1、翻译部分英文原文Stress analysis of longwall top coal cavingAlehossein, Habib1,2 Habib.Alehosseincsiro.auCSIRO Exploration & Mining, Brisbane, AustraliaUniversity of Queensland, Brisbane, AustraliaAbstract:Longwall top coal caving (LTCC) is a relatively new method of mining thick coal seams that is currently
2、 achieving high productivity and efficiency in application, particularly in China. The technique is similar to traditional longwall mining in that a cutting head slices coal from the lower section of the coal seam onto a conveyor belt installed in front of the hydraulic support near the cutting face
3、. In modern LTCC an additional rear conveyor belt is located behind the support, to which the flow of the caved coal from the upper part of the seam can be controlled by a moveable flipper attached to the canopy of the support. The mining method relies on the fracturing of the top coal by the front
4、abutment pressure to achieve satisfactory caving into the rear conveyor.This paper develops a yield and caveability criterion based on in situ conditions in the top coal in advance of the mining face (yield) and behind the supports (caveability). Yielding and caving effects are combined into one sin
5、gle number called caving number (CN), which is the multiplication result of caving factor (CF) and yield factor (YF). Analytical derivations are based on in situ stress conditions, MohrCoulomb and/or HoekBrown rock failure criteria and a non-associated elastoplastic strain softening material behavio
6、ur. The yield and caveability criteria are in agreement with results from both numerical studies and mine data.The cavingnumber is normalised to mining conditions of a reference Chinese mine (LMX mine) and is used to assess LTCC performance at fourteen other Chinese working longwalls that have had v
7、arying success with the LTCC technology. The caving number is found to be in good agreement with observations from working LTCC mines. As a predictive model, results of this analytical/numerical study are useful to assess the potential success of caving in new LTCC operations and in different mining
8、 conditions.Keywords:LTCC；Caving; Chinese caving index (CCI); Plasticity; Mohrcoulomb; Numerical; Finite difference; Finite element method (FEM); Discrete element method1.IntroductionTop coal caving is an economical underground mining method, which has recently been introduced, modified and practice
9、d in the underground coal mines of China. The method and its consecutive modifications can be linked to the original method of soutirage mining developed in France during the 1960s. Longwall top coal caving (LTCC) is cost effective because only the lower part of a coal seam is cut by a mechanical cu
10、tter and the upper part is allowed to cave under gravity, provided the ground conditions are appropriateChinese experience has highlighted the importance of the stress abutment peak in fracturing the coal in advance of the face to allow the coal to cave onto the rear conveyor. Fig.1 illustrates the
11、concept of a typical abutment stress change as a result of mining by the modern LTCC. As shown in the figure, a major difference between the modern LTCC and traditional longwall mining methods is the existence of an additional rear conveyor belt behind the support, on which the caved coal from the u
12、pper part of the seam is drawn by a moveable flipper attached to the canopy at the rear of the support. The mining method relies on the fracturing of the top coal by the front abutment pressure to achieve satisfactory caving into the rear conveyor. Because of the high efficiency and output, this tec
13、hnique is, at present, popular for thick coal seams, particularly in China. Fig. 1There are several favourable characteristics observed in LTCC. Support load normally increase with coal seam height, however, a rise in the cutting height of the coal seam may reduce the LTCC support load. The movement
14、 of the overburden rock stratum over the coal face shows periodicity due to cantilever beam effects, although this periodic effect is not very strong. However, distribution of the normal and shear loading of the support structure may not be either uniform or the same as considered in the design, whi
15、ch can cause non-uniform reaction forces and moments in the support system. In other words, an excess force or moment in an element of the support structure can cause permanent damage resulting in excessive operational costs. In practice, there is a relation between the support load and the support
16、structural behaviour. In particular, there is a mechanical relation between the recorded hydraulically powered force of the support system and the normal and friction forces generated in the props in relation to the fracturing, yielding and caving processes of the top coal.Chinese experience indicates that application of modern LTCC in thick coal seams is limited by the overburden rock, coal strength and thick
