Roof Bolts Research Articles

Study on Anchor Cable instead of Single Hydraulic Prop Support in Advance Support of Deep Roadway

In order to solve the problems of complicated advanced support process, high labor intensity, affecting the rapid advance of working face and the destruction of roof bolt (cable) by advance single hydraulic prop in ultra kilometer deep mine roadway, the deformation characteristics of roadway surrounding rock is analyzed. Taking the 27304 working face of Wanglou coal mine as the engineering background, numerical simulation, field monitoring, and theoretical calculation were used to analyze the deformation characteristics of roadway surrounding rock within the advanced influence range of 27304 working face. This paper puts forward the active advance support technology scheme, in which grouting anchor cable replaces the existing single hydraulic prop in the advance influence range of the working face in the ultra‐kilometer deep mine, and observes and analyzes the deformation and failure characteristics of the surrounding rock of the working face advance roadway. The numerical simulation results show that in the advanced influence range of deep roadway, grouting anchor cable was used to replace the previous single hydraulic prop, and the vertical stress at both ends of the working face decreased by 15 MPa, with a decrease rate of 33.3%; the displacement of roadway roof, floor, and two sides decreased by 10 mm, 55 mm, and 20 mm, with a decrease rate of 40%, 68.75%, and 47.6%, respectively. The field monitoring results show that the roof separation is obviously improved after using grouting anchor cable as the active advance support scheme. It solves the problem of safe and efficient production faced by the ultra‐kilometer deep shaft in Wanglou coal mine and provides theoretical and technical support for unmanned double roadway advance support under the condition of safe and efficient mining.

Application Study on Active Advanced Support Technology in Deep Roadway under Mine Goaf

To solve the problems of the rapid advance of the working face was delayed by complicated working procedure and high labor intensity, and the severe damage of roof bolt (anchor cable) induced by advanced hydraulic support, the deformation characteristics of surrounding rock, and the supporting principle of grouting truss anchor cable were analyzed theoretically by taking the roadway of 3_(down) coal seams 2326# working face in Sanhekou coal mine as the research object; then, the mechanical model of supporting structure of roadway under goaf was established. Based on this model, the optimal supporting scheme was determined, and the active advanced support technology scheme of “advanced grouting truss anchor cable” was proposed to take the place of the existing single pillar. The deformation and failure characteristics of surrounding rock of the working face leading roadway were observed and analyzed on-site. Within the allowable range of reading error, the results showed that the maximum displacement of medium-deep base point and shallow base point of two roadways was 15.2 cm and 10.9 cm, respectively; the pressure value had a more obvious jump increase when the distance between each measuring point and the working face was about 35 m, which means the range is strongly affected by the advance mining, and the area affected by advanced mining was 35 m ahead of the working face. It was observed that the lowest position of roof separation development ranged from 0.71 m to 2.73 m. The separation layer was generally distributed in the range of 0.73 m-2.49 m, and the fracture area was roughly distributed in the range of 0.01 m-0.62 m. Under the condition of overlying goaf, there was a complete stress structure, which can meet the requirements of suspension support.

Roof bolt identification in underground coal mines from 3D point cloud data using local point descriptors and artificial neural network

ABSTRACT Roof bolts are commonly used to provide structural support in underground mines. Frequent and automated assessment of roof bolt is critical to closely monitor any change in the roof conditions while preventing major hazards such as roof fall. However, due to challenging conditions at mine sites such as sub-optimal lighting and restrictive access, it is difficult to routinely assess roof bolts by visual inspection or traditional surveying. To overcome these challenges, this study presents an automated method of roof bolt identification from 3D point cloud data, to assist in spatio-temporal monitoring efforts at mine sites. An artificial neural network was used to classify roof bolts and extract them from 3D point cloud using local point descriptors such as the proportion of variance (POV) over multiple scales, radial surface descriptor (RSD) over multiple scales and fast point feature histogram (FPFH). Accuracy was evaluated in terms ofprecision, recall and quality metric generally used in classification studies. The generated results were compared against other machine learning algorithms such as weighted k-nearest neighbours (k-NN), ensemble subspace k-NN, support vector machine (SVM) and random forest (RF), and was found to be superior by up to 8% in terms of the achieved quality metric.

