Effect of soil microstructure on the small-strain shear modulus of saline soil

The behavior of soils at small strains (< 10−5) is of significant interest for geotechnical engineers. Compared with the small-strain properties of sand or clay, those of saline soil have been investigated less extensively and therefore remain poorly understood. Accordingly, this study investigates the influence of microstructure on the small-strain shear modulus (G0) of saline soil. A series of specifically designed experiments was conducted on saline soil specimens under unsaturated conditions via the resonant column technique and scanning electron microscopy. The results showed that the G0 of saline soil increases with the dry density. The obtained values of the fitting parameter, A, are between 52.06 and 63.42, with an average value of 58.82, while those of the fitting parameter, n, are between 0.284 and 0.363, with an average value of 0.322. The Na2SO4 content was employed as a state variable, using which Hardin’s equation was modified for proper consideration of the influence of the Na2SO4 content on the prediction of G0. The results show that G0 increases with the Na2SO4 content. The inflection point of the Na2SO4 content with a significant change in G0 is 20%. The main contact forms of soil particles are edge–edge, edge–surface, and surface–surface contacts. With increasing Na2SO4 content, the cementation of soil particles by salt crystals gradually replaces the inter-particle contact, and sulfate crystal cementation becomes the dominant factor affecting G0.