# Model Experiment Study on Vertical Bearing Characteristics of Large-Diameter Ring Piles
###### Abstract  
The hollow structure of large-diameter ring piles (LDRPs) reduces the amount of concrete used, is economically efficient, and reduces the weight of the pile. However, its bearing characteristics and safety performance are still not fully known. In this study, to determine the properties of the LDRP structure, a combination of the indoor scale model test and numerical simulations was used, and a new parameter, \(K\), which is the thickness-to-diameter ratio, was introduced. A comparative study of LDRPs with different hollow ranges was conducted. The results show that for a value of \(K\) in the range of 0.2-1, the ultimate bearing capacity of LDRPs is not significantly different from that of large-diameter solid piles (LDSPs), and they can ensure sufficient safety reserves. Under ultimate bearing capacity, the strain on an LDRP is large, but it does not exceed its own material strength, and the strain variation law is similar to that of a solid pile. LDRPs show the characteristics of end-bearing piles, and concrete savings can reach up to 50% for \(K\) in the range of 0.2-1.  
model experiment; thickness-to-diameter ratio; large-diameter ring pile; bearing characteristics +
Footnote †: journal: Applied  
[PERSON] (2020) [1] and [PERSON] et al. (2020) [2] combined numerical simulation experiments, theoretical analysis, and field measurement to show the superiority of large step-tapered hollow piles and proposed the analytical solution for this pile foundation settlement. [PERSON]'s (2019) [3] research on large-diameter hollow composite piles shows that the bearing capacity of large-diameter hollow composite pile foundations is 19.1% higher than that of solid pile groups with the same side area. In addition, in terms of seismic performance, [PERSON] (2011) [4] demonstrated that hollow piles are superior to solid piles by comparing the deflections, rotation angles, bending moments, and shear forces of hollow piles and solid piles with the same cross-sectional area. In the field of pile foundation, the most important things are its settlement law and load-transfer mechanisms, but most of the research is based on large-diameter solid piles. For example, [PERSON] (2017) [5] proposed a practical algorithm for the bearing capacity of large-diameter pile ends based on displacement control and the Mindlin solution for the load stress distribution in the semi-infinite space. This method considers the belled diameter, embedded depth, thickness of the bearing, and soft substratum. The calculation results of the influence of physical and mechanical properties on the bearing capacity are consistent with the actual project. [PERSON] (2018) [6] studied the longitudinal coupling vibration of large-diameter end-bearing piles in saturated soil and analyzed the influence of the pile slenderness ratio on the transverse inertia effect of piles based on the saturated soil theory proposed by [PERSON] and the Rayleigh-Love rod, considering the transverse inertia effect. The results show that the transverse inertia effect should be considered in the low-strain integrity test of large-diameter piles, and the Poisson's ratio, slenderness ratio, and pile-soil modulus ratio have a significant effect on the transverse inertia effect of large-diameter piles, while the seepage force of saturated soil has little effect. To meet engineering needs, considering the transverse inertia effect of large-diameter piles is a necessary condition. Taking the load-transfer curve of large-diameter single piles as the object, [PERSON] (2020) [7] quantified the relationship between pile diameters and their bending stiffness in sand and established a relationship with the p-y curve for lateral load. With an increase in pile diameter, the correction of the p-y curve is mainly related to the change in the soil deformation mechanism around the pile. The influence of surface friction, foundation shear force, and foundation moment of large-diameter piles on the p-y curve was almost negligible.