Analysis of Mine Roof Support (AMRS) for US Coal Mines

During the past 15 years, roof fall rates have fallen dramatically in US coal mines, particularly in regions where the roof is weakest. The remarkable reduction in the number of roof falls has been accomplished with more effective roof support systems. The purpose of this paper is to present a design methodology that builds on and quantifies the basic roof support concepts that have been successful in the USA. The methodology starts by defining three modes of roof support, based on the roof strength relative to the stress level: (1) suspension, where roof bolts mainly provide skin control for strong roof; (2) beam building, where moderate strength roof can be supported by roof bolts alone; and (3) supplemental support for weak roof. Next, a large database of roof fall histories at a number of mines is used to define the approximate boundaries of these three regimes based on the coal mine roof rating and the depth of cover. Finally, guidelines are presented for site-specific design of support systems within each regime. The new computer package, analysis of mine roof support (AMRS), implements the design methodology.

Application of CMRI-ISM RMR for Stability Analysis of Development Workings for Ballarpur Underground Coal Mine - An Empirical and Numerical Approach

Abstract Roof bolt failures in the mine generally occur due to the poor identification of the weak rock layers and considered as a major concern for underground coal mines in terms of its productivity and safety. The triggering factor responsible for underground roof failure is the presence of weak bedding planes and various geological discontinuities. Geological disruptions present in the mine roof seriously affect the continuity of the rock layers resulting in block failure. However, numerous improved methods have been suggested by a number of researchers but still, the upholding of the accidents due to roof fall is considered as a major challenge for underground mine workings. Thus, it is necessary to give proper emphasis on characterization of the roof fall so that stability of the mine workings could be increased and movement of the weak and layered strata can be arrested by applying an adequate roof bolting system. This mechanism of roof support gives the composite binding between the rock layers by restricting the roof fall. The stability of mine workings can be also increased by proper application of rock mass classifications system and adequate design of support system and finally, by extensive simulation methods and statistical methods like FLAC 3D numerical and statistical modelling to ascertain the stability of the workings. CMRI-ISM RMR (Central Mining Research Institute – Indian School of Mines Rock Mass Rating System) classification system is the most popular and practiced method for roof support design in Indian coal mines which is being successfully used from last several years for roof support design in Indian geo-mining conditions. This forms the basis to estimate the rock load and support design. In this paper attempt has been made to assess the stability of workings and pillars below the railway track by using empirical and numerical approach. After both the studies it can be said that, the galleries and pillars underlying the railways track are stable, as factor of safety in each case is more than 2. Later on, the study was also extended to see the effects of subsidence on the surface which reveals that, there shall be no such effect on the surface due to underground workings as the value of NEW (non-effective width) is less than 0.4 for both the cases.

Stability analysis of integral load-bearing structure of surrounding rock of gob-side entry retention with flexible concrete formwork

According to the factors affecting the stability of the integral load-bearing structure of the surrounding rock of a retained gob-side entry, the load-bearing capacity of roadside supports with flexible concrete formwork is studied to propose a new integrated supporting control technology. This approach is based on a bolt and anchor cable support with a wire mesh for retaining the surrounding rock of a roadway. Moreover, the core of this technology involves roof bolts and steel beam supports with a steel–plastic wire mesh on the side of the gob beside the retained roadway, combined with the strengthening support of dual single props with upper and lower crossbars in the roadway. The roof-strata pre-stressed anchorage composite load-bearing structure, roadside flexible concrete formwork load-bearing structure, wire-mesh wall structure, solid coal wall load-bearing structure, and four-in-one load-bearing and stress-transferring control device in the retained roadway are formed in the surrounding rock of the retained roadway using integrated supporting control technology. Additionally, their supporting mechanisms are analyzed, and the corresponding construction technologies are clarified. Practical field results indicate that the integral load-bearing structure of the surrounding rock of the retained roadway formed by the integrated supporting control technology effectively controls the deformation and destruction of the surrounding rock, ensuring the success of the retaining roadway. Furthermore, dual gas channels are successfully constructed using this technology, thereby validating its efficient gas extraction.

