Investigation on deterioration of mechanical properties of Jiangxi lateritic soil subjected to drying-wetting cycles

Numerous earth dams using Jiangxi lateritic soil undergo drying-wetting (D-W) cycles due to reservoir fluctuations. A multi-scale investigation on the mechanical properties deterioration of Jiangxi lateritic soil was conducted, with a maximum value of D-W cycles N = 5. This multi-scale study was conducted, including the determination of shear strength by triaxial shear tests, the identification of cracks using image processing techniques, and the examination of microstructure through mercury intrusion porosimetry and scanning electron microscopy tests. The results showed that at the macro-scale, a fast decay in shear strength was observed at N = 1-3, with an obvious slow decay at N = 3-5. At the meso-scale, the crack dynamic hysteresis was observed, including the drying-induced desiccation cracks and wetting-induced healing behavior. With increasing N , the desiccation crack initiated at N = 0-1, propagated at N = 1-3, and stabilized at N = 3-5. At the micro-scale, increasing D-W cycles resulted in aggregation decomposition, changes in particle contacts, and an increase in pore volume. From these tests, the multi-scale properties deterioration with N can be divided into two zones: for the 1st zone ( N = 1-3), the cementation between aggregates was destroyed due to the hydration effect of hydrophilic clay mineral, resulting in pore volume increase and cracks propagation. This led to a fast decay in shear strength. For the 2nd zone ( N = 3-5), due to the dissolution of clay minerals in the 1st zone, the weak hydration occurred. The separated particles were found, and a crack network was gradually formed, which led to the slow decay in shear strength. The deterioration of these multi-scale properties under D-W paths exhibited the hysteresis characteristics. The shear strength decay hysteresis was related to the crack dynamic hysteresis and pore structure hysteresis. With increasing N , this multi-scale hysteresis effect was weakened, owing to the gradual loss of hydrophilic clay minerals.