Elastoplastic responses of unsaturated highly expansive clay stabilized by MOC-based multiphase agent under static and cyclic loadings

This paper investigates the volumetric behaviors, soil-water and microstructural characteristics, and static and cyclic elastoplastic responses (including the shear strength q u , initial tangent modulus E , resilient modulus M R , and permanent strain ε p ) of a natural and stabilized expansive clay. The clay was stabilized by a magnesium oxychloride cement (MOC) based multiphase cementitious agent, which is a novel, sustainable, and eco-friendly binder. Experimental results demonstrated that (i) the MOC-based agent effectively reduces the swelling potential, volumetric strain, and water-retention capacity of the expansive clay; (ii) The stabilization process improves the q u , E , M R of the clay by about 2–7 times and reduces its ε p by about 50–80% upon cyclic loading. Such improvement was especially significant under wet conditions when subgrade soils are prone to water damage. The sensitivity of the q u , E , M R , and ε p to moisture content fluctuation is significantly reduced (by 57–70%); (iii) the agent modifies the clay’s microstructure by extensively reducing the volume of macropores while moderately reducing the volume of micropores, which are considered responsible for the increase in the clay’s mechanical properties and the decrease in their moisture sensitivity; (iv) the q u - M R and E - M R relationships show unique and linear characteristics for the natural and stabilized soils. Linear empirical equations are proposed for predicting their M R at various moisture contents. Besides, a semi-empirical model is developed to describe the variation of the q u , E , M R with soil suction and moisture content for the natural and stabilized soil, which has achieved good agreement between the model predictions and experimental measurements.