In previous train operations, traffic loads were typically considered continuous, disregarding the intermittent effects of successive trains on subgrade loess. To investigate the cumulative plastic strain behavior and critical dynamic stress of subgrade loess under intermittent train loads, a series of dynamic triaxial tests were conducted considering factors such as cyclic stress ratio, confining pressure, and frequency. The deformation characteristics of subgrade soil under different stress levels were analyzed, and the dynamic behavior of specimens was categorized based on the development trends of strain rate and cumulative plastic strain. Then the critical dynamic stress levels for plastic shakedown and plastic creep states were determined. The results indicate that intermittent effects suppress the development of cumulative plastic strain and excess pore water pressure in the soil. The more cycles of the unloading-drainage stage the soil undergoes, the stronger its resistance to failure. Under intermittent loads, cumulative plastic strain increases with higher cyclic stress ratios and frequencies. When the cyclic stress ratio is constant, the increase in confining pressure enhances soil stiffness, but this increase is insufficient to counteract the strain induced by greater dynamic stress amplitude, resulting in increased cumulative strain. Combining cumulative plastic strain and plastic strain rate, a classification standard for the deformation behavior of subgrade loess under intermittent loading conditions was established, and the critical dynamic stress was identified. The critical dynamic stress increases with higher confining pressure but decreases with frequency. Accordingly, empirical formulas for critical dynamic stress concerning confining pressure and frequency were proposed. These findings are crucial for understanding the mechanism of intermittent train load effects and analyzing subgrade settlement.

To investigate the impact of traffic loading on the deformation characteristics of soft dredger fill, a series of dynamic triaxial tests of soft dredger fill were carried out. The deformation characteristics of the soft dredger fill under varying confining pressures and dynamic stress ratios were analyzed comparatively. The test results indicate that the cumulative plastic strain curve of the soft dredger fill exhibits three distinct patterns: destructive, critical, and stable; Based on the cumulative plastic strain development law of the dredger fill, an empirical formula of critical dynamic stress and the prediction model of cumulative plastic strain development were established, considering the influence of confining pressure. Under continuous loading, the hysteresis curve of soft dredger fill showed pronounced non-linearity, and hysteresis. Initially, the curve exhibited an ellipse shape, transitioning to a crescent shape in the middle and late stages. The higher the dynamic stress ratio, the greater the height and width of the hysteresis loop. These findings provide valuable insights into the dynamic behavior of dredger fill under traffic loading.

The reliability of the absorbing layer is crucial for realizing protective engineering's protection function. However, the typical wave-absorbing material, sand, is unable to fulfill its intended wave-absorbing function in areas with seasonally frozen soil. This is because the internal pores of the material become filled with ice and the particles freeze. To address this issue, alumina thin-walled hollow particles were chosen as a new wave-absorbing material. These particles can introduce the gas phase into the absorbing layer which is essential for attenuating the stress waves and its wave-absorbing capacity under freezing conditions was investigated by the split Hopkinson bar (SHPB) test. According to the test data, the alumina thin-walled hollow particles are less dense than sand and have a lower wave impedance, allowing them to reflect more incident energy. Moreover, these particles have a better capacity for dissipating the absorbed energy, as compared to sand. Under freezing circumstances, the average transmittance coefficient of alumina thin-walled hollow particles is only 21.95% to 49.30% of ordinary sand. Additionally, the particle size positively correlates with the capacity for wave-absorption. The capacity of alumina thin-walled hollow particles to shatter and release the gas phase under impact stress significantly increases the compressibility of the absorbing layer under freezing conditions, which accounts for their enhanced wave-absorbing effectiveness. The stress-strain curve specifically manifests as a smoother curve and a longer stage of plastic energy dissipation. Other than that, the dynamic deformation modulus of the material and peak stress is lower, while the peak strain is larger. The findings of this study provide a low-cost, high-reliability solution to the problem of frost damage in the absorbing layer in regions with seasonal freezing.

In this paper, a comprehensive series of dynamic triaxial tests were conducted to delve into the influence of temperature and moisture content on the behavior of frozen silty clay. Upon scrutinizing the experimental outcomes under prolonged reciprocal cyclic loading, insights were gained into how varying temperatures and moisture contents impact the cumulative permanent strain (CPS) and critical dynamic stress (CDS) of frozen clay. The results show that the variation curves of CPS with the number of cyclic loadings show significant changes at different temperatures and moisture contents. Additionally, based on the assessment of vertical CPS recorded at the 100th and 1000th loading iterations, criteria for assessing the plastic stability and plastic creep threshold of frozen silty clay were devised. Consequently, an analysis was conducted to delineate the correlation between the variation in vertical cumulative strains and the dynamic stresses applied within the frozen clay, resulting in the formulation of a series of correlation curves. The relationship between the changes in CDS affected by different temperatures and water contents were analyzed. The CDS under the plastic stability and plastic creep limits showed a slowly increasing trend with decreasing temperatures and a slowly decreasing trend with increasing water contents.

The cumulative deformation and fatigue failure of roadbeds induced by dynamic loads are fundamental considerations in road traffic design. To gain a more comprehensive understanding of the impact of drainage conditions and loading cycles on the performance of roadbeds composed of granite residual soil in southern China under various loading modes, this study conducted high-cycle dynamic triaxial tests using a DDS-70 dynamic triaxial apparatus. Through analysis of sample deformations, pore pressure development, and changes in critical cyclic stress ratio under different simulated waveforms, it was observed that the simulated waveform significantly influences the dynamic characteristics of the soil, with the half-sine wave proving effective in simulating the complex dynamic stress caused by traffic vehicles. Meanwhile, the study revealed uncertainties in the development of cumulative deformation under undrained conditions, thus indicating a need for dynamic tests to be conducted under drained conditions to more accurately replicate the effects of traffic loads. Additionally, the deformation of samples at 1000 cycles can serve as a crucial reference for estimating final deformation, which is essential for determining sample types and obtaining key parameters of foundation soil. This approach can help reduce testing workload and save time and costs.

