Roof Fall Accidents Research Articles

Application of Research on Risk Assessment of Roadway Roof Falls Based on Combined Weight Matter Element Extension Model

Roof falls in coal mine roadways are the main causes of many casualties, shutdowns and production plan delays. To understand the relationship between the influencing factors of roadway roof fall accidents and the importance ranking of the accidents, we will reduce safety accidents in coal mines. To enable the timely prediction and control of roadway roof fall risks, based on the investigation of many roadway roof fall risk factors, 12 evaluation indexes such as the roadway roof rock thickness, geological conditions and roadway section shape were selected. An evaluation index system of roadway roof fall risks is constructed. A risk degree standard of roadway roof falls is proposed. The risk evaluation model of roadway roof falls was established by using the combination weight of the analytic hierarchy process (AHP), entropy weight method (EW) and matter element extension theory. According to the principle of the maximum membership degree, the risk degree of roadway roof falls is determined. Based on Java Web, a risk assessment system for roadway roof falls was developed. We name the system Multiple Weight-Material Element Web (MW-MEW). The MW-MEW system was used to evaluate the risk degree of roof falls in the C9 return airway of the Xingu Coal Mine. Compared with the evaluation results of the AHP matter element extension model, it is found that the evaluation results of the MW-MEW system are more in line with the actual engineering conditions. The successful application of the MW-MEW system will provide new avenues for the quantitative evaluation of roof fall risks in coal mine roadways.

Ontology-Based Semantic Modeling of Coal Mine Roof Caving Accidents

The frequency of roof-caving accidents ranks first among all coal mine accidents. However, the scattered knowledge system in this field and the lack of standardization exacerbate the difficulty of analyzing roof fall accidents. This study proposes an ontology-based semantic modeling method for roof fall accidents to share and reuse roof fall knowledge for intelligent decision-making. The crucial concepts of roof fall accidents and the correlations between concepts are summarized by analyzing the roof fall knowledge, providing a standard framework to represent the prior knowledge in this field. Besides, the ontology modeling tool Protégé is used to construct the ontology. As for ontology-based deep information mining and semantic reasoning, semantic rules based on expert experience and data fusion technology are proposed to evaluate mines’ potential risks comprehensively. In addition, the roof-falling rules are formalized based on the Jena syntax to make the ontology uniformly expressed in the computer. The Jena reasoning engine is utilized to mine potential tacit knowledge and preventive measures or solutions. The proposed method is demonstrated using roof fall cases, which confirms its validity and practicability. Results indicate that this method can realize the storage, management, and sharing of roof fall accident knowledge. Furthermore, it can provide accurate and comprehensive experience knowledge for the roof fall knowledge requester.

Rapid determination of fuzzy number in FAHP and assessment risk in coal mine roof fall

This study proposed a rapid approach to determine the fuzzy number to evaluate roof fall risk in the coal mine. In risk assessments by fuzzy theory, the determination of fuzzy numbers using triangular fuzzy numbers (TFN) incorporated into the analytic hierarchy process is a difficult and time-consuming task. A novel approach to determine fuzzy number in TFN was proposed. To reduce occurrence of roof fall accidents, it is necessary to identify the main risk factors in roof fall risk assessments. A nine-score table-type questionnaire was adopted to collected expert judgement, based on which language scales were determined, ranging from 0.1 to 0.9, with increments of 0.1. Each language scale corresponded to the selected value of the experts. Subsequently, a triangular fuzzy complementary judgement matrix and a consistent possibility judgement matrix were constructed. The effectiveness of this proposed method was verified via analysing a case of roof collapse at Chaidar coal mine, Qinghai Province, China. The final ranking results of the risk factors were consistent with those observed in the field.

Mechanical Characteristics Analysis and Structural Optimization of Key Component of Self-Moving Temporary Support

In order to prevent a roof fall accident of a coal mine roadway mining face, temporary support must be provided before the permanent support of the roadway. At present, the commonly used forepoling bar support has poor reliability and low efficiency, and other machine-mounted or self-moving temporary supports are also difficult to use widely due to the complex geological conditions and limited working space at the heading face. On the basis of the mechanical characteristics analysis and numerical simulation of the wall rock support system, we propose a temporary support scheme that can adapt to the uneven roof of the roadway and the complex geological conditions on site, and that can ensure the cooperative operation of multiple equipment on site. A self-moving temporary support (SmTS) is designed, and its mechanical characteristics are analyzed to meet the mechanical requirements of the wall rock support system on the mining face. The multiobjective optimization of the main beam structure based on response surface methodology (RSM) is carried out to eliminate the design redundancy on the premise of meeting the support requirements of the main beam. Our research provides a novel method and corresponding equipment for the temporary support of a mining face. Applications of the proposed approach in the 7900 mining area of a mine proves the effectiveness of the method and equipment.

