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.

To investigate the effect of combined end-and-shaft post-grouting on the vertical load-bearing performance of bridge-bored piles in the Dongting Lake area of Hunan, two post-grouted piles were subjected to bi-directional O-cell and top-down load tests before and after combined end-and-shaft grouting, based on the Wushi to Yiyang Expressway project. A comparative analysis was conducted on the bearing capacity, deformation characteristics, and load transfer behavior of the piles before and after grouting. This study also examined the conversion coefficient gamma values of different soil layers obtained from the bi-directional O-cell test for bearing capacity calculations. Additionally, the characteristic values of the end bearing capacity, obtained from the bi-directional O-cell and top-down load tests, were compared with the values calculated using the relevant formulas in the current standards, which validated the accuracy of existing regulations and traditional loading methods. The results indicate that the stress distribution along the pile shaft differed between the two test methods. In the bi-directional O-cell test, the side resistance developed from the end to the head, while in the top-down load test, it developed from the head to the end. After combined post-grouting, the ultimate bearing capacity of the piles significantly increased, with side resistance increasing by up to 81.03% and end resistance by up to 105.66%. The conversion coefficients for the side resistance in silty sand and gravel before and after grouting are 0.86 and 0.80 and 0.81 and 0.69, respectively. The characteristic values of the end bearing capacity, as measured by the bi-directional O-cell and top-down load tests, were substantially higher than those calculated using the current highway bridge and culvert standards, showing increases of 133.63% and 86.15%, respectively. These findings suggest that the current standard formulas are overly conservative. Additionally, the measured values from the top-down load test may underestimate the actual bearing capacity of piles in engineering projects. Therefore, it is recommended that future pile foundation designs incorporate both bi-directional O-cell testing and combined post-grouting techniques to optimize design solutions.