Experimental Investigation of Freezing Front Detection Behind Shield Tunnel Segments Using Ground-Penetrating Radar.

Monitoring and determining the development of frozen walls is a critical aspect of ensuring safe tunnel construction during freezing periods. Traditional temperature measurements for estimating freezing front expansion are constrained due to the limited number of measurement points and their fixed distribution. Here we introduce an innovative non-destructive detection method to investigate freezing wall expansion behind tunnel shield segments. First, dielectric properties of frozen and unfrozen clay and sandy soil were measured through laboratory experiments. Second, a freezing front model was established using a combination of numerical simulations and laboratory experiments. A 600 MHz radar was employed for detection and identification. Results indicate substantial differences in the dielectric constants of frozen and unfrozen soil, which can be employed as a convincing parameter for GPR to distinguish between them. Detection results demonstrate that GPR possesses the capability to determine the development pattern and approximate location of the frozen front behind shield tunnel segments. This method exhibits significant potential as an efficient and rapid means of detecting freezing wall expansion in tunnel engineering. Highlights: The difference in dielectric properties of frozen & unfrozen soils depends on the unfrozen water content. The electromagnetic responses of freezing front were studied by numerical simulation and indoor experiment. The accuracy of detection results from ground-penetrating radar was verified by conventional thermal methods. A fast and non-destructive method for determining the development of freezing fronts behind shield tunnel segments was proposed. [ABSTRACT FROM AUTHOR]