Cutter Roof Research Articles

Discrete Element Modeling of Delamination in Laboratory Scale Laminated Rock

Laminated rock can delaminate and fail under certain stress states. Delamination-caused roof fall and cutter roof failure is a common failure mechanism in roadways in Pittsburgh coal seam due to the existence of laminated shale roof. Two-dimensional numerical models were developed at laboratory scale based on the bonded particle method in order to simulate the delamination with particle flow code. In these models, an assembly of bonded particles and parallel weak planes represents the laminated rock. This model calibrated the micro-parameters of the bonded particle material and weak planes with laboratory data. The mechanism of fracturing and delamination in a laminated specimen was investigated using unconfined and confined compression test and unsupported roof compression test. The numerical results show that, under a constant horizontal stress, delamination occurs when the stress is much lower than its compressive strength. The confined compressive test indicates that delamination is restrained by applying confining stress since delamination-caused failure does not occur during any stage of the confined compressive test. Unsupported roof compression tests showed propagation of cutter roof failure with initiation of cracks and delamination at the intersections of the roof and ribs. An outer failed zone and inner failed zone form separately. The separated zones connect and form an opening in the roof. The presented numerical results provide additional insight into process of delamination.

An evaluation of roof support plans at two coal mines in Illinois using numerical models

•Roof control plans at two mines are compared using strain-based rock mass failure criteria.•Shearing strains at pillar corners near the roof and floor are critical for failure initiation.•Shear and tensile strains at the coal-floor interface are also critical.•High compressive strains along the pillar ribs in entries result in cutter roof.•Failure initiation occurs around the mid-height of pillar ribs and progresses downward.

3D topographic stress perturbations and implications for ground control in underground coal mines

It is well known that the perturbed stress field beneath valleys can result in roof instabilities in shallow underground coal and stone mines. Quantitatively predicting the magnitude of these stress perturbations, particularly beneath complicated three-dimensional (3D) topography, has not become commonplace in mine planning, perhaps due to the complexity and time-consuming nature of the problem. Here we utilize 3D digital elevation models and the 3D boundary element method (BEM) approach to efficiently calculate the pre-mining topographically perturbed stress field in the vicinity of the Carroll Hollow coal mine in eastern Ohio. We find that regions of elevated compressive stress in the mine correspond to areas in which cutter roof failure is a common source of roof instability. Furthermore, both the magnitude and inclination of the principal stresses calculated from the 3D topographic BEM model are found to be consistent with observed failure distributions within the mine. We propose that the approach outlined in this study can be efficiently applied to the mine planning process in order to mitigate or avoid potentially hazardous mining conditions.

Discrete element modelling of cutter roof failure in coal mine roadways

Cutter roof failure is a common failure mechanism in coal mine roadways due to the oblique orientation of the major horizontal stress with respect to roadway advance direction. In the present study, two 3D numerical models based on the discrete element method have been developed to simulate cutter roof failure. In the first model created using PFC3D, the rock surrounding a roadway is represented by an assembly of spheres glued together at their boundaries. High horizontal stress at varying orientations to the roadway advance direction is applied to the model to investigate the mechanism of fracturing around the roadway. The numerical results indicate that a roadway driven at a large angle (75°–90°) with respect to the maximum horizontal stress suffers significantly more fracturing than that driven at a small angle (0–15°). The second model created using the distinct element code 3DEC adopts a newly developed Trigon logic in which the roadway roof is represented by an assembly of tetrahedral blocks bonded together at their contacts. Both the PFC3D and 3DEC models successfully simulate the cutter roof failure process which is characterized by a fracture zone initiating at the corner where the major horizontal stress and the roadway roof intersect; this fracture zone propagates across the roof span with continued roadway advance. The influence of pre-existing fractures is evaluated in the PFC3D model and the results show that incorporating bedding planes and cross joints in the roadway roof promotes the development of distinct cutter roof failure immediately behind the advancing face. The numerical results presented provide additional insight into cutter roof failure mechanisms and important insight for guiding design and layout of roadway support.

Discrete element modelling of cutter roof failure in coal mine roadways

Cutter roof failure is a common failure mechanism in coal mine roadways due to the oblique orientation of the major horizontal stress with respect to roadway advance direction. In the present study, two 3D numerical models based on the discrete element method have been developed to simulate cutter roof failure. In the first model created using PFC3D, the rock surrounding a roadway is represented by an assembly of spheres glued together at their boundaries. High horizontal stress at varying orientations to the roadway advance direction is applied to the model to investigate the mechanism of fracturing around the roadway. The numerical results indicate that a roadway driven at a large angle (75o-90o) with respect to the maximum horizontal stress suffers significantly more fracturing than that driven at a small angle (0-20o). The second model created using the distinct element code 3DEC adopts a newly developed Trigon logic in which the roadway roof is represented by an assembly of tetrahedral blocks bonded together at their contacts. Both the PFC3D and 3DEC models successfully simulate the cutter roof failure process which is characterized by a fracture zone initiating at the corner where the major horizontal stress and the roadway roof intersect; this fracture zone propagates across the roof span with continued roadway advance. The influence of pre-existing fractures is evaluated in the PFC3D model and the results show that incorporating bedding planes and cross joints in the roadway roof promotes the development of distinct cutter roof failure immediately behind the advancing face. The numerical results presented provide additional insight into cutter roof failure mechanisms and important insight for guiding design and layout of roadway support.

