Multiangle helical piles are used to support multidirectional loads. The load transfer behavior of inclined piles may differ from that of vertical piles. Vertical compressive and oblique uplift load field tests were conducted on a multiangle helical pile group and two single helical piles embedded in silty clay. The load-bearing capacities, group effects, load transfer behavior, earth pressure, and excess pore water pressure were investigated. The results show that the vertical compressive and oblique uplift capacities of the 10 degrees-inclined single helical pile were improved by 12% and 95% compared to those of the vertical single helical pile, respectively. The inclined installation of helical piles significantly optimized the load transfer mechanism of the piles under oblique loads. The group efficiency of the multiangle helical pile group was approximately 102%, attributed to the increased pile spacing resulting from the inclined installation. During loading, the helices and pile toe together contribute more than 50% of the bearing capacities of helical piles. The earth pressure and excess pore water pressure around the grouped helical pile, particularly near the bottom helix, exhibited less variation than those around the single pile, suggesting a smaller disturbance in the surrounding soil.

With the rapid development of urbanization and infrastructure construction, the requirements for the foundation design of high-rise buildings and large bridges are increasing. Pile foundations, as important supporting structures, are widely used in weak foundations and high-rise buildings. However, pile groups show significant advantages in bearing capacity, settlement control, and structural stability, while also bringing complex pile-soil interactions and group pile effects. Based on an FLAC3D numerical simulation (version 3.0), this paper constructs a pile group composite foundation model under different pile length conditions and analyzes the influence of pile-soil interaction on the group pile effect. The results show that pile length has a significant impact on the settlement and bearing capacity of the pile group composite foundation. When the pile length exceeds a certain critical value (23.4 m in this study), the interaction between piles is enhanced, the bearing capacity of the soil between piles is improved, the pile-soil stress ratio is reduced, and the overall settlement is effectively controlled. Moreover, there are obvious differences in settlement and stress distribution between pile group composite foundations and single-pile composite foundations, and the group pile effect can lead to greater settlement and more complex stress distribution. Therefore, when designing pile group composite foundations, factors such as pile length, pile spacing, and geological conditions should be fully considered to optimize foundation performance. This study provides a theoretical basis and reference for the design and optimization of pile group composite foundations, highlighting the importance of considering pile length and pile-soil interaction in practical engineering applications.

The effects on the upper masonry structure and the construction parameters of shield cutting piles were studied during shield construction, focusing on a shield interval of Zhengzhou Metro Line 5. The study utilized the actual engineering case of left and right double-lane shields superimposed on cutting cement soil group pile composite foundations beneath masonry structures. Findings revealed that masonry structures within approximately 30 m (5.0 times the tunnel diameter) were impacted before and after shield cut pile construction, resulting in deflection and twisting deformations of houses along the central axes of the left and right tunnel lines. Implementation of clay shock grouting outside the shield shell, radial grouting through small conduits, shield tail synchronous grouting, and secondary reinforcement grouting effectively mitigated the disturbance caused by shield construction to the ground. When shield cut piles passed beneath masonry structures, pressure on the soil chamber, total thrust, and cutterhead speed were consistently controlled. Furthermore, the cutterhead torque was appropriately reduced, and slurry injection volume increased, contributing to better control of house settlement.