Study On The Overburden Movement Principle And Integrated Water-sand Prevention And Control Technology Of Fully-mechanized Top Coal Caving Under Soft Overburden And Multi-aquifers

The study on the fully-mechanized top coal caving under soft overburden and strong aquifers in the first mining panel of Mindong No.1 mine with particular strata is greatly significant for either safe production or surface ecological environment suffered from impact of coal mining.In this work,the water abundanceof aquifers was assessed and the water control scheme was proposed with the consideration of overburden movement principle and the effect of water filling and sand bursting on face.The main results of this study are listed as follows:(1)Based on the geological data,the filling water source and water abundance of aquifers in the first mining panel was thoroughly explored by employing surface electrical survey and underground mine electrical prospecting.It was found that these two detection methods played an important role in supplying hydrogeological information becausethe result obtained from them suited well with field situation.(2)The height of “two-zone” in overlying strata of the first mining panel was measured by drilling hole and injecting water experiment.The results indicated that the height of caving zoneand fractured water-conducting zoneis 36.65 m and 3.78 m respectively;the height ratio of caving zone and fractured zone to coal seam is 4.76 and 10.88 respectively.Moreover,based on the mechanical properties testand simulation parameters calibration in UDEC,the inversion of overburden movement characteristics and “two-zone” heights with different mining heights can get biggest and smallest value of caving-height ratio is 4.25 and 3.5 respectively,and which of crack and mining ratio is 11 and 8.1 respectively.The modelling results fitted well with measured data.(3)The development of water-conducting fractures was studied by using analogy simulation.It showed that first caving step of immediate roof was notably greater than measure in field while the periodical caving step of main roof was close to field data.The strata in caving zone shown as layers filled gob,which cause the heights of the two zones gained from test was greater than in-situ measure.To solve these problems,we can lay granular dinas,construct joints and increase the strength of immediate roof to process the strata for improving the simulation reliability.(4)On the basis of the research above,contrast tests were carried on to explore the effect of different grain diameters(0-0.5 mm and 0.5-1 mm)of fine sand aggregate on the development of water-conducting zone in strata.The result indicated that strata strength augmented with the decrease of grain diameter,and the main failure mode of test specimenturned from shear form to tensile form with the increasing grain diameter.Additionally,the larger the grain diameter is,the bigger caving step of strata would be,which is conducive to the development of water-conducting fractures.(5)By analyzing the hole data and water-controlled measures in Mindong No.1 mine,water control system was built aiming at hindering water disaster in fully mechanized caving face under soft overburden and strong aquifers.