Abstract
In order to solve the water sealing problem of soil between pipes of long distance curved pipe-jacked technology, Freeze-Sealing Pipe Roof (FSPR) as an innovative pre-supporting method in tunnel engineering is being applied to the Gongbei Tunnel in the Hong Kong-Zhuhai-Macau Bridge. The definition of FSPR is that large diameter steel pipes are laid out in a circle around the cross section of tunnel in advance, then the artificial ground freezing method is adopted to freeze soil between steel pipes to form water-sealing curtain. An effective freeze control system, which contains master freezing tubes, enhancing freezing tubes and limiting freezing tubes, is established for building up the frozen soil curtain, maintaining its stability during excavation and controlling the volume of frozen soil to limit frost heave dynamically. An in-situ test was carried out to explore the optimal freezing scheme and control mode. The results of the test show that the principal freezing scheme of the solid pipe with hollow pipe as a complement is the most optimal scheme in active freezing phase of the real construction. Meanwhile, cold control mode is suggested to control frost heave in maintained freezing phase. The conclusions have important guiding significance for this kind of engineering construction.
Highlights
With the increasing complexity of the underground construction environment, the construction technology is becoming more and more complex and difficult
This paper aims to explore the optimal freezing scheme of Freeze-Sealing Pipe Roof (FSPR) and optimal control modes of frost heave by an in-situ test, the study results have been applied to actual construction
According to the arrangements of freezing tubes in the curtain, the test in this paper studied the following four active freezing schemes: single freezing mode of the solid pipe, synergy freezing mode of the solid pipe and hollow pipe, principal freezing of the solid pipe with hollow pipe as complement and single freezing mode of the hollow pipe
Summary
With the increasing complexity of the underground construction environment, the construction technology is becoming more and more complex and difficult. Shallow-buried underground excavation, as a major underground construction method, has an important role in tunnel engineering and its development relies on an auxiliary construction method. Pre-supporting method is widely applied in shallow-buried underground excavation, because of simple technology and low cost. The pipe-roofing method is a primary method of pre-supporting. As the complexity of underground environment increases, it is difficult to meet the requirements of project quality with only one auxiliary method, especially in the construction of large cross-section tunnel with a rich aquifer. The combination of pipe-roofing method and different innovative methods have been carried out to ensure the safety of construction, which is proposed by many scholars.
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