Study Of Mechanism Of Surface Subsidence When Deep Mining Under The Weakly Cemented Overburden

In order to provide reference for the assessment of mining surface damage in the deep mining area under the weakly cemented overburden in the west,the Hugierte and Nalinhe mining areas are used as examples.Using the research methods of actual measurement research,indoor simulation and theoretical analysis,the geological and mining conditions in the study area are introduced,the special laws of mining subsidence in the study area are summarized,and the inherent mechanism is revealed.Research indicates:(1)Overburden rock in the study area is Jurassic-Cretaceous.The burial depth of the coal seam ranges from 500 to 800m,and the lithology of the overburden is mainly sandstone,which can account for up to 61.3%.The layered thickness of sandstone is large,and the proportion of sandstone with layered thickness greater than 10m can be as high as 67.4%.The Cretaceous stratum contains weakly cemented sandstone with poor cementing properties and soft and fragile.The microscopic composition of the sandstone is mainly brittle minerals,the clay mineral content is extremely low,the maturity of rock and mineral components is relatively low,the internal structure is loose,and the pores The rate is too large and the pore diameter is too large.When the weakly cemented sandstone is subjected to external loads,it can release large plastic deformation in the pore compaction stage,and the post-peak failure stage exhibits the characteristics of brittle failure.The mechanical strength and stiffness of weakly cemented sandstone are relatively small,no significant expansion occurs in water absorption,the initial crushing expansion coefficient is relatively high,but the residual crushing expansion coefficient is relatively low.Although the mechanical strength of the overburden rock in the study area is generally low,showing the property of weakly cemented overburden rock,the overburden rock is not all soft rock with compressive strength less than 25MPa.Compared with the Cretaceous sandstone,the Jurassic sandstone has a dense internal structure and high rock maturity.The mechanical rigidity and strength are generally greater than the Cretaceous sandstone.Most of them are weak to semi-hard rocks,and some are hard rocks.There are multiple layers of thick and hard sandstone rock mass in the entire deep stope.The coal mines in Hugierte Mining Area and Nalin River Mining Area adopt comprehensive mechanized mining technology of full-height mining to recover coal resources,and adopt the collapse method to manage the roof.(2)The average fore effective angle of some coal mines in Hujierte and Nalinhe mining areas is 79.5°,angle of the maximum subsidence velocity lag is 54°,subsidence ratio of the first mining face is 0.051~0.18,tangent of main influence angle is 0.7~1.49.The integrated limit angle in the strike direction is 55°,the integrated boundary angle in the downhill direction is50°,and the integrated limit angle in the uphill direction is 46.5°.The inflection point offset is generally 0.07H~0.1H,and the propagation angle of mining subsidence is generally 89°.Compared with some coal mines in the eastern mining area and the Shendong mining area,the mining surface subsidence law of the Hugierte and Nalinhe mining areas presents some characteristics of coal mining under the condition of hard overburden rock,and the mining movement surface boundary of some coal mines in the mining area is deviated Big.(3)When the overlying rocks are weakly cemented soft rocks,the mining subsidence law does not show some of the characteristics of coal mining under the conditions of hard overlying rocks;the mining surface subsidence of coal mining under weakly cemented sandstone is generally less than that under clay Mining surface subsidence;multiple layers of sandstone rock with large thickness and high mechanical strength control overburden movement and surface subsidence in Hugierte Mining Area and Nalinhe Mining Area,leading to mining subsidence law in this mining area It presents some characteristics of coal mining under the condition of hard overburden.At the same time,it was found that the cracking ratio of mining overburden in the study area is generally greater than 18,and based on the measured value of the height of the water-conducting fissure zone of the mining overburden in the Hugierte mining area,an empirical formula for predicting the height of the water-carrying fissure zone in the mining area is given:H=24M+4(R~2=0.99),which can be used as a reference for major coal mines in this mining area.There are 55 pictures,24 tables,and 110 references in the paper.