As a new type of granular backfill material, calcareous sand is widely used in the construction of marine transportation infrastructure. And they are subjected to complex irregular long-term dynamic loading such as that from waves, traffic and even earthquakes. In this paper, 22 groups of undrained cyclic shear tests were performed with calcareous sand under various cyclic stress ratios and cyclic stress paths. The influence mechanism of stress path on the cyclic shear behavior of calcareous sand was investigated. The results show that the ultimate residual pore pressure at critical state was not affected by cyclic stress ratios and paths. But the cyclic shear behaviors of calcareous sand including failure pore water pressure and long-term deformation were changed significantly. Axial load plays a dominant role in each stress path. A stress path parameter omega was proposed to characterize the vertical shaking impact of cyclic stress paths with different initial orientation of the sigma 1 axis to vertical alpha sigma 0. And a power function of omega was used to describe the involvement level of soil skeleton in anti-liquefaction. This parameter performs well in representing cyclic stress paths with different orientation to the vertical. A series of formulas were proposed to predict the failure residual pore pressure and the long-term cumulative deformation behavior of calcareous sand. More accurate shakedown discriminant boundaries suitable for almost unbroken calcareous sand were proposed.

Silty clay is a common compressible soil found in many engineering projects, where its deformation behavior is particularly complex under cyclic loading. This study uses the GDS dynamic triaxial testing system to examine how silty clay deforms under different moisture contents, confining pressures, and cyclic stress ratios (CSR). The results show that the cumulative strain of silty clay follows a three-phase pattern: an initial rapid increase (N = 0-300), followed by a slower rise (N = 300-1000), and finally reaching a stable state (N > 1000). Among the factors tested, CSR has the most significant impact on cumulative strain, with moisture content coming second, while confining pressure has a relatively minor effect. After 1000 cycles, cumulative strain shows a clear linear growth trend. Linear fitting analysis indicates that the uncertainty in the fitted curve is influenced by moisture content, confining pressure, and CSR. Uncertainty is greater at both low and high moisture content levels, while it is lower under moderate moisture conditions. These findings provide valuable insights into predicting soil deformation in engineering applications, helping to improve our understanding of silty clay behavior under cyclic loading.

The offshore wind turbines (OWT) are subjected to cyclic loads, such as ocean waves and wind, over extended periods. The soil surrounding the pile experiences bi-directional cyclic shear. As a result of the low-frequency and long-term loading in the pile-soil interaction, the cumulative deformation of pile foundation increases, posing a risk to the operational safety of wind turbine system. The soil around the piles is distributed with soft clay and clay layers. To study the cumulative deformation properties of clay under complex stress states. A series of tests are conducted, the variation of resilient modulus under different cyclic stress levels and confining pressures is analyzed based on test results. Then an empirical model uniformly reflecting strain-hardening and strainsoftening properties of clay is proposed. The variations of model parameters are investigated. Then the established empirical model is used to modify the maximum elastoplastic modulus at each unloading within the bounding surface constitutive model, a parameter reflecting the magnitude and rate of strain accumulation is also introduced. This method is characterized by a simple expression and requires fewer model parameters. Finally, the predicted results of modified constitutive model are compared with test results to verify the validity of the established model.

