Analysis Of Large Diameter Shield Tunneling Crossing Underneath Existing Trunk Canal Of South-to-North Water Transfer Project

At present,the influence of the large diameter shield tunnel through the construction environment and the deformation control of the existing structures are important problem in the current underground engineering.The present article investigates the trunk canal of South-to-North Water Transfer Project constructed beneath the "Yu-ji" railway tunnel and crossing it.The influence of shield tunneling through construction was studied by the empirical estimation method and field measurement data analysis method,besides,the three-dimensional numerical simulation FLAC3D is carried out to simulate the construction process,Specially,shield tunneling under different strata loss and under different buried depth were discussed.Major contents and conclusions of this study are as follow:(1)On the basis of summarizing the mechanism of the surface subsidence caused by the shield tunneling,the surface subsidence rule under shield construction was analyzed according to the most widely used formula of Peck experience.Specially,the surface settlement caused by different strata loss and different overburden thickness was calculated.The calculation results showed that the surface subsidence increases with the increase of the strata loss under the same buried depth;In the same strata loss,the surface subsidence decreases with the increase of buried depth.(2)A 3D finite element model about the main structure of shield tunnel and the interaction of surrounding strata was established,which using the formation-structure method,combining with engineering design data and geological conditions.Analysed the surface subsidence caused by shield tunneling and its influence on the structure of the canal,the results showed that the canal structure is relatively stable when the distance between the top of the tunnel and the bottom of the trunk is about 32.24 meters.Besides,the displacement becomes small when the ground loss rate is controlled within 0.5%or the overburden thickness is more than twice the diameters.It was also demonstrated that the settlement increases with the increase of ground loss rate,while it decreases along with the increase of soil thickness.The results of numerical simulation are compared with the empirical formula,and the results show that they are in high agreement.(3)The actual impacts of shield excavation were analysed through the analysis of the field monitoring data.By using the grey correlation analysis method,the sensitivity of surface subsidence to the parameter sensitivity of shield tunneling was analysed.Based on the microperturbation of shield construction technology system,relevant construction control measures were put forward.