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Piled raft foundations are increasingly used in construction due to their cost efficiency, requiring fewer piles than traditional pile foundations. Their ability to withstand cyclic lateral loads, such as those from earthquakes and wind forces, is crucial for structural stability. Understanding their response under cyclic loading conditions is essential, and finite element modeling (FEM) is a valuable tool for analyzing these behaviors. A recent 3D FEM study examined the performance of piled raft foundations in clay soils, focusing on loading pattern, frequency, and number of cycles. Results showed that lateral load capacity decreased as cycle count and frequency increased, with full cyclic loading (FCL) having a more pronounced effect than half cyclic loading (HCL). The raft shared 20.57-39.07 % (HCL) and 27.68-55.13 % (FCL) of lateral loads at frequencies of 0.1-10 Hz over 20 cycles. Additionally, locked-in moments increased by 21 %, and the degradation factor ranged from 65 to 80 % for HCL and 70-90 % for FCL. These findings provide valuable insights into pile-soil interaction and foundation stability under cyclic lateral loading, ensuring more effective design strategies for structures exposed to dynamic forces. Future research should explore long-term cyclic effects to further optimize foundation performance.

期刊论文 2025-05-30 DOI: 10.1016/j.oceaneng.2025.120977 ISSN: 0029-8018

The premature failure or early deterioration of mine haul roads due to increasing problems of overrutting, potholes, and excessive settlement is a major issue. These problems mainly arise from the mismatch of overburden soil strength and stresses exerted by moving dumpers, inadequate compaction of soil, and improper assessment of the load-deformation characteristics of overburden soil under repeated loading. In the past, several research studies have been conducted; however, most of the studies are related to the geotechnical characterization and stabilization of mine overburden soil. In this study, the deformation characteristics, i.e., plastic and resilient deformations, of an overburden soil extracted during mining operations have been addressed, taking into account the influence of varying compaction densities, cyclic deviatoric stress, and loading frequencies. Compaction density notably affects soil strength, with 5.82% and 16.4% increases in density resulting in 23%-48% and 297%-410% strength gains, respectively. Meanwhile, cyclic deviatoric stress and confining pressure primarily influenced the axial strain behavior of mine overburden soil subjected to cyclic loading. At higher compaction densities, higher resilient modulus values were obtained. For a confining pressure of 48 kPa, increases of 5.82% and 16.4% in compaction density resulted in an increase in the resilient modulus by 32.6%-48.9%, 36.5%-67.6%, and 73%-201.3%, for increasing levels of cyclic deviatoric stress. The plastic deformations obtained were also notably high. Thus, mine overburden soils with high resilient modulus values can still experience premature failure, owing to the significant accumulation of plastic strain under high repeated deviatoric stresses. From the analysis of test results, three-parameter strain models have also been developed as a function of the number of load repetitions and the applied cyclic deviatoric stress to predict the rutting phenomenon in overburden soil at different compaction densities, applied cyclic deviatoric loads, and loading frequencies.

期刊论文 2025-03-01 DOI: 10.1061/IJGNAI.GMENG-10243 ISSN: 1532-3641

Climate change in recent decades has increased the frequency and intensity of extreme rainfall events, causing varied moisture contents in the ballasted track, which greatly challenges railway operation and track maintenance. Currently, most research about permanent deformation of fouled ballast are under dry condition or with a moisture content in the individual tested sample, which could not fully represent varied moisture conditions in the field induced by varying rainfall intensities. In this paper, permanent deformation of field-sourced fouled ballast under progressive wetting condition was investigated using large-scale triaxial cyclic tests. The results indicate that, with progressively rising water contents (0% to 12%), the fouled ballast sample maintained their stability; however, the rate of permanent strain increases to a peak value before experiencing a slight decline, aligning with classified shakedown ranges. This observed deformation features can be attributed to both the negative effect of suction loss under progressive wetting and the positive cyclic densification effect of coarse aggregates under repeated loading, an aspect that existing research have not elaborated on. To encapsulate the identified deformation characteristics, this study proposes and validates a new predictive model for the permanent deformation of fouled ballast capturing the feature of progressive wetting.

