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    <title>Transport Research International Documentation (TRID)</title>
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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Transport Research International Documentation (TRID)</title>
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    <item>
      <title>Railway Subgrade Characterization Through Repeated Loading Triaxial Testing</title>
      <link>https://trid.trb.org/View/2113115</link>
      <description><![CDATA[Currently, the improvement of means of transportation is a great challenge. Brazil has a large ore production, which will continue in the next decades, and seeks to reduce the transportation times between production and export centers, as well as reduce the emission of contaminants to the environment. In this sense, railways are a more efficient and environmentally friendly means of land transportation, and their proper conservation and operability affect the net gains that Brazil receives from the export of commodities. The implementation of this program proposed in the engineering practice would allow taking more precise decisions regarding the activities of maintenance of railroads, generating significant savings. The first step of the research is the analysis and interpretation of results of repeated load triaxial tests carried out in Brazil on railway subgrade soils. An engineering methodology is presented considering the geotechnical properties of the foundation soil obtained through field and laboratory tests for performing of geotechnical analysis. To ensure the railway stability, criteria of bearing capacity, elastic deflection and permanent deformation for the railway substructure must be met. A prediction model of permanent deformation is used, as well as the influence of moisture on the behavior of the foundation soil. This study aims to contribute to the finding of a comprehensive methodology for evaluating the useful service life of the track substructure so that the most appropriate material can be selected for use as a railroad formation material in order to limit stresses on the railway subgrade, which in turn cause progressive loss of geometric profile of the railway, and to maintain a safe operation of the trains. This will allow significant savings in the periodic maintenance of the substructure, which are one of the activities to restore the track geometry of railways.]]></description>
      <pubDate>Thu, 28 May 2026 17:09:37 GMT</pubDate>
      <guid>https://trid.trb.org/View/2113115</guid>
    </item>
    <item>
      <title>Mechanical responses and reinforcement assessment of non-typical in-situ enlargement for closely spaced tunnel groups in weak surrounding rock</title>
      <link>https://trid.trb.org/View/2667258</link>
      <description><![CDATA[In weak surrounding rock, the closely spaced tunnel group in this study adopts a downward in-situ enlargement restricted to the overlapping segment between the existing and the new tunnels, where the interaction of evolving excavation paths and construction sequences markedly amplifies deformation and stability challenges. To examine the applicability of a non-typical stepwise “remove–backfill–downward enlargement” scheme (hereafter abbreviated as fill–then-excavate) for such settings, an ongoing closely spaced tunnel group in weak surrounding rock project along the new Chengdu–Chongqing Central Line was investigated. Laboratory tests were performed to characterize the mechanical behavior of mudstone interbedded with sandstone, and numerical simulations were integrated with in-situ monitoring to compare ground and structural deformations. Alternative backfilling strategies prior to enlargement and reinforcement options for the inter-tunnel rock pillar were assessed for construction optimization. Results indicate that stress–strain curves remain similar in shape across confining pressures, while triaxial strength and deformation characteristics vary markedly; bedding and sand-lens heterogeneity leads to pronounced mechanical anisotropy. Rightward advancement after backfilling induces early unloading in the upper-right transition zone, shifting the settlement center toward the upper-right and forming an asymmetric, unimodal pattern aligned with the enlargement contour. Excavation of the upper-bench core triggers a jump in circumferential displacement around the enlarged tunnel, with a peak of 7.79 mm. Distinct backfilling schemes perturb the surrounding rock at different stages and thereby affect both surface and lining deformations; the full backfill followed by unified enlargement scheme reduces crown settlement by 3 mm. Moreover, small-pipe grouting lowers crown settlement by approximately 20%, raises the cumulative vertical stress at the core of the middle rock pillar to 3.77–4.43 MPa, and—with simple procedures and low disturbance—emerges as a preferred option for reinforcing the pillar in closely spaced tunnels within weak rock.]]></description>
