Ground Control Mechanism Of Mining Extra-thick Coal Seam Using Upward Slicing Longwallroadway Cemented Backfilling Technology

After years of development,thick coal seam has become the main coal seam in China.The coal production from thick seam accounts for 45% of the total coal yield approximately.Therefore,thick coal seam mining with special geological conditions,such as aquifers,buildings and railways on the surface,is a deeply concerned issue.Especially the seam with a thickness of 8 meters or more,its mining activity damage the overburden seriously and the ground control is very difficult.Although backfill has been proved to be an effective way to control the ground for mining,the mature backfill technology to mine extra-thick coal seam with a high recovery ratio and the filling ratio has not formed yet.In this thesis,the upward slicing longwall-roadway cemented backfill mining technology(USL)is established for the extra-thick coal seam.Comprehensive methods including laboratory test,statistical analysis,mechanical analysis,physical and numerical simulation and field application are used in this research.The core technical parameters such as the distance between backfill mining crosscuts and the lateral pressure on the backfill barricade are analyzed.The supporting cemented backfilling material is developed and the influence of the ratio on the rheological and mechanical properties of the cemented backfill mixture are studied.The roof control mechanism,overburden movement and strata behavior during mining extra-thick coal seam with USL are studied.The USL is applied in the field with good results.The innovative results of this thesis are as follows:(1)The cemented backfill material with gangue,fly ash and the mixed binder is developed.The influence of the ratio on the rheological properties of the backfill is studied by converting the slump value into yield stress.The evolution characteristics of the strength and the Poisson's ratio of backfill material under the coupling effect of ratio and curing age are presented.The prediction model of the cemented backfill material based on the improved BP neural network and the measured data is established,and the mechanism of the influencing factors is revealed.(2)The dynamic non-uniform composite elastic foundation beam model is established to study the roof deformation characteristics in the process of extra-thick coal seam mining with USL.The mechanism of roof movement control is analyzed and the performance requirements of backfill material are proposed.The time-dependent evolution of lateral pressure on backfill barricade is calculated based on the time-dependent rheological properties of cemented backfill.(3)The vertical displacement,fracture development and stress evolution of overburden are analyzed using a combination of physical and numerical simulation.It is revealed that the ground control principle of mining extra-thick coal seam with USL.The study shows that the disturbance of overlying strata caused by the exploitation of fifth slice and sixth slice is significantly greater than any other slice.(4)The method of USL for mining extra-thick coal seam is presented.The production system and technology of mining and backfilling are designed and applied to Gonggeyingzi coal mine to mine the extra-thick coal seam with the thickness of 21 meters under the aquifer,the field measured results show that the application is effective.