Prediction of Rock Load Emphasizing Excavation Damage of <i>in situ</i> Rocks Caused by Blasting in Coal Mines

Roof failure in coal mines is strongly related to the frequency of laminations and their movement when the load acts upon them. Detachment of roof bolts from mine roof due to improper estimation of extent of weak zone is one of the major problems in underground coal mines, thus affecting the safety and productivity of workings. The most popular and practised method for roof support design in Indian coal mines is the Central Mining Research Institute-ISM geomechanical classification system. Irrespective of such an established system of support design, accidents due to roof fall still persist. Here we review various available classification systems for rock load estimation and identify their limitations. The study has been extended taking into consideration the case study of KTK-6 incline of Singareni Collieries Company Limited by proposing a modified rock mass classification system based on seismic wave velocity as a key descriptor. A modified rock mass rating (RMR) system (RMRdyn) with inclusion of seismic velocity as one of the parameters is proposed for the estimation of rock load. Enhancement in rock load by 20% has been found for RMR CMRI-ISM values less than 40 according to the new rock load relation. This resulted in under-supporting of the roof and thus might have caused failures. For cases with RMR CMRI-ISM values more than 60, the earlier equation overestimates rock load by about 25% resulting in over-supporting. Thus, estimation of rock load from the proposed new equation appears to be more rational as it takes into account the actual damage zone.

A case study on the efficacy of different roof bolting schemes in Lhoist North America’s Crab Orchard Mine

Roof bolting has long been used in underground mines across the world to provide ground support. Modern roof bolts are cheap and easy to install with the use of specialized machines as a part of the production cycle. Lhoist North America’s Crab Orchard Mine is an underground room and pillar limestone mine that uses mechanically anchored roof bolts for ground support. The mine currently employs two different roof bolting patterns: a standard 1.5 × 1.5 m pattern, and another 0.8 × 0.8 m pattern for use in areas with particularly hazardous roof conditions. The purpose of this study is to evaluate the relative effectiveness of each bolting pattern. A series of numerical models were created using RocScience’s RS2. The models were based on a symmetrical section of the mine at its deepest point, and were modeled using generalized Hoek-Brown failure criterion along with a discrete fracture network. A series of sensitivity analyses were performed on the models by varying parameters such as joint friction angle, crack persistence, joint randomization, and tensile strength of the limestone. Based on the results of the original models and sensitivity analyses, it appeared that the standard bolting pattern provided sufficient roof support capacity under almost all the expected conditions at the mine, since safety factors below the design value of 1.5 were only found for individual bolts in a few of the worst test cases considered. These results can help improve the mine’s productivity and reduce operating costs without compromising safety.

Design and Evaluation of the Roof Bolt Corrosion Test System in a Simulated Underground Coal Mine Environment

Corrosion of steel roof support systems can cause potential premature failure of the support, thus adversely affecting the excavation stability and rock-related safety. An in-house corrosion test system was designed and developed to test full-length roof bolts for material performance based on tensile load capacity and strength under different corrosive conditions found underground. The roof bolts tested are also used to identify the possible corrosion mechanisms that influenced the bolts’ performance over time. Initially, the most commonly used bolt material in the USA, the ASTM A615 grade 60 steel roof bolts, was tested with and without stresses in a simulated underground coal mining environment for approximately 6 months, and the results are discussed. Localized corrosion forms such as crevice and pitting were mainly observed after testing. The stressed and unstressed roof bolts with and without threads that were tested in alkaline coal mine corrosive environment for 6 months passed their load-bearing capacity as per ASTM F432 test standards. From the results, it is concluded that this test protocol could be applicable to test the material performance of different roof bolt metallurgies and coatings with desired modifications to the proposed methodology for the specific underground mine environment. This paper mainly discusses the test system and protocol and shortcomings of the system and makes recommendations based on the observations and results.

