Laboratory Study on Temperature Field and Moisture Field Distributed Sensing of Subgrade in Freezing and Thawing

Abstract:

In this paper， a laboratory test device for multi-physical field sensing during soil freezing and thawing was established. Traditional point sensors and distributed optical fibers were used in the test to monitor the temperature field， moisture field， and deformation of the subgrade during freezing and thawing process. Distributed sensing characteristics of the temperature and moisture fields of the soil under single-ended freezing and double-ended thawing condition were investigated， and the monitoring performance of the active heating distributed optical fiber technology was verified. The results show that， under the condition of -15 ℃ single-ended freezing， the soil freezing process is divided into three stages according to the cooling rate， i.e.， the rapid cooling stage， the gradual cooling stage， and the stable equilibrium stage. The freezing front gradually moves down during freezing， and the maximum freezing depth is about 35% of the height of soil column. The pore water is affected by the frost heave migration force to the freezing front and causes the redistribution of soil moisture field before and after freezing and thawing， thus causes frost heave deformation of the soil， which accounts for 7.8 % to 10.9 % of the maximum freezing depth of soil column. The distributed optical fiber can accurately obtain the characteristics of the soil temperature and moisture fields during the freezing and thawing process， and identify the range of the freezing area in the soil. The goodness of fit R² of temperature and moisture monitoring reaches 0.98 and 0.94， respectively.

Key words:subgrade engineering;temperature field;moisture field;distributed sensing;subgrade in seasonal frozen area;active heated fiber optics