Multi-hazard risk characterization and collaborative control oriented to space in non-coal underground mines

In order to realize accurate risk assessment and collaborative control of multi-hazard risk in non-coal underground mines, a space-oriented risk characterization and collaborative control model of multi-hazard risk in non-coal underground mines is proposed. Statistical analysis of non-coal underground mine accidents from 2000 to 2022, revealing the characteristics of non-coal underground mine accidents and 5 risk types were identified, including cage fall accident, powered haulage accident, fire accident, mine water inrush accident, and roof fall and rib spalling accident. A multi-hazard risk analysis and assessment framework for non-coal underground mines based on the inherent risk of the system, the vulnerability of the disaster-bearing body and the adaptability of the disaster-bearing area is proposed. The multi-hazard inherent risks in non-coal underground mines are comprehensively identified and evaluated in five aspects, including hazardous equipment and facilities, hazardous materials, hazardous processes, hazardous operations and hazardous places, and the characterization and unified measurement of multi-hazard risk is realized by combining the vulnerability index of disaster-bearing body and the adaptability index of disaster-bearing area. Regional multi-hazard risk aggregation is achieved through the Nemerow pollution index and space-oriented multi-hazard risk is obtained. Constructed a multi-hazard safety risk collaborative control system of source identification, classification and control, process control, continuous improvement, and full participation. Finally, the validity and rationality of the risk characterization model and the risk collaborative control system are verified. The research can both support the formulation of macro policies for non-coal underground mines and provide guidance for the specific spatial layout.

Safe and Efficient Recovery Technique of Horizontal Isolated Pillar under Loose Tailings Backfill; A Case Study in a Zinc-Lead Mine

The presence of loose medium backfill above the horizontal pillar will technically hinder the efficient recovery of the pillar since the improper design and preserved roof protection layer height will potentially lead to casualties and equipment damage caused by large area collapse of filled tailings as well as roof fall accidents. In this study, a safe and efficient technique for the recovery of isolated pillars under loose tailings backfill was carried out via field investigation, theoretical analysis, numerical simulation, and analytic hierarchy process using the isolated pillars in the 855 middle sublevel of Hongling Zinc-Lead Mine, Chifeng, Inner Mongolia, as a practical engineering background. Current studies have revealed that the optimal scheme for an isolated horizontal pillar recovered via the cut-and-fill stoping of a drift vertical to ore body strike involves preserving a 1.0-m roof protection layer above the crown pillar combined with a spaced mining extraction sequence. This design minimizes ore dilution and losses during the pillar extraction process under safe operation. Our research results provide theoretical and technical support for the safe and efficient recovery of isolated pillars under loose tailings backfill in similar mines.

Analysis on Influence Factors of Roadway Instability in High-Stress, Steeply Inclined Extra-Thick Coal Seam

In order to solve the problem of roadway support safety in coal mining under high stress conditions and to improve safe and efficient production in coal mines, the control countermeasures of the surrounding rock stability and the optimization scheme of support are put forward and the model and numerical simulation of roadway bolt support system are established. Based on bolt support theory and instability mechanism of the coal rock dynamic system, this paper puts forward the evaluation of support effect and the optimization parameters of bolt support, and the scheme of mine pressure monitoring and the corresponding support optimization system are established. The roof fall accident and the bolt and cable of support have been broken in the Wudong coal mine, the phenomenon of bolt pulling out in the roadway. The causes of roof fall are analyzed and the solutions are put forth, judging the influence of different factors on roadway support. In view of the roof fall accident in the North Lane of the east wing of the +575 level 43 #coal seam in the north mining area of the Wudong coal mine, the cause analysis and support suggestions are made. And, according to the performance of the bolting material and anchoring agent, the laboratory theoretical research was carried out. Through the experiment, it is concluded that the FRP bolt with a diameter not less than 27 mm is the first choice for the side support of the working face in the mining roadway, then ribbed steel bolt with a diameter not less than 20 mm for the nonworking face, and the length of the anchor rod not less than the range of the loose circle. Therefore, full-length anchoring should be carried out in roadway support, the anchorage length of the anchor cable should be increased, and the integrity of the roof should be improved, so as to reduce the amount of roadway roof separation and improve the support effect.

