The accurate modeling of water and heat transport in soils is crucial for both geo-environmental and geothermal engineering. Traditional modeling methods are problematic because they require well-defined boundaries and initial conditions. Recently, physics-informed neural networks (PINNs), which incorporate partial differential equations (PDEs) to solve forward and inverse problems, have attracted increasing attention in machine learning research. In this study, we applied PINNs to tackle hydraulic and thermal transport coupling forward problems in silty sands. A fully connected deep neural network was utilized for training. This neural network model leverages automatic differentiation to apply the governing equations as constraints, based on the mathematical approximations established by the neural network itself. We conducted forward problems and compared the solutions derived from PINNs with those from Finite Element Method (FEM) simulations. The forward problem results demonstrate the PINNs model’s capability in predicting hydraulic transport, heat transport, and thermal–hydraulic coupling in silty sands under various boundary conditions. The PINNs exhibited great performance in simulating the thermal–hydraulic coupling problem. The accuracy of the PINNs solutions shows its potential for simulation in geotechnical engineering.

Buffer material is crucial for the engineering barrier system to dispose of high-level radioactive waste in a geological repository. A reliable buffer material should be able to maintain good sealing characteristics and minimize desiccation cracking. In this study, the effectiveness of inorganic fiber-reinforced engineering barrier material in reducing desiccation cracks in bentonite was evaluated via desiccation tests, image analysis, and air permeability tests. The effects of fiber type (E-glass fiber and basalt fiber) and fiber content (0.0%, 0.5%, 1.0%, 1.5%, 3.0%, and 5.0% of dry weight of the bentonite) on the development of desiccation cracks in the fiber–bentonite mixtures with the same given initial moisture content were evaluated. The results indicated that the addition of fibers could significantly reduce the crack size and area in bentonite during the drying. Basalt fibers showed a slightly better reinforcement effect than E-glass fibers when the fiber content was lower than 3.0%. The addition of fibers prevented the development of penetrating cracks and significantly reduced the permeability of the bentonite after drying. The permeabilities of basalt fiber- and E-glass fiber-reinforced bentonite composites with 3% reinforcement were 5.81 × 10^–11 m² and 7.24 × 10^–11 m², respectively, which were 64 and 51 times smaller than that of pure bentonite. X-ray–CT observation of the internal structure of the samples after drying showed that the addition of fibers significantly changed the crack morphology and potentially increased the tortuosity.

Bentonite is widely used as a buffer material in deep geological repositories because its low hydraulic conductivity and swelling pressure help limit advective radionuclide transport. Elevated temperature, however, can cause drying and shrinkage, which may alter swelling behavior and reduce mechanical integrity. Fiber reinforcement has been proposed to mitigate these effects, but the behavior of fiber-reinforced bentonite at elevated temperature remains poorly understood. This study investigates the swelling pressure, compressibility, and consolidation behavior of glass microfiber-reinforced Na-bentonite at 22 °C and 50 °C with fiber contents of 0, 1, and 3 wt%. The fiber sensitivity of swelling pressure decreased by 42% over the 28 K temperature increase, from − 72.9 kPa/wt% at 22 °C to − 42.5 kPa/wt% at 50 °C, even though the overall swelling pressure increased with temperature. To interpret the results, a thermo-Barcelona Basic Model (BBM) framework with a volumetric homogenization fiber composite term was calibrated against the experimental data. The analysis indicates that the reduced fiber sensitivity at elevated temperature is mainly related to a decrease in the apparent fiber–matrix interfacial bond strength, τ _b , from 16 to 9 kPa, whereas the bentonite-phase parameters λ(0) and p ₀ changed only slightly. These findings suggest that the effectiveness of fiber reinforcement depends not only on fiber properties, but also on the thermal stability of the fiber–clay interface under hydrothermal conditions. Scanning electron microscopy (SEM) observations showed fiber–clay contact and clay coating on fiber surfaces, supporting the proposed interfacial mechanism. Overall, the results suggest that interfacial bond stability should be considered when selecting inorganic fiber reinforcement for engineered barrier materials subjected to coupled thermo-hydro-mechanical conditions.