approaches, it is possible to reconstruct the most probable scenario for the roof failure before its full collapse. As an example of building behavior and vulnerability to an atypical rain-on-snow event in the Mediterranean area of France, this detailed case study provides useful key points to be considered in the future for a better mitigation of such events in non-mountainous areas.

Factors influencing the evolution of sandstone sea caves: A case study from the Apostle Islands National Lakeshore (Lake Superior, USA)

Caves in coastal cliffs in the Apostle Islands were analyzed for factors controlling their origin and evolution. Even though the Bayfield Group quartz sandstones were found to be of relatively low tensile strength, the traditional explanation attributing speleogenesis to localized zones of lithological and tectonic weakness does not adequately explain all geomorphic features of the caves. The caves were found to be formed by coalescence of smaller arcade-shaped cavities serially developed along subhorizontal discontinuities. In concordance with the previously formulated “arcade principle”, positions and shapes of the cavities are defined by areas of reduced stress within the gravity-induced stress field. Evacuation of material from the rock massif can be attributed to wave action including the effect of water-pressurized air, and frost action. Compound cavities above the discontinuities tend to form “higher-order” arcade-like cavities/caves while those beneath more resistant strata rather develop into elongated overhangs similar to ordinary coastal notches. Propagation of the largest cavities, formed along steeply dipping joints and faults, is attributed to mass wasting and roof collapses. Similar examples of discontinuity-related cavities in coastal settings, suspectedly also controlled by gravity-induced stress distribution, can be found worldwide, being mostly concentrated to areas covered by ice sheets in the Pleistocene. The interplay between post-glacial isostatic uplift and Holocene lake-level rise is responsible for the development of mature forms of coastal caves in the Apostle Islands where present cliffs are estimated to have been exposed to the effects of wave action for the last 3–5 ky.

Laboratory tests to understand tephra sliding behaviour on roofs

Following explosive eruptions, loading from tephra fall deposits can lead to roof collapse. However, the load may be reduced significantly by tephra sliding on pitched roofs. We present small-scale laboratory tests to investigate tephra sliding behaviour on metal, fibre cement sheet and tile roofing. We tested 10–30 cm thicknesses for dry and wet deposits of pumice, scoria and basaltic ash. We found that tephra did not slide on roof pitches ≤ 15° for coarse-grained deposits and ≤ 12° for dry ash. Thin deposits of wet ash were stable at pitches ≤ 30°. In addition, tephra was mainly shed on pitches ≥ 32° for metal roofs and ≥ 35° for fibre cement and tiles. Using these results, we have produced an initial set of sliding coefficients for tephra for simply pitched roofs that can be used to help prioritise roofs for clearing during an eruption and assist in designing roofs to withstand tephra fall.

A Comprehensive Review on Mining Subsidence and its Geo-environmental Impact

Over the course of several decades, subsidence has exerted a notable impact on the mining sector. The preponderance of subsidence occurrences is evident within coal mines. Remote sensing and Geographic Information Systems (GIS) have emerged as principal instruments for the evaluation and characterization of subsidence phenomena. The manifestation of mininginduced subsidence engenders concerns encompassing roof collapse, infrastructural damage, and the formidable challenge of preserving human lives. The repercussions of mining-related subsidence extend to indigenous flora and subterranean water reservoirs. This phenomenon critically impedes the sustainable advancement of mining zones, precipitates the depletion of natural reservoirs, and engenders a host of ecological and environmental predicaments that cast an adverse influence on socio-economic dynamics. Within mining contexts, subsidence manifests as both vertical and horizontal ground displacement, presenting as fissures, depressions, troughs, and sinkholes. The present article furnishes a comparative discourse on diverse methodologies harnessed for the assessment of mining-induced subsidence. The scholarly community has employed a repertoire of eight predominant techniques, as delineated in the conclusive remarks of this study. Over the bygone two decades, considerable strides have been taken, enabling the deployment of sophisticated paradigms, such as remote sensing and GIS, Light Detection and Ranging (LiDAR), and Differential Interferometric Synthetic Aperture Radar (DiNSAR), for the identification and quantification of land subsidence phenomena.

