| The tunnel affected zone is an easier way to predict the influence scope of tunnel deformation,which first appeared in the《Technical Specifications for Urban Rail Engineering Technical Monitoring》.Then,Professor Zheng Gang optimized this method and proposed a new method to classify tunnel impact.The method can be used to estimate the influence of foundation pit excavation on the adjacent existing tunnel.However,this method only considers the soil layer in Tianjin area and simplifies the soil layer to one layer,which has certain limitations and cannot be applied to other areas.On the basis of Professor Zheng Gang,this articles puts forward a method of tunnel affected zone which is suitable for Nanchang area and conforms to the actual soil layer distribution.In the process,the influence law of four kinds of influence factors on tunnel deformation is analyzed simultaneously.The main contents are as follows:1、In order to verify the rationality of soil parameters and calculation model,taking the deep foundation pit project of a tunnel of a nearby Metro Line 1 in Nanchang as the background,the hardened soil analysis model(HS)was used to analyze the influence of deep foundation pit excavation on the adjacent existing tunnels.The results show that:When the excavation reaches the second support position,the deformation shape of the retaining structure obtained by finite element software analysis is similar to the measured deformation shape of the retaining structure.The simulation value of the maximum horizontal displacement of the envelope is 6.34mm,which is close to the measured value of 5.1mm.At the same time,the simulated maximum horizontal displacement of shield tunnel is 0.36mm,which is basically consistent with the measured value of 0.3mm,indicating that the soil parameters and analysis model are basically reasonable.2、PLAXIS 2D finite element software is used to obtain tunnel impact zones in two typical areas of Xihu District and Honggutan Central District in Nanchang City by means of isoline method.The influence area considers the distribution of soil layer in different areas,the relative position of the tunnel,the maximum horizontal displacement of the envelope structure and the presence or absence of prestress in the inner support,etc.The results show that:(1)The tunnel deformation increases with the closer the relative position of the tunnel is to the foundation pit retaining structure.However,in a certain range above the foundation pit bottom,the deformation amplitude of the tunnel changes obviously and produces settlement deformation,while in a certain range below the pit bottom,the deformation amplitude of the tunnel changes very little and produces upward deformation.(2)The change of the maximum horizontal displacement of the retaining structure of the foundation pit has a significant effect on the tunnel deformation in the range of 6m<L_t<21m,9m<H_t<16m(L_t is the horizontal distance between the tunnel center and the retaining structure,H_t is the buried depth of the tunnel center).(3)In the case of the same relative position of the tunnel and the maximum horizontal displacement of the foundation pit retaining structure,when the tunnel is located in the central area of Honggutan,the tunnel deformation caused by the excavation of the foundation pit will be significantly greater than that caused by the tunnel located in the West Lake area.That is to say,for the tunnel located in the central area of Honggutan,the deformation control requirements should be stricter than the West Lake area.(4)Under the same condition of other parameters,the deformation of the adjacent tunnel with inner support prestressed is smaller than that of the adjacent tunnel without prestressed,and the deformation of the adjacent tunnel decreases with the increase of prestressed value.Prestress plays a positive role in reducing the deformation of the adjacent tunnel.However,it should be noted that this positive effect does not increase indefinitely with the increase of prestress. |
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