Calculation Model of Supporting System for Tunnel Under Shallow and Weak Surrounding Rock Considering the Synergistic Effects

In order to give full play to the bearing capacity of the various components of a tunnel supporting system under shallow and weak surrounding rocks, a study is conducted on the synergistic mechanism of the tunnel supporting system in these conditions. In this paper, the synergistic mechanism of the tunnel supporting system is investigated by considering each function of the supporting equipment. Then, a theoretical model is proposed to calculate the overall bearing capacity of the supporting system for the tunnel under the shallow-buried weak surrounding rocks. The ultimate calculation formula for the supporting system, which includes advanced pipe roof, leading conduit, steel arch and feet-lock anchor bolt, is obtained on the basis of the structural mechanics and elastic foundation beam theory. To validate the proposed model, the interacting forces and deformation of each support structure component are calculated respectively. Next, the calculation results are compared with those of the load-structure method and strata-structure method. Statistical analysis shows that the deformations obtained by the three methods are consistent, and that the results of each method are rather similar. It indicates that the theoretical method proposed is reliable and applicable.

Experimental Study of an Orientation and Resin-Lifting Device for Improving the Performance of Resin-Anchored Roof Bolts

During roof bolting in underground coal mines, the effect of gravity on the resin for anchoring the bolts, resin mixing methods, and borehole wall collapse can easily lead to resin outflow, nonuniformity of the resin, and poor bolt concentricity. In this study we developed an orientation and lifting device (OLD) for resin-anchored rock bolts. Theoretical analysis and numerical model simulations were used to analyze the working principles of the device and to optimize its important features. After manufacturing prototype devices using a 3D printer, the devices were tested by installing roof bolts into both steel tubes and a simulated mine roof in the laboratory. Push tests, pull tests, and ultrasonic tests were conducted on the bolts to measure the performance of the device. The results indicate that the device mixes resin from the resin cartridges better and has a better lifting effect on the resin than standard bolt ribs. The device can prevent the resin from flowing downward, promote uniform resin mixing and density, and improve bolt concentricity because of the device’s orientation constraint and spiral lifting capabilities. The device can raise the load bearing capacity and stiffness of the roof bolts, contribute to roadway deformation control, and enhance the energy dissipation capacity of the bolting system when subjected to static and (or) dynamic loads. Both the theoretical analysis and the laboratory experiments demonstrate that the OLD can improve the quality of the anchorage, thus enhancing mine safety. This research provides a new method for improving the quality of roadway roof bolting.

Fast, non-destructive measurement of roof-bolt loads

Abstract This paper discusses the pull-out laboratory tests and the monitoring of expansion-shell bolts with a length of 1.82 m. The bolts comprised the KE-3W expansion shell, a rod with a diameter of 0.0183 m and a profiled, circular plate with a diameter of 0.14 m, and a gauge of 0.006 m. The bolts were installed in a concrete block with a compressive strength of 75 MPa. The tests were conducted on a state-of-the-art test stand owned by the Department of Underground Mining of the AGH University of Science and Technology. The test stand can be used to test roof bolts on a geometric scale of 1:1 under static and rapidly varying loads. Also, the stand is suitable for testing rods measuring 5.5 m in length. The stand has a special feature of providing the ongoing monitoring of bolt load, displacement and deformation. The primary aim of the study was to compare the results recorded by two different measurement systems with the innovative Self-Excited Acoustic System (SAS) for measuring stress variations in roof bolts. In order to use the SAS, a special handle equipped with an accelerometer and exciter mounted to the nut or the upset end of the rod was designed at the Faculties of Mining and Geoengineering and Mechanical Engineering and Robotics of the AGH University of Science and Technology. The SAS can be used for nondestructive evaluation of performance of bolts around mining workings and in tunnels. Through laboratory calibration tests, roof bolt loads can be assessed using the in-situ non-destructive method.

