Hydromechanical behaviour of unsaturated expansive soils is complex, and current constitutive models failed to accurately reproduce it. Different from conventional modelling, this study proposes a novel physics-informed neural networks (PINN)-based model utilising long short-term memory as the baseline algorithm and incorporating a physical constraint (water retention) to modify the loss function. Firstly, a series of laboratory tests on Zaoyang expansive clay, including wetting and drying cycle tests and triaxial tests, was compiled into a dataset and subsequently fed into the PINN-based model. Subsequently, a specific equation representing the soil water retention curve (SWRC) for expansive clay was derived by accounting for the influence of the void ratio, which was integrated into the PINN-based model as a physical law. The ultimate predictions from the PINN-based model are compared with experimental data of unsaturated expansive clay with excellent agreement. This study demonstrates the capability of the proposed PINN in modelling the hydromechanical response of unsaturated soils and provides an innovative approach to establish constitutive models in the unsaturated soil mechanics field.

Desiccation crack is a prevalent natural phenomenon that plays a significant role in the stability of soil slopes. In this study, a hydromechanical coupling model incorporating a layer of stochastic cracks is developed for analyzing cracked soil slopes. To properly consider the anisotropy and spatial variability of desiccation cracks, three crack indices are generated through cross-correlated random fields via Cholesky decomposition. The seepage and mechanical behavior of a cracked slope are analyzed by adjusting stochastic parameters and rainfall conditions. Applied to the Ningzhen Mountains area in China, the model investigates the stability of slopes under various annual meteorological conditions. The results indicate that neglecting the spatial variability of cracked layer properties can lead to inaccurate assessments of instability risks at the base and water accumulation at the top of slopes. During heavy rainfall, slopes with deeper (up to 5 m) and weaker cracked layers often show a roughly planar sliding morphology. Moreover, the uncertainties in crack depth have the most pronounced influence on the uncertainties of the slope stability, more than horizontal permeability or crack aperture. The average crack aperture's influence on slope stability depends on the relationship between crack infiltration rate and rainfall intensity.