# Study on Vertical Uplift Resistance Characteristics of Pre-Drilled Planted Piles in Boulder Strata
## 1 Introduction  
As urbanization accelerates and infrastructure construction rapidly develops, the demand for foundation reinforcement is increasing, particularly in land reclamation and rock dumping projects, where the frequency of boulders has risen, significantly impacting engineering projects [1, 2, 3]. Piling technology has been widely used due to its effectiveness in improving the bearing capacity and stability of weak foundations, as well as its minimal environmental impact during construction [4, 5, 6, 7, 8, 9, 10]. Traditional methods for dealing with boulders, such as avoidance, excavation, blasting, and multi-pile integration, are only suitable for situations with fewer boulders and are difficult to implement [11, 12, 13]. Past research on pre-drilled piles has primarily focused on settlement and deformation under vertical loads, with less emphasis on studies regarding uplift bearing capacity [14, 15, 16]. However, in geological conditions such as sandy soils, sand, or strata containing boulders, the uplift performance of piles tends to be significantly compromised. In boulder-stratum environments, the discontinuous pile-soil interface and the difficulty in mobilizing end-bearing resistance leads to a reduction in the anti-floating capacity of the pile foundation. Therefore, investigating the uplift characteristics of piles under these conditions can provide a scientific basis for engineering design, ensuring the reliability of pile foundations in such challenging geological environments. The geological conditions are complex, as traditional pre-drilled piles may fail to meet the bearing capacity requirements. Many scholars have investigated the use of pre-drilled piles to form rock-embedded piles or enlarged base piles to enhance bearing capacity [17; 18; 19]. [PERSON] et al. [20] conducted experimental studies using a half-space small-scale 1 g model and Particle Image Velocimetry (PIV) technology to examine the uplift behavior of enlarged base piles in layered strata. The results indicated that anchoring the pile base in deeper, stronger strata facilitates an increase in the pile's uplift capacity. In a study by [PERSON] et al. [21], through model tests, the uplift capacity of both open-ended piles and enlarged base piles in sandy soil was evaluated, and the experimental results showed that as the relative density of the sand increases, the uplift capacity of the enlarged base piles significantly improves. The study found that anchoring the pile base in deeper, stronger strata helps increase uplift capacity, and enlarging the base area of the pile also contributes to better load-bearing capacity. However, the above methods do not fully consider the influence of boulders and their potential load-bearing effects during the pile formation and construction processes. Considering that many laboratory tests are time-consuming, labor-intensive, and may lead to difficulties in data acquisition and limited reproducibility, many scholars [22; 23; 24] have adopted a research approach that combines laboratory tests with numerical simulations. FLAC3D and PFC3D each have their advantages in numerical simulations of pile foundations in geotechnical engineering. [PERSON] et al. [25] used FLAC3D to numerically simulate the cement-soil mixing pile composite foundation, verifying that FLAC3D 7.0 is suitable for handling large deformations and nonlinear problems. [PERSON] et al. [26] employed the discrete element analysis software PFC3D 6.0 to investigate the pile-soil-cap interaction problem related to the pile cap effect, observing the micromechanical mechanisms of granular materials. [PERSON] et al. [27] conducted laboratory tests to study the bearing capacity of offshore wind turbine piles and then used PFC3D numerical simulations to establish models corresponding to the laboratory tests, validating their microparameters. The simulation results were in good agreement with the laboratory test results, accurately reflecting the interaction between the pile and clay during the shearing process.