In situ monitoring of frost heave pressure during cross passage construction using ground-freezing method

Abstract

The artificial ground-freezing method has the dual effect of ground reinforcement and waterproof sealing, and the frozen curtain can be designed flexibly. It is widely used in the construction of cross passages for shield tunnels in soft ground with high groundwater levels. However, due to the lack of in situ monitoring data, it remains difficult to determine the frost heave pressure acting upon a tunnel. In this study, based on the use of an anti-freezing pad-type earth pressure gauge, in situ monitoring was carried out to measure the frost heave pressure acting upon tunnel segments during the construction of cross passages for the Shanghai Yangtze River Tunnel. The monitoring results show that the earth pressure acting upon the tunnel could decrease dramatically during freezing, and this kind of decrease can take place suddenly and unpredictably, which can be illustrated using the finite element method. The maximum measured frost heave pressure during freezing and cross passage excavation was approximately 0.2 MPa, which was much smaller than the predicted value. Combining the distribution of temperature in the ground and construction countermeasures, the observed phenomena are mainly related to three factors: water migration during the freezing process, the tunnel–ground interaction, and the countermeasure of pressure release holes. The tunnel showed a horizontal extension–deformation, which was consistent with the releasing frost heave pressure acting upon it.