Study On The Law Of Pressure Appearance Of Forced Roof Caving Near Short Wall Face In Shallow Seam Of Shi-Yangou Coal Mine

Shallow-buried coal seams have significant ore pressure,and high-resistance hydraulic supports are generally used in fully mechanized mining face.For the small and medium-sized coal mines in the shallow coal seam in northern Shaanxi,which are restricted by the mine field area and resource reserves,how to achieve the safe advancement of the working face under the conditions of reducing the length of the working face and selecting medium resistance hydraulic supports is worthy of in-depth study.The thesis focuses on the occurrence characteristics of shallow buried medium-thick coal seams in Shi-Yangou coal mine and the characteristics of the near-short wall layout of working face.Theoretic analysis,physical similarity simulation,numerical simulation and field test research methods were adopted.The law of rock pressure appearance and support resistance under two conditions of forced roofing were compared and analyzed,and the applicability of combined suspension support near short wall face was analyzed.Theoretical analysis was based on the theory of elastic mechanics,the basic roof thin plate mechanical model of the shallow coal seam near the short wall working face was established,and the basic roof breaking criterion is given;with the help of the key layer theory,the normal mining of the Shi-Yangou coal mine 8105 working face is determined the limit span of the first break of the basic roof is 58.12m.It is clear that the limit span and cycle pressure step of the basic roof generally decrease with the increase of the height of the cutting roof;determine the length of 50-100m near the short wall working face,the range is the area where the basic roof breaks have significant changes.The working face adopts near-short-wall layout,and the area of the rock slab that is basically broken for the first time is relatively small,which is beneficial to the control of the mining face pressure.The physical similarity simulation carried out a comparative test study,which showed that the first step of normal pressure face was 56m,the average step of periodic pressure was 14.2m,and the fifth,sixth and ninth period of pressure face of working face all occurred.Roof rock strata falling along the coal wall;under the condition of forced roof caving(caving height is 7m away from the coal roof),the first step of the face pressure is increased to 69m,the average step of the period pressure is 17.7m,and the average time of the period pressure is There is no rock falling along the coal wall;the forced cutting state is more normal mining,which reduces the support strength and rated working resistance of the working face bracket.The numerical simulation studies the bearing pressure and the peak point position in front of the coal wall of the working face,and shows that the use of forced roof caving can reduce the leading bearing pressure value of the working face,and the peak point of the supporting pressure is reduced from the working face in the early stage of the face.The distance of the coal wall helps to reduce the risk of the roof rock layer caving down along the coal wall of the working face.The on-site mine pressure monitoring verified that the pressure step of the 8105 working face is basically the same as the pressure step of the physical similarity simulated forced caving;the 8105 working face uses the ZH4200/17/25LP chain type beam-splicing hydraulic support,and the maximum work is measured.The average value of resistance is 1701.2kN,and the pressure manifestation value when the working face is first pressed is 3675.1kN.The ZH4200/17/25LP chain type beam-splicing hydraulic support selected for this working face can fully support the roof.The study on the law of the pressure appearance of the forced roof caving in the short wall face of the shallow seam in shiyangou coal mine will provide theoretical support for the reform of the mining methods and support methods in the middle and small coal mines in Northern Shaanxi,and also have reference significance for the mining of the working face with similar geological conditions.