Polypropylene fiber and cement were used to modify iron tailings and applying it to roadbed engineering is an important way to promote the sustainable development of the mining industry. However, the existing studies are mostly concerned with the static mechanical properties, and lack the deformation characteristics of cyclic loading under different loading modes. The effects of fiber content, dynamic-static ratio (Rcr) and curing age on the deformation characteristics of fiber cement modified iron tailing (FCIT) under different cyclic loading modes were explored through dynamic triaxial tests. The research results show that: (1) Polypropylene fibers significantly reduced the cumulative strain of FCIT. Under intermittent loading, the cumulative strain decreased by 36 similar to 43 %, and under continuous loading, the cumulative strain decreased by 48 similar to 55 %. (2) The deformation behavior of FCIT under both intermittent and progressive loading was in a plastic steady state with cumulative strain <= 1 %. (3) The cumulative strain variation of FCIT with intermittent loading of 0.316 % was significantly lower than that with continuous loading of 0.417 %, and the resilience modulus was higher with intermittent loading. (4) The stress history effect of step-by-step loading can be eliminated by the translational superposition method, and the strain evolution law under continuous loading is predicted based on the progressive loading data, and the minimum error between the expected and actual results is 6.5 % when Rcr is 0.1.

Shaking-table model experiments were conducted to study the dynamic response and damage mechanisms of pile-network composite high-speed railway foundations under seismic action. By inputting seismic waves of various types and acceleration amplitudes, the surface damage phenomena, acceleration response, and displacement response of the roadbed during vibration were analyzed. The time frequency information and energy distribution were examined using Hilbert marginal spectrum theory. Additionally, the damage mechanisms of the model were explored through transfer function analysis. The results indicated that the soil surface deformation measured using particle image velocimetry closely matched the observed macroscopic phenomena. The Peak Ground Acceleration amplification coefficients exhibited clear delamination before the structure showed signs of damage, indicating a significant energy-absorbing effect of the bedding. Spectral analysis revealed that as the vibration intensity increased, the nonlinear characteristics and damage effects of the model became more pronounced, and its ability to dissipate energy strengthened. Energy became more concentrated in the left half of the top of the model. Moreover, as the vibration intensity increased, the self-oscillation frequency of the roadbed decreased, the stiffness diminished, the damping ratio increased, and the seismic energy dissipation improved.

The freeze-thaw cycle poses a significant threat to foundations and roadbeds in seasonally frozen regions. This article conducts model experiments to analyze changes in the temperature field, water migration patterns, and settlement deformation characteristics of sand-gravel replacement foundations during freeze-thaw cycles. The experimental findings indicate that the low-temperature zone primarily exists within the sand-gravel replacement layer at the base of the slope. As the number of freeze-thaw cycles increases, the freezing depth of the sand-gravel replacement layer continues to rise. During the cooling phase, changes in soil volume moisture content result from self-weight and water migration during freezing. With an increase in the number of freeze-thaw cycles, the moisture content of external measurement points on the embankment rises at the end of the freezing period, whereas the moisture content of internal measurement points decreases. At the end of the thawing phase, measurement point 6 experiences an increase in moisture content due to the upward migration of water in the lower soil layer, while other measurement points exhibit reduced moisture content. The foundation's settlement deformation exhibits a horizontal tilted shape, with cumulative settlement amounts and settlement deformation rates determined at various positions. These results suggest that the settlement deformation tends to stabilize one month after the completion of embankment filling construction. The maximum freezing depths at the left and right slope toe positions are 1 m and 1.2 m, respectively. Furthermore, the maximum frost heave at the slope toe position is less than the maximum thawing settlement, illustrating the irreversible soil deformation following freeze-thaw cycles.

