###### Abstract  
This study proposes a new form of underground diaphragm wall foundation with hexagonal sections, called the grid pile foundation (GPF), which is used for long-span bridges. To investigate the lateral bearing capacity characteristics of the integrated pile foundation, the quasi-static test as well as numerical simulations were conducted. Firstly, the quasi-static test was conducted to obtain the lateral load-displacement curve, the soil pressure distribution, and the deformation and stress distribution of the pile foundation and the surrounding soil. Then, the finite element model of the proposed GPF foundation was built, which was verified and calibrated based on the test data. Finally, the parametric analysis was performed to investigate the effects of soil friction angle, pile foundation Young's modulus, and pile length on the lateral bearing capacity characteristics of the proposed GPF. It is concluded that the GPF would transition from the stiffness stage to the plastic strain stage under lateral load, and deformation occurred simultaneously. The stress in the soil around the pile foundation is high in the upper portion and low in the lower portion, and the active and passive failure zones of the soil are formed under the action of the GPF. Both experimental and numerical simulations indicate that the GPF has a good lateral load capacity, and the lateral load capacity is most affected by the length of the piles. The GPF is expected to provide a new solution to the construction of large-span bridges with diaphragm wall foundations. underground diaphragm wall foundation; lateral load capacity; quasi-static test; numerical simulation +
Footnote †: journal:  
0000-0001-6500-7999-3399-3999 pile foundation followed an exponential distribution along the depth, while the external frictional resistance approximately followed a triangular distribution along the depth. [PERSON] et al. [16] conducted vertical load model tests on rectangular closed-loop underground continuous walls to study the load distribution of the foundation slab. It is found that the maximum soil reaction is located at the corners of the slab. [PERSON] et al. [17] performed lateral static load tests on single-hole closed-loop walls with different cross-sectional sizes to study the lateral load-bearing characteristics of closed underground continuous wall foundations. Although significant progress has been made in the research on the load-bearing characteristics of underground continuous wall foundations, the current studies mainly focus on the vertical load-bearing capacity of rectangular grid-type foundations [18; 19; 20; 21; 22; 23]. There is relatively less research on the lateral load-bearing characteristics of underground continuous wall foundations with irregular cross-sections. Irregular cross-section underground continuous wall foundations possess advantages such as high overall stiffness and uniformity and offer convenient construction. Furthermore, they can be adjusted and combined to form composite sections with enhanced applicability, as shown in Figure 1, meeting practical engineering requirements for large-span bridges [24]. In light of this, this paper presents a novel underground continuous wall foundation with a hexagonal cross-section called the grid pile foundation (GPF). The objective is to investigate the lateral load-bearing characteristics of the GPF by conducting quasi-static tests to analyze the force-displacement curves, distribution, and variation of soil pressure on the foundation soil under lateral loading. Subsequently, the accuracy of the finite element model is validated using experimental data. Furthermore, a parametric analysis is performed to study the influence of variations in soil friction angle, pile modulus of elasticity, and pile length on the lateral load-bearing characteristics of the GPF. The lateral stiffness of the proposed GPF was compared with widely used pile foundations.