DIRECT AND INDIRECT MEASUREMENT OF SOIL-FREEZING CHARACTERISTIC CURVE

Abstract

SWCC (Soil-water characteristic curve) and SFCC (Soil-freezing characteristic curve) are the main concepts describing the properties of unsaturated and frozen soil, respectively. SWCC is the relationship between matric suction and water content of the soil and can be used for the understanding of unsaturated soil characteristics while SFCC demonstrates the relationship between the unfrozen moisture content of soil and sub-freezing temperature and can be used to predict the frozen soil behavior. In this study, SFCCs of natural soil from Turan Avenue near Nazarbayev University, Astana and engineered soil (sand-kaolin mixtures) are investigated. The study involved determination of SFCC using direct and indirect methods. For direct measurements, laboratory experiments were conducted by measuring soil moisture and suction of the investigated soils under different temperature. The determination of SFCC using indirect method was performed utilizing various mathematical equations from SWCC of the investigated soils. The fundamental theory of the mathematical equations is based on the similarity of characteristics between SFCC and SWCC. The equations used in this study include Van Genuchten, Fredlund& Xing, power and exponential equations. The hysteresis effect during freezing-thawing, which is more noticeable at higher temperatures, complicates the observed SFCC patterns. The effect of soil type was studied utilizing mathematical SFCCs for a variety of soils, including Astana soil, sand-kaolin combinations, and SFCC envelopes based on the Unified Soil Classification System. Fine-grained soils exhibited a higher unfrozen water content, even at temperatures below -10 °C, due to their superior water absorption capabilities. The revised SFCC equation provided an important advance by accurately describing SFCC fluctuations during freezing. Its examination utilizing experimental data from Astana soil revealed a better fit than the Fredlund & Xing (1994) SFCC model. A similar pattern was observed in the verification of sand-kaolin blends, with the slope of the SFCC graph rising as the amount of kaolin increased. This characteristic was consistent across the Fredlund & Xing and Satyanaga SFCC models.