Stress corrosion testing of roof bolt grade 60 steel in simulated underground coal mine atmosphere

ABSTRACTCorrosion of roof bolts in underground mine environments could have an adverse impact on ground control, which is directly related to workforce safety. Past studies state that stress corrosion cracking (SCC) of roof bolts is a significant problem in underground coal mines, resulting in premature bolt failures. However, it has not been seriously studied in U.S. underground coal mines. As a preliminary study, the most common roof bolt material used in U.S. mines, ASTM A 615 Grade 60 steel, was studied under stress corrosion conditions. ASTM G30 standard was applied to achieve this and tested in the simulated coal mine conditions. SCC was observed on samples that were tested for 180 days. Chloride SCC (ClSCC) was found to be the corrosion mechanism resulting in cracks from the EDS data. This paper mainly discusses the test protocol, shortcomings of this preliminary testing and makes recommendations based on the observations and results.

Investigation of sudden faults instability induced by coal mining

Study on the mechanism of coal burst induced by faults instability is a major concern for the safety mining and efficient production in the underground coal mine. In this paper, the sharp change of roof bolt loading, roof separation, roadway deformation and mining face support stress were observed during the routine field tests. According to the preliminary estimation, the reason for such a phenomenon was possibly relevant to the sudden instability of fault structures. To investigate the sudden faults instability, a physical test was carried out with two fault structures. The modelling results suggest that the strain rate from relatively low to sudden changes may be identified as a precursor of fault slip. The overlying strata was severely collapsed under the interactive effect of two faults. The depth of collapsed strata between two faults was higher than that influenced by a single fault. The difference between the first-stage and the second-stage coal mining is studied in three aspects: the area of fault influenced zone, characteristics of stress distribution near fault and the degree of fault slip. Due to the severely collapsed strata between two faults, the abrupt stress change could be induced during excavation of coal mining face, and thus, more attention should be paid to the influence of overlying strata movement above goaf between two faults. The sudden collapse of roof strata and abrupt stress change could release tremendous strain energy and induce coal bursts.

Concept of workings reuse with application of resource-saving bolting systems

The new support patterns have been revealed for controlling the combinations of the roof rocks strengthening processes in extraction mine workings with combined roof-bolting systems. It has been established that in adjacent roof rocks, by means of a combination of rope bolts and resin-grouted roof bolts, an armored and rock plate is formed, the high load-bearing capacity of which is achieved by maintaining the horizontal thrust forces that reduces the concentrations of all the stresses components to a level many times lower than the strength characteristics of the lithotypes. The criterion has been substantiated for assessing the resistance level of roof-bolts as a part of the combined roof-bolting system, which is used for determination of the most important geomechanical factors in terms of the system loading degree. The patterns have been established of a degree of loading the roof-bolts being a part of the combined roof-bolting system from the main influencing geomechanical factors. The calculated expressions have been obtained to determine the needed parameters for effectively strengthening the roof in workings by a combined roof-bolting system. The mine experiment analysis has been performed as well.

Modification of the roof bolt support technology in the conditions of increasing coal mining intensity

The modification of the technology roof bolt supporting of mine workings in the conditions of increasing the coal mining intensity has been made. The technological schemes have been developed for the phased construction of roof bolting and frame support. This schemes make it possible to temporarily postpone the setting of frames in the mine working face, reduce the time and labour intensity for covering with a grid of the mine working arch and setting the bolts, as well as to increase the safety. The analysis of changes in the stress state of the border massif during the phased construction of roof bolting and frame support has been made. It is shown that the technology of phased construction of roof bolting and frame support ensures the maintaining a stable state of host rocks. In addition, the time between the extraction of the coal-rock mass and the setting of the primary support, as well as the distance between the face and the first row of roof bolts has been reduced to a minimum. The suggested approach makes possible to ensure the rate of preparatory mine workings development that are necessary for the intensification coal mining.