      <pubDate>Mon, 11 May 2026 08:50:45 GMT</pubDate>
      <guid>https://trid.trb.org/View/2667258</guid>
    </item>
    <item>
      <title>Influence of geogrid stabilization on ballast breakage under monotonic triaxial loading</title>
      <link>https://trid.trb.org/View/2647976</link>
      <description><![CDATA[Railway ballast particle breakage leads to fines generation, increases fouling, reduces drainage capacity, and ultimately weakens track performance. While geogrids are known to stabilize ballast by limiting particle movement and redistributing contact stresses, their effectiveness in reducing breakage, particularly at different ballast depths, remains unclear. This study employs a large-scale monotonic triaxial testing framework to evaluate particle breakage in clean ballast, with and without geogrid stabilization, under both loose and compacted density conditions. Each specimen was divided into four vertical zones: Top, Top-Mid, Bottom-Mid, and Bottom, and particle size groups were color-coated to enable breakage tracking. The results show that geogrid-stabilized specimens exhibited greater strength and stiffness in both density conditions. For loose ballast, geogrid inclusion reduced total particle breakage by approximately 27%, with the most significant reduction occurring in the middle zones. In contrast, for compacted ballast, the total breakage remained nearly unchanged with geogrid use; however, breakage was more evenly distributed across all zones, with noticeable reductions in the Top and Top-Mid zones. Corner breakage dominated in the middle zones, and splitting breakage near the top and bottom. Marsal’s breakage (Bg) index proved most sensitive for zone-by-zone evaluation. The findings highlight the benefit of geogrids in mitigating ballast degradation and emphasize the importance of zone-specific analysis under varying density conditions. The proposed monotonic triaxial framework provides a mechanistic baseline for future cyclic triaxial studies, where repetitive loading will further clarify long-term stress redistribution, particle migration, and cumulative breakage under realistic railway service conditions.]]></description>
      <pubDate>Tue, 24 Mar 2026 09:09:08 GMT</pubDate>
      <guid>https://trid.trb.org/View/2647976</guid>
    </item>
    <item>
      <title>Influence of consolidation history on the transitional behavior of silty clay</title>
      <link>https://trid.trb.org/View/2647958</link>
      <description><![CDATA[Understanding the mechanical response of silt–clay transitional soils is increasingly important for underground transportation infrastructure, where complex stress paths and one-dimensional (K₀) consolidation histories are common. However, most existing studies rely on isotropic consolidation, leaving the effects of K₀ consolidation on transitional behavior insufficiently understood. This study presents a systematic series of undrained triaxial tests on reconstituted silty clay consolidated under isotropic and K₀ conditions across a range of overconsolidation ratios (OCRs). The results show that phase transformation—a hallmark of transitional soil behavior—appears only in isotropically consolidated specimens at low OCRs, whereas it does not occur in K₀-consolidated specimens tested under comparable OCRs. K₀-consolidated specimens exhibit a counter-intuitive non-monotonic relationship between void ratio and mean effective stress at the end of shearing, reflecting persistent anisotropic structural effects consistent with anisotropic critical state theory. While K₀ consolidation produces more complex stress–strain responses, the stress-ratio evolution remains broadly comparable to isotropically consolidated cases. Overall, the findings demonstrate that consolidation history critically governs the undrained behavior of silt–clay transitional soils and underscore the importance of incorporating realistic K₀ consolidation conditions in laboratory characterization and geotechnical design for transportation applications.]]></description>
      <pubDate>Tue, 24 Mar 2026 09:09:08 GMT</pubDate>
      <guid>https://trid.trb.org/View/2647958</guid>
    </item>
    <item>
      <title>Assessment of Slope Failure Using Advanced Geotechnical Tests: Case Study in Harrisonburg, Louisiana</title>
      <link>https://trid.trb.org/View/2192145</link>
      <description><![CDATA[The failure of a slope along a segment of Highway 8 near Harrisonburg, Louisiana resulted in its partial closure in December 2008. The Louisiana Department of Transportation and Development needed to assess the damage and find a way to remedy the problem. Soil borings were taken and the slope was monitored using a vertical inclinometer. Then the aerial photos were used to evaluate the site conditions and map the progress of slope failure over time. Further, a series of laboratory tests were performed on the samples obtained by boring from the site to determine the stress path followed by the soil which led to the slope failure. Laboratory testing program included conventional unconsolidated undrained (UU) triaxial tests, multistage consolidated undrained (CU) triaxial tests, and Ko-consolidated undrained (CKoU) triaxial lateral extension tests. Using the extensive laboratory test results, the soil design parameters were selected for slope stability analyses. The limit equilibrium analyses showed different results based on parameters obtained from different stress path testing. Further, partial stabilization at the toe of the slope was recommended as the most suitable remedial measure.]]></description>
