PSI - Issue 28

A. Prokhorov et al. / Procedia Structural Integrity 28 (2020) 1579–1589 Author name / Structural Integrity Procedia 00 (2019) 000–000

1581

3

clay samples, the deformations caused by the frost heave are greater than in the sand samples, since ice lens do not form in the latter in the frozen zone. In Zhang et al. (2017) it was found that at the beginning of the freezing process, deformations caused by frost heave are determined by the initial moisture saturation. With a longer freezing, a significant contribution to the frost heave is made by moisture migration to the freezing front. In Wang et al. (2018), it was found that with an increase in the freezing temperature, frost heave becomes more pronounced, since the consolidation of the unfrozen part of the soil reduces. It is also noted that the cryogenic structure in the samples is nonuniform. Experimental studies of the phenomena and effects caused by the phase transitions of water into in saturated soils during the freezing process require using modern methods of temperature and deformation control. One of the actual methods for monitoring mechanical response of various objects, both on a laboratory scale and on the scale of real structures, is use of fiber-optic sensors based on Bragg gratings Hill et al. (1997). Fiber-optic sensors are actively used by engineers and researchers to monitor temperature during artificial freezing of rock mass Levun et al. (2019, Panteleev et al. (2017), to determine conditions for appearance of bends during construction of complex structures Zhu et al. (2007), Hong et al. (2010), to analyze a stress-strain state of structures during operation Caponero et al. (2019). Compared with traditional methods of control, fiber-optic systems have a number of advantages such as small size, low weight,absence of an influence of electromagnetic fields on the readings of sensors, high data transfer rate Hong et al. (2016). The main difficulty in using these systems lies in the fact that when one of the parameters of the process under consideration is measured, it is necessary to physically isolate the sensors of the system from the influence of associated processes or to compensate their influence by mathematical processing of the obtained measurements Shardakov et al. (2017). To describe frost heaving in water-saturated soils, thermohydromechanical models actively developed Zhou et al. (2013). In the models presented in Bekele et al. (2017), Lai et al. (2014), moisture migration in the soil is described by Darcy's law, in Wu et al. (2015) by a chemical potential depending on temperature, and in Li et al. (2018), by a moisture gradient. In Liu et al. (2018), the change in the volume of the pore space is associated with the pressure difference between ice and water. In Lai et al. (2014), additional volumetric deformations caused by frost heaving are calculated from the change in porosity. In Li et al. (2018), the contribution of frost heaving to the deformation of the skeleton is determined from the volumetric values of ice content and moisture content. 2. Experimental conditions The experiments were carried out under water saturated sandy soil. Physical parameters (Table 1) of soil were obtained by experiment and solution of invers problem of heat transfer.

Table 1. Physical parameters of soil

ρ, kg/m3

С, J/kg·deg

λ, W/m·deg

Directory

1823

700-840

1,5

Experiment 1,3 For the monitoring of conditions of freezing process two types of detectors were applied: temperature and strain FBG sensors and thermocouples. Two types of experiments were carried out. In the first one all sides freezing of the soil specimen was performed. In the second one the one-side freezing process was conducted. 1870 715