Study On Laws Of Overburden And Surface Movement When Mining Under Thick Alluvium

Compared with general geological and mining conditions, there are greatdifferences in the laws of surface subsidence mining under thick alluvium which insome areas of North China, Central China and East China. Due to the particularity ofthe mining subsidence and rock moving when mining under thick alluvium, wegrasped the ground surface movement dynamic-static laws by using fieldmeasurements, similar material simulation and numerical simulation study. We madethorough research in the the overlying strata when mining under thick alluvium andthe moving mechanism of alluvium, and build up bedrock-alluviumcouplingsubsidence model. Meanwhile, we also established soil compression model accordingto the laws of vertical deformation of alluvium. The following is main work andresults in the paper:(1)We grasped the dynamic-static laws of the surface movement in mining underthick alluvium through analysis of observation data in strata movement of severalthick alluviumcoal face in Baodian Coal Mine. Meanwhile, we discovered the laws ofground surface movement parameter variation when mining under thick alluvium bythe comparative analysis between angle dimension parameters and probability integralparameters in the coal face of thick alluvium and the coal face under generalgeological and mining conditions. We made regression analysis on the relationshipbetween surface bedrock, thickness of alluvium and geologic and mining factors inYanzhou mining area, and concluded some empirical formula of surface movementcharacteristic parameters and forecasting parameters suited to this area.(2)Using similar material simulation to study the movement laws of strata andalluvium when mining under thick alluvium. The result shows that there is differencesbetween bedrock and alluvium in the mechanism of moving deformation. The movingdeformation of the bedrock is mainly resulted from spread up of underground mining,but the movement of alluvium is not only due to the mining subsidence along with thebedrock but also make the compressive stratum when the bedrock is relatively flimsy.Therefore the reason of the ground settlement when mining under thick alluvium consists of two parts: mining subsidence and compressive stratum.(3)Based on simulation prototype of geological mining conditions in BaodianCoal Mine, Yanzhou Coal Mining Area, the Flac3D numerical simulation model isestablished. Also using the regression analysis to analys the relationship between thethickness of bedrock and alluvium and the surface subsidence coefficient, themaximum subsidence and horizontal movement. Through analyzing the deformationof alluvium soil, make clear the significant effect and control attction on the alluviumsoil deformation by the bedrock, and the soil deformation laws of different thicknessof alluvium.(4)Based on the analysis of the numerical model simulation, monitoring ofdeformation soil, soil sample test and the hydrology geological data, it considered thatthe water levels fall is just a form of ground surface subsidence which caused thecompression of soil is difficult to reflect in a specific working face, but main reason ofcompression of soil is the effect caused by additional stress. According to the aboveanalysis conclusion, combining experimental study of soil compression and the theoryof “soil arching effect”, the mechanism of soil recopression is put forward, whichthink that the soil of alluvium in the process of subsidence through a process of“unloading–compression”, and based on Terzaghi’s Effective Stress Principle and theDisturbed State Concept (DSC) to get the analysis and solution of soil disturbedcompression caused by dffective stress, and we established a one-dimension mode ofsoil compression.(5)Since the bedrock and alluvium have different movement and deformationmechanism，combing the elasticity theory, we respectively established discriminantmodel of key stratum based on the elastic beam and elastic plate theory. According tothe discriminant analysis of the deformation forms build the subsidence model ofbedrok. On the basis of the principle of probability integral method and using thetwo-dimensional and three-dimensional probability integral model, we created thebedrock-alluvium coupling subsidence model.(6)Through the analysis of the measured results and the simulation experimentresults of soil deformation in alluvium, combing the mining engineering actualities on the basis of “arch theories” to give the criterion condition where the soil of alluviumin mining area becomes arch(H≥2b fk). When the soil of alluvium does not satisfythe condition of arch, we calculated the amount of compression of soil subsidencearea according the established additional stress soil compression model. Then wemade the superposition of the bedrock-alluviumcoupling subsidence model and soilcompression model, and get the result that the ground surface finally subsidence:W=W(x, y)+s.(7)Combining the geological mining conditions and data from geotechnicalanalysis in the5304-1and1312working face in the Baodian coal mine Yanzhoucolliery section, we compared the date of subsidence on the main section usingprediction model and the data we measured are goodness of fit, which is furtherverified the possibility for deformation calculation of surface movement by establishthe bedrock-alluviumcoupling subsidence model and soil compression model.