Structural properties of unsaturated compacted loess for various sample moisture contents

This paper investigates the structural properties of compacted loess by focusing on the influence of structural changes incurred by varying sample moisture content on matric suction and stress-strain characteristics of unsaturated compacted loess. Two tests are conducted on unsaturated compacted loess with different structural properties: soil-water characteristic curve test and triaxial shear test. Samples are maintained and tested at the same moisture content and dry density through humidification or dehumidification. Test results show that structural changes incurred by sample moisture content markedly influence the soil-water characteristic curve of unsaturated compacted loess. Below the plastic limit, matric suction increases with increasing sample moisture content. At the optimal sample moisture content, unsaturated compacted loess exhibits a homogeneous micro-pore aggregation structure and thus a relatively high suction. In the optimal structural state, the stress-strain curve was located at the top of the stress-strain graph. For moisture contents below the optimal sample moisture content, the degree of structural weakening is relatively low, and the stress-strain curve gradually moves down the stress-strain graph. For moisture content above the optimal sample moisture content, the degree of structural weakening of the soil sample is relatively high, and the stress-strain curve moves to the bottom of the stress-strain graph. A structural parameter mɛr is defined that could reasonably reflect the structural properties of compacted loess and is of great significance for evaluating the engineering quality of compacted loess.