A Review of In Situ Stress Measurement Techniques

Changes in stress orientations and magnitudes can have a significant adverse impact on mining conditions such as increasing the risk of violent failures. Knowledge of these changes can indicate the high-risk zones within a mine sites, which will enable mine operators to implement appropriate controls. At deep underground excavations, there are some difficulties in collecting reliable data at reasonable costs and majority of methods provide point measurement per test only. Thus, the utilisation of borehole techniques has received more attentions. In this paper, traditional stress measurement techniques are reviewed, including their pros and cons. Under specific geological conditions, some methods have significant advantages over others. Following the illustration of benefits and shortcomings of these techniques, the development potential of an in situ stress measurement technique using borehole breakout is briefly addressed in conjunction with the future research plan

An Integration Method of Bursting Strain Energy and Seismic Velocity Tomography for Coal Burst Hazard Assessment

AbstractThe occurrence of coal burst in underground coal mines is complex, abrupt, and diverse, and the evaluation and prediction of coal burst hazard is the premise of effective prevention and control of coal burst. In this study, a coal burst carrier system model under the synergistic action of roof, coal seams, and floor was established, and the evolution of coal burst in underground coal mines was discussed based on the stress-vibration-energy coupling principle. On this basis, an integration method of bursting strain energy and seismic velocity tomography for coal burst assessment was proposed. With the deep and complex panel in a mine as the research object, the coal burst risk of the panel during excavation was evaluated in time and space domains, respectively. Results showed that the bursting strain energy and the active seismic velocity tomography technology can accurately identify both the positive anomalies and the negative anomalies of stress field and energy field in the mining period. Moreover, the method can not only evaluate the coal burst risk of the panel in the temporal domain but also predict the area with potential strong seismic events in the spatial domain. The research conclusions can accurately illustrate the whole complex evolution process of coal burst in underground coal mines

Coal Burst Induced by Horizontal Section Mining of a Steeply Inclined, Extra-Thick Coal Seam and Its Prevention: A Case Study from Yaojie No. 3 Coal Mine, China

At present, coal bursts in working faces of steeply inclined coal seams (SICSs) have rarely been investigated, and current research focuses on the influences of roof breaking and instability of overlying structures in goaf on coal bursts; however, the stress state of coal masses in working faces being subjected to coal bursts is rarely researched. To overcome the above defects, a model for analysing stresses on coal masses in horizontal section of SICSs was established based on the coal burst that occurred in LW5521-20, Yaojie No. 3 Coal Mine, Lanzhou, Gansu Province, China. Moreover, the mechanism underpinning such a coal burst in SICSs was analysed based on the superposition mechanism of dynamic and static loads. The results show that the side abutment pressure near the roof and floor under the horizontal sections of SICSs is asymmetrically distributed in the vertical direction in which the peak of side abutment pressure near the roof is closer to the working face and therefore is taken as the source of static loads for coal bursts in working faces. When the superimposed dynamic load caused by hanging roof breaking and high static load borne in the coal masses is larger than the critical load for coal burst inception, a coal burst will occur. Furthermore, the superimposed dynamic load induced by coal bursts on the support and the initial static load on the supports are larger than their limiting load, which leads to support collapse and eventually causes dynamic failure of the working face. The coal burst in working faces in horizontal sections of SICSs can be prevented by using deep-hole presplit blasting in a hard roof, destress blasting in coal masses, and support optimisation of working faces, showing a favourable preventative effect

A Review of In Situ Stress Measurement Techniques

Changes in stress orientations and magnitudes can have a significant adverse impact on mining conditions such as increasing the risk of violent failures. Knowledge of these changes can indicate the high-risk zones within a mine sites, which will enable mine operators to implement appropriate controls. At deep underground excavations, there are some difficulties in collecting reliable data at reasonable costs and majority of methods provide point measurement per test only. Thus, the utilisation of borehole techniques has received more attentions. In this paper, traditional stress measurement techniques are reviewed, including their pros and cons. Under specific geological conditions, some methods have significant advantages over others. Following the illustration of benefits and shortcomings of these techniques, the development potential of an in situ stress measurement technique using borehole breakout is briefly addressed in conjunction with the future research plan

Numerical Study on Failure Mechanisms of Shaft Wall Consisting of Steel Plate and Concrete under the Effects of Explosion

To enhance the antidynamic and static load resistance of reinforced concrete structures, the measure of covering steel plates on the inner surface of concrete structures arises, which has been rapidly developed and applied in civil engineering and other fields and has achieved a good performance. A new shaft wall structure consisting of steel plate reinforced concrete has been widely used in shaft of deep mining. In order to investigate the stability and obtain the optimum structure parameters of the new shaft structure, the numerical software of LS-DYNA was used to analyze the influences of different factors, including the explosive payload, steel plate thickness, concrete strength grade, and the included joint angle between two plates, on the stability of steel plate reinforced concrete structures. After the verification of the accuracy of numerical simulation results, 23 simulation schemes were proposed and numerically calculated. For all the tests, the principal tensile stress and particle vibration velocity were, respectively, chosen as the failure criteria to evaluate the impacts of those four factors. The results indicate that a quadratic function can be well used to describe the relationships between each factor and both the principal tensile stress and particle vibration velocity. Based on the results, the optimum structure parameters were finally determined, which are suggested as 250 kg, 15 mm, C85, and 40° for the explosive payload, steel plate thickness, concrete strength grade, and joint angle, respectively. The research results can provide a certain theoretical basis and design guidance for solving the problem of water leakage of single-layer shaft wall structures

