After analyzing fully-mechanized sub-level caving technology in the case of special thick and hard coal seam, it is presented that the increment of cavability of hard roof coal and available control of gas are the main difficult technology problem to be faced.

Manufacture of fully-mechanized sublevel caving hydraulic support for hard and superhigh seam;

Study on top coal blasting technique of full mechanized caving in the hard thick coal seam;

During caving the hard thick coal seam,the weakening treatment of top coal is a key problem influencing the comprehensive benefits of coal mine.

The paper describes selection of key equipment and relationship among them in fully-mechanized roof-caving face in hard thick coal seam.

Based on the practice of the worksite with extra hard thick seam fully mechanized mining coal caving, the pattern of activities of the roof using fully mechanized mining coal caving located in Jincheng mining area 3 # seam, caving techniques and parameters are analyzed and summarized.

The paper introduces how to select coal plow in accordance with measuring cutting resistance of the machine in hard coal seam and analysing the result.

Cutting resistance test of hard coal seam and the analysis of its difficulty degree of digging were introduced in this paper with an example of full-automatic slicer successfully used in the mining of hard coal seam in Jinhuagong Colliery of Datong Colliery Group.

The paper mainly applied the theory of fracture mechanics to deduce the formular of the minimum water pressure, analyzed the influcential factor which had influcence upon water infusion pressure in the steep hard coal seam, and revealed the relationship between water infusion pressure and coal seam pitch and depth.

These are obviously different from those of the commonly soft or medium-hard seam fully mechanized caving feces.

Base the seam conditions of hard, density, undeveloped joints and cracks, and 16 m average thickness, with the pre-comprehensive weakening technology and the mining technology study of the coal mining face, the difficult issue of the fully mechanized high top coal caving mining in hard seam has been overcame with a safe and high efficient production.