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.

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The artificial ground freezing method has been widely used in shield tunneling breakthrough working shafts. The freezing effect was mainly considered in the previous research, and the heat generation of the shield machine was not considered, which has great influence in actual engineering. In this paper, a coupling calculation model, considering phase change latent heat, is establishes that by containing the freezing process and heat generation of the shield machine, the model is verified. A numerical simulation is carried out for several working conditions that may occur in actual projects, and the following conclusions are obtained. Although the heat dissipated by the normal tunneling of the shield machine will melt the frozen soil curtain that originally meets the design requirements, the thickness of the frozen soil curtain after melting cannot reach the initial design, though it is still within the safe range. In the process of a continuous rotation working condition, the bottom and sides of a cup-shaped frozen soil curtain are partially melted in the early 6 day stay of the shield machine, and the thickness is reduced to a relatively stable value of 0.8 m. In a temporary shutdown working condition, when the contact surface temperature between the shield machine shell and the frozen soil drops to −12 °C after almost 4 days of shutdown, the shield machine may not keep tunneling forward due to the freezing effect. The research results will benefit the freezing design and management of the shield tunneling breakthrough working shaft under extreme conditions.

Complicated soil conditions are direct difficulties for high-rise building projects. A new device called a deformation adjustor, which is used to optimize the stiffness distribution in the piled raft system, has achieved good results for this challenge. This paper presents a case study on the application of deformation adjustors to improve the performance of a piled raft foundation. This case study describes the preliminary design of pile-raft foundations with deformation adjustors, followed by numerical analysis. Based on the numerical study, the potential savings are demonstrated due to the good performance of soil bearing capacity. Comparing the numerical results with the monitoring results in raft settlements, earth pressures, deformation amount of deformation adjustors, pile top reactions, and load-sharing ratios between soils and piles, the accuracy of the design schemes with an aided numerical analysis is verified. Through a long-term monitoring, soils below the raft carried 63% of the total applied loads, while the piles bear 37% of the loads. This case study proved that a piled raft foundation with deformation adjustors was an effective and economical design scheme, which can make full use of the soil bearing capacity. It is of great significance to facilitate the design and construction of piled raft foundations in complicated soil conditions.