In order to investigate the diffusion mechanism of slurry in post-pile grouting, this study develops a formula for calculating the diameter and the climb height of the cement core of jet grouting (CCJG). This research conducts field orthogonal tests using a self-developed grouting nozzle to analyze the effects of disturbance pressure (DP), disturbance time (DT), grouting pressure (GP), and the water–cement ratio (W/C) on the dimensions and strength of the CCJG. The findings revealed that the theoretical formula for calculating the diameter of the CCJG deviates by approximately 8% from the field test results, confirming the formula’s validity. In addition, the DP and DT significantly influence the volume of the CCJG, displaying a linear increase with their augmentation. Conversely, the W/C and DP predominantly affect the CCJG’s strength. Notably, an increase in the W/C results in diminished strength, whereas an increase in the DP enhances it. In addition, soil reinforcement is achieved through replacement, mixing, and compaction as the grout flows outward from the center of the grouting hole. These insights offer a theoretical foundation and technical support for effective grouting construction practices.

Conducting a reasonable assessment of whether the durability and bearing capacity of concrete used in existing bridge pile foundations can meet all requirements is an important prerequisite for ensuring the reuse of existing bridge pile foundations. With this in mind, this study evaluates the project of the Beijing–Taibei Highway in Shandong Province that must be restored and enlarged. Using static load and concrete durability testing methods, the bearing capacity characteristics and durability of seven existing bridge pile foundations were investigated. Using attribute identification theory, a systematic technique for determining the reuse value of existing piles is proposed. The test examination findings demonstrate that the change curve corresponding to the pile foundation’s ultimate bearing capacity matches the concrete compressive strength curve. The pile foundations had lower ultimate bearing capacity than average. The concrete compressive strengths of the three test piles were 18%, 16.3%, and 17.5% lower than the average compressive strengths of the seven test piles. A comprehensive durability evaluation method for assessing existing piles can effectively evaluate the reuse value of existing piles and promote sustainable highway reconstruction and expansion projects.