Comprehensive early warning of rock burst utilizing microseismic multi-parameter indices

Rock bursts have become one of the most severe risks in underground coal mining and its early warning is an important component in the safety management. Microseismic (MS) monitoring is considered potentially as a powerful tool for the early warning of rock burst. In this study, an MS multi-parameter index system was established and the critical values of each index were estimated based on the normalized multi-information warning model of coal-rock dynamic failure. This index system includes bursting strain energy (BSE) index, time-space-magnitude independent information (TSMII) indices and time-space-magnitude compound information (TSMCI) indices. On the basis of this multi-parameter index system, a comprehensive analysis was conducted via introducing the R-value scoring method to calculate the weights of each index. To calibrate the multi-parameter index system and the associated comprehensive analysis, the weights of each index were first confirmed using historical MS data occurred in LW 402102 of Hujiahe Coal Mine (China) over a period of four months. This calibrated comprehensive analysis of MS multi-parameter index system was then applied to pre-warn the occurrence of a subsequent rock burst incident in LW 402103. The results demonstrate that this multi-parameter index system combined with the comprehensive analysis are capable of quantitatively pre-warning rock burst risk. Keywords: Rock burst, Microseismic (MS) monitoring, Multi-parameter indices, Comprehensive early warnin

Comparison of rockburst occurrence during the extraction of thick coal seams using top-coal caving versus slicing mining methods

In recent years, rockbursts have frequently occurred during the mining of thick coal seams in China. The use of the caving or slicing mining method to extract these thick seams may result in distinct geomechanical responses in the strata and, in turn, the pattern of rockburst occurrence around longwall layouts. In order to establish a thorough understanding of which method (caving or slicing) is better when it comes to preventing rockbursts during the extraction process, a suite of in situ rockburst measurements were conducted. Six typical rockburst-prone collieries were monitored during which a total of 110 rockburst events were experienced. Numerical modelling was used to help interpret the observations. Here, we focus on the analysis of these field observations and the numerical simulations employed to develop a conceptual model for rockburst occurrence during caving mining of thick coal seams. We find that caving mining significantly decreases, or even avoids, the occurrence of rockbursts at coalfaces. It reduces the scope of the damage likely to be suffered and the severity and frequency of rockbursting. This rockburst pattern arises because caving mining results in reduced stress concentration, less bottom coal being retained, and wider ranging fracture zones around the mine openings.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The complete chloroplast genome and phylogenetic analysis of Salix triandra from China

Salix triandra is a great willow for bees and an excellent choice for living willow structures. In this study, we assembled and annotated the complete chloroplast (cp) genome sequence of S. triandra. The whole cp genome is 155,821 base-pairs (bp) in size, which comprises one small single copy (SSC) region of 16,223 bp and one large single copy (LSC) region of 84,532 bp separated by a pair of inverted repeats (IRs) of 27,533 bp. There are 131 genes, including 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis with the Neighbour-joining method indicates that S. triandra is closely related to S. tetrasperma. The complete cp genome will facilitate the biological studies in the order Malpighiales in future

Statistical analysis of distribution patterns of coal seams in fold zones in Northwest China

The mechanisms for rock bursts occurrences in fold zones are complex, and the redistribution of in-situ stresses is closely related to the complexity of the structures. Analysis of the geomorphology of fold structures and changes of coal thickness can help identify zones prone to rock bursts to improve safety and productivity in coal mines. This study investigated the distribution characteristics of fold structures in coal seams in fold zones in four mines in northwest China. Geometrical characteristics of fold structures in coal seams and changes of coal thickness were analysed, based on comprehensive evaluation indexes, such as the length–width ratio of folds, interlimb angle, ratio P1 of projected width of fold limbs to that of the hinge zone, curvature ratio P2, the maximum curvature and amplitude. The statistical analysis of the four coal mines shows that the length–width ratio of folds changed from 0.78 to 2.03 and the maximum curvature of cross sections of folds was less than 0.04. The curvature ratio of cross section of a fold in the structure was no more than 1.4 and the interlimb angles of cross sections of 89% of folds were larger than 150°. Gentle fold structures were dominant and the specific geological morphologies were domes or basins. The isopleth of coal thickness above the coal mines showed a fluctuation trend similar to the contour line of the floor of coal seams. The coal thickness in an anticline area was smaller than that in the neighboring syncline area. Therefore, the overall variation of coal thickness in the mining areas was likely to have a relation with the direction of the regional principal stress. Keywords: Rock burst, Fold structure, Distribution pattern, Changes of coal thickness, Principal stres