Development of Double-arm Rock Drilling Car for Full Face Tunnelling

Blasting excavation is widely used in coal mine roadway excavation, its construction method is flexible, convenient, low cost and adaptable. It can excavate mine tunnels of any shape and length under any environmental conditions. However, the main rock drilling equipment used in the mine is pneumatic rock drilling equipment generally. Although these equipment are simple and reliable, their drilling efficiency is low, the degree of automation is poor, and the working conditions are bad, especially the ability to drill deep holes and large holes is poor, which can not meet the needs of large structural parameters mining method. The newly developed double-arm rock drilling rig for full-face roadway excavation is suitable for the current common construction method of roadway blasting driving. It can replace the traditional pneumatic rock drilling equipment, and drill large holes and small holes simultaneously. It fully meets the requirements of blasting technology. It can not only drill and excavate holes, but also drill roof, side wall and floor bolts holes, to achieve high and low position of drilling operations, for improving the efficiency of roadway excavation, promoting the level of coal mine machinery and equipment in China, these have important practical significance.

Improving the capability of detecting joints and fractures in rock mass from roof bolt drilling data by using wavelet analysis

To optimise ground supporting and mitigate ground instability, a proper understanding of the ground conditions is critical. The concept of monitoring drilling parameters of a bolter for ground characterisation, which refers to identifying geological features included locations of joints and strengths of rock layers, has been studied in the past few decades. Several intelligent drilling units have been developed for joint detection but have limited capabilities. For instance, the existing systems fail to discriminate joints with the aperture of less than 3.175 mm and tend to generate false alarms. The objective of this research was to develop more efficient and sensitive detection programs for joint detection. To achieve this objective, a series of full-scale drilling tests with various simulated joint conditions have been conducted, and new detection programs have been proposed based on pattern recognition algorithms. Moreover, wavelet analysis has been applied to pre-process data to further promote detection programs. [Received: July 15, 2017; Accepted: November 18, 2017]

Effects Of Roof Bolt Pressure On Properties Of Short Fiber And Rubber Composite Material

Roof bolt pressure is one of the important factors which impacts the mixing process and roof bolt pressure of SFRC greatly. The effects of different roof bolt pressure on mixing process of SFRC have been researched by experiments. In the paper, the roof bolt pressure was changed from 0.3MPa to 0.6MPa respectively. And also the addition of short fibers was about 0phr∼6phr. The experimental results indicated that SFRC had better physical and mechanical properties as roof bolt pressure was about 0.6MPa, and the addition of short fibers was about 3phr.

Asymmetrical Support Technology for Dynamic Pressure Roadway: A Case Study from Guotun Coal Mine in China

To form a kind of support technology that was universally applicable to all kinds of dynamic pressure roadways, This paper proposes asymmetrical support technology for dynamic pressure roadway. Firstly, the asymmetry characteristics of surrounding rock structure and stress distribution in dynamic pressure roadway were analyzed. The mechanism of asymmetric support technology for dynamic pressure roadway was preliminarily explored. Taking the 1303 dynamic pressure roadway in Guotun Coal Mine as the engineering background, the coal pillar width and support parameter were determined by numerical simulation and theoretical analysis. In the asymmetric support scheme, the roof bolts and the side bolts are respectively Φ20 × 2200 and Φ20 × 2000 mm, the spacing-discharge distance of roof bolts, coal pillar side bolts and coal body side bolts are respectively 800 × 900, 600 × 900 and 800 × 900 mm. Through field observation, the overall deformation of roadway surrounding rock supported by the asymmetric support scheme was not large and the deformation of the roof, coal pillar side and coal body side were basically equal. So, this asymmetric support technology can effectively control the deformation of surrounding rock in dynamic pressure roadway.