The influence of seismic history on the liquefaction resistance of saturated sand is a complex process that remains incompletely understood. Large earthquakes often consist of foreshocks, mainshocks, and aftershocks with varying magnitudes and irregular time intervals. In this context, sandy soils undergo two interdependent processes: (i) partial excess pore water pressure (EPWP) generation during foreshocks or moderate mainshocks, where seismic loadings elevate EPWP without causing full liquefaction and (ii) incomplete EPWP dissipation between seismic events due to restricted drainage. These processes leave behind persistent residual EPWP, reducing the liquefaction resistance during subsequent shaking. A series of cyclic triaxial tests simulating these mechanisms revealed that liquefaction resistance increases when the EPWP ratio r(u) < 0.6-0.8 (peaking at r(u) similar to 0.4) but decreases sharply at higher r(u). Crucially, EPWP generation during seismic loading plays a dominant role in resistance evolution compared to reconsolidation effects. Threshold lines (TLs) mapping r(u), the reconsolidation ratio (RR), and peak resistance interval (the range of r(u) where the peak liquefaction resistance is located) indicates that resistance decreases above TLs and increases below them, with higher cyclic stress ratios (CSR) weakening these effects. These findings provide a unified framework for assessing liquefaction risks under realistic multi-stage seismic scenarios.

Creep, once considered an inherent characteristic of granular materials, is primarily governed by time and the current stress state. However, recent studies indicate that creep development is also influenced by the loading history. To better reveal the creep revolution law of the rockfill under the influence of loading history such as historical stress rates, creep tests were conducted under oedometric loading. Alternative loading-creep steps, different stress increment sizes, and various precreep stress rates were considered. Independent of other factors, the development of the creep rate was governed by the recent precreep stress rate (the prior stress rate defined in this study). When the prior stress rate was higher than a threshold value, the relationship between the creep rate and time was double logarithmic linear; thus the creep strain-time relationship tended to converge on a power law (referred to as the creep baseline herein). However, when the prior stress rate was lower than the threshold value, the initial creep rate was lower than that of the creep baseline and did not decrease until several minutes after the start of the creep. The development of the creep rate with time in the initial stage can be generalized as a straight horizontal line, suggesting that the rate remains almost unchanged for a certain time, until the straight horizontal line approached the creep baseline. The inheritance and hysteresis of different strain rates in the initial stage of subsequent creep resulted in differences in the creep magnitude and time development process of the creep rate. The above findings are constructive for predicting the deformation of deep layers of rockfill, such as embankments, with more accuracy, especially for that with some large-sized rigid-structure buildings on its surface.

Rubber-sand mixtures (RSM), characterized by low unit weight, strong elastic deformation ability, good durability, and high energy dissipation, hold significant potential for civil engineering applications. However, research on the time-dependent dynamic behavior remains relatively scarce, limiting their broader application in practical construction. A thorough understanding of this behavior is critical for ensuring long-term performance of RSM across various engineering contexts. In the study, the effects of rubber's thermal aging and loading history, two key factors of time-dependent behavior, on the dynamic properties of RSM under small to medium strains were investigated. Aging of rubber particles was accelerated through oven aging experiments, followed by resonant column tests to determine the dynamic shear modulus and damping ratio of RSM samples with rubber particles of varying aging levels (5 %, 10%, 15 %, and 20% rubber content). Furthermore, multiple load tests were also conducted on the same samples to assess the impact of loading history on RSM's dynamic properties. The results reveal that thermal aging causes volumetric expansion and a reduction in compressive strength of rubber particles, leading to changes in the dynamic shear modulus and damping ratio of RSM. Specifically, the dynamic shear modulus initially decreases during early aging stages, then increases, eventually stabilizing, while the damping ratio consistently decreases with prolonged aging. With repeated loading cycles resulting in a reduction in dynamic shear modulus and an increase in damping ratio. These results improve our understanding of this composite's long-term behavior and offer practical advice for its use in seismic isolation and geotechnical engineering.

Nowadays, with the widespread supply of very powerful laboratory and computer equipment, it is expected that the analyses conducted for geotechnical problems are carried out with very high precision. Precise analyses lead to better knowledge of structures' behavior, which, in turn, reduces the costs related to uncertainty of materials' behavior. A precise analysis necessitates a precise knowledge and definition of the behavior of the constituent materials, which itself requires applying an appropriate constitutive model to show the behavior of materials. Constitutive models used in the generalized plasticity framework are very powerful constitutive models for the simulation of sand behavior. However, the simulation of a cyclic behavior in these models, especially the simulation of the undrained cyclic behavior, is not well-recognized. In this study, in order to eliminate the weakness of generalized constitutive models under cyclic loading, a new equation is presented to substitute the so-called coefficient of the discrete memory factor to consider the loading history in such a way that the plastic modulus is modified during reloading and, as a result, more appropriate predictions of sand behavior are obtained. The performance accuracy of the proposed coefficient was evaluated in accordance with the experimental data. Finally, the results show that after using the modification of the loading history coefficient, predictions of the constitutive model are significantly improved.

Understanding the characteristics of the development of excess pore water pressure during cyclic loading is important to evaluating the dynamic behavior of soils. Many researchers have proposed experimental models to estimate pore water pressure. However, existing experimental models are mainly based on experimental results obtained under isostatic and constant amplitude loading. In this study, K0-controlled cyclic loading is undertaken by simulating a horizontal stratified ground, and the development of excess pore water pressure is evaluated by measuring the accumulated shear strain; a modified accumulated shear strain is proposed based on these results. The results show that the excess pore water pressure can be predicted from the modified accumulated shear strain, regardless of soil type, initial soil pressure coefficient, initial shear stress, or the shape of input waveform.