Roads in places with seasonal frost undergo several freeze-thaw (F-T) cycles annually, resulting in variable degrees of deterioration in the mechanical properties of the subgrade. To methodically investigate the mechanical properties of subgrade clay during freeze-thaw cycles and to develop a precise constitutive model, triaxial tests were conducted under the most unfavorable soil conditions. The studies indicate that the degrading impact of the freeze-thaw cycle on the mechanical characteristics of the soil predominantly transpires during the initial freeze-thaw cycle. Soil strength reaches its minimum after the third freeze-thaw cycle, followed by a slight increase, and ultimately stabilizes between the fifth and seventh cycles. The maximum strength reduction at confining pressures of 100 kPa, 200 kPa, and 300 kPa was 39%, 37%, and 33%, respectively. As confining pressure escalates, the reduction in soil strength lessens. The soil demonstrates differing degrees of degradation following F-T cycles at both high and low compaction levels, with the degradation becoming increasingly evident as compaction intensifies. Utilizing the experimental database, a genetic algorithm (GA) enhanced backpropagation neural network (BPNN) model (GA-BPNN) and a BP-aided Duncan-Chang (D-C) model were developed to forecast the mechanical properties of freeze-thaw clay. The R2 values for the two models on the test set were 0.995 and 0.967, respectively. The efficacy of these two models demonstrates that machine learning can attain commendable outcomes in extensive data structures (total stress-strain curve) as well as exhibit superior performance in limited data (model parameters) while developing the constitutive model of soil.

Accurate inversion of geotechnical parameters is essential for assessing foundation-bearing capacity and stability, which directly impact structural safety and serviceability. Accurate prediction of load settlement behavior is crucial to prevent overdesign and underperformance, ensuring that foundations support anticipated loads without excessive deformation or failure. This paper presents an integrated optimization system combining ABAQUS (2022), Python (PyCharm21.3.3), and MATLAB (2022b) software, based on the Duncan-Chang (DC) model, for inversion of key geotechnical parameters. The ABAQUS UMAT subroutine customizes the DC model, facilitating its application in finite element simulations for soil-structure interaction analysis. To improve the optimization process, an adaptive genetic algorithm that dynamically adjusts crossover and mutation rates, thereby improving solution searches and parameter space exploration, is implemented. Key parameters of the DC model-the initial tangent stiffness (K) and nonlinear deformation characteristics (n) of soil-are inverted. The accuracy of this inversion is validated through comparisons with experimental pressure-settlement curves obtained from indoor bearing plate tests. Therefore, this optimization system effectively integrates intelligent algorithms with finite element analysis, serving as a reliable tool for precise geotechnical parameter inversion, with potential for improving foundation design accuracy, optimizing soil-structure interaction predictions, and improving the overall stability and safety of geotechnical structures.

The complex distribution characteristics of root-soil composites pose challenges in understanding their mechanical behaviour during conservation tillage. This study aims to analyse mechanical parameters of root-soil composites at different soil depths, considering root distribution, and establish an empirical critical state model. Three layers were defined based on root density distribution: Shallow Aggregated Root Zone (SARZ: 0-60 mm), Middle Enriched Root Zone (MERZ: 60-150 mm), and Deep Extended Root Zone (DERZ: 150-210 mm). Triaxial tests revealed varying shear strengths, with MERZ exhibiting the highest and SARZ the lowest. The Duncan-Chang model parameters, initial modulus of deformation, and initial Poisson's ratio were significantly influenced by soil depth, mirroring shear strength trends. An empirical formula incorporating soil layer depth into the Duncan-Chang model was proposed. Critical state stress ratios for SARZ and MERZ were determined as 0.93 and 1.11, respectively, quantifying their relationship with soil depth and root distribution. This study provides theoretical and parameter support for understanding the failure mechanism of root-soil composites.

This study presents a comprehensive investigation into the mechanical properties of lime-stabilized lateritic soil, with a focus on developing an improved constitutive model that incorporates both curing time and strain-softening effects. Current constitutive models fail to accurately capture the stress-strain behavior of lime-stabilized soils, particularly over extended curing periods. To address this, unconfined compressive strength (UCS) tests were conducted using lime contents of 0%, 1%, 3%, 5%, 7%, 9%, and 11% revealing that 7% lime content optimally enhances the compressive strength of the soil by 1202.66% compared to untreated soil. Triaxial consolidated-drained tests were then performed with the optimal 7% lime content, considering curing times of 3, 7, 14, and 28 days under confining pressures of 100 kPa, 200 kPa, 300 kPa, and 400 kPa. The results demonstrated that the shear strength, cohesion, internal friction angle, and initial tangent modulus of lime-stabilized lateritic soil increased with longer curing times and higher confining pressures. These findings were integrated into a re-modified Duncan-Chang model, which incorporates both strain softening and curing time as key factors. The revised model was validated through comparisons with experimental data, achieving an average relative error of 2.12% at 7 days, 1.46% at 14 days, and 17.55% at 28 days. This validation demonstrates the model's ability to accurately predict the stress-strain behavior of lime-stabilized lateritic soil under different curing conditions. The novelty of this research lies in the successful integration of curing time and strain-softening effects into the Duncan-Chang model, providing a more accurate tool for predicting the long-term mechanical performance of stabilized soils. The findings have significant implications for engineering applications, particularly in the context of soil stabilization for infrastructure projects in tropical and subtropical regions.