期刊论文 2025-01-01 DOI: 10.1139/cgj-2024-0321 ISSN: 0008-3674

The availability of quality materials for construction has been an issue in some regions. This scarcity obliged using marginal materials reinforced with geosynthetic materials as one of the quests for sustainability in the pavement industry. In this study, an attempt was made to stabilize the marginal materials by incorporating geosynthetics. The different geosynthetics used in the study are geogrid, geocell, double geogrid, and geocell + geogrid. A series of unreinforced (UR) and geosynthetic reinforced (GR) pavement prototypes were constructed in the laboratory with landslide debris as base material underlain by black cotton soil subgrade. Large-scale cyclic plate load (CPL) tests were performed on test prototypes constructed in the laboratory under cyclic loading following the trapezoidal loading pattern with 0.77 Hz frequency. The efficacy of geosynthetic reinforcement was quantified concerning permanent deformation (PD), resilient deformation (RD), Rut depth reduction (RDR), Traffic improvement ratio (TIR), and reduction in vertical stresses transmitted to the subgrade and reduction in base layer thickness. The test results indicate that the GR significantly reduced the rut depth and improved the traffic capacity. In addition, over all types of GRs, the combination of geogrid and geocell outperformed in terms of permanent deformation and rut depth reduction.

期刊论文 2024-12-31 DOI: 10.1080/10298436.2024.2318605 ISSN: 1029-8436

Repetitive traffic loads lead to particle rearrangement and breakage in granular trackbeds and roadbeds, resulting in irreversible deformations that hinder normal operations. Current models for cyclic deformation primarily address rearrangement-induced densification but overlook breakage-induced degradation. Particle breakage disrupts inter-particle interlocking and creates finer debris, promoting volumetric contraction and weakening material stiffness. This study introduces a novel cyclic constitutive model for predicting plastic strain in coarse granular materials, emphasizing the role of particle breakage. The model extended from the existing cyclic densification model within the framework named Shakedown Surface Model, integrating breakage effects. In this model, shakedown thresholds, associated with material densification, are influenced by both plastic strain and breakage-induced loosening. Parameters for shearing contraction/dilation decrease with breakage, capturing breakage-induced contraction. Additionally, the model accounts for principal stress rotation from moving loads. Implemented via an implicit Euler-backward algorithm and Newton-Raphson iteration, the model was validated against cyclic triaxial and full-scale tests, demonstrating its accuracy in predicting the permanent deformation of granular materials under traffic loads.

期刊论文 2024-12-18 DOI: 10.1680/jgeot.24.01145 ISSN: 0016-8505

The long-term performance of pavement structures is heavily reliant on the sustained load-carrying capacity of the subgrade soil. Under repetitive traffic loads, permanent deformation (PD) gradually accumulates in the subgrade due to plastic yielding and soil particle rearrangement, which can compromise the serviceability and durability of overlying pavement layers. This study aimed to enhance the understanding of compacted clay response under long-term cyclic loads through a systematic repeated load triaxial (RLT) testing approach. The proposed approach considered depth-dependent static and dynamic stresses exerted on compacted clay beneath pavement structures and traffic loads. A series of RLT tests were conducted to investigate the impact of key factors, including soil properties (moisture content and compaction degree), stress conditions (confining pressure and deviator stress), and load characteristics (load duration and rest period), on the PD behaviour of compacted clay subgrade. Stress-strain hysteresis loops and damping ratios were analyzed to enhance the fundamental understanding of subgrade PD evolution. The results showed that higher moisture content and lower compaction degree significantly increased PD, with the PD response transitioning from plastic shakedown to plastic creep. Greater deviator stress also exacerbated PD accumulation. Variations in loading duration and rest period influenced the PD behaviour, demonstrating the importance of accurately simulating the stress history experienced by subgrade soil elements under traffic loading. The findings provide valuable insights to optimize subgrade design and implement performance-based management of pavements.

期刊论文 2024-12-01 DOI: 10.1016/j.soildyn.2024.108972 ISSN: 0267-7261

This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods.

