Research On Dynamic Response Of Goaf Ground Soil Of High-speed Railway In Qinshui Coalfield

China is a large country of coal resources and coal consumptions.A large number of goaf are left after coal mining.When the high-speed railway passes through the goaf site,the goaf ground may be damaged under the influence of the cyclic dynamic load,which posing a serious threat to the security operation of high-speed railway.In order to grasp the dynamic response characteristics and laws of goaf ground soil under the cyclic dynamic load of high-speed railway,the additional stress of goaf ground are theoretically analyzed.The goaf ground soil along the Tai-Jiao high-speed railway is selected.The dynamic triaxial tests with different frequencies,different waveforms,different confining pressures and different cyclic stress ratios are carried out by using GDS.Finally,the numerical simulation analysis of high-speed railway goaf ground under different working conditions is carried out.The main conclusions are as follows :(1)Additional stress at the same depth of goaf ground of high-speed railway from large to small are train rendezvous,single car and no car;The influence depth of additional stress in goaf ground of embankment section is greater than that in cutting section,but the additional stress in cutting section on ground surface is greater than that in embankment section;The attenuation law of ground additional stress with depth in goaf of embankment section and cutting section is the same,but the attenuation rate of cutting section is greater than that of embankment section;With the increase of embankment height,the influence depth of additional stress increases almost linearly..(2)Considering the frequency,confining pressure and cyclic stress ratio of goaf ground soil,dynamic triaxial tests were carried out under different frequencies(1,2,3Hz),confining pressures(50,100,200 k Pa)and cyclic stress ratios(0.05,0.075,0.1,0.15,0.2);The test results show that the cumulative plastic strain and residual pore pressure ratio of the sample are not beyond the damage range,and the goaf ground of the high-speed railway is in a safe state;The cyclic stress ratio has the greatest influence on the dynamic characteristics of goaf ground soil.The cumulative plastic strain and pore pressure increase exponentially,and they increase linearly under other conditions;Under the action of cyclic vibration,the cumulative plastic strain and pore pressure increase abnormally at2Hz-3Hz,so the natural frequency of goaf foundation soil is between 2Hz-3Hz;The stress-strain backbone curve of effective confining pressure 100 k Pa is obtained,and the stress-strain modified H-D dynamic constitutive model related to cyclic vibration times is constructed.The fitting effect of the model is better than that of the traditional model.(3)The model of high-speed railway crossing goaf ground is established by ABAQUS numerical simulation software.The results show that the dynamic stress of350km/h is twice of 250km/h at the depth of 21 m under the two subgrade forms(embankment and cutting),and the increase of speed significantly increases the dynamic stress in the ground.The vertical displacement and maximum dynamic stress of the ground surface in the cutting section are greater than those in the embankment section.When the speed is 250 km/h,the maximum dynamic stress(15.8k Pa)of the ground surface in the cutting section is close to twice that of the embankment section(8.4 k Pa).It is suggested to strengthen the ground surface soil in the goaf of the cutting section.(47figures,13 tables,111 references.)...