      <pubDate>Mon, 23 Mar 2026 15:24:24 GMT</pubDate>
      <guid>https://trid.trb.org/View/2192145</guid>
    </item>
    <item>
      <title>Investigation on the triaxial creep behavior of red-stratum mudstone soil-rock mixture with different rock contents</title>
      <link>https://trid.trb.org/View/2644849</link>
      <description><![CDATA[Red-stratum mudstone, due to its wide distribution and convenient availability, has been widely used in high-fill subgrade projects in western China, but its low strength and susceptibility to fracturing make the problem of creep deformation particularly prominent. In this paper, a series of triaxial creep tests on red-stratum mudstone soil-rock mixture were carried out, focusing on the influence of rock content and stress state on creep behaviors. The development of axial and volumetric creep strains, the effect of rock content on the viscoplastic flow direction was clarified, and the time-dependent evolution of particle breakage was further analyzed. The results show that creep strain develops rapidly in the initial stage, then gradually slows down and tends to stabilize, and the overall curve exhibits a hyperbolic feature. At the same time, the final axial creep strain decreases first and then increases with the increase of rock content, with the optimal range being 0.5–0.7. Moreover, the volumetric creep path differs significantly from the conventional shear path, meaning the traditional dilatancy equation cannot directly describe the viscoplastic flow direction. Finally, particle sieve tests reveal that creep behaviors depend not only on particle breakage but also on the internal pore structure of the mixture. A denser pore structure will weaken the contribution of particle breakage to macroscopic creep deformation.]]></description>
      <pubDate>Tue, 17 Mar 2026 09:48:46 GMT</pubDate>
      <guid>https://trid.trb.org/View/2644849</guid>
    </item>
    <item>
      <title>A Comparative Study of Spatially Mobilized Plane (SMP) Based Extensions to the Modified Cam Clay (MCC) Model for Lode Angle Dependency</title>
      <link>https://trid.trb.org/View/2669740</link>
      <description><![CDATA[The fundamental Cam-Clay constitutive model for soils did not include strength anisotropy in the deviatoric plane (i.e., Lode angle effects) through a modified failure criterion, so there was no difference in deviatoric stress between the compression and extension paths. However, the extension triaxial and true triaxial tests exhibit differences in shear resistance response compared to the compression path. This difference in shear stress response can impact numerical simulations because the stress paths can be uncertain throughout the domain of the simulated model. The paper presents three straightforward methods to incorporate Lode angle effects using the Matsuoka-Nakai criterion. Triaxial compression and extension tests under drained and undrained conditions were simulated. Several lessons were learned from these simulations about the ease of incorporating the Matsuoka-Nakai criterion and the differences between simulations using three methods. Finally, an extensive discussion focuses on identifying the most suitable alternative for simulating soil mechanical behavior. This discussion was intended as a simple improvement to the modified Cam Clay model for basic simulations or as a basis for further, more complex model development.]]></description>
      <pubDate>Wed, 18 Feb 2026 12:00:54 GMT</pubDate>
      <guid>https://trid.trb.org/View/2669740</guid>
    </item>
    <item>
      <title>A DEM creep contact model with damage evolution for frozen soil</title>
      <link>https://trid.trb.org/View/2640872</link>
      <description><![CDATA[Frozen soil creep is a key factor in the settlement of cold region subgrades. Clarifying its macro and micromechanical deformation and damage mechanisms is essential for mitigating subgrade distress. To overcome the limitations of the existing creep contact model in PFC for accurately simulating the non-attenuating creep behavior of frozen soil, this study proposes a new discrete element creep contact model that incorporates damage evolution. By introducing a variable-stiffness damage element, the model effectively captures the third-stage creep behavior of frozen soil. Using the central difference method, the study derives the mechanical response equations for each stage of the contact model and compiles a dynamic link library (DLL) in C++ for direct use within the PFC3D software. A