Support Optimization of Open TBM Tunneling in Luohe Formation Sandstone by CT Test and Numerical Simulation

As underground engineering extends into the western and deeper regions of China, more and more Luohe Formation sandstone layers will be encountered, which have weak cementation and high water content. It is a significant challenge to apply the open TBM, and the support system is crucial in determining whether TBM can excavate quickly and safely. Therefore, in order to optimize the support scheme, this paper analyzes the pore structure and porosity through CT scanning, the results indicate that the volume percentage of pores ≥34 μm is 2.3% and 1.5%, respectively, the large pore apertures are predominant, the surrounding rock has strong permeability, and there is a high risk of rock burst and roof collapse accidents, hence requiring reinforced support measures. On this basis, numerical simulations were conducted to evaluate the support effectiveness. The results show that replacing the “bolt + mesh” with a “bolt + cable + mesh + steel belt”, and replacing the top three bolts with 7.3 m anchor cables, can better control the deformation and provide sufficient thrust force for the TBM, ensuring excavation speed. After the implementation of this scheme at the Kekegai coal mine in Shaanxi, China, the TBM excavation speed increased by 70%, from the previous 10 m/day to 17 m/d, significantly reducing the project duration and construction costs.

Experimental investigation on stress distribution and migration of the overburden during the mining process in deep coal seam mining

Coal mining has a significant impact on the movement of the overburden, leading to potential safety hazards in the working face. In this paper, a similarity simulation experiment was conducted to investigate the migration of overburden during the mining process of a specific working face in the Liuzhuang Coal Mine located in southern China. Sand and gravel were used to simulate the geological environment of each rock stratum. The deformation of the stratum was monitored using strain gauges, the fracture and displacement changes of the overburden stratum were recorded using cameras, and the characteristics of roof collapse was monitored using infrared thermal imager. The experimental model fully simulated the situation of the working face, and the actual working face size was obtained by enlarging the model by 100 times. The experiment found that during the initial stage of mining, there was no significant subsidence of the roof. In the course of the advancement of the working face, the primary roof intermittently fractured behind the working face, with subsequent propagation of upper cracks in an upward direction. The overburden rock layer above the goaf experienced continuous compaction, leading to the gradual closure of the separation layer. Simultaneously, new cracks constantly emerged in front of the working face, resulting in the progressive stabilization of the height of the crack zone. The stress measurements at each point exhibit a pattern of initial increased, followed by decrease, and ultimately stabilization. By considering the stress variation law of the overburden rock, the stress changes in key layers of the bedrock during mining could be categorized into four zones: the stress stable zone, stress increasing zone, stress reducing zone, and compaction stable zone. During the initial phase of coal seam mining, the presence of rock layers provided support, resulting in minimal subsidence of the overburden rock. However, as the mining operation progressed, the disturbance force and collapse of the overburden rock leaded to further downward subsidence. When the working face reached the stop line, the collapsed overburden rock gradually consolidates, resulting in a deceleration of energy release and the formation of a pressure relief zone. Consequently, the overburden rock above the working face underwent a slight additional subsidence, reaching its maximum level. A short cantilever rock beam structure was formed in the experiment. This study will provide valuable reference for future coal mining and serve as a vital theoretical basis for roof control in deep coal seam mining.

Automated Stratum Interface Detection Using the Optimized Drilling Specific Energy through Self-Adaptive Logistic Function.

The precise detection of stratum interfaces holds significant importance in geological discontinuity recognition and roadway support optimization. In this study, the model for locating rock interfaces through change point detection was proposed, and a drilling test on composite strength mortar specimens was conducted. With the logistic function and the particle swarm optimization algorithm, the drilling specific energy was modulated to detect the stratum interface. The results indicate that the drilling specific energy after the modulation of the logistic function showed a good anti-interference quality under stable drilling and sensitivity under interface drilling, and its average recognition error was 2.83 mm, which was lower than the error of 6.56 mm before modulation. The particle swarm optimization algorithm facilitated the adaptive matching of drive parameters to drilling data features, yielding a substantial 50.88% decrease in the recognition error rate. This study contributes to enhancing the perception accuracy of stratum interfaces and eliminating the potential danger of roof collapse.

Investigation of Microseismic Monitoring of and Precursor Information on Roof Collapse

Understanding the characteristics and evolution of crack propagation in rock masses is crucial for evaluating their stability. By applying clustering theory to analyze recorded microseismic events, we differentiate the development positions of individual cracks amidst multiple crack formations. Three distinct crack cluster distribution patterns are identified, allowing for the evaluation of regional stability through microseismic event density and ellipsoidal model parameters. The process of crack propagation involves independent development at nucleation positions, mutual influence between adjacent locations, and subsequent crack growth and propagation. Additionally, we examine crack evolution prior to roof collapse and establish a connectivity model between surface and goaf roof cracks. When microseismic events are identified as developing along a plane, it indicates a higher risk of damage in that area. Through the analysis of crack propagation location and angle, our study provides a theoretical foundation for predicting crack direction. Notably, our model’s findings align with onsite observations, demonstrating its practical effectiveness. The results of this research offer valuable insights for collapse prediction and early warning systems for mine roofs, contributing to advancements in mining safety and operations.

