| The widespread distribution and large area of coal mining subsidence area are common problems in China's coal mining areas.Ensuring foundation stability of large-scale construction in coal mining subsidence areas is a major problem in the construction of coal cities.Therefore,it is very necessary to carry out research and stability analysis of settlement and deformation of large-scale building foundations.This dissertation takes the large-scale construction of the subsidence area of Xiangcheng Coal Mine in Huaibei Mining Area as the engineering background,mainly studies the settlement and stability of large-scale building foundation by using field measurement,numerical simulation,similar simulation,software modeling and theoretical analysis.The dissertation combines the drilling data of the goaf to analyze the type of overlying strata in the goaf;main control factors of surface residual settlement by orthogonal simulation of FLAC3D;Analysis of distribution of voids and settlement of unconsolidated layer in old goaf under mining and loading by similar simulation experiments;Calculation model for additional stress at any point in the space below the rectangular load and the calculation model for soil space settlement compression is established by Matlab soffware;calculation formula for residual settlement of fallen rock mass in central goaf is established by theoretical analysis,stability and settlement characteristics of fractured sandstone structures in old goaf is analyzed by using voussoir beam "S-R" stability theory,the stability of residual coal pillar and the calculation formula of coal pillar instability settlement is analyzed by ultimate strength theory and catastrophe theory;Based on stochastic medium theory,calculation model of cooperative settlement of rock and soil above goaf under load and foundation settlement model of foundation soil compression settlement and geotechnical cohesion settlement under the action of load is established.;Through the study of foundation settlement and deformation,the stability of foundation is evaluated,and effective treatment measures are proposed to reduce the settlement of foundation soil and residual settlement of goaf under load.This dissertation has reached the following conclusions.(1)Through the analysis of overlying strata in the goaf,the bedrock layer is a single sandstone key layer structure.The instability of the residual coal pillar and boundary sandstone fracture structure as well as the fissure compaction of the central collapse rock mass are the main reasons for the settlement of the goaf.The results of FLAC3D orthogonal simulation show that the surface residual settlement is positively correlated with building load and loose layer thickness factor,and negatively correlated with bedrock thickness,bedrock lithology and coal pillar width.(2)Calculation model for additional stress at any point in the space below the rectangular load is established by Matlab software.The larger area or the larger aspect ratio or the smaller Poisson's ratio of rectangular load,the greater additional stress directly below the center of the rectangle,which is attenuated from the center to the periphery,additional stress contour is approximate rectangle,the degree of change is small,and the force is more uniform.However,the additional stress decreases rapidly near the rectangular boundary,The greater degree of change,the more obvious uneven force.As the depth increases,the additional stress extreme value decreases,which is attenuated from the center to the periphery,additional stress contours is approximate ellipse,the degree of change is smaller,and the influence range of the additional stress increases.The additional stress effect of the load on the shallow soil is more concentrated.As the depth increases,influence of additional stress diffuses to the surrounding soil and the effect is weakened.(3)Calculation formula for residual settlement of fallen rock mass in central goaf.The greater the overburden load,the lower the compressive strength of the rock mass,the greater the additional stress of the building load and the larger the residual swell coefficient,the larger the residual compression settlement of the fallen rock mass in the middle of the goaf.The compression settlement is mainly related to the self-strength of the fallen rock mass and the size of the residual crack space.(4)According to the "S-R" stability theory of masonry beam structure,when the fault block of the sandstone layer in the goaf boundary is slipped and unstable,the fracture settlement of the sandstone layer can be calculated as follows.(5)Coal pillar instability settlement can be divided into:?When the coal pillar width is less than or equal to 9m,the coal pillar will be unstable and destroyed during the mining stage.During the loading stage of the building,the coal pillar sinking can be analyzed according to settlement of rock mass in the goaf;?When the coal pillar width is greater than 9m and less than 9.7m,the coal pillar is unstable and sinks during the loading phase,and the settlement is calculated according to ?S=2l0+B+2l0?When width of coal pillar is greater than 9.7m,the coal pillar is stable,but coal pillars and direct roof failure may occur in the plastic zone of the coal pillar,and the rock mass may have sedimentation,and the settlement is calculated according to?S=Ml0/x0+l0(6)According to the results of similar simulation experiments,the gap between two sides and the middle layer of the goaf in the mining stage are the main reasons for settlement of the goaf in the loading stage.Under the load,the settlement in the middle of the goaf increases and gradually stabilizes,but settlement on both sides of the goaf is related to stability of the coal pillar,roof and rock fracture joint structure.If the structure is unstable,the settlement will increase rapidly;if the structure is stable,the void space will always exist,which is the main concentrated area of "residual"settlement of the goaf.The settlement of unconsolidated layer increases with the increase of the load.The settlement of unconsolidated layer under the influence of the load can be regarded as the superposition of the compacted settlement of unconsolidated layer's own pores and the synergistic settlement caused by the overlying strata of the goaf.(7)The stratified total settlement model of foundation soil was established by Matlab software to calculate the compression settlement of foundation soil.The compression settlement value of the soil under the load is 0.359m at the maximum,and gradually decreases from the center to the periphery.The settlement in the central area is relatively uniform,and the degree of inclination change is small.At the load boundary,the settlement is rapidly reduced and the inclination is maximum,with a maximum of 14 mm/m.The foundation is inclined at the boundary and the degree of change is large,and the building is prone to uneven settlement.(8)Based on the stochastic medium theory,the settlement of the sandstone layer is used as the "equivalent mining thickness" to calculate the co-sedimentation of the rock and soil above the goaf.The maximum settlement of the foundation under the load is 0.196m,the maximum inclination is 1.45mm/m,the maximum horizontal deformation is 1.44mm/m,and the maximum curvature is 0.06(10-3/m).(9)The foundation settlement under load can be regarded as the superposition of the compression settlement of the foundation soil and the co-sedimentation of the rock and soil.After stacking calculation,the maximum settlement of the foundation below the building is 555mm,the maximum inclination is 14.9mm/m,the maximum curvature is 0.06(10-3/m),and the maximum horizontal deformation is 1.44 mm/m.(10)Through analysis of foundation stability and total settlement and deformation of old goaf under the influence of integrated building loads,The stability of the office building base is poor,and the foundation needs to be strengthened and treated.Reduce the settlement of goaf by stowing goaf,and reduce the compression settlement of the soil layer by reinforcing pile foundation.(11)After pile foundation reinforcement,the measuring points are arranged to monitor settlement of the foundation.From the construction of the building to the end of the monitoring(2105 days in total),the maximum settlement of the foundation is 34.8mm,and the maximum inclination observation of the building is 0.142mm/m,which is smaller than the allowable value of the high-rise building settlement(200 mm)and the allowable inclination value(2 mm/m).Therefore,the foundation stability is good. |
PDF Full Text Request