The Mitigation Measurement Analysis Of The Low-frequency Vibration Induced By Subway Load

With the development of city constructions, subway has been an important part of city transportation system. However, low-frequency vibration due to subway has influenced on the normal daily life of people and some sensitive instruments in laboratories badly. Environmental vibration has attracted considerable attention home and abroad, environmental vibration and noises induced by traffic loads are recommended to one of the seven world environmental pollution, so it's very necessary to study the mitigation measurements of the ground vibration induced by traffic loads.Reduction and mitigation measure of vibration due to traffic loads were studied at sixties, such as open trench and continuous wall. The results show that when the depth of trench is less than 30% of ground superficial wave length, trench has almost no effect on low-frequency vibration. Some investigation about the mitigation of vibration showed that ground vibration could be reduced 2~5dB by using underground continuous wall. However, for low-frequency vibration with longer wavelength, it was effective only when its depth was enough. So open trench and filled ditch are applicable to isolation of middle and high-frequency vibration.Since 1990s, Schmid has put forward to build "artificial bedrock" to shield soil vibration, it was also known as WIB-Wave Impeding Block. Peplow(1999) studied mitigation effect of WIB and his results showed WIB could effectively reduce responses of low-frequency vibration in far field and decrease greatly amplitude of vibration. Gao Guangyun, Li wei studied WEB active vibration isolation of layered ground and also drew a similar conclusion. In view of above studies, WIB has good mitigation effect for vibration due to ground superficial loads, but very few people study low-frequency vibration. In this paper, mitigation effect of WIB used in low-frequency vibration induced by subway will be studied. Main work follows as:First, the numerical calculation model of train, tunnel and ground is established, simplified the train load as moving dynamic load series along the tunnel, the mitigation effect of continuous wall and open trench under ground is studied, then different depth, width and position are also considered; the ground vibration with WIB and without WIB is compared and the mitigation effect of WIB with different depth, thickness and shape is analysis; finally, three kinds of methods are compared, the mitigation effect of WIB for low-frequency vibration due to subway is got.Conclusions can be drawn: (1) for low-frequency vibration induced by subway, WIB has good reduction vibration effect, decrease ground superficial vibration acceleration effectively makes vibration intensity reduce to above 5～10dB, prior to continuous wall and open trench under ground greatly; (2) for 5～15Hz low-frequency vibration, continuous wall and open trench have almost no effect, but WIB can decrease energy amplitude to above 50%; (3) the mitigation effect of WIB is related to its depth, thickness, shape and soil characteristic. So WIB is a very effective mitigation vibration measurement for residents and laboratories and so on sensitive to low-frequency vibration.