The purpose of this study is to solve the problem of the harmless treatment of dredged silt and soil extraction during road construction in lake areas. The silt in the project area is used as the research material to evaluate its engineering applicability as an improved filling material for the roadbed of the lake's surrounding road. Through indoor pretreatment and a series of mechanical performance tests, including compaction tests, unconfined compressive strength tests (UCS), bearing ratio tests (CBR), triaxial compression tests (CU consolidated undrained), and consolidation tests, we obtained key mechanical parameters of modified sludge soil, such as maximum dry density, optimal moisture content, unconfined compressive strength, bearing ratio, shear strength, and compression characteristics. The research results show that with the increase in modifier dosage, the optimal moisture content of modified sludge soil increases, the maximum dry density decreases, and its compressive strength and shear strength significantly improve. The CBR value also meets the technical requirements of each layer of the roadbed. Specifically, after 7 days of curing, the compaction degree of 10% modified sludge soil can exceed 96%, the unconfined compressive strength reaches 0.819 MPa, the CBR value reaches 17.5, the cohesion measured by triaxial tests is 78 kPa, the internal friction angle is 27 degrees, and it exhibits low compressibility. These findings provide new solutions for environmentally friendly treatment, resource utilization, and road engineering in river and lake sediments.

Road infrastructure construction in developing countries such as Vietnam requires an enormous amount of natural sand. The scarcity of river sand is becoming increasingly severe, with predictions indicating a sustained drop in its supply. Hence, it is essential for the construction industry to implement a sustainable strategy by combining waste materials with abundant resources in order to effectively address this challenging situation. The objective of this study is to investigate the mechanical properties and evaluate the potential application of mixtures comprising rock quarry dust and sea sand for the roadbed layers of expressways. The researchers conducted a series of experiments, including the moisture content, specific gravity, angle of repose of material, and triaxial tests to study the composition and mechanical behaviors of mixtures at different ratios. Extensive parametric investigations in conjunction with the calibration in Plaxis' soil-test module obtain the Young's modulus E50 and confining pressure curves. Based on the assessment of materials utilized in roadbed layer of highway, as determined by the California bearing ratio (CBR) coefficient, it demonstrates that combining sea sand and quarry dust can generate the mixtures possessing appropriate properties for application in the construction of the roadbed of highway.

The deformation and damage to seasonal permafrost roadbeds, as seasons shift, stems from the intricate interplay of temperature, moisture, and stress fields. Fundamentally, the frost heave and thaw-induced settlement of soil represent a multi-physics coupling phenomenon, where various physical processes interact and influence each other. In this investigation, a comprehensive co-coupling numerical simulation of both the temperature and moisture fields was successfully executed, utilizing the secondary development module within the finite element software, COMSOL Multiphysics 6.0. This simulation inverted the classical freezing-thawing experiment involving a soil column under constant temperature conditions, yielding simulation results that were in excellent agreement with the experimental outcomes, with an error of no more than 10%. Accordingly, the temperature, ice content, and liquid water content distributions within the seasonal permafrost region were derived. These parameters were then incorporated into the stress field analysis to explore the intricate coupling between the moisture and temperature fields with the displacement field. Subsequently, the frost heave and thaw settlement deformations of the roadbed were calculated, accounting for seasonal variations, thereby gaining insights into their dynamic behavior. The research results show that during the process of freezing and thawing, water migrates from the frozen zone towards the unfrozen zone, with the maximum migration amount reaching 20% of the water content, culminating in its accumulation at the interface separating the two. Following multiple freeze-thaw cycles, this study reveals that the maximum extent of freezing within the roadbed reaches 2.5 m, while the road shoulder experiences a maximum freezing depth of 2 m. A continuous trend of heightened frost heave and thaw settlement deformation of the roadbed is observed in response to temperature fluctuations, leading to the uneven deformation of the road surface. Specifically, the maximum frost heave measured was 51 mm, while the maximum thaw settlement amounted to 13 mm.

The shear strength of geocell-reinforced railway roadbeds is influenced by diverse factors. This research aimed to explore the shear deformation performance of the geocell-reinforced railway roadbed under conditions of different reinforcement locations, confining pressures, and numbers of reinforced layers. To this end, large-scale undrained triaxial tests were conducted to measure the mechanical properties of a geocell-reinforced railway roadbed. The results show that geocell reinforcement plays a significant role in improving the peak deviatoric stress of the railway roadbed. The stress-strain relationship of the railway roadbed always exhibits strain-hardening characteristics, and the railway roadbed shows the optimal shear deformation resistance and strength when it is reinforced in its upper part. As the confining pressure increases, the shear strength and stiffness of the railway roadbed both increase while the secant modulus decreases with increasing axial strain. Meanwhile, the shear strength and strength coefficient of reinforcement of the railway roadbed both increase significantly with the increasing number of reinforced layers, along with large increases in the stiffness and energy absorption of the railway roadbed. The research results can provide a reference for the structural design of railway ballast layers to comprehensively control the stability and deformation of existing heavy railway roadbeds.