Study on the Stage Failure Mechanism and Stability Control of Surrounding Rock of Repeated Mining Roadway

China is one of the leading countries in the mining and utilization of coal resources, and the problems of coal-mining technology and safety have been concerned by the world, while the serious deformation and destruction of surrounding rock and the difficulty of support have brought inconvenience to the mining of coal resources due to repeated mining. This paper takes the actual engineering 22205 mining roadway in Buertai mine as the research background, through the combination of numerical simulation and field measurement. In this paper, the stress environment, plastic zone, and surrounding rock deformation in the advancing process of coal-mining face are studied, and the stress evolution law of surrounding rock in repeated mining roadway is obtained. It is clarified that the surrounding rock deformation is the failure mechanism under the combined action of principal stress difference and stress direction deflection. As a result, the surrounding rock of the roadway is asymmetrically deformed and destroyed, and the corresponding surrounding rock control scheme is put forward. The results show that the influence of repeated mining on roadway stress environment can be divided into four stages with the mining process: the stability stage of mining influence, the expansion stage of primary mining, the stable stage after primary mining, and the expansion stage of second mining. At the same time, the shape changes of the plastic zone and the displacement monitoring results of the monitoring are analyzed, and the results are obtained; the stage of stress change is suitable, and combined with the failure characteristics of surrounding rock in each stage, it is put forward that reinforcement measures should be taken in the stable stage after mining; the specific reinforcement scheme is determined according to the expansion form of plastic zone and field measurement. The on-site monitoring shows that there is no roof fall accident during the use of the roadway, which ensures the safety in production.

Safety Pre-Control of Stope Roof Fall Accidents Using Combined Event Tree and Fuzzy Numbers in China’s Underground Noncoal Mines

Among the accidents in China’s underground noncoal mines including ferrous metal mines, nonferrous metal mines and nonmetallic mines, roof fall accidents are always extremely bad. The application of risk assessment to avoid roof fall accidents in coal mines is widespread. However, the traditional method has defects in its accuracy, cost, and simplicity. It cannot fundamentally ensure that workers survive a roof fall accident. Therefore, there is no great referential significance for noncoal mines. In this paper, supposing that roof fall accidents in underground noncoal mines are inevitable, we assess where we should start to take measures to prevent worker deaths. On the basis of a detailed investigation, units including those working far from the roof, noticing the signs, etc. were identified, and then a concise event tree model was built. Under this framework, the event tree model has 2 consequences, including being alive and death, and 13 scenarios related to accident occurrence. In this research, the probability of unit events was evaluated by using triangular fuzzy numbers. In addition, we found 3 scenarios with death, and then we calculated their respective probabilities. Finally, regarding the death scenario with the highest risk value, the paper recommends that priority measures should be taken to prevent deaths in roof fall accidents. The method in this paper provides a theoretical basis for pre-control measures and it is efficient, inexpensive, and simplified. Even if a roof fall accident is inevitable, we know where to start to take pre-control measures to prevent worker deaths.

Disaster-inducing mechanism in a roadway roof near the driving face and its safety-control criteria

Roof-fall accidents, happening near the driving faces of coal roadways, threaten the safety of construction operatives. Taking Jining No. 3 Coal Mine of Yanzhou Coal Mining Group Corp. (Jining City, Shandong Province, China) as the research object, we analysed the roof structure near the driving face of a coal roadway. Meanwhile, the disaster-inducing mechanism was studied through mechanical analysis and numerical simulation. The results demonstrated that the artificial support structure and C-shaped bracing structure co-determine the safety of the roof. With the length of unsupported roof (LUR) increasing, the control effects of the two structures experienced three stages of behaviour (i.e. a superimposed support stage, collaborative support stage, and independent support stage) on the roof. In these, coal at the top corners became looser and the roof span increased. As a result, the safety of the unsupported roof deteriorated, with the rear part being the first to become damaged, thus triggering a roof-fall accident. Based on the above conclusion, the research proposed safety-control criteria for an unsupported roof, and thus provides a critical basis for assessing support strength and ensuring the safety of tunneling construction operations.

