Abstract: The frost heave effect is significant in artificial ground freezing (AGF) projects involving shallow underground metro stations. To address this, an integrated whole-circle control technology is developed to mitigate frost heave. During the design stage, the frozen wall thickness is optimized to ensure bearing capacity, utilizing safety-reduction design approaches such as soil-cement modification and frozen composite structures. In the construction stage, comprehensive frost heave suppression technology considering spatiotemporal effects is applied. Temporally, staggered freezing schedules precisely control the volume of frozen soil in each phase, preventing cumulative frost heave. Spatially, intermittent freezing combined with soil extraction for pressure relief allows refined control over the frozen wall′s development rate and boundary conditions. On the premise of ensuring the functional safety of the frozen wall, the impact of frost heave on adjacent buildings is suppressed by optimizing and controlling the thickness and boundary of the frozen wall throughout the whole-circle. A field test was conducted at the Jiangpu road station of Shanghai metro line 18. The test data show that: (1)When the cement mixing ratio reaches 12.5%, the frost heave rate of gray clay is reduced by 53.5% compared with the original state. (2)Compared with the frozen soil structure, the frozen wall thickness is reduced by 42.53% with the frozen soil-steel pipe composite structure. (3)The measured data demonstrate that the proposed technology effectively mitigates frost heave in shallow underground metro stations, reducing the change rate of vertical displacements at monitoring points by up to 150.71%.

Key words: shallow-buried metro station, artificial ground freezing, frost heave, integrated control technology