Classification of conditions for short-wall continuous mechanical mining in shallowly buried coal seam with thin bedrock

The room and pillar method is usually used to extract coal from shallowly buried seams with thin bedrock. This results in a very low production efficiency and in a low degree of extraction. In recent years short-wall continuous mechanical mining has been extensively used in many situations except shallowly buried coal seams with thin bedrock. The principles governing movement of the overlying strata above the 2-2 coal seam were deduced from in-situ experience, laboratory data, calculations and computer simulations. The thicknesses of the bedrock in the Shendong Coal Field where the coal is shallowly buried are classified into 5 types: <10 m, 10–15 m, 15–25 m, 25–35 m and >35 m, which was done using fuzzy clustering results. A series of reasonable, relative parameters in each category have been calculated and analyzed. One proposed way to perform short-wall continuous mechanical mining in shallowly buried coal seams is given. This is significant for coal mines with similar geological conditions.

Practice and adaptable conditions classification of aquifer-protective mining in longwall coalface for shallow seam with thin bedrock

A set of adaptable conditions classification of aquifer-protective mining in thelongwall coalface for shallow coal seams with thin bedrock was put forward to deal withthe conflict between water protection and high efficiency for the mining field in west China.This classification was suitable for shallow coal seams with different thickness and wasbeneficial to the local environmental protection.Using the 3-Universal Distinct ElementCode (3DEC) numerical software, the height of the fractured zones for shallow coal seamswith thin bedrock was calculated and analyzed, and its predicting formula was achieved.Meanwhile, according to the lithology and the weathering degree of the shallow coal seam,the thickness of the protective layer was determined as 10 m and the overlying water bodyof loose water-bearing sand for shallow coal seams with thin bedrock was divided intothree types, namely, weak, medium and strong.Based on these, the necessary bedrockthickness of the longwall coalface for shallow coal seams with thin bedrock was confinedaccording to the different mining height and water yield nature of the overlying loose water-bearing sand.Combined with the present mining status, a set of new methods ofadaptable conditions classification of aquifer-protective mining technology in the longwallcoalface for shallow coal seams with thin bedrock was put forward.

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Numerical simulation analysis by solid-liquid coupling with 3DEC of dynamic water crannies in overlying strata

To solve the problem of water loss during mining of shallow, buried coal seams, we have first analyzed the mechanism and suitability of solid-liquid coupling, i.e., we used the FLUID-MECHANICS system of 3-Dimensional Distinct Element Code (3DEC) in simulating dynamic water crannies in overlying strata, under mining conditions of a large longwall coalface. Next the dynamic initiation of a water cranny, its propagation and close phases were studied with 3DEC, along with the overlying strata breakage and recombination as the mining space of the shallow, buried coal seam increased. Combined with the change in the stress and displacement fields, the distribution features of the mining cranny were systematically studied. The effect of regularities and their effective measures of local filling and mine slicing technology in controlling mine crannies were investigated and the potential danger areas of water loss identified. Our results can be applied to decrease water loss during the exploitation of shallow, buried coal seams with a thin bedrock. The results also prove that 3DEC is a credible numerical analytical method to predict initiations of dynamic water crannies, their propagation, their closure phases and other concomitant hazards.

Structural effect of a soft-hard backfill wall in a gob-side roadway

The stability of a backfill wall is critical to implement gob-side entry driving technology in which a small coal pillar is substituted by a waste backfill wall. Based on features of surrounding rock structures in the backfill wall, we propose a mechanical model on the structural effect of a soft-hard backfill wall using theory analysis, physical experiments and a numerical simulation. The results show that the deformation of the structure of the soft-hard backfill wall is coordinated with the roof and floor. The soft structure on the top of the backfill wall can absorb the energy in the roof by its large deformation and adapt to the given deformation caused by the rotation and subsidence of a key rock block. The hard structure at the bottom of the backfill wall can absorb the strong supporting resistance from the top surrounding rock. The soft structure on the top protecting the hard bottom structure by its large deformation contributes to the stability of the entire backfill wall. An application indicated that the stress in the backfill wall effectively decreased and its deformation was significantly reduced after the top coal remained. This ensured the stability of the backfill wall.