Study On The Characteristic Of Pressure Wave Fluctuation And Influencing Law In High Geothermal Railway Tunnel

Affected by geological conditions,there are various complex environments in high-speed railway tunnels in some regions.Among them,there are multiple tunnels along some plateau railways with extreme environments such as high geothermal,which cause drastic changes in the temperature distribution along the length of the tunnels.When a train enters it at high speed,it will produce more complex aerodynamic effects.In this regard,this thesis carried out research on the pressure fluctuation characteristics and influencing law of high geothermal railway tunnels.Through the methods of moving model test and numerical simulation,the influence law of different geothermal area parameters on the pressure fluctuation of railway tunnels was studied,and a research model for the influence weight of pressure fluctuations in high geothermal railway tunnels was proposed,which provided a scientific method for the study of the evolution mechanism of pressure fluctuations in high geothermal tunnels.The main work of this thesis includes the following:Firstly,the tunnel wall heating device,tunnel insulation device and temperature/pressure measurement system were designed,and an experimental platform for accurately capturing the moving model of the coupling of pressure field and temperature field was constructed.Based on this platform,a tunnel local heating moving model test was carried out for the study of aerodynamic effects in high geothermal railway tunnels.As the air temperature in the tunnel increases and the air density decreases,the piston effect after the train enters the tunnel and the friction effect between the train and the air weakens,so that the peak-to-peak values of the pressure transients at each measuring point in the tunnel show a downward trend.Then,combining the experimental data of pressure and temperature,a numerical simulation method for tunnels under high geothermal conditions was established.The results of the moving model test and the simulation are in good agreement,which verifies the reliability of the numerical algorithm.The proposed research method provides a basis for the study of the pressure fluctuation mechanism and propagation law of high geothermal railway tunnels.Secondly,the influence law of the parameters of the geothermal length in the tunnel on the pressure fluctuations was studied,and the influence law of the length of the different high geothermal zone on the initial pressure wave in the tunnel was revealed.For the initial compression wave,when L_H（length of geothermal zone）<L_T（length of train）,as the L_Hincreases,the peak value of the initial compression wave at the measuring point decreases significantly.When L_H>L_T,the peak value of the compression wave remains stable at this time.For the initial expansion wave,in the area within 110 m from the tunnel entrance,the peak value of the initial expansion wave fluctuates in a small range.In areas beyond 110m from the tunnel entrance,the peak value of the initial expansion wave decreases gradually with the increase of the length of the geothermal tunnel zone.Then,according to the change law of pressure fluctuation,the characteristic length L_T of geothermal area was proposed.Based on the characteristic length L_T,geothermal zones with different distributions were set up,and the law of pressure fluctuations under the corresponding geothermal distribution environment was explored.When the geothermal zone is located at the front end of the tunnel,the initial compression peak change rate is 8-10%,and the initial expansion wave change rate is 5-10%.When the geothermal zone is located in the middle front of the tunnel,the rate of change of the initial compression wave and expansion wave peak value is small,but the peak value of the initial expansion wave can increase by up to 9%after measuring point 208 m.When the heating zone is located in the meso-posterior of the tunnel,the initial compression and expansion wave change very small.When the heating zone is located at the end of the tunnel,the change laws of the peak value of the compression wave and the peak value of the expansion wave are basically the same,and the overall rate of change is small.Finally,based on the above research results and the characteristics of high altitude and low pressure on the plateau railway,the influence of different factors on the pressure value was studied.A sensitivity study of influencing factors was carried out,and the influence weights of temperature（T）,train speed（V）and atmospheric pressure（P）on the pressure wave peak value were ascertained.And the sensitivity analysis results show that V has the greatest first-order and global sensitivity to pressure results,and T has the least influence.The difference between the first-order sensitivity index S_i of each influencing parameter and the global sensitivity index S_Ti is small,which indicates that the coupling effect between parameters P,T and V is can be ignored and decoupled for research.