This paper uses shake table tests to study tunnel landslide failures in earthquake zones under four conditions: (GK1) the tunnel intersects the sliding mass, (GK2) the tunnel is perpendicular to the sliding surface, (GK3) the tunnel is positioned below the sliding surface, and (GK4) the tunnel is situated above the bedrock. The dynamic responses under the four conditions are analyzed using time-domain strain analysis methods. Additionally, from an energy perspective, the amplified Arias intensity (MIa) is employed to characterize the cumulative deformation damage of the tunnel lining. The results indicate that under four working conditions, the upper landslide region of the tunnel landslide system exhibits a settlement-compression-shear type of sliding failure. However, in conditions GK1 and GK2, where the lining structure is present, the tunnel lining provides additional support to the landslide, resulting in less severe damage to the slope compared to conditions GK3 and GK4. However, under conditions GK1 and GK2, the left sidewall of the tunnel lining experiences more severe damage due to landslide pressure. The maximum soil pressure and bending moment on the left sidewalls in GK3 and GK4 are only 40-60% of those observed in GK1 and GK2. In addition, based on the trend of MIa, the cumulative deformation evolution of the tunnel lining can be categorized into three stages: the initial stage (0.1-0.2 g), the progressive deformation stage (0.2-0.4 g), and the failure deformation stage (0.4-0.6 g). Further research confirms that under seismic action, the slope experiences a significant progressive catastrophic evolution. This process is characterized by typical seismic cumulative damage effects, with sustained seismic loading causing deformation and damage to gradually expand from localized areas to the entire slope. This continuous fatigue effect progressively weakens the stability of the lining structure, ultimately leading to its failure. Therefore, the deformation and damage of the slope under seismic loading pose a serious threat to the safety of tunnel linings, highlighting the need for close attention to their long-term stability. The research results provide a scientific basis for reinforcing tunnel linings in earthquake-prone mountainous areas.

To address the long-term settlement of embankments over structured soft soil during the in-service stage, artificial structured soils with different interparticle bonding strengths and initial void ratios were prepared, and repeated triaxial loading tests were conducted to investigate the effects of bonding strength, initial void ratio, stress amplitude and cycle number on the accumulative deformation characteristics. The results show that the relationship between the accumulative plastic strain and cycle number can be classified into stable, critical and destructive types, and an empirical relationship between the stress sensitivity and dynamic stress ratio is established. Furthermore, two different empirical models for accumulative plastic strain are presented that incorporate soil structure. Reasonable agreement between the model predictions and the experimental results for different natural soft soils demonstrate that the proposed models can accurately capture the accumulative deformation behaviour of structured soils. In addition, considering the accumulated plastic deformation of soil subjected to cyclic loading as static creep, a simplified method for calculating three-dimensional cyclic accumulative deformation is proposed by implementing the proposed model in a finite-element simulation utilizing an implicit stress integration algorithm. Finally, the effects of the dynamic stress level and structural strength on the accumulative deformation are analyzed. This has important implications in controlling the long-term settlement of embankment in soft soil area.

Piles in marine environments are subjected to various loads of differing magnitudes and directions, and their long-term stability has attracted much attention. Most research focuses on lateral cyclic loading; there are few full-scale tests that consider the effects of cyclic loading at different inclined angles. A long-term inclined cyclic loading strategy was used to carry out laboratory tests to study different inclined angles on the pile. The results show that a smaller inclined angle (theta L) or a larger pile-soil relative stiffness (T/L) results in wider and deeper sediment subsidence after 10,000 cycles. As theta L increases from 0 degrees to 80 degrees, the peak displacement at the pile head during the first load decreases, while the accumulated displacement initially decreases and then increases. For slender piles, the normalized inclined cyclic loading stiffness (klN/kl1) and unloading stiffness (kuN/ku1) first decrease and then increase. For semi-rigid piles, both klN/kl1 and kuN/ku1 gradually decrease. On the other hand, as theta L increases, klN/kl1 and kuN/ku1 increased more sharply in the initial stage, with a quicker transition from rapid growth to stability. At theta L = 80 degrees, peak values are reached early during the initial loading phase. Based on this, prediction formulas for inclined cyclic cumulative displacement, loading stiffness, and unloading stiffness were established and verified.