Influences of Water Vapor on Roof Fall Accidents in Selected Underground Coal Mines in Malawi

To develop affordable countermeasures against the roof falls, the accident records of Mchenga Mine were investigated as the first step. Based on the accident records, it was found that roof falls occurred most in April and May. Humidity measurements were taken both in the underground mine and at surface, and humidity peak appeared in April. The accident occurrence and the underground humidity had a positive correlation in which no roof falls could be expected under a humidity of less than a certain value. Effect of humidity on the indirect tensile strength of the rock samples collected from the mine was investigated, and it showed that the indirect tensile strength decreased with humidity. The diffusion coefficient was measured for the rock samples collected from Mchenga Mine as well as from Kaziwiziwi Mine, and the migration of water vapor into rock mass in the roof was calculated for Mchenga case. It was clarified that the weakening of tensile strength was transmitted upward at several centimeters per day from the immediate roof. This could explain the slight difference of the accident peak in April and May from the humidity peak in April. Introducing fresh and dry outside air, if possible, will not only improve the working environment but also contribute to a decrease in roof falls.

Different bedding loaded coal mechanics properties and acoustic emission

Using TAW-2000KN electro-hydraulic servo rock press machines and the American Physical Acoustics Company’s SH-II acoustic emission systems, experimental studies began to address the mechanical properties in different beddings of loaded coal and the related acoustic emission characteristics, established based on the acoustic emission damage model, and verify the model. The results show that the mechanical properties of different coal sample beddings are distinctive, with maximum uniaxial compressive strength and elastic modulus of vertical stratification of coal samples and the minimum Poisson’s ratio. Thus, the minimum uniaxial compressive strength and elastic modulus of oblique bedding coal samples along with the maximum Poisson’s ratio in the processes of loading result in different bedding coal samples having different stress–strain curves, especially when different bedding coal samples experience the stages of fissure compression, elastic deformation, plastic deformation and instability and destruction. In addition, the displacement proportions of each stage of the loading process have relatively obvious differences: the loading times of vertical, parallel and oblique bedding coal are 495, 382 and 331 s, respectively, and their acoustic emission mutation points of peak stress are approximately 60, 41 and 33%, respectively. Thus, we can use the mutation point as precursor information to estimate the damage intensity in different bedding seams. The theoretical and experimental stress–strain curves obtained by the coal damage model are basically identical, verifying the reliability of the model and reflecting the feasibility of acoustic emission technology in the study of coal damage. The results can effectively forecast coal and gas outburst hazard in coal mines, especially highly gassy and outburst mines. It can also make comprehensive predictions for flooding accidents, roof fall accidents and other disasters, and provide valuable evacuation time for underground coal mine workers. The results are of great scientific significance in safeguarding the safety of coal mines.

Field Investigation of a Roof Fall Accident and Large Roadway Deformation Under Geologically Complex Conditions in an Underground Coal Mine

An investigation was undertaken to study the characteristics of large roadway deformation and driving force of roof fall in a geologically complex zone at Huangyanhui underground coal mine, Shanxi Province, China, and to determine the main factors contributing to a roof fall accident that occurred in this mine. A series of field tests were conducted in the mine to study the geological structures, in situ stress, excavation-damaged zones of the roadway, roof-to-floor and sidewall convergences, roof separation, bolts loading and island coal pillar stress. The results of these tests have revealed that the driving force of the large roadway deformation and roof fall was not the activation of the karst collapsed pillars or concentration stress in island coal pillar, but high levels of horizontal tectonic stress and fault slip were induced by mining activities.

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

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

Hydraulic support crushed mechanism for the shallow seam mining face under the roadway pillars of room mining goaf

While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed (HSC) accidents. In this case, longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The “overburden strata-key strata-roadway pillars-immediate roof” integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.

