Abstract This paper presents a novel and comprehensive approach to minimizing track deformation by assembling recycled truck tire cells infilled with granular material in a square pattern as an alternative to a traditional capping layer (i.e., uppermost layer of subballast) constructed with compacted sandy gravel. A full-scale test track was constructed at the National Facility for Heavy-Haul Rail Testing, supported by numerical modeling using the finite element method, to evaluate the effectiveness of a tire cell assembly used as the capping layer beneath the ballast. This system builds on prior research demonstrating that a tire cell assembly, when infilled and compacted with granular material, forms a more confined and resilient substructure layer with enhanced energy dissipation capacity (i.e., higher damping ratio) that effectively limits lateral movement and reduces ballast breakage. In this study, multistage cyclic loading is applied to simulate heavy-haul freight trains with typical axle loads ranging from 20 to 35 t, subjected to equivalent loading–unloading frequencies of 10 and 15 Hz, corresponding to typical train speeds of 50 – 80 km / h . Test results on track settlements, lateral displacements, resilient modulus, ballast breakage are reported, with the infilled tire cells contributing to enhanced substructure stability. The presence of a semirigid capping layer beneath the ballast layer contributes to reduced lateral displacement of the track, while providing a robust and stiff foundation for the primary load-bearing ballast-sleeper system. The analysis of stress distribution with depth confirms that the tire cell–reinforced layer has contributed to an increase in the stiffness of the load-bearing stratum as well as an accompanying reduction of the stress transferred to the underlying softer subgrade. Even in the final loading stage under an increased simulated load of 35 t at 15 Hz, the track did not encounter any significant settlement. A finite element model was also developed and validated by full-scale experimental results, where the emphasis was placed more on the understanding of how tire cells would integrate within the track substructure to control stress distribution and deformation (mobilized strain).
Abstract This multiscale study investigates the influence of three-dimensional (3D) particle shape on the stress–dilatancy behavior of granular materials under low-stress simple shear conditions. High-resolution X-ray micro-computed tomography (micro-CT) was first used to quantify the particle shapes of 11 different sands, spanning silica, carbonate, and mixed compositions. The images with a reconstructed voxel size of 5.5 μm were segmented using a watershed-based algorithm, which isolated more than 10,000 grains per material. This enabled particle-level quantification of 3D shape descriptors for each sand. The analyzed particle-size distributions were validated against those measured from mechanical sieve analysis. In the second phase, direct simple shear tests were conducted on three selected materials, UWA superfine silica, ledge point, and glass beads, considering relative densities of 0.4 to 0.9 and normal pressures of 25 to 150 kPa. The results show that particle shape affects peak friction, excess friction, and dilation response, but the magnitude of this effect depends on density and normal stress. Particle-shape effects are strongest at lower density and lower normal stress, where particle rearrangement and dilation are more readily mobilized. As relative density or normal stress increases, the responses of the three materials converge, indicating that the mechanical response becomes less sensitive to particle shape. These results suggest that particle shape should be treated as a state-dependent modifier of stress–dilatancy behavior at low stress, rather than as a single fixed material correction.
Abstract Amid escalating sea-level rise, seepage cutoff walls have become critical infrastructure for costal protection. However, conventional bentonite used as a sealing material in the walls suffers from degradation in seawater, posing workability and durability concerns. Meanwhile, large volumes of waste marine clay (MC) are excavated in coastal regions, characterized by poor engineering properties but notable fineness and low permeability. Hence, this study investigates the use of MC, which naturally formed in a seawater environment and is inherently stable as a sustainable alternative to bentonite. Experiments were conducted to evaluate engineering and physicochemical properties of MC-based cutoff walls in freshwater and seawater, compared to bentonite-based cutoff walls. The results showed that bentonite mixtures exhibited better flowability control and bleeding resistance in freshwater, but their performance degraded in seawater, becoming comparable to that of the more stable MC mixtures. MC mixtures demonstrated higher strength in freshwater, with further enhancement in seawater; however, bentonite mixtures exposed to seawater exhibited strength degradation. At equivalent dosages, bentonite outperformed MC in impermeability; nonetheless, increasing MC content, which also promoted sustainable waste utilization, reduced its permeability to comparable levels. Physicochemical analyses revealed that MC maintained high stability in seawater because of its strong resistance to changes in water-retention, swelling, and cation exchange capacity. This stability was also attributed to its kaolinite-dominant mineralogy; conversely, bentonite underwent mineralogical transformation from Na-montmorillonite to Ca-montmorillonite, accompanied by disordered smectite and agglomerated microstructure. These findings underscore the potential use of MC as a durable, cost-effective, and sustainable alternative to bentonite in coastal cutoff walls.
Abstract Plate anchors offer an attractive anchoring solution for floating renewable energy devices in deep water, whereas the uplift behavior of plate anchors in sand and the associated failure mechanisms remain insufficiently explored. This study investigates the uplift behavior and the corresponding three-dimensional (3D) failure mechanisms of rectangular plate anchors in sand through finite element (FE) analysis. The critical state–based NorSand model, implemented in the FE package Abaqus/Standard, was employed to describe sand behavior. The FE model was validated against both element tests and centrifuge data. A parametric study was conducted to investigate the effects of relative density and embedment ratio on the uplift capacity of rectangular anchors in sand. The 3D failure mechanism of rectangular anchors in sand was revealed and discussed, with particular focus on the inclination angles of shear bands and the extent of the failure zone, which provide key parameters for improving the predictive capability of existing analytical solutions. Stress paths at representative positions within the failure zone were examined, revealing a progressive failure mechanism that is analogous to triaxial compression and simple shear loading modes. Based on the simulation results, the shape factor predictions for rectangular anchors were discussed, showing the conservatism (i.e., underestimation) of existing methods in medium-dense sand. Practical relations were further developed to provide FE-based shape factor estimates for the rectangular anchors investigated. The findings highlight the importance of considering the 3D failure mechanism in plate anchor design.
Abstract Internal erosion is an important concern in coarse-grained soil engineering, yet large-scale triaxial experimental studies on this subject remain extremely scarce. As a prerequisite for seepage erosion test design, the selection criteria for leakage opening size lack a reliable experimental basis or quantitative guidelines. A self-developed large-scale triaxial testing system with coupled seepage and stress was used to study the suffusion process involved in internal erosion. The controlling constriction size, D C * , was introduced as a characterization parameter for the leakage opening size to systematically analyze the evolution of particle loss, gradation evolution, and hydraulic characteristics under different D C * conditions. Under stepwise loading, an increase in D C * lowers the critical hydraulic gradient for particle migration and increases the cumulative loss rate of fine particles. Under the tested material and loading conditions, a marked transition in fine-particle loss was observed between D C * / P min = 1.5 and 2.0, with the fine-particle loss rate at D C * ≥ 2 P min reaching 20 to 25 times that at D C * ≤ 1.5 P min , where P min denotes the minimum particle size missing from the gap-graded soil. When D C * ≤ 1.5 P min , fine particles clog the seepage path and accumulate at the bottom of the specimen; when D C * ≥ 2 P min , the gradation curves of all sections shift toward the coarser direction. The postsuffusion void ratio e n , calculated by comprehensively accounting for the fine-particle loss rate and volumetric strain, is introduced. The results indicate that D C * controls the evolution of hydraulic conductivity by regulating fine-particle loss and the associated postsuffusion void ratio e n . A positive correlation between e n and hydraulic conductivity k was identified, and an empirical prediction formula was established based on the experimental data under different D C * values.