Investigation on application of filling mining technology pass through abandoned roadway of reclaimed working face.

This paper aims to analyze the roof stability when the reclaimed working face passes through abandoned roadway. The mechanical model of main roof in abandoned roadway was established for the purpose of theoretical analyses. To ensure the stability of the abandoned roadway, the strength formula of backfill body was deduced. The optimum ratios among different compositions of the filling material were determined by experiment, while the viscosity, bleeding, hydration temperature and compressive strength of filling material were also studied. Test results indicated that the optimum ratio among coal ash, lime and compound activator is 80:15:5, and the ideal water cement ratio is 0.7:1. It was also found that no bleeding occurred, the rheological behavior of slurry presented shear thinning fluid and the hydration temperature of filling body was relatively stable which is mainly maintained at 40°C. The uniaxial compressive strength of filling material with 28 and 90 days curing were 3.35 and 6.62 MPa respectively. Under a confining pressure environment, the filling material presented an obviously plastic deformation. Field test showed that the filling rate was almost 100%, when working face passed through abandoned roadway, the surface of filled body was complete and no roof collapse was triggered. Therefore, a better bonding effect was proved for the filling body.

Study on Overburden Fracture and Structural Distribution Evolution Characteristics of Coal Seam Mining in Deep Large Mining Height Working Face

Coal mining has gradually entered the deep mining era, and large-height mining is an important way to mine thick coal seams in the deep. The high coal wall will inevitably make the distribution of the overburden structure in the coal mining face more complicated, and the large buried depth will also cause more intense mine pressure. The study of the distribution and evolution of the overburden structure and stress in the mining site can provide theoretical guidance for safe mining. In this work, a physical similarity modeling test was carried out based on the physical–mechanical parameters of overburden rock and similarity theory, taking the mining of a deep, large-height working face in Pingdingshan Coal Mine as an example. The results show that the deformation and breakage of overburden rock in deep, large-height workings occurring during mining is persistent and not only in a short period of time. The breakage form of overburden can be categorized into two types based on the deformation characteristics: (I) non-separation-induced type, and (II) separation-induced type. Among these, the breakage induced by separation can be divided into two categories: (i) dominated by self-weight stress, and (ii) affected by shear cracks. It also summarizes the form of the overburden structure and the structural morphology of the stope. The overburden structure shows a “combined cantilever beam structure-articulated rock-slab structure-non-articulated rock-slab structure”. Among these, the periodic breakage of the upper cantilever beam evolved articulated and non-articulated rock-slab structure in the lower part, which weakened the supporting effect of the lower gangue and further aggravated the breakage of the upper overburden rock. The shape of the main structure of the stope mainly depends on the fracture line from the advancing coal wall to the upper overburden: from a rectangular shape without collapse to a trapezoidal shape at the initial stage of collapse, to a trapezoidal shape with multiple steps after the main roof collapse.

Development of PSS-bolt with high load and large deformation capacities

As mining migrates to deep levels, engineering disasters such as excessive deformation, rockburst and massive roof collapse occur frequently. It is important to develop rockbolts that have high load and large deformation capacities, which translates into high energy-absorption capacity, for ground support. This paper presents a piston self-swelling bolt (abbreviated as PSS-bolt) that utilizes steel stretching and frictional sliding to maximize the bolt’s energy absorption capacity. The structure design and working mechanism of the PSS-bolt are introduced. The influence of rod strength, piston length and tube shape on the load–displacement curves of the PSS-bolt was investigated. Laboratory and field static pull-out tests were carried out to optimize the piston length of the PSS-bolt. The test results show that when the piston length is 1350 mm, the load varies between 180 and 210 kN, the displacement can reach 500 mm, and the energy absorption capacity is 95 kJ. In addition, the bolt can reach 71.4% and 100% of its ultimate strength 12 h and 24 h after installation, respectively. The PSS-bolt presented in this paper has high force and large deformation capacities, which can provide a large energy capacity for ground support in high stress and large deformation conditions.