This paper investigates the durability and long-term bearing behavior of post-grouted piles in sand. Laboratory tests were conducted on cement-stabilized sand exposed to seawater erosion environments to investigate the effects of curing times and cement ratios on soil strength using micro-cone penetration (MCPT), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The strength distribution, microstructure, and phase composition of cement-stabilized soil were analyzed to determine the characteristics of strength changes. Furthermore, long-term field static load tests were performed on the Yinchuan Beijing Road extension and Binhe Yellow River Bridge project to investigate the relationship between the change in strength of cement-stabilized soil under erosion environments and the time effect of post-grouting at the pile tip. The results indicated that erosion damage to the cement-stabilized soil occurs from shallow to deep as the curing time increases, resulting in a reduction in its strength due to the formation of hydration products and products with poor gelation and low strength. Conversely, an increase in cement ratios resulted in heightened hydration products, which subsequently increased strength and significantly reduced the depth of erosion damage. The change in strength of cement-stabilized soil under seawater erosion environment is a combined result of the strengthening effect of hydration reaction and the weakening effect of erosion reaction. This change is the main reason for the time effect of post-grouting at the pile tip, allowing for effective control of pile foundation settlement with increasing time. The research findings provide valuable insights for evaluating the durability and long-term bearing behavior of post-grouted piles in sand.

The self-weight stress in multilayered soil varies with depth, and traditional consolidation research seldom takes into account the actual distribution of self-weight stress, resulting in inaccurate calculations of soil consolidation and settlement. This paper presents a semi-analytical solution for the one-dimensional nonlinear consolidation of multilayered soil, considering self-weight, time-dependent loading, and boundary time effect. The validity of the proposed solution is confirmed through comparison with existing analytical solutions and finite difference solution. Based on the proposed semi-analytical solution, this study investigates the influence of self-weight, interface parameter, soil properties, and nonlinear parameters on the consolidation characteristics of multilayered soil. The results indicate that factoring in the true distribution of self-weight leads to a faster dissipation rate of excess pore water pressure and larger settlement and settlement rate, compared to not considering self-weight. Both boundary drainage performance and soil nonlinearity have an impact on consolidation. If the boundary drainage capacity is inadequate, the influence of soil nonlinearity on consolidation diminishes.

Triaxial compression tests were conducted on the alfalfa root-loess complex at different growthperiods obtained through artificial planting. The research focused on analyzing the time variation law of the shear strength index and deformation index of the alfalfa root-loess complex under dry-wet cycles. Additionally, the time effect of the shear strength index of the alfalfa root-loess complex under dry-wet cycles was analyzed and its prediction model was proposed. The results show that the PG-DWC (dry-wet cycle caused by plant water management during plant growth period) causes the peak strength of plain soil to change in a V shape with the increase of growth period, and the peak strength of alfalfa root-loess complex is higher than that of plain soil at the same growth period. The deterioration of the peak strength of alfalfa root-loess complex in the same growth period is aggravated with the increase of drying and wetting cycles. Compared with the 0 days growth period, the effective cohesion of alfalfa root-loess complex under different dry-wet cycles maximum increase rate is at the 180 days, which are 33.88%, 46.05%, 30.12% and 216.02%, respectively. When the number of dry-wet cycles is constant, the effective cohesion of the alfalfa root-loess complex overall increases with the growth period. However, it gradually decreases comparedwith the previous growth period, and the minimum increase rate are all at the 180 days. For the same growth period, the effective cohesion of the alfalfa root-loess complex decreases with the increase of the number of dry-wet cycles. This indicates that EC-DWC (the dry-wet cycles caused by extreme natural conditions such as continuous rain) have a detrimental effect on the time effect of the shear strength of the alfalfa root-loess complex. Finally, based on the formula of total deterioration, a prediction model for the shear strength of the alfalfa root-loess complex under dry-wet cycles was proposed, which exhibits high prediction accuracy. The research results provide useful guidance for the understanding of mechanical behavior and structural damage evolution of root-soil composite.

Increasingly frequent extreme rainfall as a result of climate change is strongly damaging the global soil and water environment. However, few studies have focused on daily extreme sediment events (DESE) in heterogeneous karst watersheds based on long-term in -situ observations. This study quantitatively assessed the time effect of DESE on rainfall response, decoupled the impact of environmental factors on DESE by using structural equation modelling, and finally explored the modelling scheme of DESE based on the hybrid model. The results showed that DESE had the highest frequency of occurrence in May -July, with dispersed distribution in the value domain. Rainfall with a time lag of 1 day and a time accumulation of 2 or 3 days was an important contribution to DESE ( P < 0.01, R = 0.47 -0.68). Combined effects of environmental factors explained 53.6 % -64.1 % of the variation in DESE. Runoff and vegetation exerted the strongest direct and indirect effects on DESE, respectively (8 = 0.66/ -0.727). Vegetation was the dominant driver of DESE in Dabanghe and Yejihe (8 = -0.725/-0.758), while the dominant driver in Tongzhihe was climate (8 = 0.743). In the future, the risk of extreme sediments should be prevented and resolved through the comprehensive regulation of multiple paths, such as runoff and vegetation. Hybrid models significantly improved the modelling performance of machine learning models. Generalized additive model -Extreme gradient boost had the best performance, while Partial least squares regression -Extreme gradient boost was the most valuable when considering performance and input data cost. Two methods can be used as recommended solutions for DESE modelling. This study provides new and in-depth insights into DESE in

The increasing demand for high-speed railways has risen, to solve the age-old problem of bridge abutments, the step between the backfill and the bridge deck. Examples prove that inadequate technical solutions can generate damage that may require long-term speed restrictions or lead to short maintenance cycles, significantly increasing the total cost of ownership. The problems associated with the transition zones require complex analysis. The complex interaction of structural elements with different stiffnesses and different dynamic behavior varies over time due to the time-dependent behavior of the soil, and in addition, a bridge deck and its connecting elements can be constructed in several sequences. This study investigated a typical single-span railway bridge and its soil environment using PLAXIS 3D geotechnical finite element software. Different constitutive soil models were used to approximate the behavior of the bridge and the connecting elements. To model the soil behavior, the HS-small constitutive model was implemented. Loads of the structure are transferred onto the subsoil by 60 cm diameter piles modeled as embedded piles. Six different construction schedules were analyzed using time-domain analyses. The importance of high-speed railways was highlighted, and a 250 km/h train speed was applied, using dynamic analysis. The study focuses on the effect of different construction schedules on settlement, consolidation time, the behavior of the transition, and the substructure movements. The results of this study show that geotechnical approaches by themselves are not enough to solve the problem of the transition zone, highlighting the collaboration of geotechnical, structural and railway engineers.