| Loess is a question soil of continental deposition under Quaternary arid and semi-arid climatic conditions.Its distribution area is about 640,000 square kilometers in China.Especially in the northwest of China,the loess is most developed.With the rapid development of transport engineering in the west,a large number of tunnel projects were built on the Loess Plateau in the northwest,which brought many technical problems.In the tunnel construction,the engineering characteristics and deformation mechanism of the collapsible loess tunnel have attracted extensive attention from the engineering and academic circles,and are the hotspots of many scholars.As for tunnel operation stage,the dynamic stability of the loess tunnel under the long-term effect of high-speed trains restricts the safe operation of the tunnel,but the research results are rare.Based on NSFC,the dynamic characteristics of high-speed railway loess tunnels considering the random irregularity of the track and the structural parameters of the tunnel,this paper takes a high-speed railway loess tunnel as the research object,and analyzes the random vibration analysis model of the high-speed railway loess tunnel.The solution method was studied in depth and the following research results were obtained.(1)Tunnel vibration caused by high-speed train operation belongs to the internal source fluctuation of complex system.The system includes four elements:vehicle,track,tunnel structure(including tunnel bottom filling)and surrounding rock.According to the D’Alembert principle,the motion equation of the vehicle-track-tunnel coupling system under the track irregularity excitation is established.The vehicle-track-tunnel dynamics problem is solved by frequency domain analysis.In this paper,based on the Fourier transform relationship between unit impulse response function and frequency response function,according to the characteristics of train random vibration,the principle and method of digital characteristic calculation of linear system random vibration are analyzed and organized,including mathematical expectation,variance,autocorrelation function,power spectral density.(2)Based on the vehicle-track coupling dynamics theory,a vehicle-track-tunnel bottom vertical vibration coupling model is established.The model takes the influence of tunnel bottom structure and surrounding rock on train vibration into consideration,which can be used to refine the vibration of tunnel train.Based on the transfer function theory,the method for solving the vehicle-track-tunnel bottom vertical random vibration is deduced and the calculation program is compiled.The correctness of the model and method is verified by comparison with existing research results.The numerical results show that power spectrum of the rail in consideration of tunnel bottom structure system and wheel-rail force has a tendency to move at a high frequency,and the response amplitudes are increased to different extents.Based on the numerical theory of near-field fluctuations,a numerical model of track-tunnel-surrounding rock is established.Also based on the theory of impulse response function,the solution method of system dynamics equation is derived.(3)Considering the structural characteristics of the vehicle,track,tunnel bottom base and random irregularities of the track,the vehicle-track-tunnel vertical vibration coupling model is used to calculate the train random vibration responses of the vehicle-orbit-tunnel subsystem under different operating speed(250、300、350km/h)and different surrounding rock conditions(new and old loess)The numerical results show that the train speed has obvious influence on the vibration response of the system,especially the impact on the wheel-rail force and the rail acceleration.The surrounding rock conditions of the loess tunnel have little effect on the vibration acceleration response,but there are slight differences in several frequency points.When the surrounding rock condition is old loess,the system vibration acceleration responses are more prominent.Compared with the driving performance standard,the vehicle body acceleration exceeds the comfort standard of 1.3 m/s~2,but both are within the safety standard of 2.0 m/s~2;the wheel load reduction ratios meet the requirements,but,when the train speed reaches 350km/h,the wheel load reduction ratios are close to the limit of 0.6;the wheel-rail forces exceed the limit when the driving speed reaches 350 km/h;the rail accelerations and the rail displacements meet the standard requirements;So in order to ensure the safety of the vehicle in high-speed conditions,the track structure must be improved.(4)Using the track-tunnel-surrounding rock subsystem model,the mean values and standard deviations of random vibration displacements and principal stresses of high-speed railway loess tunnel under random train load are calculated.The result shows that for the single-hole double-track loess tunnel,when the high-speed train driving on the tracks,the train vibration loads are created by the track irregularities,the vibration loads have little effect on the horizontal displacement of the tunnel lining,and no impact on the vertical displacement of the lining.Meanwhile,the vibrations have little influence on the tunnel lining stress,which mainly affect the stress of the left and right wall and the bottom of the lining,especially the stress of the side wall.When single driving on the upper line,the train vibrations have obvious influence on the first principal stresses of the tunnel lining,the stress characteristics show the biasing property,the left wall bottom stresses are increased.Compared with the single-line driving,when double-line driving,the influences on the displacements of the lining are multiplied,and the influences on the lining stresses are also multiplied in addition to the left,right wall and bottom of the lining.This is more disadvantageous for sections that are subjected to large eccentric compression under static force.The most unfavorable positions of the lining under the train vibration load are the tunnel side wall and the bottom.(5)Considering the combined of dead and train vibration load,the reliability indexes of high-speed railway loess tunnel lining are calculated by JC method.The result shows anti-compression reliability indexes of the parts of the tunnel lining are greater than 2.4,the anti-compression reliability indexes of the side wall are 2.62,and that of other positions are above 4.0;The anti-shear reliability index of the bottom is less than 2.4.When single driving on the upper line,the anti-shear reliability index of the right wall is 2.31,and which of the left wall is 1.08,which of the other parts are 2.6.When double-line driving,the anti-shear reliability indexes of the right side wall and the left side wall are 1.63,which of other parts are above 2.6,and that of the hance is 2.67.The single-passing makes the anti-shear reliability index of the left wall smaller than that of right,while the double-line driving makes the anti-shear reliability index of the left and right walls the same.Therefore,C40 reinforced concrete should be used in the lining structure of loess tunnel,which conforms to the stipulation that secondary lining of high speed railway tunnel needs reinforcement above IV grade surrounding rock with Railway Tunnel Design Code. |
PDF Full Text Request