期刊论文 2024-11-01 DOI: 10.1080/14680629.2024.2310823 ISSN: 1468-0629

Rutting is a major distress mode in flexible pavements, results from the repetitive loading caused by traffic movement. Pavement deformation consists of both recoverable (elastic) and unrecoverable (plastic) components. The continuous movement of vehicles contributes to the overall deformation in the flexible pavement system, involving all pavement components. In regions with hot climates or in the hot summer season, rutting tends to be more prominent due to the substantial reduction in the viscosity of the asphalt binder. This decrease in viscosity, which is inversely linked to rutting, occurs as temperatures rise, leading to a heightened susceptibility of the Hot Mix Asphalt (HMA) blend to rut formation. However, according to studies, a significant amount of permanent deformation takes place in the unbound layers beneath the asphalt course, it is therefore essential to prioritize attention on these layers. Temperature exerts besides viscosity a substantial impact on asphalt stiffness, leading to the transfer of higher vertical deviatoric stresses to the unbound layers beneath the asphalt course (base, subbase, subgrade). This research presents a study integrating the High Cycle Accumulation (HCA) model into a laminar model to determine permanent deformations in the unbound granular layer of flexible pavements and taking into account the temperature dependent stiffness of asphalt. Rutting depths at the end of the design lifetime were computed, accounting for seasonal stiffness variations. It was shown that the softer asphalt behavior significantly increases the development of ruts in the underlaying soil layers. The findings were compared with results obtained from mean annual temperature and the typical equivalent asphalt stiffness utilized in fatigue tests. Additionally, an analysis was conducted to assess whether the timing of road implementation influences settlements throughout the design lifetime. The results suggest that the sequence of seasons is most relevant during the first year of service, showing a distinct effect at that time. However, with a higher number of axle passes, the initial differences fade away, and the curves start to merge.

期刊论文 2024-10-09 DOI: 10.1007/s42947-024-00466-4 ISSN: 1996-6814

The stabilization of asphalt pavement bases with granular soil and aggregates emulsified with asphalt is a widely used technique in road construction and maintenance. It aims to improve the mechanical properties and durability of the lower pavement layers. Currently, there is no consensus on the most suitable method for designing emulsified granular aggregates with reclaimed asphalt pavement (RAP), as it is very complex. Therefore, the methodology is generally based on compliance with one or more volumetric or mechanical parameters established in the highway regulations for conventional asphalt mixtures, which does not guarantee the optimization and characterization of the recycled mixture in the base course. In this study, granular mixtures were developed, including five with emulsion and one emulsion-free as a control mix. Granular RAP mixes were designed in this study, including five with emulsion and one emulsion-free as a control mix. The five mixes ranged from 1% to 5% emulsion and were characterized by multi-stage triaxial tests with repeated load resilient modulus (RM) and permanent deformation (PD) to evaluate their mechanical behavior. The results showed that the mixes had RM values between 350 and 500 MPa, consistent with literature values. However, they showed similar levels of accumulated deformation to the control mix without RAP emulsion. The sample with 1 % RAP emulsion exhibited a satisfactory RM value and better performance in PD than the control mix (5 mm) and showed accumulated PD values of up to 4 mm. In contrast, the other samples exhibited deformations of up to 6 mm. In this study, the multi-stagge triaxial RM and PD tests were found to be an effective predictive method for characterizing the behavior of RAP materials in base courses, regardless of the types of admixtures contained. Multi-stage resilient modulus and PD tests can be considered as a predictive method for the behavior of milled material in base courses. They were able to provide initial data for interpreting the behavior of ETB mixtures.

期刊论文 2024-07-01 DOI: 10.3390/su16135335

In this study, a series of cyclic triaxial tests were performed on intact lean clay samples from a highway construction site. Various combinations of static and cyclic stress levels, loading frequencies, over -consolidation ratios of soil samples and stress histories were adopted by single- and multi -stage loadings. The results show that three patterns are identified for the development of permanent deformation and residual pore water pressure of the soil samples: quickly stabilized (QS), progressively developing (PD), and dramatically failed (DF). These three patterns are significantly influenced by the stress levels, the over -consolidation ratios of soil samples and the stress histories, while the effect of the loading frequency is limited. Following these three patterns, the cyclic stability diagrams are proposed for soil samples with and without stress histories. The stable, metastable and unstable zones in the cyclic stability diagram correspond to the QS, PD and DF patterns, respectively. To maintain the soil at the stable state, the loading conditions are suggested to be controlled in the stable zone. Furthermore, to enhance the cyclic stability of the soil, the stress history with a relatively low increment of cyclic stress amplitude is beneficial.

期刊论文 2024-07-01 DOI: 10.1016/j.trgeo.2024.101285 ISSN: 2214-3912
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