Evaluation of the Performance of a Finite Volume Physics-Based Model for Soil Erosion Simulation

Numerical modelling of suction diffusion in unsaturated expansive soils under climatic fluctuations

The behaviour of expansive clay soils is highly influenced by climatic variations that govern the hydric exchanges between the atmosphere and the ground surface. These fluctuations cause changes in soil suction, leading to significant volumetric variations in expansive soils and resulting in differential settlements of lightweight structures, which can induce structural damage. Despite the critical role of these hydroclimatic processes, few models are able to describe the evolution of soil suction under realistic boundary conditions. In this study, a two-dimensional diffusion model is proposed to simulate the temporal and spatial evolution of suction beneath a structure, considered as impermeable, under the influence of climatic fluctuations and over selected time steps. The model is based on the numerical solution of the diffusion equation in unsaturated porous medium, formulated in terms of suction. The boundary conditions incorporate a surface water balance accounting for infiltration and evaporation, using meteorological data from the Météo-France SIM2 model. Hydraulic soil parameters, such as unsaturated permeability and water retention curve expressing suction as a function of water content, are defined from empirical relationships reported in the literature. The model is applied to a clay soil whose parameters are derived from the Chaingy experimental site (France) using daily climatic data for the year 2025. The simulations highlight a strong seasonal variability of suction concentrated within the upper soil layers, while the presence of an impermeable surface zone representing the structure significantly attenuates suction fluctuations beneath the foundation and induces marked horizontal gradients during dry periods.

Modeling Environmentally Driven Seasonal Moisture Migration and Ground Movements in Expansive Clays

This paper describes the formulation of a numerical model for simulating environmentally driven one-dimensional (1D) ground movements of expansive clay. The formulation is based on a finite-element model that simulates the redistribution of matric suction through a diffusion-type equation, explicitly accounting for volume changes due to wetting and drying of the clay. We synthesize and modify highly nonlinear constitutive relationships for (1) hysteretic soil water retention; (2) reversible soil shrinkage and expansion of clay; and (3) hydraulic conductivity, explicitly incorporating desiccation cracks through a multidomain framework and assuming a critical surface crack depth. These models are well-calibrated to published laboratory tests on a reference expansive clay, Denver bentonite. We demonstrate capabilities of the proposed formulation to simulate the response of a homogeneous expansive clay to periods of drying and wetting, considering the initial matric suction, saturated hydraulic conductivity of the intact clay, and critical crack depth as three primary sources of uncertainty. We compare ensemble model simulations with measured ground movements from an instrumented expansive clay test site in Texas over a 3-year period using detailed records of potential evapotranspiration and precipitation. By assigning weights to the ensemble simulations based on their performance, we constrain the ranges of the three key uncertain parameters. The results showed very reasonable first-order agreement with the measured data and highlight the potential of the proposed formulation. We anticipate that more reliable predictions can be achieved through direct measurements of actual in situ evaporation rates and local soil properties.

An Unsaturated Soil Material Point Method for Simulating Rainfall-Induced Landslides

Rainfall infiltration frequently triggers slope failures by elevating pore water pressure and compromising the shear strength of unsaturated soil layers. Modeling these severe geological events remains computationally challenging. Standard grid-based techniques, such as the Finite Element Method (FEM), typically fail due to severe mesh distortion under large deformations, whereas the Discrete Element Method (DEM) demands excessive computational resources. Addressing this gap, we develop an advanced theoretical framework utilizing the Material Point Method (MPM) integrated with a liquid-solid-gas three-phase mechanics model. We first verify the algorithmic accuracy using a 1D unsaturated soil column test. Subsequently, the framework is deployed to capture the dynamic displacement and mechanical responses of a 2D rainfall-induced landslide. Benchmarking against FEM data confirms that our multiphase MPM accurately models the infiltration process and subsequent structural collapse. Ultimately, this approach offers a highly robust computational strategy for analyzing large-scale landslide deformations and improving predictive assessments.

Hydro-mechanical Model for Slope Stability Assessment: A polygonal stabilization-free discretization

Rainfall-induced landslides are governed by the interaction between subsurface water flow and soil mechanics, requiring robust numerical methods for the simulation of variably saturated porous media. In this work, we consider a semi-coupled hydro-mechanical model based on Richards'equation and linear elasticity and propose a numerical framework based on a stabilization-free Virtual Element Method for its spatial discretization. The proposed approach naturally accommodates general polygonal meshes while avoiding problem-dependent stabilization terms, whose design may become challenging when heterogeneous and strongly non-linear coefficients are involved. The approach is combined with a mass-lumping technique to improve stability in the treatment of the storage term and with Nitsche's method to weakly impose seepage-face and infiltration boundary conditions, allowing for the automatic switching between Neumann and Dirichlet conditions. Time integration is performed using the backward Euler scheme, while non-linearities are handled through a Picard iteration. Numerical experiments demonstrate the stability and robustness of the proposed methodology and show its effectiveness in simulating rainfall infiltration and evaluating slope stability through the Local Factor of Safety.

Enhancing runoff-infiltration partitioning in the SVS land surface model improves streamflow simulations under frozen soil conditions

Enhancing runoff-infiltration partitioning in the SVS land surface model improves streamflow simulations under frozen soil conditions

Abstract. Soil freezing is a major cold region process that influences hydrological response of northern catchments, in particular during winter rainfall and snowmelt events. In land surface models, frozen soil infiltration is difficult to represent because soil structure and hydropedological processes vary at scales finer than the model grid. This is particularly true in operational modeling, where physical process integration must balance performance improvements against computational efficiency and complexity. In this study, we propose a new configuration of the Soil, Vegetation, and Snow (SVS) model used within the operational prediction systems of Environment and Climate Change Canada (ECCC) that enhances frozen soil infiltration by reducing both surface runoff and sub-surface lateral flow. We assessed the effects of this new configuration (Fr-Inf) on streamflow simulations at more than 580 hydrometric stations located in the Great-Lakes and Saint-Lawrence domain over a five-year period. Fr-Inf significantly improves the Kling-Gupta Efficiency (KGE) compared to the default soil freezing configuration (Fr; ΔKGE = 0.28) but slightly underperforms the configuration of SVS without frozen soil (noFr; ΔKGE = −0.07). Strong degradations relative to the no freezing configuration (ΔKGE < −0.5) are observed only at 4 stations with Fr-Inf (< 1 %) as opposed to 172 stations under the Fr configuration (33 %), highlighting the robustness of the approach. To ensure that the proposed change is also acceptable in the context of operational numerical weather prediction, an evaluation of its impact on soil freezing depth as well as screen-level temperature and dew point temperature predictions is performed against in-situ observations. These results support the potential operational implementation of soil freezing at ECCC for numerical weather and streamflow prediction.