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 The mechanics response and ultimate bearing behavior of piles are significantly influenced by static loading rate. This study investigates the variation in monotonic axial capacity of closed-ended piles subjected to different loading rates. A distinct reduction in total bearing capacity is observed as loading rate increases, primarily attributed to a moderate enhancement in base resistance and a pronounced reduction in shaft resistance. Base resistance is progressively mobilized through densification of sand beneath the pile tip. Simultaneously, fine particles generated by particle breakage form a sandy crust along the shear zone surrounding the shaft. The combined effects of particle crushing, interface shearing, and relative displacement lead to a significant reduction in shaft friction at higher rates, driven by the transition from static to kinetic friction. This behavior is classified in four stages: fully static, nominally stationary, presliding, and rolling. At higher rates, interaction shifts from a sand–steel to sand–sand interface, reducing the friction coefficient, lateral stiffness, and normal stress. A velocity-based friction model, incorporating a backbone curve and capacity prediction formula, is proposed to quantify this transition. The model accurately captures rate-dependent behavior, offering practical value for design and analysis.
Abstract This paper presents results from a laboratory investigation of constant-volume direct simple shear (DSS) behavior of reconstituted authigenic and allogenic glauconite sands. This complex soil is formed in shallow marine depositional environments and primarily exists in situ as peloidal sand-sized grains but upon progressive degradation releases clay minerals and transitions to a plastic fine-grained soil. It has been studied extensively in the geosciences, but there is limited knowledge of its geotechnical engineering behavior. Natural samples of two glauconite sands with different geologic histories were collected from outcrops in New Jersey. Air-dried samples were reconstituted into DSS specimens using air pluviation. The samples were also degraded by mixing in a hydrometer dispersion cup, and the resulting slurry was reconstituted into DSS specimens. The DSS test program explored variations in reconstitution method, initial density, effective stress state, and overconsolidation ratio. Results show that the authigenic glauconite sand degraded much more readily than the allogenic glauconite sand. For the same applied degradation duration of 60 min, the authigenic glauconite transitioned from a silty sand to a high plasticity clay whereas the more resilient allogenic glauconite remained primarily a sand with a transition from a poorly graded sand to a clayey sand. These differences in the nature and composition of the glauconite grains in each soil controlled the normally consolidated DSS consolidation and shear behavior with a clay-like contractive behavior for the authigenic glauconite versus a sand-like dilative behavior for the allogenic glauconite. The results on the intrinsic behavior of two glauconite sands with different geologic histories inform interpretation of the shear behavior of intact and degraded glauconite, supporting development of a framework for constitutive model development.
