High-suction polymer sensor for measurement of soil suction under freezing and thawing conditions

Soil-water characteristic curves (SWCC) are one of the most essential elements of unsaturated soil properties, yet the instruments employed for acquiring them have distinct limitations, for example, the tests are time-consuming, tedious and costly. High-suction polymer sensor (HSPS) with modified polyacrylamide (PAM) polymer is an alternative of measuring soil suction that relies on osmosis pressure rather than capillary pressure alone. The sample examined originated in Astana and was defined as clayey sand (SC). The ambient temperature of the Astana soil (sample 1) was used to assess soil suction using HSPS, which was verified by typical unsaturated equipment such as the Tempe Cell and dew-point potentiometer (WP4C). Once confirmed and SWCC was formed, the HSPS was utilized to detect soil suction during freeze-thaw cycles to simulate the climate in Astana. Based on the durability test, with the anticipated outcome lasting up to a year, PAM can resist the pressure for >200 days. Additionally, the modified PAM generated a stable response compared to the conventional PAM. The results from laboratory testing indicated that sample 2 has a greater average suction during freezing, while sample 3 has a higher average suction during thawing. In general, freezing cycles should produce more suction than thawing; yet, in sample 3, the water was still in supercooling stage, resulting in freezing having a lower suction average than thawing.