Multiseam longwall mining-induced strata deformation and fracture propagation patterns are different from those of single-seam mining. This difference is due to interaction of the caved zones as a ...result of longwall mining activity at different coal seams, which severely impacts formation of subsidence and permeability of the strata after multiseam mining. Understanding this phenomenon is of great importance in order to predict the multiseam subsidence reliably, evaluate the risk of water inrush and take suitable preventive measures, and determine suitable locations for placing gas drainage boreholes. In this study, scaled physical modelling techniques are utilised to investigate strata deformation, fracture propagation characteristics, and vertical subsidence above multiseam longwall panels. The results show that magnitude of the incremental multiseam subsidence increases significantly after multiseam extraction in comparison with single-seam mining. This increase occurs to different extent depending on the multiseam mining configuration. In addition, interstrata fractures above the abutment areas of the overlapping panels propagate further towards the ground surface in multiseam extractions compared with single-seam extractions. These fractures increase the risk of water inrush in presence of underground/surface water and create highly permeable areas suitable for placing gas drainage boreholes.
Multi-seam mining-induced subsidence profile is observed to be different from that of single-seam mining. Understanding the characteristics of multi-seam subsidence is the first step in achieving ...reliable subsidence predictions. Characteristics of multi-seam subsidence are investigated by means of several sand-plaster physical models. Geological and site specific parameters are kept constant in all the models in order to compare the multi-seam subsidence parameters for different mining configurations. Based on observations from the physical models, it is concluded that the panel configurations of the two seams have significant impact on the multi-seam subsidence development. Based on the relative location of the panels the multi-seam mine area can be divided into different zones, to which suitable subsidence characteristics can be assigned. Dividing the mine area into different zones enables characterisation of the strata movement and multi-seam subsidence for various multi-seam configurations. The proposed characterisation of the multi-seam subsidence can also be utilised in subsidence prediction methods in order to achieve reliable prediction results.
•Physical modelling is used to investigate multi-seam subsidence characteristics.•Effects of different mining configurations on subsidence profile are investigated.•The multi-seam subsidence is characterised based on the physical modelling results.•The proposed characterisation can be employed in subsidence prediction methods.
•A physical testing protocol for modelling mining-related problems has been presented.•A new method for monitoring fracture propagation pattern has been introduced.•Laser based and optical devices ...have been used for physical modelling of subsidence.•Multiple-seam subsidence has been measured by photogrammetry, DIC analysis, optoNCDT and 3D TLS.
Field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur. Physical models, comprising sand and ...plaster obeying relevant similarity rules, were used to investigate the subsidence mechanisms. Displacements within the models were measured using a combination of optical transducers, photogrammetry and laser scanning. The observed results were compared with finite element models. The models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones. These zones undergo different horizontal and vertical movement characteristics. The zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness. The limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined-out area above.
•We investigated the mechanism of ground surface subsidence due to multiple-seam longwall coal mining.•We used physical and numerical modelling techniques to simulate a multiple-seam mining case study.•The simulated mining configuration resulted in three different substrata movement zones•Ground surface subsidence after multiple-seam mining is different from single-seam mining.•Results can be utilized for developing a prediction method for multiple-seam subsidence.
A predictive methodology for multi-seam mining induced subsidence Ghabraie, Behrooz; Ren, Gang; Barbato, James ...
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
March 2017, 2017-03-00, 20170301, Letnik:
93
Journal Article
Recenzirano
Multi-seam longwall mining-induced subsidence profiles are often different from those of single-seam mining. As a result, conventional subsidence prediction methods are less reliable for multi-seam ...subsidence predictions. In this study, significant differences between the single and multi-seam subsidence parameters are studied in a multi-seam case study in Australia. Results from this case study are employed to establish a characterisation of the multi-seam subsidence, which is applicable for every multi-seam mining configuration. The proposed characterisation is then utilised for modification of a conventional Influence Function Method (IFM). In the modified method, namely Discrete-IFM, a mine section is divided into discrete segments with certain subsidence parameters. The resultant subsidence of each segment is calculated and then superimposed to achieve the final subsidence profile. Application of the Discrete-IFM is demonstrated in an example case study, where reliable subsidence predictions are achieved. It is illustrated that the Discrete-IFM offers a flexible approach for consideration of multiple subsidence parameters for different segments, which enables this method to predict irregular subsidence profiles.
•A multi-seam longwall case study is employed to investigate multi-seam subsidence profile.•Multi-seam subsidence profile is characterised based on the subsidence observations.•The proposed characterisation is employed to modify conventional IFM.•Reliable multi-seam subsidence predictions are achieved by Discrete-IFM.•Discrete-IFM shows better reliability compared with other described methods.
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.
In underground excavations, optimum design of reinforcement systems is largely based on geological features of the surrounding rock such as in-situ stress distribution, rock strength properties, ...thickness of the layers, etc. In current design of truss bolt systems these parameters are yet to be considered. In this study, effects of changing thickness of roof layers on optimum design of truss bolt have been investigated using three stability indicators, namely reduction in the loosened area above the roof, number of plastic points and horizontal movement on the first bedding plane. Total of 7 different bedding configurations have been generated and 100 different truss bolt designs have been tested on each bedding configuration. Results showed that by changing the thickness of the roof layers, the optimum design of truss bolt changes drastically. In highly laminated formations, it has been demonstrated that a gently inclined bolt angle is more effective, while by increasing the thickness of roof layers, truss bolt systems with a higher bolt angle and longer bolts, i.e. similar to systematic rock bolt systems, responds better.
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