## 1 Introduction  
Cast-in-place bored pile foundations are extensively utilized in the construction of high-rise buildings, highways, and large-span bridges due to their numerous advantages, including simplified construction process, minimal noise, adaptability to different soil layers, flexible selection of length-diameter ratio, and high load-bearing capacity [1; 2; 3; 4]. However, during construction, sedimentation on the pile bottom and the formation of slurry cake can have adverse effects on the bearing capacity of bored piles. To address these challenges, post-grouting has emerged as a common practice in practical engineering [5; 6; 7]. Post-grouting technology involves injecting cement-based grout as the primary agent into the pile tip or adjacent soil through grouting pipelines, once the concrete forming the pile body reaches a specific level of strength. This process, known as pile post-grouting, effectively pressurizes the grout, thereby improving the overall performance of the piles [8; 9; 10]. Post-grouting methods generally encompass three forms: tip grouting, side grouting, and tip-side combined grouting. Tip grouting significantly enhances the mechanical properties of the weak layer at the pile bottom, mitigates the effects of sedimentation, and improves the pile-tip bearing capacity. Side grouting primarily fills the weak surface between the pile and soil, enhancing the shear performance of the surrounding soil and increasing the lateral friction resistance of the piles. Combined grouting exhibits characteristics of both methods [11; 12]. Since its initial application to bridge pier pile foundations in the last century [13], post-grouting technology has been subject to extensive research in the field of pile foundations. These studies have focused on several key aspects: (1) grouting technology research, which constituted a significant research direction in the early stages. This line of inquiry encompassed investigations into various aspects, such as different grouting positions, grouting devices, and grouting methods [14; 15; 16]. (2) Field test research, which is the most prevalent method employed to study post-grouting technology. Field tests provide accurate data on the bearing characteristics of piles and the physical and mechanical properties of soil layers. Notably, [PERSON] and [PERSON]'s post-grouting tests in sandy and cohesive soil [17] demonstrated that post-grouting can increase the tip-bearing capacity of large-diameter bored piles threefold. [PERSON]'s pile side grouting test [14] revealed that grouting can ameliorate soil stress relaxation resulting from drilling, leading to a 2.5-fold increase in side friction resistance. [PERSON] et al. 's field tests on three large-diameter super-long rock-socketed piles [5] demonstrated that combined grouting can enhance side resistance, tip resistance, and ultimate bearing capacity by 34-179%, 111-180%, and 113-138%, respectively. (3) Model test research, offering greater flexibility in experimental design and lower implementation costs compared to field tests. Model tests are typically conducted to investigate the bearing characteristics of grouted piles in specific soil layers or validate new grouting methods [2; 6; 7; 9; 18; 19]. (4) Numerical simulation research, which is primarily employed to study complex real-world conditions and verify test results. However, due to the challenges associated with accurately simulating the grouting effect, this approach is relatively less utilized [18; 20; 21]. (5) Grout diffusion research, encompassing investigations into the rheological and diffusion characteristics of cement grout, as well as the diffusion range in post-grouting [22; 23; 24; 25; 26; 27; 28; 29]. (6) Theoretical research, primarily involving the establishment of models to analyze the reinforcement mechanism of grouting and the load transfer mechanism of grouted piles [30; 31; 32; 33].