comprehensive description of the model development process is provided, and the contact model is validated using a double-sphere model, reproducing the non-attenuating creep curve and revealing the influence of new parameters on creep behavior. As a representative case, a series of triaxial creep tests on frozen subgrade soil under varying temperatures, confining pressures, and deviatoric stresses are conducted, leading to the establishment and calibration of a corresponding discrete element method (DEM) model. The results demonstrate that the model can accurately reproduce the creep mechanical properties of frozen soil across all stages under complex conditions. Furthermore, microscopic analysis of frozen soil reveals the evolution of particle displacement, damage development, internal structure, and pore distribution during different creep stages. The findings extend the application of DEM in studying the mechanical properties of frozen soil and provide a more precise contact model for DEM simulations of creep in frozen soil. It can be further applied to engineering-scale DEM studies of creep in cold region subgrades.]]></description>
      <pubDate>Tue, 17 Feb 2026 13:12:50 GMT</pubDate>
      <guid>https://trid.trb.org/View/2640872</guid>
    </item>
    <item>
      <title>Non-Isothermal Mechanical Response of Clayey Sands</title>
      <link>https://trid.trb.org/View/2636640</link>
      <description><![CDATA[The mechanical characteristics of clayey sands are crucial for evaluating behaviors pertinent to temperature-related geotechnical engineering. The undrained triaxial shear response of clayey sands, characterized by a constant skeleton void ratio, is experimentally investigated under varying fines contents, temperatures, and initial mean effective stresses. The effects of fines content and temperature on heating induced volumetric strain, peak deviatoric stress, peak excess pore pressure, stress ratio at the undrained instability state, and collapsibility index are comprehensively investigated. Furthermore, a unified critical state line is proposed in the equivalent intergranular void ratio versus mean effective stress plane for clean sands, sand-slit mixtures, and sand-clay mixtures, irrespective of temperature. Additionally, the equivalent intergranular state parameter can be utilized to predict the mechanical responses of binary mixtures under both undrained instability state and critical state. It is valuable to use the equivalent skeleton void ratio to assess the stability in thermally influenced geotechnical engineering involving binary mixtures, particularly sand-dominated mixtures.]]></description>
      <pubDate>Thu, 05 Feb 2026 09:16:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/2636640</guid>
    </item>
    <item>
      <title>Mechanistic evaluation of time-dependent deformation in reclaimed asphalt pavement (RAP)–virgin aggregate blends under varying impulse durations in repeated load triaxial test</title>
      <link>https://trid.trb.org/View/2636301</link>
      <description><![CDATA[This paper evaluates the time dependent response of reclaimed asphalt pavement (RAP) and RAP- virgin aggregate (VA) blends on the accumulation of permanent deformation (PD) in a repeated load triaxial (RLT) test. The haversine loading curve in a PD test typically uses a 0.1 s peak load and 0.9 s resting period. However, the duration of impulse loading on pavement structure varies depending upon speed of a vehicle and depth of observation from the surface. RAP is a mixture of aggregate and asphalt, is considered to have viscoelastic-viscoplastic properties that may alter the performance, if the duration of loading impulse changes. This manuscript has two testing phases: 1). Evaluates the performance of RAP and VA at similar gradation but two different loading impulses at a range of stress conditions to characterize the performance dependency of RAP on the duration of loading impulse and compares it with VA, 2). Determine the response of RAP, RAP-VA blends and VA at their native gradations but different loading impulses at a range of stress conditions. The results show that RAP and RAP-VA samples subjected to higher frequency impulses consistently showed significantly higher PD accumulation than those tested under lower frequency impulses. While VA exhibited an impulse frequency−independent behavior across the range of impulse frequency and stress levels tested.]]></description>
      <pubDate>Thu, 05 Feb 2026 09:16:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/2636301</guid>
    </item>
    <item>
      <title>Sustainable subgrade reinforcement using areca fiber-reinforced soil: mechanical behavior and carbon emission evaluation</title>
      <link>https://trid.trb.org/View/2636295</link>
