1、19翻译部分英文原文Stress analysis of longwall top coal cavingHabib Alehossein， Brett A. Poulsen CSIRO Exploration & Mining, Brisbane, AustraliaUniversity of Queensland, Brisbane, AustraliaABSTRACTLongwall top coal caving (LTCC) is a relatively new method of mining thick coal seams that is currently achievin
2、g high productivity and efciency 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. In modern
3、 LTCC an additional rear conveyor belt is located behind the support, to which the ow of the caved coal from the upper part of the seam can be controlled by a moveable ipper attached to the canopy of the support.The mining method relies on the fracturing of the top coal by the front abutment pressur
4、e 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 single number calle
5、d 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 behaviour. The yield and
6、 caveability criteria are in agreement with results from both numerical studies and mine data.The caving number 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 varying success w
7、ith 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 conditions. 1.
8、INTRODUCTIONTop coal caving is an economical underground mining method,which has recently been introduced, modied and practiced in the underground coal mines of China. The method and its consecutive modications can be linked to the original method of soutirage mining developed in France during the 1
9、960s 1. Longwall top coal caving (LTCC) is cost effective because only the lower part of a coal seam is cut by a mechanical cutter and the upper part is allowed to cave under gravity, provided the ground conditions are appropriate 214. Chinese experience has highlighted the importance of the stress
10、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 concept of a typical abutment stress change as a result of mining by the modern LTCC 5. As shown in the gure, a major difference between the modern LTCC and traditiona
11、l longwall mining methods is the existence of an additional rear conveyor belt behind the support, on which the caved coal from the upper part of the seam is drawn by a moveable ipper attached to the canopy at the rear of the support. The mining method relies on the fracturing of the top coal by the
12、 front abutment pressure to achieve satisfactory caving into the rear conveyor. Because of the high efciency and output, this technique is, at present, popular for thick coal seams, particularly in China.There are several favourable characteristics observed in LTCC. Support load normally increase wi
13、th coal seam height, however, a rise in the cutting height of the coal seam may reduce the LTCC support load. The movement 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 th
14、e normal and shear loading of the support structure may not be either uniform or the same as considered in the design, which 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 d
15、amage resulting in excessive operational costs. In practice, there is a relation between the support load and the support 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 gene
16、rated 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 thickness and dip angle of the coal seam. For example, if coal is too strong, or the front abutment stress peak is too low, then the coal ahead of the face may not be sufciently fractured to cave into the rear conve
