Abstract
Bound water in saturated clay, owing to its unique electrical double-layer structure, plays a pivotal role in governing the macroscopic thermo-mechanical behavior of clay. This paper centers on discussing the mechanism of bound water variation with temperature in saturated clay. Through comparative analysis of research findings from various scholars, it is revealed that minor discrepancies in bound water density can induce substantial differences in the calculated bound water content, thereby influencing the analysis of thermal response patterns. Additionally, this study examines the applicability and limitations of the isothermal adsorption method, noting that this approach essentially simulates unsaturated conditions, often yielding bound water content measurements lower than the true values under saturated states, and encountering difficulties in distinguishing bound water from free water at high humidity levels. Concerning the trend of bound water content variation with temperature, this research employs an improved specific gravity test to measure specific gravity changes during temperature elevation from 20 °C to 50 °C, and integrates theoretical calculations to derive the evolution law of bound water content, proposing that bound water exhibits a characteristic "slow-fast-slow" attenuation pattern with increasing temperature. The investigation demonstrates that this thermal response of bound water fundamentally stems from alterations in electrical double-layer thickness and reconstruction of the particle-water interface energy structure. In engineering practice, accurate characterization of the temperature dependence of bound water is essential for predicting clay volume and strength variations, and can significantly enhance the safety and reliability of underground energy structures, geothermal systems, and similar facilities operating under thermo-mechanical coupling conditions.
Full Text
Study on the Temperature-Dependent Variation of Bound Water Content in Saturated Clays
Zilin Yuan¹, Zhongtao Wang¹, Hao Wang¹
¹State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024
Abstract
Bound water in saturated clays, owing to its distinctive electrical double-layer structure, plays a pivotal role in governing the macroscopic thermo-mechanical behavior of clayey soils. This paper delves into the mechanisms underlying temperature-induced variations in bound water content. A comparative review of existing literature reveals that even minor discrepancies in bound water density can yield substantial differences in calculated bound water content, thereby significantly affecting the interpretation of thermal response characteristics. Additionally, this study critically evaluates the applicability and limitations of the isothermal adsorption method, noting that this technique fundamentally simulates unsaturated conditions. As a result, measured bound water contents often underestimate true saturated values, and the method encounters difficulties in distinguishing bound water from free water at elevated humidity levels. To elucidate the temperature dependence of bound water content, we conduct improved specific gravity tests across a temperature range of 20°C to 50°C, and combine these measurements with theoretical calculations to derive the evolution law of bound water content. Our findings demonstrate that bound water exhibits a characteristic "slow-fast-slow" attenuation pattern with increasing temperature. This thermal response is shown to originate fundamentally from variations in electrical double-layer thickness and the reconstruction of energy structures at the particle-water interface. In engineering practice, accurate characterization of bound water's temperature dependence is essential for predicting volumetric and strength changes in clays, thereby enhancing the safety and reliability of underground energy structures and geothermal systems subjected to thermo-mechanical coupling.
Keywords: saturated clays; bound water content; bound water density; temperature; thermo-mechanical coupling