The traditional calculation method of the surrounding strata pressure of the tunnel does not consider the tunnel construction process. The excavation of the large-section tunnel mostly adopts the section excavation method, which is to excavate and support at the same time. The stress state of the pressure of surrounding strata changes gradually during the excavation process. The traditional calculation results of tunnel surrounding strata pressure are generally large. In this paper, the large-section tunnel is simplified into three parts, and the degree of influence (η1, η2, η3) of the excavation height h and width b of the advance pilot hole and the distance d between the advance and rear pilot tunnels on the surrounding rock pressure calculation are analyzed. The regression equation for calculating the influencing factors (tunnel depth H, tunnel span B, internal friction angle ϕ, and rock weight γ) of surrounding rock pressure (p) is established. Through the numerical analysis, the influence coefficient η is obtained, the weight coefficient is introduced, and the computing formula of the pressure of surrounding strata of the large-section tunnel excavation is derived. The formula is used to the computing of the pressure of surrounding strata with a large-section subway station and the correct conclusion is obtained.
In this paper, the evolution characteristics of overburden caving and void during multi-horizontal sectional mining in steeply inclined coal seams are studied. Based on the typical engineering background of steeply inclined coal seams mining in Wudong Coal Mine, the physical simulation model is build. The evolution characteristics of overburden caving and void during multi-horizontal sectional mining is systematically studied, combined with the monitoring data of overburden infrared thermal image, void ratio, void network fractal dimension, and peak mine pressure. It is showed that, during multi-horizontal sectional mining in steeply inclined coal seams, the movement rule of overburden is extremely complicated, and the temperature changes in infrared thermal image were significant.
This paper is aimed at solving the technical problems such as low recovery ratio and frequent disasters in steeply inclined and extrathick coal seams at residual high sectional coal pillar. It takes the Wudong Coal Mine as an engineering background, a typical mine of steeply inclined and extrathick coal seams; the structural features of the top-coal caving at the steeply inclined residual high sectional coal pillar were analyzed using methods such as field monitoring and numerical simulation; a mechanical model of the top-coal arch structure was constructed, and the calculation method of top-coal caving height and related influencing factors was obtained. The results showed that the top-coal caving in the steeply inclined residual high sectional coal pillar was characterized as arch. Due to the existence of arch structure, the smooth caving of the top coal was hindered, resulting in a low top-coal recovery ratio, low support pressure at the working face, and differences detected by borehole television on the distribution of the top-coal cracks. With the advancement of the working face, the top-coal arch structure was in the process of dynamic evolution, as the old arch balance system was continuously replaced by the new arch balance system, and it continuously moved towards the upper top coal. The top-coal caving height was affected by factors such as length of the working face, bulk density of overlying coal rock, and cohesion of the top coal. The top-coal caving height increased with the length of the working face and the bulk density of the overlying coal rock mass but was inversely proportional to the cohesion of the top coal. Under the current mining conditions, the top-coal caving height was 39.8 m, which was much lower than the residual high sectional coal pillar height (71 m); the top coal cannot collapse completely. Based on the characteristics of the top-coal caving structure, the technology of sublevel advanced presplitting blasting was adopted to weaken the top coal in engineering practice, so that the top-coal caving structure moved up naturally. The daily coal production in the working face has increased by an average of 2419.6 tons, which has significantly improved the top-coal recovery ratio and production efficiency. The result provided a theoretical basis and application reference for similar residual high sectional coal pillar recovery.
Strata stress distribution and roof moving characters and rock deformation of roadway retainingalong gobControl, is introduced in this paper. The theory with strata blasting is referred.The theory is used to design roof support in roadway retaining along gob in Mine Chengshan seam No23 faceR7. The loading to control construction technology and technical requirement is pointed out.Field test was held, The test results show that strata blasting is effective and feasible technology roof control in roadway retaining along gob.
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