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

Rockburst mechanism caused by the mining-induced drainage of confined water in deep extra-thick aquifer

Extra-thick sandstone confined aquifer is widely spread in the overburden strata in Shaanxi and Inner Mongolia provinces. During coal mining, the water inflow in the working face is severe and the confined water level in the roof aquifer decreases significantly. The monitoring of rockbursts and high-energy seismicity shows that the mining-induced drainage of the confined water in the extra-thick sandstone confined aquifer has a certain effect on inducing rockburst. For a better understanding of rockburst mechanism as a result of the drainage of the roof confined water, the fluid-solid coupling numerical simulations were carried out. The mechanical behavior of rock mass with different pore water pressures and the evolution of stress-energy field in surrounding rock under the condition of mining-induced drainage of the confined water in the overburden aquifer were analyzed, and the effect of the mining-induced drainage of the confined water in aquifer on the stress field in surrounding rock was determined. On this basis, considering the effect of extra-thick strata on the dynamic and static stress in surrounding rock, the rockburst mechanism caused by the mining-induced drainage of the confined water in aquifer was proposed. The results show that the dynamic behaviors under extra-thick confined aquifer, including rockbursts and high energy seismicity, occur during the rapid drop of water level in overburden confined aquifer, and the mining-induced drainage of confined water causes stress disturbance to surrounding rock. Under the condition of mining-induced drainage of the confined water, the pore water pressure of the confined aquifer decreases, the strength and bearing capacity of the sandstone strata increase, and the overburden load is transferred to both sides of the goaf, which results in the increase of the stress and elastic energy in the surrounding rock. The effect of the mining-induced drainage of the confined water in aquifer on the stress-energy field is positively correlated with goaf scale and drainage degree, and negatively correlated with the distance between coal seam and confined aquifer, the thickness and strength of confined aquifer. The large-scale roof cantilever-hinged structures under the extra-thick confined aquifer lead to high static stress and strong dynamic stress in the surrounding rock. Under the effect of the mining-induced drainage of the confined water in the aquifer, the superimposed stress in coal and rock mass exceeds its critical load and the total energy released exceeds the energy consumed by its failure, which induces rockburst. In the process of rockburst, high static stress is the stress basis, and the stress disturbances caused by seismicity and the mining-induced drainage of the confined water are important inducements. In view of the influence of the mining-induced drainage of the confined water and the extra-thick strata structure on the rockburst risk, the confined water plugging of the extra-thick aquifer by ground grouting and optimizing the panel size were put forward. Field application indicates the two measures inferred above can reduce the effect of the mining-induced drainage of the confined water on the stress-energy field, and avoid the formation of the large-scale cantilever-hinged structures, which can reduce the rockburst risk significantly

Key strata of mining-induced seismicity in overburden rocks in coal mines and the energy-releasing mechanism of its fracture

Mining-induced seismicity in strata has become one of the main dynamic phenomena in some coal mines. The theoretical identification of the main controlling rock stratum where mining-induced seismicity occurs is the basis for accurate prevention and control of mining-induced seismicity. In this paper, theoretical analysis, numerical simulation and on-site observation are used. The connotation and type of mining seismic events and mining-induced seismicity are sorted out, and the relationship between mining seismic events and mining-induced seismicity is clarified. The concept of the Key Strata of Mining-induced Seismicity (KSMIS) in overburden rocks is put forward, and the characteristics of the KSMIS are summarized, and the difference between the KSMIS and key strata is presented. The identification method of the KSMIS is proposed, the crack development and energy evolution during the fracture process of the KSMIS are analyzed, and the energy release mechanism for the fracture of the KSMIS is revealed. The results show that: ① Mining seismic events can be classified into micro-seismic events, high-energy seismic events and mining-induced seismicity, and mining-induced seismicity can be classified into overburden rocks, faults, coal pillars, floor, folds and composite types; ② The KSMIS in overburden rocks refers to a layer or group of layers in the roof that control the occurrence and distribution of the mining-induced seismicity, and is classified into two types of high-level and low-level according to the location of the KSMIS; ③ Considering the failure criteria and energy characteristics of thick and hard rock layers, a method of identifying the KSMIS is proposed, and the method is verified by case study; ④ In addition to the crack zones on both sides of the mined area, horizontal shear cracks appeared between the KSMIS and the roof in low position. The strain energy and shear dissipation energy of the interlayer joints were concentrated, and the shear slip between the rock layers occurred. There are strain energy and shear dissipation energy accumulation zones in some areas of the KSMIS, and layering damage exists within the KSMIS; ⑤ When the actual maximum stress of the rock exceeds the strength limit of the rock layer or structural contact surface, the KSMIS will be broken or unstable, resulting in the formation of mining-induced seismicity in overburden rocks. In the process, some of the elastic strain energy and gravitational potential energy is converted into mining-induced seismicity energy as well as various types of dissipation energy, etc. The results of the study can provide theoretical guidance for the prevention and control of mining-induced seismicity in overburden rocks

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

Research on Prevention of Rock Burst with Relieving Shot in Roof

AbstractDuring hard roof rupture or slip instability with the sudden release of large amount of elastic energy, rock burst will be caused by violent shock easily. Based on the geological conditions of 6303 working face in Jisan Colliery, numerical simulation was carried out systematically of relieving shot in roof, then the reasonable parameters of relieving shot was provided. The results of danger-breaking measures of relieving shot in roof on-site shows that the danger of rock burst is reduced with fractured circle connected and values of electromagnetic emission and drillings decreased

A new general fractional-order wave model involving Miller-Ross kernel

In the paper we consider a general fractional-order wave model with the general fractional-order derivative involving the Miller-Ross kernel for the first time. The analytical solution for the general fractional-order wave model is investigated in detail. The obtained result is given to explore the complex processes in the mining rock.</jats:p