Analysis Of Effect Of Large Area Unloading On Underling Metro Tunnel And Study On Deformation Control Methods

With the booming development of the national economy and the accelerating of urbanization in China, in order to alleviate traffic pressure on the ground, underground rail transit developed rapidly.More and more foundation constructions were built over or near the existing shield tunnel. As metro vehicle is sensitive to the deformation of the shield tunnel, if the shield tunnel has excessive deformation, it will affect the safety of subway. Therefore predicting the characteristic of shied tunnel deformation effected by the large area of unloading upper reasonably and taking proper construction measures to control the deformation of the shield tunnel and foundation pit are of great significance.Based on the above background, the main works are summarized as follows:1.Summarize the domestic and foreign research status related about the influence of existing shield tunnel effected by the large area of unloading upper. Analysis the mechanism of unloading deformation of clay in excavation of foundation pit, expound the main factors affecting the deformation of the shield tunnel, and introduce the method to calculate the vertical displacement of the shield tunnel.2. Combined with the soil characteristics of Hangzhou, using PLAXIS software to simulate the influence of shield tunnel effected by two-dimensional unloading and three-dimensional unloading upper to get the law of shield tunnel deformation which caused by many factors such as soil intensity, reinforcement of soil, uplift pile, dewatering depth, block excavation, the size of foundation pit, soil where shied tunnel lies and so on. Then discuss and analysis the effect of construction measures which could control the heave deformation of shield tunnel.3. Based on the engineering background of Hangzhou East Railway Station West Plaza foundation pit which lies above No.1 line of Hangzhou Subway, build a 3D FEM model to simulate the whole excavation of this project, and compare the calculated results with monitoring results. The construction measures to control heave deformation of shield tunnel taken in this project including dewatering and consolidation, excavating by layers and blocks, soil mass consolidation, bedding course with bar arrangement and etc. The analysis result shows that with these measures, it greatly strengthens the anti-heave capacity of the subway shield tunnel, which makes tunnel deformations controlled in safe range.