Abstract
The high risk of metro tunnels that are underneath buildings in a water-rich layer has received much attention. The base slab of an upper structure deforms due to frost heave and settlement, which needs to be predicted before freezing and excavation. In this paper, simulation experiments with a similarity ratio of 1/25 were performed based on an engineering project where two tunnels underpass a running station through an artificial ground freezing method. The displacement of upper structures was analyzed under simultaneous and sequential freezing modes, with a simple formula proposed to estimate the frost heave in closely underpassing projects. It is shown that, under freezing and excavation stages, the base slab displacement displays a zigzag shape. These results are instructive to the construction of underpassing projects in a water-rich layer.
Highlights
With the massive increase of the urban population, underground space has been utilized to tackle relevant problems like traffic congestion
Most of underpassing tunnels were constructed by tunnel boring, artificial ground freezing (AGF), and grouting
After active freezing of 104 min (i.e., 45 days in the project), average temperatures of the first, second and third groups on the outer fringe of a frozen wall were −4.60 ◦ C, −4.48 ◦ C and −4.42 ◦ C, respectively. This implies that the thickness of a frozen wall formed by a sequential freezing mode is similar to that by a simultaneous freezing mode, and the designed thickness of frozen soil can be achieved
Summary
With the massive increase of the urban population, underground space has been utilized to tackle relevant problems like traffic congestion. A metro station platform enlarged by AGF, located in the center of the city, is 10 m beneath a building, and the heave and settlement were measured with a total deformation of 12 mm [27] These studies are instructive for the construction of underpassing projects, there are still some significant differences. The freezing similarity simulation experiments have been adopted for predicting frost heave and settlement in the AGF engineering cases These studies mainly involve three areas, namely, the ground deformation behavior under heave and settlement [34,35,36], the formation of a frozen wall under high seepage-flow [37,38,39,40], and the ground deformation under freezing effect of a freeze-sealing pipe roof method [41,42,43].
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