Research On The Vibration Prediction Of The Belowground Subway In Chengdu

At present, many domestic cities to ease traffic congestion in urban are under construction subway. But with the increasing miles of subway and the improving speed per hour, environmental issues are increasingly raised by the subway; especially environmental vibration problem has attracted attention of the authorities and residents around the subway. The vibration impact on the environment of the metro in operation period has a lot to do with the vibration environmental impact prediction before the metro construction. The accuracy of the prediction results have a profound impact on many aspects of the metro project, such as vibration control measures and project investment, etc. Therefore, the study of how to predicting vibration environmental impact caused by the metro scientifically and objectively has a high practical significance, it can provide decision-making basis for construction units and government departments.This article is based on the domestic and foreign research of vibration prediction method caused by the metro, summaries the characteristics and problems of the urban metro vibration prediction method, focus on the following research:In the working conditions of Chengdu Metro Line 2, according to vibration environment impact prediction formula recommended by appendix C of Technical Guidelines for Environment Impact-Assessment of Urban Rail Transit (HJ453-2008), select underground line between Jin Zhou road station and Bai Cao road station (downward, YDK18+300)to predict the surface environment vibration within the scope of 75m from outside the center line of the rail. At the same time, measure the surface environment vibration within the scope of 75m from outside the center line of the rail of underground line between Jin Zhou road station and Bai Cao road station(downward,YDK18+300)which already mentioned above to obtain the test datum. Compare predicted values with measured values. According to the measured values on the spot and mathematical calculation, put forward the parameters of’a’and’b’which recommended by appendix C of Technical Guidelines for Environment Impact-Assessment of Urban Rail Transit(HJ453-2008) to calculate distance decay in the Chengdu Plain of specific environmental and geological conditions.The results show that:Under the geological conditions of the Chengdu plain, the vibration prediction results which calculated by formula that recommended by appendix C of Technical Guidelines for Environment Impact-Assessment of Urban Rail Transit(HJ453-2008) are greater than the measured value, the minimum difference is about 8dB.Above the tunnel(horizontal distance from the center line of outer rail^5m),predicted values and measured values differ biggest, approximately 18dB.According to the vibration prediction formula that recommended by appendix C of Technical Guidelines for Environment Impact-Assessment of Urban Rail Transit(HJ453-2008),reverse derivation of measured values of Chengdu Metro Line 2 underground line to get the values of parameters ’a’ and ’b’ which are used for calculating distance decay in the Chengdu Plain of specific environmental and geological conditions.The end result is that ’a’ is equal to 20.16and ’b’ is equal to 2.79.Compare the predicted results that ’a’ generally value 20and ’b’ generally value 12 with the predicted results that ’a’ value 20.16 and ’b’ value 2.79,we can come to the conclusion that the predicted results which come from vibration environmental impact prediction formula that correct parameters ’a’ and ’b’ are more closer to the actual environmental vibration caused by the subway in the Chengdu Plain of specific environmental and geological conditions.