A Study on Truss Bolt Mechanism in Controlling Stability of Underground Excavation and Cutter Roof Failure

The truss bolt reinforcement system has been used in controlling the stability of underground excavations in severe ground conditions and cutter roof failure in layered rocks especially in coal mines. In spite of good application reports, working mechanism of this system is largely unknown and truss bolts are predominantly designed based on past experience and engineering judgement. In this study, the reinforcing effect of the truss bolt system on an underground excavation in layered rock is studied using non-linear finite element analysis. Different indicators are defined to evaluate the reinforcing effects of the truss bolt system. Using these indicators one can evaluate the effects of a reinforcing system on the deformation, loosened area, failure prevention, horizontal movement of the immediate layer, shear crack propagation and cutter roof failure of underground excavations. Effects of truss bolt on these indicators reveal the working mechanism of the truss bolt system. To illustrate the application of these indicators, a comparative study is conducted between three different truss bolt designs. It is shown that the design parameters of truss bolt systems, including tie-rod span, length, and angle of the bolts can have significant effects on the reinforcing capability of the system.

Integrated reinforcement system to stabilize cutter roof : Khair, A W Proc International Symposium on Rock Support, Sudbury, 16–19 June, 1992P531–539. Publ Rotterdam: A A Balkema, 1992

Integrated reinforcement system to stabilize cutter roof : Khair, A W Proc International Symposium on Rock Support, Sudbury, 16–19 June, 1992P531–539. Publ Rotterdam: A A Balkema, 1992

Modelling of outbursts at #26 Colliery, Glace Bay, Nova Scotia. Part 3: Comparison of model results and field data

The outburst mechanism and model proposed in Part 2 of this paper has been used to simulate the outbursts at #26 Colliery. The cavities generated by the model were compatible with the actual outburst cavities in both size and shape. The model was also used to explain the presence of different size cross-sections within the same cavity; they are a result of the changing width of the sandstone exposed above the heading. The narrower the exposed sandstone, the smaller is the resulting cavity. In addition, the model shows that if an outburst is not terminated by a change in the excavation shape, it could spall indefinitely unless terminated by variations in the geology. A siltstone bed often occurs between the sandstone channel and the coal seam. If the sandstone is not penetrated, then the overlying siltstone must fail prior to initiation of spalling (outbursting) from the sandstone. This siltstone failure has been analysed as a ‘cutter roof’ failure of a beam loaded by the gas pressure at the sandstone/siltstone interface. Results from this analysis are also compatible with the field observations. Remedial measures should be taken when mining near an area prone to outbursts. Several potential remedial measures are discussed in the light of the model results. Further evaluation of these potential remedial measures is needed by means of on-site testing. However, the prime concern regarding the previous practice is that the entry support immediately behind the face was passive; it is thought that the installation of an active support as close to the face as possible would be a benefit.

Tips on controlling cutter roof failure : Bauer, E R CoalV26, N5, May 1989, P80-80D

Tips on controlling cutter roof failure : Bauer, E R CoalV26, N5, May 1989, P80-80D

Geomechanical evaluation of a coal mine arched entry

In an effort to minimize cutter roof failures in longwall development entries of a West Virginia coal mine, a three-entry system was developed with the center entry arched into the strata above the coal seam. The purpose of the arched entry was to modify the horizontal stress envelope associated with the three-entry system and improve roof conditions in the adjacent outside entries. Contrary to the predictions of elastic analyses, the presence of the arched entry improved roof conditions by eliminating cutter roof failures in the outside entries.In situ stress determinations and numerical modeling techniques were employed to quantify the impact of the arch and investigate the mechanism of stress relief associated with the arched entry. Stress determinations and underground observations indicated that the roofs of the outside entries were within the zone of stress relief generated by the arch, and that failure or movement along bedding plane discontinuities played a major role in the formation of the stress relieved zone. The numerical model incorporated horizontal joints to simulate bedding plane discontinuities. The properties of the joints were adjusted until roof stresses predicted by the model were in agreement with measured stress profiles. This process resulted in a calibrated analytical tool that could be used to evaluate alternate mining geometries.

Cutter roof and its causes : Su, W H; Peng, S S Min Sci TechnolV4, N2, Jan 1987, P113–132

Cutter roof and its causes : Su, W H; Peng, S S Min Sci TechnolV4, N2, Jan 1987, P113–132

Cutter roof and its causes

This paper examines the intrinsic mechanisms of cutter roof failures by combining field investigations, laboratory testing, underground instrumentation, and numerical modelling. Cutter roof occurred during the development of a set of longwall panel entries in a West Virginia coal mine, and is presented as a case study. Mining alternatives applicable to the mine are recommended. Cutter roof occurrences in two other West Virginia coal mines were also investigated. Detailed comparisons were made between the three cases to derive useful information regarding the intrinsic cutter roof mechanisms. Three-dimensional finite element analyses were employed to validate the cutter roof mechanisms. As a result of the extensive investigation, intrinsic mechanisms of cutter roof failures under various conditions are presented from the practical and theoretical points of view. Mining alternatives for controlling cutter roof formed under various mechanisms are recommended.

Investigation of the causes of cutter roof failure in a central Pennsylvania coal mine: a case study : Hill J.L.; Bauer E.R. In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984)P603–614. Publ New York: AIME, 1984

Investigation of the causes of cutter roof failure in a central Pennsylvania coal mine: a case study : Hill J.L.; Bauer E.R. In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984)P603–614. Publ New York: AIME, 1984