综放开采顶煤的三个特征变形参数及多次损伤分析

对顶煤变形的三个特征参数进行了分析,得出在不同条件下不同参数的变化规律,对顶煤的变形内在因素进行了更深入的研究,认为顶煤变形是一个多次损伤的过程,而多次损伤的关系就是顶煤与顶板的相互作用结果。在一定的顶煤变形、损伤因子、顶板和顶煤特性基础上,可以确定顶板与顶煤应力作用形式。而这些结论和观点是研究综放开采围岩活动和支架围岩关系的关键。

Fracture mechanics model of fully mechanized top coal caving of shallow coal seams and its application

Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack's length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam.

Effects of caving–mining ratio on the coal and waste rocks gangue flows and the amount of cyclically caved coal in fully mechanized mining of super-thick coal seams

Aimed at determining the appropriate caving–mining ratio for fully mechanized mining of 20 m thick coal seam, this research investigated the effects of caving–mining ratio on the flow fields of coal and waste rocks, amount of cyclically caved coal and top coal loss by means of numerical modeling. The research was based on the geological conditions of panel 8102 in Tashan coal mine. The results indicated the loose coal and waste rocks formed an elliptical zone around the drawpoint. The ellipse enlarged with decreasing caving–mining ratio. And its long axis inclined to the gob gradually became vertical and facilitating the caving and recovery of top coal. The top coal loss showed a cyclical variation; and the loss cycle was shortened with the decreasing in caving–mining ratio. Moreover, the mean squared error(MSE) of the amount of cyclically caved coal went up with increasing caving–mining ratio, indicating a growing imbalance of amount of cyclically caved coal, which could impede the coordinated mining and caving operations. Finally it was found that a caving–mining ratio of 1:2.51 should be reasonable for the conditions.

Study on first caving fracture mechanism of overlying roof rock in steep thick coal seam

Based on the elastic plate theory, a mechanical model of thin plate for the first caving of overlying roof rock in steep mining face was established. The analytical solution of the deflection and stress distribution of roof rocks was obtained. According to the specific geological conditions of the 5-103 panel in Shanxi,the failure of roof rocks and the influence of seam dip on it during the exploitation were theoretically investigated. Meanwhile, the first caving characteristics of the overlying rock in the steep coal seam were investigated based on its stress contour. The results show that the dip angle has a distinct influence on the caving interval and the first caving interval for the 5-103 panel is 37 m in theory. Finally, a systematic monitoring on the behavior of rock pressures was conducted. The measured results agree well with the theoretical prediction, which provides a good reference for practical steep coal seam mining.

DIFFERENT ROOF BEHAVIOUR UNDER DIFFERENT UPPER MINING BOUNDARY CONDITION IN DATONG

Understanding roof behaviour and immediate roof failure patterns of longwall face is a prerequisite for establishing correct roof control theory and appplying effective roof control measures. Roof behaviour and immediate roof failure pattern have a close relationship with upper mining boundary conditions of longwall face. According to actual situation of Datong Mining Area,upper mining boundary conditions of longwall face have been classified into 5 types in this paper.Roof behaviour and immediate roof failure pattern under each upper mining boundary condition are discussed in details.

Trial of small gateroad pillar in top coal caving longwall mining of large mining height

Coal seams in Tashan Mine of Datong Coal Group in China average 15 m thick and have been mined by the top coal caving longwall mining method of large mining height. Mining height was 3.8 m and the top coal caving height was 11.2 m. The gateroad pillar between panels was 38 m. During retreat mining,serious bumps occurred in the gateroads on both sides of the pillar affecting safety production. Therefore,pillarless mining was experimented. Using numerical modeling and comparative study of cases of similar mining condition,it was decided to employ a 6 m wide pillar,rather than the previous 38 m wide pillar.Support system for the gateroads was designed and implemented. During gateroad development,pillar failure conditions and entry deformation were monitored. Hydraulic fracturing method was employed to cut off the K3 sandstone along the entry rib so as to reduce the abutment pressure induced during retreat mining. Support reinforcement method combining grouting and advanced reinforcement methods was proposed to insure stable gateroad ahead of mining. Methane drainage and nitrogen injection were implemented to eliminate hazards associated with mine fire and spontaneous combustion. Since the development of gateroad has just completed,and retreat mining has not begun,the effectiveness of the proposed methods is unknown at this point. However,monitoring will continue until after mining.The results will be published in a separate paper.

The Research of thick seam mining methods

China＇s total coal reserves are enormous, in which recoverable reserves of coal seam thickness ofmineable coal reserves in China accounted for 43% of recoverable reserves When correctly using thick seam mining, mining methods can improve the proper thick seam mining rate and reduce coal loss. Using proper thick seam mining method can effectively reduce the thick seam mining costs. In mining safety, the use of appropriate thick seam mining methods can effectively prevent thick seam mining accidents. But in the process of development and current situation from the perspective of the Chinese coal mining, there are certain aspects of thick seam mining problems. These problems are mainly in the thick seam mining and the coal recovery rate is low, resulting in lots of waste coal. Besides, thick coal mining is less secure, safe and there are frequent accidents. These problems have seriously affected the thick seam mining. And a lot of thick coal seams of coal resources can not be effectively taken out. Now Chinese mining methods in thick seam mining areas are mainly open-pit mining and underground mining exploitation. Because of the open-pit coal burial depth has more stringent requirements, only used in shallow-depth areas. Underground mining is the primary way China is now using in thick seam mining. Underground mining methods include full-height slice mining and mechanized mining caving mining method once adopted. Research on these thick seam mining methods can provide theoretical and technical support for thick seam mining, thick seam mining techniques to enhance the level . I will combine the current situation of thick seam mining in Chinese study with thick seam mining methods, comments and suggestions for the current thick seam mining study

GENERAL RELIABILITY THEORY STUDY ON SEMI-FLEXIBLE OUTPUT TYPE AND REPAIRABLE PRODUCTION SYSTEM

This paper puts forward the conceptions of semi-flexible units and semi-flexible system, and builds up the theory of semi-flexible output type and repairable production system general reliability analysis and general reliability design, which discusses the reliability problems of semi-flexible units and semi-flexible system from three aspects of time, task and capacity.