| With the development of the economy and the acceleration of urbanization,urban space is becoming smaller and smaller,the construction of underground tunnels has become a new direction in the field of construction.The conventional two circular tunnels occupy a large number of underground space,seriously affect the surrounding environment and greatly increases the demolition of residential places.Usually the underground tunnel is located in the city center or downtown area,resulting in a lack of space to bring in and move the construction machinery and equipment.The Double rectangular shield tunnels can solve all of the above problems.Rectangular shield tunnel occupies less surface area,saving 30%-40% space as compared to circular tunnel,it has a lesser influence on the environment,it effectively reduces ground demolition,it can accommodate dual lines in single structure,it saves construction time,and due to that it has high economic benefits.The tunnel section of the rectangular shield tunnel is basically static after the assembly,the impact on the surrounding environment is small,and at the same time,it can achieve long-distance curve tunneling.However,due to nature of this all steel structure the structural stress on the rectangular tunnel has to be analyzed and accounted for.This project is based on the Ningbo Metro Line 3(test section)of the project,the test section is using an 11.83 m × 7.27 m dimensioned rectangular earth pressure balance shield machine "Yang Ming".The shield machine starts from Chenpodu south head and finally reaches the shield tail.The rectangular shield segment total length is 429.3m,and the minimum turning radius is 400 m.The maximum longitudinal slope of the line is 39.5 %,the minimum longitudinal slope is 2%;the maximum depth of the tunnel is 10.46m;the minimum depth is 2.5m.A revolution in tunneling industry indeed but unfortunately very less research has been done on this topic especially in the English language(which by far is regarded as the lingua franca of the scientific community).In this thesis we will try to analyze the structural limitations and the mechanical effects of such kind of tunnel lining.Steel has proved itself a great material for the construction of large span structures.This is why we were tasked with the important work of carrying out the feasibility study of using steel instead of composite material.Aiming at the problem of low rigidity and large deformation of the tunnel section constructed in Ningbo Mero Line 3,PLAXIS software was used to analyze the soil-tunnel interaction and determine whether a steel structure Quasi-rectangular tunnel can replace the composite material based tunnel.It is also worth mentioning here that in reality this project(which I have worked on)does not exist henceforth there is no actual data to compare to our studies which is a limitation for me but on the other hand it has been a matter of prestige to work on such a unique project.This thesis entails three novel pieces of work:-1.Using PLAXIS to carry out an analysis on the Ningbo Line-3 project.There have been a few studies on this topic but none of the studies has used a geotechnical software for analysis on this project2.The thesis uses a whole-steel structure for the tunnel.This has not been used in the real project and such a quasi-rectangular shaped tunnel doesn't exist yet.This study has provided a glimpse into the realm of possibilities in case such a tunnel is constructed.3.A parametric study was carried out and discussed using actual soils data to assess the effects of tunnel thickness and depth on a quasi-rectangular tunnel. |
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