Numerical Solution for Chloride Transport at the Corners of Square Piles Subjected to Wetting–Drying Cycles

Factors Influencing Chloride Diffusion in Recycled Aggregate Concrete: Based on Three-Dimensional Polyhedral Aggregate Model

In saline soil and coastal environments, the recycled aggregate concrete (RAC) exhibits high sensitivity to chloride ion erosion, while the long-term erosion process is difficult to be reproduced by the experiment. For the simulation of the chloride ion diffusion, many contributions have been reported based on the two-dimensional aggregate model, which ignores the three-dimensional characteristics of the shape and distribution for the aggregates. In this study, a three-dimensional random polyhedral aggregate model is developed employing the Python programming language. And then, a polyhedral RAC model considering the chloride diffusion is established based on the Fick’s second law. The validity of the proposed model is verified by comparing the chloride concentration in RAC obtained by simulation and experiment. Finally, the effect mechanism of structural parameters on the chloride diffusion in RAC is revealed. The simulation results indicate that, compared to the other parameters, the diffusion coefficient of the new mortar has the greatest impact on the apparent diffusion coefficient of RAC. Furthermore, the external chloride ion concentration has the greatest impact on the chloride ion concentration of RAC. Specifically, when the RA content and the diffusion coefficient of the new mortar increased by 40%, the apparent diffusion coefficient of RAC increased by 23.9% and 41.47%, respectively. This study provides fundamental insights for modeling and predicting the long-term diffusion process of chloride in RAC.

Research on Multiscale Simulation Methods for Thermal Response of Cemented Sand–Gravel Dams

Cemented sand and gravel (CSG) dams have been widely applied due to their simple construction and use of local materials. With the increasing occurrence of extreme weather events, temperature has become an important factor affecting the safe operation of dams. To investigate the temperature stress response of CSG dams under low-temperature conditions and achieve cross-scale analysis, an adaptive macro–meso finite element method is proposed. Through an iterative “solution–evaluation–mesh adjustment” procedure, meso-scale modeling is performed in high-stress regions, and the results are compared with those obtained using the conventional submodeling method. The results show that, under low-temperature conditions, temperature gradients and thermal stresses are mainly concentrated near the dam surface, with limited influence on the interior, while hydraulic load remains the dominant controlling factor. The local stress distribution patterns obtained by the two methods are generally consistent, and both can reflect stress concentration near the aggregate–mortar interfaces. The proposed method can characterize local meso-scale responses within a global computational framework, providing a reference for cross-scale analysis of the temperature response and the identification of local unfavorable stress regions in CSG dams.

Numerical investigation of coupled heat and mass transfer in deformable granular beds during humid-air and superheated-steam drying

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.

Experimental–Numerical Analysis of the Ultimate Lateral Capacity of PHC Piles

This study investigates the ultimate lateral behavior of prestressed high-strength concrete (PHC) piles in layered ground conditions at a thermal power plant site in Nhon Trach, Vietnam. Full-scale free-head lateral load tests were conducted on single PHC piles with diameters of 300, 400, and 500 mm, and the measured load–displacement responses were used to calibrate a three-dimensional finite element model in Plaxis 3D. The calibrated model reproduced the experimental H–u curves with good agreement and was further used to examine the effects of soil stratification and head boundary conditions. Comparison with the Japanese Road Association (JRA) analytical approach shows that JRA provides conservative displacement predictions for the larger-diameter piles (D400–D500) over practical displacement ranges, while the agreement improves for D300 at larger deformations, reflecting the stronger influence of the underlying soft clay and the limitations of equivalent-soil idealizations in layered profiles. Normalized head displacements at maximum test loads fall within u/D≈0.06–0.13, consistent in order of magnitude with reported full-scale lateral pile tests in the literature. The results support using JRA for rapid screening, whereas calibrated 3D numerical analysis is recommended for working design and for translating free-head test outcomes to fixed-head or pile-group boundary conditions in similar layered ground settings.