An apparatus for measuring water content of unsaturated soil based on the van der Pauw principle

Abstract

Understanding water migration in soil specimens under triaxial test conditions is of great significance for investigating the mechanism of distress in railway subgrades. However, the water content distribution along the specimen height is difficult to determine with current equipment. Motivated by such limitations, we developed an apparatus relying on the van der Pauw principle, to measure the water content based on the specimen’s electrical properties. Additionally, a series of exploratory tests on unsaturated soil specimens were conducted to evaluate the performance of this apparatus. To verify the practicability of the apparatus, a water-supply dynamic triaxial test was also carried out with an unsaturated dynamic triaxial test system (GDS). The results indicate that this apparatus is stable, as the measurement accuracy is not influenced by the electrode position or the soil geometry or dimensions. In a narrow triaxial pressure chamber, this apparatus can be used to determine the distribution of water content in unsaturated specimens nondestructively and consecutively during a triaxial test. The maximum error obtained from the apparatus when measuring the gravimetric water content was 0.7%. The soil resistivity calculation function was obtained considering the dry density and gravimetric water content with high correlation and precision. This apparatus has broad applications for investigating the mechanism of water migration within some geotechnical materials.