Study On The Ground Vibration Induced By Trains Moving On Subgrade Of High-Speed Railway

High-speed railway, as a kind of transportation with energy saving, environmental protection, low carbon and economical means, has been developing rapidly in china. The high-speed railway is the mainly developing trend for passenger rail. Although High-speed railway brings us convenience, it will induce the vibration problem which is cannot be ignored during the operation. Compared with the ordinary railway, the ground vibration induced by high-speed railway is shorter duration, higher amplitude, and higher operation frequency, so it may brings more serious environmental problems. Subgrade is an important part of high-speed railway line. The ground vibration amplitude at the same distance from the center line of subgrade section is larger than that in bridge section. It has important significant to study the ground vibration induced in subgrade section of high-speed railway. This thesis has studied the ground vibration induced by trains moving on subgrade of high-speed railway by means of in-situ tests, numerical simulation, and theoretical analysis. The research contents include the ground vibration response characteristics in subgrade sections, the propagation path of vibration wave, the effects of subgrade and site geological conditions on ground vibration, the rebound mechanism of ground vibration and railway environmental vibration prediction.1.The in-situ tests were completed in Xi’an-Baoji high-speed railway, Chengdu-Dujiangyan railway and Zhenzhou-Xi’an high-speed railway. The tests results shows that the ground vibration in subgrade sections is not a monotonic attenuation with the increase of distance, and the vibration amplification phenomenon is appeared in a certain distance. The attenuation speed of the high frequency vibration is higher than that of the low frequency vibration with the increase of distance. Ground vibration response is affected greatly by the train length and speed of the train moving. The ground vibration induced by trains of 16 cars is longer duration, larger amplitude and faster attenuation speed than that induced by trains of 8 cars. But the train length has little impact on the ground vibrations frequency. The faster the train moves, the shorter the duration of vibration is, the more discrete the distribution of vibration frequency is, and the higher attenuation speed of ground vibration is. When the train speed is more than or equal to 290 km/h, a series of single peaks, which are in approximate spacing distribution, are appeared in the ground vibration. The relationship between of vibration frequency and the train moving speed was analyzed in the cutting sections in the loess area, and it is find that there is a certain mathematical relationship between of the peak frequency and the speed.2. According to the law of propagation of vibration wave in geological body, the propagation path of ground vibration in the subgrade sections is analyzed, and the components of ground vibration of embankment sections and cutting sections were gotten in the different sites. In homogeneous site, the ground vibration of embankment sections is made up of Rayleigh surface wave and Body wave near the ground surface, and that of cutting sections is made up of Rayleigh surface wave and Body wave near the ground surface and Body wave spreading up from the cutting slope body interior. In the double layer site, the ground vibration of embankment sections is made up of Rayleigh surface wave, Body wave near the ground surface and reflected Body wave, and that of cutting sections is made up of Rayleigh surface wave and Body wave near the ground surface, reflected body wave (or the transmission body wave) and Body wave spreading up from the cutting slope body interior.3. The numerical simulation results show that embankment and cutting play a role of reducing ground vibration. The ground vibration of Z direction is given priority to ground vibration in embankment sections, and it decreases with increase of embankment height and rigidity. The vibration amplitude of X direction is close to Z direction vibration in cutting sections. The cutting depth and cutting depth has little impactt on ground vibration amplitude.4. In homogeneous site, the ground vibration amplitude decreases with increase of medium density, Poisson ratio and damping. The vibration amplitude is not monotone linear change with increasing elastic modulus. Through sensitivity analysis, it is found that the order of geological parameters for influence sensitivity on the ground vibration is:elastic modulus> damping> poisson ratio> density. In the strata structure of covering soil and underlying bedrock, the covering thickness affecting on the ground vibration has a critical thickness. In this thesis, when the covering thickness is less than 10m, the vibration increases with increasing thickness; when it is more than 10m, it has little impact on the ground vibration by thickness change.5. Through Fourier transformation, the influence on the vibration frequency is analyzed by embankment, cutting slope, elastic parameters, damping and the covering thickness, and the results show that embankment height and stiffness have little impact on vibration frequency. The distribution spread of the ground vibration frequency dominant frequency is wider when the cutting slope is steeper. When elastic modulus of site medium is 100-400MPa, the vibration energy of frequency distributing in range of 60-85Hz increases with increasing elastic modulus; when elastic modulus is more than 400MPa, the influence on vibration energy by elastic modulus is little. The medium damping has little effect on the vibration frequency. In the condition of the same distance, the larger damping is, the lower vibration frequency is.6. The "vibration rebound" phenomenon will be appeared in a certain distance in the process of the ground vibration attenuating with distance. The generating mechanism for this phenomenon includes:the wave reflection between the different stratums; the vibration wave superimposition induced by multiple point vibration sources; the superimposition by the different types wave in the transmission process during long duration excitation; and the body wave propagates from slope inner to ground and superpose with the vibration wave near the ground in cutting section. According to the law of vibration wave reflection and different propagation speed for vibration wave difference, where the vibration rebound may occur is deduced7. There is a different attenuation speed corresponding to the different vibration frequency. Aimed at the characteristics of vibration attenuation, the appropriate prediction methods based on the environmental vibration frequencies spectrum are put forward respectively to the embankment sections, the cutting sections and the bridges. Comparing the prediction methods with the measured results, a good prediction effect has been gotten.