This study investigates the influence of age on the mechanical properties of lime-modified dispersed soils through consolidation undrained triaxial tests conducted at various age (t) and lime content (a). Empirical equations for Duncan-Chang model parameters K, n, c, and phi incorporating the age factor were established based on experimental results, focusing on lime modification at 2% content. The stress-strain curves of dispersed soils exhibit strain-hardening characteristics, with stress levels increasing notably with age, displaying significant variation between short and long durations. Conversely, the stress-strain curve for lime-modified dispersed soil at 2% content shows strain-softening behavior. Age exerts a substantial influence on model parameters K, n, c, and phi of the Duncan-Chang model, with a minor impact on Rf. The modified model demonstrates a strong fit to stress-strain curves of lime-modified dispersed soil before reaching failure, validated against experimental data at age of 14 days and 90 days. Importantly, the modified model accurately predicts stress-strain relationships for modified soils over extended age beyond 28 days, providing meaningful insights for the long-term stability assessment of soil-modified structures.

The strength damage and deformation failure of frozen soil-rock mixture (FSRM) often restrict the safety of the major engineering construction in cold areas or the spatial development of urban underground water-rich rock and soil masses. To investigate the uniaxial strength damage evolution and failure characteristics of FSRM under different loading rates (0.3, 0.6, 3, 6, 30, and 60 mm min -1 ) in the quasi-static range, resistivity monitoring and image recognition technology were used to study the time-stress-volumetric strain-resistivity changes. The results indicate that the peak stress, peak strain, initial yield modulus, and tangential modulus of FSRM increase rapidly before increasing slowly as the loading rate increases, and there are critical loading rates and post-peak failure phenomenon. Three distinct types of failure modes, bulge failure, oblique shear failure, and fragmentation failure were observed at low (0.3-0.6 mm min -1 ), medium (3-6 mm min -1 ), and high loading rates (30-60 mm min -1 ), respectively. The macroscopic failure of the FSRM at different loading rates arises from a combination of strain rate hardening of the strength and damage softening of the structure. To predict the stress-strain characteristics at various loading rates, a damage prediction model with a damage variable correction factor considering residual strength was employed based on the improved Duncan-Chang model and damage theory of electrical resistivity, and the predicted results were in good agreement with the experimental data.

In order to study the mechanical propertied and change rules of undrained shear behavior of saline soil under the freeze-thaw cycles, an improved constitutive model reflecting the effects of freeze-thaw cycles was proposed based on the traditional Duncan-Chang model. The saline soil in Qian'an County, western Jilin Province, was selected as the experimental object. Then, a set of freeze-thaw cycles (0, 1, 10, 30, 60, 90, 120) tests were conducted on the saline soil specimens, and conventional consolidated undrained triaxial shear tests were conducted on the saline soil specimens that underwent freeze-thaw cycles. The stress-strain relationship was obtained by the triaxial shear test. The model parameters have a corresponding regression relationship with the number of freeze-thaw cycles. Finally, based on the function expression of the model parameters, the modified Duncan-Chang model with the number of freeze-thaw cycles as the influence factor was established, whilst the calculation program of the modified model is compiled. Based on the test results, the stress-strain relationship of the saline soil specimen shows strain hardening. The shear strength gradually decreases with the increase of freeze-thaw cycle. The 10 freeze-thaw cycles are the turning point in the trend of changes of the mechanical properties of saline soils. The calculated and experimental stress-strain relationship are compared, and the comparison between the calculated value of the model and the experimental value showed that the two had a good consistency, which verified the validity of the modified Duncan-Chang model in reflecting the effects of the freeze-thaw cycle.

The dynamic compaction method has been widely adopted in foundation treatment to densify the soil fillers. However, for the complexity of the impact behavior and soil mechanical properties, the theoretical research of dynamic compaction lags behind its practice for complex soil properties and stress paths. This paper presents a theoretical model applied to describe soil column plastic deformation under impact load. The relationship among stress increment, strain increment, and plastic wave velocity was derived from the aspect of propagation characteristics of stress waves in soil first. Combined with the Duncan-Chang Model, a one-dimensional theoretical model was established then. A numerical model was developed further to check the performance of the model. It showed that the deformation at the end of the soil column was mushroom-shaped. Both the axial and lateral deformation increased with the impact velocity. While some particles located at the side of the soil column end may splash under repeated impact. The theoretical deformations of the soil column were consistent with the experimental results both in the direction of axial and lateral.