Studying train-induced response characteristics is essential for safely operating permafrost railway subgrades. A three-dimensional thermal-mechanical coupling nonlinear dynamic model of train-track-subgrade-ground relationships was established to analyse the train-induced dynamic stress, acceleration and stress path characteristics of a permafrost railway subgrade, and field monitoring data were used to verify this model. The differences between the 2D and 3D models are also discussed, along with the seasonal changes, train speed, axle load, and train type affecting permafrost subgrades. The main results are as follows. First, the vibration load significantly impacts the subgrade 6 m below the sleeper, producing distinct vertical dynamic stress waves due to the wheels and bogies. Dynamic compression stress dominates the subgrade and is influenced by the train structure, speed, and sleeper spacing. While the 2D model tends to underestimate the dynamic stress in shallower layers, it concurs with the 3D model in deeper subgrade dynamics within a 10% margin of error. Then, the principal stress axis of the subgrade soil rotates synchronously with train movements, exhibiting regular stress paths in the YZ plane (longitudinal section) with depth-dependent variations in the stress cycles and deviatoric stress. Finally, predominantly originating from sleeper-induced vibrations, the subgrade vibration acceleration varies with the train speed, sleeper spacing, and season and is most pronounced in the vertical direction. This study provides theoretical guidance for the vibration response of permafrost subgrades on the Qinghai-Tibet Railway (QTR).

On July 20, 2021, over 2000 ground subsidence events and collapses occurred in Zhengzhou, China, after a heavy rainstorm. These events were mostly caused by the reduced mechanical properties of loess under moistening and repeated dynamic loading. After the conducted dynamic triaxial tests considering varying moisture content, envelope pressure and 10,000 vibrations, the dynamic properties evolution of undisturbed loess under moistening has been clarified. The experimental results showed that the dynamic strain of undisturbed loess under moistening conditions increases gradually with increasing dynamic stress, following the Hardin-Drnevich hyperbolic model. The initial dynamic shear modulus, maximum dynamic shear stress, and dynamic strength decrease linearly with increasing moisture, while the dynamic strain is the opposite, and the damping ratio is less affected by the increased moisture. The dynamic strain rises with increasing dynamic stress and moisture content considering the same vibrations. Increased vibrations and greater moisture content under identical dynamic stress cause a faster accumulation of dynamic strain in undisturbed loess, making it more susceptible to damage. The results are of guiding significance for the evaluation and analysis of the dynamic properties of loess and provide technical support for disaster prevention and mitigation in Zhengzhou.

The shakedown state of the subgrade is crucial for the sustainable design and long-term stability evaluation of pavement structures. In order to characterize the plastic deformation and shakedown behavior of subgrade soil in seasonal frozen regions, cyclic triaxial tests were conducted on the thawed subgrade soil after seven cycles of freeze-thaw. The influences of the numbers of cycle loading, the amplitude of cyclic deviator stress, and the confining stress were considered variables. The evolution features of accumulative plastic strain, accumulative plastic strain rate, and critical dynamic stress were experimentally analyzed. Based on the shakedown theory, the ensuing discoveries were that the accumulative plastic strain response-behavior of thawed subgrade soil was typically divided into plastic shakedown, plastic creep, and incremental collapse under the long-term cyclic loading. Furthermore, the shakedown standard for thawed subgrade soil was also proposed based on the evolution of the accumulative plastic strain rate. The critical dynamic stresses can be obtained by the proposal formula to determine the different plastic deformation ranges.

In road engineering, the applications of piezoelectric ceramics on road energy harvesting or electronic sensing have drawn many attentions. However, the application potential of piezoelectric sensor on UGMs (unbound granular materials) in road is unclear. The main problem is the applicability of piezoelectric equation considering that the soil structure of UGMs and the working environment that the transducer may suffer may influence the transferred stress on the piezoelectric transducer and then the electricity generation. In this study, a twodimensional piezoelectric transducer made by PZT-5H piezoelectric ceramics was installed in the sample of UGMs, and a series of cyclic tests were performed on the UGMs samples by a large-scale triaxial apparatus. This test method is specially designed for the case that the piezoelectric transducer is installed in UGMs of pavement base/subbase layers and then undergo traffic loading under complex working environment. Test results show that the electricity generation is primarily dependent on the magnitude and frequency of cyclic loading, while the influences of other factors are limited. The piezoelectric equation to calculate the open-circuit voltage is deduced and verified under the complex working environment. This indicates that the piezoelectric equation is applicable to the case that the applied stress on the piezoelectric transducer is transferred from the soil medium, and the two-dimensional piezoelectric transducer has a sensor potential to monitor the dynamic vertical and horizontal soil stresses under traffic loading.

A deformation model of buried pipeline under complicated geotechnical conditions of soil slit fracture is developed. The classical theory of rods on an elastic foundation and the membrane theory of shells are used. The influence of the contingency of cyclic discontinuities of transversal displacement in damaged foundation on the stressed state and limit equilibrium of pressurized pipe has been studied in quasi-static and dynamic statement with analytical methods. It is assumed that the frequency of kinematic perturbation does not exceed the cutoff frequency of the system.