Study On Mining Overlying Strata Movement And Fracture Evolution Law In Shallow Coal Seam With Gully Developed Landscape

Shallow coal seams with gully-developed landscape are common in northwest mining area of China. Strata-pressure behavior law of working face and surface fracture present new characteristics due to more sensitive and intensive interaction between gully-developed coal seams and conventional ones. Water in the gully, which can flow into working face through strata fractures, has an adverse impact on safe and efficient coal mining. Based on geological conditions of shallow gully-developed No.1 Selian Mine, this paper studied overburden movement and fracture development law of shallow gully-developed coal seams mining with the combination of theoretical analysis 、 numerical simulation 、 physical simulation 、 transient electromagnetic exploration and field measurement. The thesis obtained the following results:(1)Establish models of numerical simulation and physical simulation to analyze overlying strata movement law during passing gully. Overburden movement before developing into gully is basically identical to that of conventional coal mining. Gully affected overburden movement significantly in the process of passing gully, periodic broken step and intensity of main roof、movement characteristics of gully slope and vertical stress 、displacement change、roof collapse and support behavior of strata under main roof and gully showed greater difference in contrast with conventional mining.(2)Field test validated the significant changes of strata behavior law of working face during passing gully compared with that of general shallow coal seams:(1)maximum working resistance of support rose;(2)dynamic load coefficient of pressure increased;(3)periodic weighting length was obviously different under gully. Different regions of gully presented characteristics as follows:(1)periodic weighting length of mining back gully is smaller than that toward gully;(2)working resistance of support of mining back to gully is larger than that toward gully;(3)dynamic load coefficient induced by mining back to gully was larger than that toward and under gully.(3)Analyzed fracture development law during working face passing gully and found slopes toward gully and in the back showed a reverse trend toward gully when fracture developed to gully. Filed measurement of slope cracks toward gully indicated that crack shape were mainly wave type, approximate line type, step sinking, graben etc and the method of safe passing gully through height drop was proposed.(4)The overburden fracture development of face during passing gully was detected by PROTEM CM transient electromagnetics and temporal change law of viewpoint resistivity、ground fracture development and water level change of aquifer were analyzed. The results showed that fissure of working face connected to gully and verified numerical and physical simulations.(5)Aiming at more rain and ponding in summer and less and frozen in winter and considering overburden movement and fracture development law of shallow coal seams with gully-developed landscape, this paper presented some controlling techniques, such as passing in non-flood season, height dropping and accelerating advancement under gully, which achieved safe and efficient mining of shallow seams during passing gully.