Granular materials are widely prevalent in nature and industry, and the discrete element method (DEM) is the most effective method for the mechanical analysis of granular materials. Because of the difficulty inherent in friction coefficient determination, the friction behavior of granular geomaterials has always been a difficult problem in DEM. In order to study the variation rules of the sliding friction coefficients in DEM, an experiment designed to determine the sliding friction coefficient between particles with different shapes and different contact forms and an experiment designed to determine the sliding friction coefficient between particles and different boundaries were proposed, and the experimental results were fitted. In order to verify the reliability of the experiments, the fitting results were embedded into DEM software, and several packing experiments and simulation experiments were carried out and compared. The simulated results are detailed and discussed with reference to the experimental results as part of this paper. The results indicate that the simulation results are highly consistent with the experimental results, and the sliding friction coefficient obtained by the proposed experiment is in accordance with that determined theoretically. The sliding friction coefficient determined by fitting according to the experimental results can determine the sliding friction coefficient in DEM simulation and improve the accuracy of simulation results.

The contact force calculation model plays an important role in the discrete element method (DEM), but the existing models have a large deviation from the actual situation when calculating the normal contact force of brittle materials. The Volume model, a new normal contact force calculation model, is established based on the overlap between two particles in collision contact. When the geometric features and contact depth δ are specified, other contact parameters are automatically followed, including contact direction, contact point and force magnitude. Due to the geometrical symmetry of spherical particles, the results can be simplified. Based on the theory of Volume model, the formula for calculating the normal contact force of spherical particle element is derived. Comparing with the existing normal contact force calculation models, the Volume model has higher accuracy in brittle materials. In addition, the complete discrete element method algorithm is developed in this paper. Taking concrete spherical particles as an example, the spherical particle experiment is designed by embedding the contact model into the program. The results show that the Volume model has higher accuracy in calculating the normal contact force of brittle materials.

Both ground source heat pumps (GSHPs) and energy underground structures are engineered systems that utilize shallow geothermal energy. However, due to the construction complexity and associated costs of energy tunnels, their heat exchange efficiency relative to GSHPs remains a topic worthy of in-depth investigation. In this study, a thermal–hydraulic (TH) coupled finite element model was developed based on a section of the Torino Metro Line in Italy to analyze the differences in and influencing factors of heat transfer performance between energy tunnels and GSHPs. The model was validated by comparing the outlet temperature curves under both winter and summer loading conditions. Based on this validated model, a parametric analysis was conducted to examine the effects of the tunnel air velocity, heat carrier fluid velocity, and fluid type. The results indicate that, under identical environmental conditions, energy tunnels exhibit higher heat exchange efficiency than conventional GSHP systems and are less sensitive to external factors such as fluid velocity. Furthermore, a comparison of different heat carrier fluids, including alcohol-based fluids, refrigerants, and water, revealed that the fluid type significantly affects thermal performance, with the refrigerant R-134a outperforming ethylene glycol and water in both heating and cooling efficiency.

The materials involved in geotechnical engineering are objects of concern in granular mechanics. In order to study the influence of the sliding friction coefficient corresponding to different-sized elements in the discrete element method (DEM) on the simulation results, we establish a two-dimensional DEM model based on the experimental method to analyze a slope example. The correctness of the DEM model is verified by comparing the sliding surface of a finite element method (FEM) model and the DEM slope model. A sliding friction coefficient algorithm based on the experimental method is embedded into the DEM slope model and compared with the original model. The comparison results show that embedding the DEM model into the sliding friction coefficient algorithm leads to an increase in displacement. The reason for this is that the contact information between elements of different sizes has changed, but the displacement trend is the same. Different sliding friction coefficients should be set based on different-sized elements in the DEM, as they can improve simulation accuracy.

The discrete element method (DEM) serves as a robust tool for simulating the mechanical behavior of granular materials. The accuracy of the DEM simulation is determined by the calculation of contact forces between elements. Compared to spherical elements, the contact modes of polyhedral elements are more complex. In this work, the contact force between polyhedral elements under different contact modes was investigated by experiment. Based on the experimental results, the normal stiffness coefficient in the Cundall’s contact model was modified. The improved contact force model was then applied in the DEM simulation and validated by means of comparison with the results of packing experiments. The research results demonstrate that the improved contact force model can be effectively applied to the simulation of different contact modes between polyhedral elements. The results of the packing experiment highly coincide with the results of the DEM simulation, which confirms the accuracy and reliability of the improved contact force model.

With the intensification of climate change and the continuous advancement of urbanization, the pressure on urban drainage systems has increased, leading to the growing prominence of urban waterlogging issues. Besides the destruction of infrastructure, urban waterlogging also affects environmental quality, economy, and residents’ daily lives. Researchers have recently analyzed the causes of urban waterlogging from multiple perspectives, including land-use changes driven by urbanization, the inadequacy of urban drainage systems, and extreme rainfall events resulting from climate change. Various strategies have been proposed to address waterlogging, including optimizing urban green spaces, establishing forecasting systems, and creating effective emergency management systems. Additionally, some scholars highlight the significance of integrated urban planning and interdepartmental collaboration, suggesting that multi-party cooperation can help mitigate the risks of waterlogging. This paper conducts a comprehensive literature review to summarize the current research status of urban waterlogging, focusing on theoretical, experimental, numerical simulation, and artificial intelligence approaches. The review aims to provide a clearer understanding of the existing knowledge, identify gaps for future research and propose ideas that combine advanced technologies and interdisciplinary approaches.