The research on the fractured blocks of the top coal in the longwall top coal caving technique of the hard coal seam;

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.

To make out the distributing character of joint and crack、chang of crack and breakage developing process of top coal with advancing of workface to hard top coal of coal seam No.

Study for macro-damage degree of weakening blast in hard top-coal;

Distribution characteristic of breaking extending area of weakening-blast in hard top-coal;

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.

The control parameters of strata stress field in pre cracked top hard coal bed are researched using water fracturing under controlling of strata stress field, and the relationship between water seepage, expanding in occlude type of top coal crack and strata stress value is analyzed in this condition.

The technology soften the mechanic property of top hard coal effectively.