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  A Study on the Mechanical Behavior of Pipe Curtain with New Interlock Joint in a Large Pipe Curtain-Box Jacking Project

  The development of underground space in urban area has been challenging in recent years, especially where there are underpass crossing roads with heavy traffic and where they are highly protected for environmental reasons. The pipe curtain-box jacking method has been applied in several such projects, because it causes minimal disturbance. However, experience gained from large section pipe curtain-box jacking projects is still limited.The use of pipe interlock joints is a significant part in the pipe curtain-box jacking method, with its irreplaceable role in water proofing and ground settlement control. While jacking the pipe curtain, a pipe interlock joint takes the loads from both the surrounding earth and the pipe-jacking machine. Both the pipes and the interlock joints are filled with concrete, when the pipe-jacking is completed. While jacking the main box, the pipe curtain not only provides a remarkable waterproof function, but also bears the load from both the soil and the jacking structure. Different forms of pipe curtain interlock joints have different mechanical behavior. This article presents a case study of an ongoing project of a large and shallow underpass that crosses the Mid-ring Road in Shanghai China. With the main box being 19.8m wide and 6.4m high, this underpass is designed to be constructed by the pipe curtain-box jacking method. Engineers adopted a special form of interlock joint, in which the cross section of most steel pipes are unclosed circles. This joint form has not previously been applied to any other project with such a large scale. With the great span and height of the cross section, difficulties to connect every steel pipe solidly and accurately is obvious. Measures such as build up welding, deviation rectification and three-dimensional monitoring are adopted. To ensure safety, engineers carried out in-situ test at the experimental section, using steel pipes with interlock joints mentioned before. The test shows this new form of interlock joint is feasible and the total joint error is controllable. In this article, the mechanical behavior of the interlock joint is studied from two aspects: numerical simulation and in-situ monitoring. The calculation and simulation results are compared with the monitoring data, making the result more reliable. The theoretical calculation and numerical simulation will not only focus on the new joint form, but also on a former interlock joint which was used in another underpass near this project. All of the research is limited to the pipe-jacking stage, due to current construction progress.

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