Study On Creep Characteristics Of Coal Column In Old Goaf And Surface Movement Law Under Building Load

China’s coal resources are continuously exploited,and at the same time,a large area of goaf has been produced in the old mining area.In recent years,with the continuous development of China’s real estate market,there is less and less land suitable for building buildings,so the construction of buildings above the goaf area has become a development trend,and its safety is also crucial.This paper takes the second-class residential and basic education land project in Xinhuayuan Factory District,Mentougou District,Beijing as the engineering background,and understands the mining status and distribution characteristics of the goaf through on-site exploration.The uniaxial compression test and the graded loading creep test are carried out on the remaining coal column in the goaf area,and the mechanical characteristics of the coal column and the creep characteristics under load are obtained.The theoretical calculation of the influence depth of additional stress is used to determine whether the "activation" instability occurs in the goaf.The vertical displacement and horizontal displacement changes of overburden and surface in goaf under different building loads are numerically simulated.The main research results are as follows:(1)Carry out drilling and geophysical exploration,analyze the hollowing of boreholes,and determine the mining status,distribution characteristics and distribution of the goaf area.(2)The uniaxial compression test is carried out to analyze the stress-strain variation characteristics of coal samples in different periods of loading according to the stress-strain curve.According to the compressive strength calculation formula,the average test results of the coal samples are averaged,and the uniaxial compressive strength of the remaining coal column in the goaf area of plot 6003 is about 16 MPa.(3)Carry out the creep test of hierarchical loading,and apply the load to the coal sample according to 50%,60%,70%,80% and 90% of the compressive strength value of the coal sample,and by analyzing the creep-time relationship curve of coal samples,it is known that the creep curve over time presents three stages,namely decelerating creep,steady state creep and accelerating creep.By analyzing the test data and using Origin software to fit the data of the creep test of the coal sample,the model parameters of the coal sample are obtained,and the creep models of the coal sample are determined.(4)According to the principle of dissipative energy,the principle of strain energy and the principle of minimum potential energy,the expression of creep instability time of coal column is derived,the effective bearing time of the residual coal column in the goaf of plot 6003 is predicted.By calculating the critical mining depth of the goaf,it is judged that the goaf of the proposed site of plot 6003 will be "activated" and instable,which will affect the surface and buildings above.(5)Using Midas GTS NX numerical calculation software,the numerical model of MC00-0005-6003 plot is established,and the vertical and horizontal displacement of overburden and surface of goaf under different building loads is numerically calculated,and the displacement change law of overburden and surface in goaf under different building loads is analyzed.The maximum vertical displacement value of the corresponding rock formation under 6-storey buildings is 14.9cm and the maximum horizontal displacement value is 5.1cm,the maximum vertical displacement value of the corresponding rock formation under 7-storey buildings is 16 cm and the maximum horizontal displacement value is 5.47 cm,the maximum vertical displacement value of the corresponding rock formation under 8-storey buildings is 17.1cm and the maximum horizontal displacement value is 5.7cm,the maximum vertical displacement value of the corresponding rock formation under 9-storey buildings is 18.2cm and the maximum horizontal displacement value is 6.1cm,and the maximum vertical displacement value of the corresponding rock formation under 10-storey buildings is 19.6cm and the maximum horizontal displacement value is 6.4cm.The closer the goaf is,the more obvious the vertical subsidence occurs.The paper has 48 figures,17 tables,and 75 references.