長壁式採掘時の地山挙動解析と岩壁圧出機構に関する一考察

Abstract

First, the features of the ground movement caused by mining a horizontal coal seam are studied by examining the results of the elasto-plastic analysis carried out by Finite Element Method. It is found that the vertical stress distribution in the coal seam, except near the longwall face, is characterized by the widthc, as shown in Fig. 7, which is defined by equation (9), namely it is the amount of the vertical loadP, newly acts on the coal seam by mining, devided by the initial vertical stresspy. As a matter of course, cis equal to the half length of the excavation unless the contact between the hangingwall and footwall occurs in the mined area. But after the contact, it is approximately proportional to the length of the cave behind the longwall face and to the rigidity of the hangingwall.Secondary, the mechanism of coal burst at the longwall face are studied by analyzing the stress histories and the plastic behavior of coal in front of the face, in the case that the coal seam is sandwiched by the rigid hangingwall and the relatively soft footwall as like as in the coal burst area of Miike mine. In the case that the internal friction angle of coal is high and the hangingwall and footwall restrict the swelling of coal, it is found, the plastic area in front of the face is reasonably narrow, the center part of the face partially swells and the high stress concentration appears near the face. In this case, if the slides occur along the boundaries among the coal seam, the hangingwall and the footwall, the plastic coal at the face is restrained the vertical compression of which the value is inversely proportional to the rigidity of footwall. When this plastic compression exceeds the limit strain, permissible for coal before the brittle rupture after the yielding, we conclude, the coal is violently destroyed at the face.