Exploring the interaction of pipe-soil under frost heave effect is the key to solving the problem of frequent damage to buried pipes. In this study, the effects of ambient temperature (AT), buried depth of pipe (BDP) and initial water content (IWC) on the interaction of pipe-soil under the condition of roadbed frost heave are studiedby experimental test. The results show that the buried pipe seriously affects the soil temperature field and the migration of pore water during roadbed frost heaving. As the AT decreases, the final strain of pipes (FSP) gradually increases, and the flatness of the roadbed gradually deteriorates. When the BDP is 2D (outer diameter of the pipe), the flatness of the roadbed is the worst. The pore water in unfrozen area tends to migrate more toward soil around pipes during the roadbed frost heaving. The IWC of roadbed has a greater impact on the FSP than the BDP These could provide a guidance for the construction of pipes under frost heave in roadbed.

Considering the engineering background of the dangerous western mountain railroad, large-scale shaking table model experiments were conducted on embankment slopes supported by single and double-row piles, subjected to El-Centro wave excitations. Based on parameters such as displacement and acceleration, an in-depth investigation was conducted to study the differences in dynamic response characteristics between the two slope models. Moreover, the reasons for the differences between the two slopes were explored using fast Fourier transform (FFT) spectra. The results revealed that both the support effect and the differences in anti-slip piles gradually increased with the increase in the input wave amplitude. At input wave amplitudes of 0.1g-0.3g, both single and double-row pile slopes remained stable, with minimal differences in their overall dynamic response characteristics. However, at an input wave amplitude of 0.4g, significant differences in the dynamic responses of both slopes emerged. Macroscopic damage was more apparent in the single-row pile slope, with high slope surface displacement, accumulated soil damage, and noticeable nonlinear characteristics. At an input wave amplitude of 0.5g-0.6g, both slope models exhibited a pronounced elevation effect in the peak ground acceleration (PGA) amplification factor. Additionally, plastic zones were observed on the road cut face and behind the piles in both models. The presence of retaining piles effectively suppressed the upward trend of PGA amplification coefficients along the slope and prevented the connection of plastic zones on the slope surface. Notably, the PGA amplification effect of the single-row pile slope was pronounced, with a wide and deep plastic zone, severe local instability, and relatively weak seismic support effect. The introduction of the FFT spectral ratio revealed that the difference in amplitude amplification effects of single and double-row pile slopes in the 5-10 Hz band was the main reason for the difference in their dynamic responses. Under seismic loading, the failure process of the single-row pile-supported slope involved three stages: initial stability of the slope, plastic deformation of the slope surface soil, and local collapse and disintegration of the slope. In contrast, the double-row pile-supported slope experienced the first two stages of this failure process.

In order to study the changes in the mechanical properties of road subgrade in cold areas after the freezing and thawing of highways in cold areas, indoor mechanical tests were carried out to investigate the effects of the number of freeze-thaw cycles, freezing temperature, water content, and circumferential pressure on the mechanical properties of road subgrade soil in cold areas after thawing. The mechanical properties of road subgrade soil in cold areas after thawing were measured under different conditions. The test results show that, within the study range: (1) After 7 freeze-thaw cycles, the destructive stress of the subgrade soil decreased from 321.7 kPa to 289.9 kPa, a decrease of 9.9%, and the elastic modulus decayed by 19.9%. (2) When the freezing temperature was reduced from -5 degrees C to -15 degrees C, the destructive stress of the subgrade soil decreased from 303.9 kPa to 290.1 kPa, a decrease of 13.8 kPa, approximately 4.5%, and the decrease in modulus of elasticity was about 1.6%. (3) The water content increased from 6% to 12%, and the destructive stress decreased from 405.43 kPa to 288.4 kPa, a decrease of 29.1%, and the modulus of elasticity decreased approximately linearly, with an attenuation of 50.4%. (4) The peripheral pressure increased from 50 kPa to 150 kPa, and the destructive stress increased from 194.7 kPa to 367.7 kPa, a growth of 88.8%, and its modulus of elasticity increased with the increase in peripheral pressure, an increase of 154.1%. The results of this research can provide a reference for highway and engineering construction in the western silt-soil distribution area.