The selection of grouting methods and parameters significantly affects the improvement in the pile-bearing capacity of cast-in-place bored piles. This study proposes a comprehensive set of test methods for constructing model piles, performing grouting at the pile tip and pile side. A series of single-pile grouting and static load tests were conducted using these test methods. The results reveal that pile-side grouting is more effective in controlling pile settlement compared to tip grouting. Furthermore, tip-side-combined grouting exhibits superior reinforcement effects compared to the other two grouting methods. After grouting, a grout bubble is formed at the outlet, consisting of a compact diffusion zone internally and a split diffusion zone externally. Additionally, a vertical diffusion of grout occurs along the pile body, establishing a lateral friction resistance enhancement region. Within this region, the lateral friction resistance of the pile shows a negative correlation with the distance from the grouting outlet. The test results emphasize the significance of grouting volume and its impact on the bearing capacity, settlement control, lateral friction resistance, and grout bubble size in grouted piles, while the influence of variation in grouting pressure in a small range on bearing characteristics is not significantly apparent.

Pile tip post-grouting technology has been widely adopted in pile foundations to improve its bearing characteristics. Grouting in the pile tip leads to the grouting cement spreading along the pile body to a certain extent. To better understand the grout diffusion mechanism along the pile body returned, a total of 45 groups of laboratory model tests were carried out on sand, with different grouting pressures, grout volumes, and soil stress histories taken into account. By comparing the characteristics of the grouted bulbs, the grout diffusion mechanism along the pile body returned was revealed. Combined with the test results, a simplified model to describe the grout diffusion pattern and the corresponding grouting mode of grouting cement along the pile body returned during the process of pile tip post-grouting was proposed. This model can comprehensively reflect the grout diffusion characteristics along the pile body, with different grouting conditions and soil stress histories taken into account.

The interface shear behaviors between sand soil and concrete were analyzed considering the soil unloading and interface roughness effects by the direct shear tests. The analysis results show that the soil unloading has a negative effect on the difference in ultimate shear stress between the adjacent roughness. Regardless of the value of consolidation normal stress, the soil unloading effect can cause the ultimate shear stress decreased and the higher value of roughness corresponding to a higher decrease rate of it. The values of roughness and soil unloading degrees also have a negative effect on the residual ratio of interface shear strength f_r. The influence of roughness on the interface shear dilation can be suppressed with the increased of the applied normal stress and make the interface transform gradually into the shear shrinkage state. A new test evaluation method of the interface shear influence range is proposed and compared with the theoretical analysis results. The analysis results may provide a new research approach for revealing the shear mechanism of the sand-concrete interface.