      <description><![CDATA[To address the dual challenges of areca waste disposal and subgrade performance enhancement, this study explores the feasibility of using areca fibers (AFs) as a sustainable reinforcement material for soft clay in transportation infrastructure. A series of consolidated undrained (CU) triaxial shear tests and cyclic triaxial tests were conducted to evaluate the static and dynamic behavior of AFs-reinforced soils under varying compaction conditions. In addition, a life cycle assessment (LCA) based carbon–force integrated evaluation model was established to quantify the carbon reduction benefits of AFs-reinforced soil in subgrade replacement applications. Experimental results show that under high compaction conditions, incorporating 2% AFs increases the shear strength of soil by 17% and the secant modulus by 65%. Under cyclic loading, the inclusion of AFs effectively restrains particle displacement and improves the dynamic stability of the soil. The LCA results indicate that AFs-reinforced soil achieves a carbon emission reduction exceeding 8.1% during the material production and construction stages, demonstrating clear environmental advantages. Comprehensive evaluation results reveal that soil reinforced with 2% AFs achieves the best balance between mechanical performance and carbon emissions, making it a promising alternative for sustainable subgrade engineering. This study offers both theoretical insights and practical guidance for the resource utilization of areca waste in geotechnical engineering, with a particular focus on its application in sustainable subgrade construction using AFs-reinforced soils.]]></description>
      <pubDate>Wed, 04 Feb 2026 16:28:52 GMT</pubDate>
      <guid>https://trid.trb.org/View/2636295</guid>
    </item>
    <item>
      <title>ANN-based optimization of single-stage triaxial tests for predicting permanent deformation in pavement granular layers</title>
      <link>https://trid.trb.org/View/2643667</link>
      <description><![CDATA[Inadequate characterization of the behavior of granular materials under accumulated plastic deformation in flexible pavements can lead to excessive rutting, severely affecting the structural and functional performance of highways. Permanent deformation (PD) is normally measured using repeated triaxial load tests, as required by Brazilian standards, which specify single-stage tests with 150,000 cycles in nine stress states per soil. Although effective, especially for tropical soils that exhibit rapid initial PD accumulation followed by rutting stabilization, the procedure requires substantial time, personnel, and laboratory resources. This study proposes reducing the number of cycles required for this characterization through prediction models. Seven soil samples were tested at nine pairs of stresses: five samples for model development and two for validation. From this, Artificial Neural Networks were trained using the data, removing the first 1,000 cycles to avoid the effects of rapid initial growth. The models generated PD predictions similar to the results obtained in tests of 150,000 load cycles using only 30,000 cycles for these predictions, with errors below 0.09 mm under severe traffic. The results confirm that the proposed approach can reduce the time required for PD characterization by approximately 50%, while maintaining reliable performance estimates.]]></description>
      <pubDate>Thu, 29 Jan 2026 17:02:24 GMT</pubDate>
      <guid>https://trid.trb.org/View/2643667</guid>
    </item>
    <item>
      <title>Mechanical properties and microscopic mechanisms of freeze–thaw sand under traffic loading</title>
      <link>https://trid.trb.org/View/2633498</link>
      <description><![CDATA[Traffic loading and freeze–thaw cycles are critical factors that limit the long-term stability and durability of sand subgrades in seasonal frozen regions. To explore the degradation mechanisms of sand’s mechanical properties under the combined effects of these factors, this study prepared sand specimens subjected to 0, 1, 3, 5, and 7 freeze–thaw cycles. Laboratory static and dynamic triaxial tests were conducted to characterize the changes in mechanical properties. In addition, scanning electron microscopy (SEM) and fractal theory were employed to analyze the variations in particle morphology, arrangement, and contact modes. Gray relational analysis was used to quantify the correlation between deviatoric stress, accumulated plastic strain, and microstructural parameters. The results showed that, with an increasing number of freeze–thaw cycles, the deviatoric stress of the sand significantly decreased, while the accumulated plastic strain markedly increased, consistent with previous studies. Simultaneously, the particle morphology became more complex, the particle arrangement became more oriented, the particle size distribution coarser, and porosity increased. A degradation trend towards point-face contact was observed. Gray relational analysis revealed that, under static loading, particle size distribution fractal dimension was the strongest correlated with deviatoric stress, indicating that the particle size distribution predominantly governs the static stress response. Under dynamic loading, porosity was the strongest correlated with accumulated plastic strain, suggesting that the pore structure plays a key role in controlling plastic deformation. This study elucidates the mechanical properties and microscopic mechanisms of freeze-thawed sands under traffic loading at the particle scale, providing valuable insights into the long-term service performance of sand subgrades in seasonal frozen regions.]]></description>