Gray algebraic curve model-based roof separation prediction method for the warning of roof fall accidents

Roof separation is one of the main precursors of coal mine accidents at the workface. At present, indicator data are usually read in an attempt to understand the real-time changes of the roof separation, but the change trend cannot be predicted. Predicting the change trend of roof separation on time can play a very important role in roof control. In this study, we apply the gray theoretical analysis method to predict the change trend of roof separation. We use Universal Distinct Element Code (UDEC) numerical simulation software to simulate the generation processes of roof separation. For this purpose, we consider four scenarios with different immediate roof heights. Using experimental separation data as original data, we predict roof separation using the gray algebraic curve model (GAM). The GAM-predicted data show little error when compared with the experimental data and are also better compared with prediction data obtained with the traditional gray model GM(1,1). Finally, in a case study using field-monitoring roof separation data from a mine, the GAM method led to good prediction results, and the predicted development trend reflected the real conditions. Thus, we prove that GAM is a very effective prediction method, which will be very useful in predicting roof separation trends for the warning of roof fall accidents.

Accident Analysis and Prevention Measure of Dynamic Load Mine Pressure of the 31201 Fully Mechanized Working Face of Shigetai Coal Mine

In order to eliminate the potential safety hazard of concentrated coal pillar of overlying coal seam occurring in the extraction process of 31201 fully mechanized working face of Shendong Shigetai coal mine, we formulate safety measures for the next extraction by analyzing the pressure data collected by the hy- draulic support in the extraction process. According to research results, there exists irregular room-mining goaf of Coal 22 above Coal 31, and the existing concentrated coal pillar and scattered coal pillar in room-mining goaf parallel to the working face may cause the fully mechanized working face to form secondary roof structure, moreover, the primary reason for large-area roof fall accident is that the concentrated coal pillar of Coal 22 is destroyed and loses stability, thus leading to the dynamic load in the extraction process of Coal 31. We analyze the data of the extraction process of Coal 31 through technical measures such as pressure observation, mi- cro-seismic monitoring, multiple position extensometer inside stratum and surface observation, aiming at the reason for roof fall; and we formulate a set of complete prevention measures, aiming at overlying goaf and ex- traction pressure of this working face, so as to offer effective safety guarantee for the next extraction of this working face and also offer reference for the extraction of similar working faces.

Geotechnical issues in the application of rock bolting technology for the development of underground coal mines in Indonesia

The application of a rock bolting system for Indonesian underground coal mines has been attempted for several years without any success. Recently, two new underground mining trials were conducted in East Kalimantan, Indonesia, in order to investigate the possibility of using rock bolting to address the technical challenges of underground coal mines under weak geological conditions. Unfortunately, one of the trials failed and was given up due to a fatal roof fall accident. However, in another trial, even though roof falls have occurred within the working area, the bolted roadways showed reasonable stability over time. Moreover, a comprehensive monitoring system has been installed in order to monitor the ground behaviour and its characteristics. This application of a comprehensive monitoring system has enhanced the ability to increase the level of support and to react to changing/deteriorating conditions. This paper describes the conditions and geotechnical issues for underground mines in Indonesia, and discusses the applicability of the rock bolting system to address problems associated with weak strata conditions in Indonesia.

Quantitative Identification and Analysis on Hazard Sources of Roof Fall Accident in Coal Mine

The roof fall accident is one of the most frequent accidents in the coal mine and its frequency is ranked the first in various coal mine accidents. Hazard identification is a common method to prevent accidents. On the basis of predecessors’ research, the concepts and identification indicators of the hazard sources in coal mine roof fall accident are defined initially. Hazard source of roof fall accident is analyzed quantitatively by the method which is combined triangular fuzzy theory and traditional fault tree to avoid the structural problems of the fault tree itself. Large area of empty-support is the greatest hazard sources in roof fall accident by the research.

Numerical Analysis and Evaluation on Supporting Parameters in Coal

At the turn of the last century, bolt supporting of coal roadway had rapidly developed with the applied range of bolt stretching continually. The bolt supporting in roadway has been implemented widely. But until now, there is no reliable theoretical support or appraisal system on the design of bolt supporting roadway and the evaluation of supporting conditions. Supporting effect is tested only by practice and roof-fall accidents take place repeatedly. This paper conducts the research on the bolt supporting parameters in No.315 transportation-up-hill roadway of Nan Ye Coal Mine with numerical analysis method; it is discovered that numerical analysis can be a good way to predict and evaluate roadway supporting effects to be worthy popularizing.