Research On The Mechanical Properties Of Super-thick Alluvium And Its Influence On The Surface Subsidence

In many coal mining areas of North China and Central China,compared with general geological and mining conditions,there are great differences in laws of surface subsidence when mining under thick alluvium.It is mainly due to the different physical-mechanical properties between the alluvium and the rock.Aiming at the particularity of the surface subsidence laws under the condition of super-thick alluvium,research on the mechanical properties of super-thick alluvium and its influence on the surface subsidence were studied by combining geotechnical test,numerical simulation and theoretical analysis.The surface cohesive soil of Jiaozuo mining area was made into remolded soil samples with different water content and dry density.The indoor triaxial shear test was carried out under different confining pressures.The influences on the shear strength of three factors which are water content,dry density and confining pressure,were studied.The stress-strain relation curves and the shear strength of each specimen were obtained.The internal friction angle and cohesive force of the corresponding sample were obtained by drawing the shear strength envelope.The internal friction angle of cohesive soil in Jiaozuo mining area is 8.1°~24°,and cohesive force range is 19.2kPa~82.4kPa.Taking the 11011 panel of Zhaogu NO.1 mine covered by the super-thick alluvium as an example,in conjunction with the results of triaxial shear test,12 kinds of numerical simulation schemes were designed.The influences of the thickness of alluvium,the friction angle of alluvium and the cohesive force of alluvium on the surface movement were studied.The numerical simulation results were compared with the measured data from the surface movement of the 11011 working surface of the mine.The result shows that the simulation results are in good agreement with the measured values,and the rationality of the numerical simulation results is verified.With reference to the simulation results,the mechanism of the compression of the soil was analyzed under the super-thick alluvium mining.There is a compression phenomenon in the soil.With the increase of the thickness of the alluvium,the amount of compression increases,and the compression settlement of the soil is the main factor for the large surface subsidence.Based on the soil mechanical properties,the geotechnical test is combined with the surface movement under the alluvium.The research results complement and expand the laws of surface subsidence under the super-thick alluvium,which have certain theoretical value and guiding significance.