Long-term cyclic loading applied to clay at stress levels lower than the critical cyclic stress leads to soil deformation without inducing damage. The Monismith model is well-known for its simplicity and ability to describe the trend of cumulative plastic strain under cyclic loading. However, the simulated cumulative plastic strain increases indefinitely with the number of cycles until damage occurs. At lower cyclic stress levels, the cumulative plastic strain tends to be stabilized with an increasing number of cycles, ultimately limits the applicability of the model. To address this issue, a series of axial-torsional bi-directional cyclic loading tests are conducted on saturated clay using a hollow cylinder torsional shear apparatus. An empirical three-parameter mathematical prediction model is proposed by analyzing the development of cumulative generalized shear strain based on test results. The relationships of model parameters a with plasticity index, frequency, generalized shear stress, and mean effective stress; b with plasticity index, and c with frequency and plasticity index are presented as functional expressions. Finally, the predicted results of the empirical model are compared with test results to verify its effectiveness, providing a basis for calculating cumulative deformation in clay under long-term low cyclic stress levels.

Under long-term horizontal cyclic loading, the evolution characteristics of the loading and unloading stiffness of piles are an important representation of pile-soil interaction. However, research in this area is limited, particularly regarding the impact of factors like pile-soil relative stiffness. In this study, laboratory tests with a long-term horizontal cyclic loading strategy were conducted to study various factors, including different cyclic amplitude ratios (zeta b), cyclic load ratios (zeta c), and pile-soil relative stiffness (T/L) in sandy soil, on dynamic pile head stiffness. The results show that the normalized cumulative displacement increases with the number of cycles and the ratio of T/L but tends to decrease as zeta c increases. As zeta b increases, the normalized cyclic loading stiffness also rises, while it has little effect on the normalized cyclic unloading stiffness. On the other hand, as zeta c or T/L increases, the cyclic loading stiffness increases while the unloading stiffness decreases. Based on these observations, prediction formulas for normalized cumulative displacement and cyclic loading and unloading stiffness were established and confirmed with test results. The findings of this study provide methodological references for establishing models of pile-soil interaction under cyclic loading and for predicting loading and unloading stiffness under different influencing factors.

The horizontal displacement of a reinforced-soil retaining wall is a common deformation mode of seismic damage. The horizontal displacement time history and accumulative deformation after earthquakes are important parameters for evaluating the seismic performance of a reinforced-soil retaining wall, but theoretical study on this issue is scarce at the moment. In this study, an analytical method is proposed to calculate the horizontal displacement time history of a block-faced reinforced soil retaining wall. The method is based on the pseudodynamic method and differential kinematics equations, and this method was used to calculate the reinforcement material's tensile displacement and overall displacement in the reinforced area under earthquake motion, while simultaneously taking into account the accumulative deformation. The rationality and accuracy of this method are verified through comparison with model experiments and existing theories. Besides, parameter analysis was carried out to further confirm the applicability of this method. The study shows the method takes into account the influence of the accumulated deformation, and can effectively calculate the horizontal displacement time history of the block-faced reinforced soil retaining wall under larger magnitudes. Although the calculated values are smaller than the actual deformation, they are still relatively close.

Foam concrete is characterized by lightweight, self-compacting and high flowability, thereby widely used as a subgrade bed filler. High-speed railway subgrades usually experience inhomogeneous deformation due to the occurrence of freezing-thawing cycles in seasonally frozen soil areas. It is essential to study the deformation behavior of foam concrete under the coupling effect of freezing-thawing cycles and dynamic loading. In this paper, dynamic triaxial tests were performed to study the accumulative deformation of the foam concrete under different numbers of freezing-thawing cycles, freezing temperatures, amplitudes and frequencies of dynamic loading. Based on the scanning electron microscopy (SEM) tests, the characteristics of the pore structure were analyzed quantitatively by introducing the directional distribution frequency and fractal dimension. The research results illustrate that the damage caused by freezing-thawing progress to the pore structure results in more significant deformation of the foam concrete subjected to dynamic loading. There exists an accumulative damage effect induced by the coupling action of long-term dynamic loading and freezing-thawing progress on the microstructure and mechanical properties of foam concrete. The development of the fractal dimension agrees with that of the accumulative strain, indicating a close connection between the microstructure and the dynamic behavior of foam concrete. The findings concluded in this study contribute to a sufficient understanding of the performance of foam concrete used as high-speed railway subgrade fillers subjected to seasonal freezing.