On Environmental Vibration Induced By Urban Rail Transit And Virtual Inversion For Track Irregularity Spectrum's Parameters

Developing rail traffic is an effective countermeasure to solve traffic problems in China, but the environmental problem by the vibration and noise from the traffic turns into a bottleneck impediment to the development in urban areas. In order to deal with the engineering measures to reduce the environmental vibration, the mechanism of vibration caused by urban rail traffic and the propagation and attenuation of wave in the ground soil layers are studied in this dissertation. Field measurement data process and analysis, analytical and numerical calculations are carried out, including the studies on railway irregularity spectra to describe the dynamic load by train,the spatial domain to frequency domain transform of the spectra, modeling of vehicle-railway-ground system, the analytical and numerical calculations, and inversion of the spectral parameters. The main progresses in this dissertation can be summarized as follows.Firstly, the data observed along the 13 line of Beijing urban rail traffic is processed, the main characteristics of the environment vibration and its attenuation law are deal with by means of time domain and frequency domain analysis on 813 records in 50 sets on a linear array perpendicular to the railway and a rectangle array parallel to the rail. The results show that vertical components of the vibrations are much stronger than those of horizontal ones; the former can be adopted as the criterion for environmental vibration evaluation. The high frequency vibration decreases fast and the low frequency one decreases relatively slower, so that the vibration near the way is predominated by high frequency component from the source, one in far field is then predominated by low frequency component from the soil dynamic feature. For purpose of the evaluation of environmental vibration and selection of engineering countermeasure, a new ground vibration level attenuation law is presented in this paper.Secondly, dynamic contact load between the vehicle wheel and rail is studied, and the requirement of analysis on vibration response of the vehicle system under the deadweight and excitation of irregularity of the wheel-rail contact surface. From the random vibration point of view, railway spectrum is adopted to describe the irregularity, on the basis of a comprehensive review on excitation models. The railway irregularity spectrum transformed from spatial domain to frequency domain is taken as input. For nonlinear analysis of vehicle-railway-ground system, the statistical characteristics in the time histories are validated.Thirdly, the vehicle model with two hanging systems is combined with simple models of railway and groundwork. Vertical contact force between wheel and rail is determined by Hertz nonlinear elastic contact theory. By means of Newmark-βdirect integral method, the dynamic responses of the total system from the time history excitations of railway irregularity are calculated, the subgrade reactions under ballast blocks are obtained.Fourthly, the vibration action on the ground caused by train running is described as the subgrade reactions under ballast blocks, the moving load on the railway is transformed as vertical vibration load on a set of given points, to make up of a series of point vibration sources spatially on a linear array. The ground vertical vibration responses under excitations of the subgrade reactions under the ballast blocks spreading one by one are calculated by an explicit finite element method. The results of an example showed that the responses increase slightly with the increasing of the amplitude railway irregularity; the contact force between wheel and rail increases with speed, and also amplitude increases in some degree. Envelop of the obtained acceleration waveform is similar with the observed ones, so is the peak value. It is shown that the procedure developed in this paper is credible at low frequency range.Finally, the feasibility to inverse the parameters of railway irregularity spectra is deal with by integrating the generation of time histories from the spectra and the detail model of the vehicle-railway system. By means of the idea of virtual inversion, the subgrade reactions under the ballast blocks and its power spectrum from the input excitation of railway spectrum are taken as the object functions; the parameters are inversed by means of the Generic Algorithm. The results showed that the values of parameters can be inversed from the response of the railway system quite well. Thus further railway spectrum parameter inversion from the ground vibration response must be feasible.