Over the past half century, with the development of economy and technology, the progress of rail transportation around the world is also extraordinarily swift. Due to the important role railway plays in national economy and transportation, lots of countries have implemented or are prepared to implement a high-speed railway plan. When a high-speed train passes through a tunnel, a strong interaction between the train and the air in the tunnel occurs, inducing a series of aerodynamic effects and simultaneously radiating outward a bunch of “low frequency pulse waves”, which bring about a blast noise as high as 140~150 dB, or even higher, that seriously disturbs the tranquility of the surrounding environment. We call these low frequency pulse waves “micro-pressure waves or low frequency noise”. When a vehicle running on an expressway passes through an expansion joint on the ground, it tends to make a very loud noise and serious vibration, which often leads to petitions from the public. Therefore, based on the characteristics of the expansion joints on the highway, we have collected control policies and improvement measures against expansion joint noise and vibration adopted at home and abroad.
The results include:
1.Completed the collection and integration of literature on noise prediction and control techniques, prediction models and analytical methods, and alleviation measures and control techniques against the noise produced at the tunnel outlet or in the tunnel of the high-speed railway at home and abroad.
2.Completed analyzing the characteristics of the noise and vibration sources of the expansion joint, control indicators, measurement methods, standard operating procedure (SOP), and the compilation and integration of materials concerning the improvement measures and methods for expansion joints on elevated sections of the high-speed railway (highway) at home and abroad.
3. Completed field measurements and analysis of the low frequency noise produced at the tunnel outlet of the high-speed railway. Totally 48 field measurements were made at various spots, including 8 measurements at the south outlet of Sihu No. 3 Tunnel, 8 measurements at the south outlet of Baoshan No. 4 Tunnel, and 32 measurements at the outlets of Mayuankeng Tunnel.
4. Completed field measurements and analysis of the noise produced at the expansion joint on the expressway. Totally 240 field measurements were made on various types of expansion joint, including 50 measurements on finger expansion joints, 50 measurements on angle expansion joints, 50 measurements on seamless expansion joints, 50 measurements on modular expansion joints, and 40 measurements on epoxy resin expansion joints.
5. In the part of the theoretical models of the low frequency noise produced at the tunnel outlet of the high-speed railway, in consideration of the relation between the compression waves in the tunnel and time, the interflow of the pressure waves in the tunnel, and the relation between the blockage ratio in the tunnel and the train speed, it is primarily suggested that equation(3.1.2), equation(3.1.6) and equation(3.1.2) be used as the theoretical models of the low frequency noise produced at the tunnel outlet of the high-speed railway. By comparison, the noise levels of the compression waves and micro-pressure waves calculated with the above theoretical models are very close to the measured values of numerical simulation and experiments, indicating that the above theoretical formulae are relatively accurate.
6. In the part of the theoretical model of noise propagation in a tunnel, in consideration of the continuous reflection of spherical waves determined by virtual sources, it is primarily suggested that equation(6.5.17) be used as the theoretical model of noise propagation in a tunnel. The theoretical solution is obtained through equation(6.1.7).In terms of the theoretical models of noise propagation in branches, the fluctuation of attenuation in numerical simulation with the increase of distance is so small that it can be predicted that the attenuations will be larger than the experimental values, which is mainly due to the lack of consideration of fluctuation and insufficient number of sound rays. On the other hand, since the fluctuation of attenuation in theoretical solution with the increase of distance is large, it can be predicted that the attenuations will be smaller than the experimental values, which is mainly due to the effect of model coupling. In the part of long enclosures, as shown by the results of experiments, with the consideration of the frequency factors and fluctuation of sound waves, this method can better simulate the attenuation trend of sound fields in long enclosures. However, due to the restriction of experimental conditions, certain deviations exist between the measured values and the theoretical simulation results.
7. Statistics of petition cases between 2002 and 2009: on the expressway – 6 cases against noise produced at expansion joints and 4 cases against noise produced at tunnel outlets; on the high-speed railway – no case against noise produced at expansion joints (due to the use of continuous welded rails on high-speed railways) and 4 cases against noise produced at tunnel outlets.