      <pubDate>Wed, 28 Jan 2026 08:52:14 GMT</pubDate>
      <guid>https://trid.trb.org/View/2633498</guid>
    </item>
    <item>
      <title>Effects of laboratory compaction schemes on the mechanical response of ballast in large-scale triaxial tests</title>
      <link>https://trid.trb.org/View/2632643</link>
      <description><![CDATA[Railroad ballast, consisting of uniformly graded coarse aggregates with angular and irregular particle shapes, plays a critical role in maintaining track stability. Accurate laboratory characterization of ballast mechanical behavior, such as stiffness, shear strength, and permanent deformation, is essential for track design, maintenance, and performance prediction. Large-scale triaxial testing is widely used to investigate these properties; however, standardized compaction procedures for specimen preparation are lacking. This gap has resulted in inconsistent preparation methods across studies, potentially contributing to variations in test outcomes. In this study, the effects of compaction method (vibratory vs. impact) and number of compaction lifts on ballast mechanical behavior were systematically examined through a series of large-scale monotonic and cyclic triaxial tests. Specimens were compacted to achieve a consistent void ratio using various combinations of compaction methods and lift counts. Results show that ballast stiffness and permanent deformation are significantly influenced by the compaction scheme. Compared with vibratory-compacted specimens, impact-compacted specimens exhibited lower stiffness and greater permanent deformation, likely due to weaker particle interlocking formed during compaction. The stiffness difference between compaction methods became more pronounced under higher confining pressures, indicating a strong confinement dependency. Moreover, increasing the number of compaction lifts enhanced aggregate interlocking, leading to higher stiffness. These findings underscore the importance of accounting for compaction effects in laboratory ballast testing and provide practical guidance for developing standardized specimen preparation procedures in large-scale triaxial experiments.]]></description>
      <pubDate>Tue, 27 Jan 2026 09:19:31 GMT</pubDate>
      <guid>https://trid.trb.org/View/2632643</guid>
    </item>
    <item>
      <title>Stress path dependence of gassy soil in triaxial testing and DEM simulations exemplified by shield tunnelling</title>
      <link>https://trid.trb.org/View/2626045</link>
      <description><![CDATA[Gassy soils, often encountered in shield tunneling, can hinder construction progress. To assess their impact, four stress paths induced by tunneling were designed. A combination of triaxial tests and DEM simulations was used to study the effects of varying saturation levels and stress paths on gassy soil deformation. A new method was proposed, using the stress path forward angle (ψ) and the stress increment ratio (Δq/Δp) to jointly describe the dependence of soil deformation characteristics on the stress path. The results show that the influence of the shield tunneling stress path on the deformation characteristics of gassy soil is greater than that of the initial saturation. The stress path determines the fundamental characteristics of the stress–strain and volumetric strain curves of gassy soil. Under the premise of these fundamental characteristics, the initial saturation induces the gassy soil sample to develop strain softening and dilatancy. The dependence of gassy soil deformation characteristics on the stress path is primarily controlled by the sample’s consolidation stress ratio (Kc), stress increment ratio (Δq/Δp), and stress path angle (ψ). The consolidation stress ratio (Kc) determines the initial stress state of the gassy soil sample, while the stress increment ratio (Δq/Δp) and the stress path angle (ψ) determine the loading direction of the stress path in gassy soil. When the stress path angle is in the range of 22°–90°, the stress–strain curve tends toward strain hardening, the initial shear modulus increases, and the volumetric strain curve tends toward contraction. When the angle is between 90° and 180°, the stress–strain curve softens, the initial shear modulus decreases, and the volumetric strain curve dilates. The comparison between the DEM simulation and triaxial test results validates the reliability of the experiments and supports the relationship between the stress path angle and the strain hardening and softening behaviors.]]></description>
      <pubDate>Thu, 15 Jan 2026 09:11:21 GMT</pubDate>
      <guid>https://trid.trb.org/View/2626045</guid>
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