Since the middle of 1980Õs, the longwall top-coal caving technique has developed rapidly in China. At present, it is one of the main approaches in the thick coal seam mining. This paper describes some mechanics problems of the caving technique, such as the damage and failure of the top-coal, the strata behaviors in the caving face, and the relation of the support and the surrounding rock. In order to employ the caving technique in a widespread scope, the problems such as the caving technique in the hard coal seam, the moving and running of the loose top-coal, and the upper floating of the gas etc. should be systematically studied.
The longwall top-coal caving Technique was invented in Europe. France, Soviet Union, Yugoslavia, Romania and Czechoslovakia etc. began to mine the thick coal seam by using the caving technique in the 1950Õs. Because the technique was mainly used in irregular working faces, the output of the face was no more than that of the common longwall face. From the middle of 1980Õs, the number of the working faces with caving technique began to decrease in Europe. At the beginning of 1990Õs, only a few collieries employed the caving technique. In 1984, China applied its first longwall top-coal caving system in the gently inclined seam, and initiated the top-coal caving experiment and application. Because of the imperfection of the support, the relevant equipment and production system, added with lacking in administrative experience, the experiment was failed. After that, the experiments on the sublevel caving technique in the thick steep seams were separately done in some coal mines and all were successful. In 1990, the top-coal caving experimental research on the gently inclined thick coal seam was done in Luan coal mine administration and Yangquan coal mine administration in Shanxi province.