## 1 Introduction  
A composite foundation refers to an artificial foundation formed by replacing or enhancing part of the natural soil in the reinforcement treatment of the natural foundation. However, after a manual treatment, how to ensure that the reinforcement body and natural soil can jointly bear the load directly under the applied force remains a topic deserving of further investigation. Therefore, analyzing the load transfer route and law under a load can provide a better understanding of the essence of composite foundations [1, 2]. The existing research methods for the load-carrying mechanism of composite foundations mainly include theoretical analyses, numerical simulations, and model testing. In terms of theoretical analyses, based on the deformation coordination conditions of the internal piles and soil in composite foundations, as well as the constitutive models of piles and soil, relevant research on the internal deformation and mechanical properties of composite foundations can be conducted. Previously, [PERSON] considered the force mechanism of rigid pile-based composite foundation piles and soil with cushion layers. By observing the settlement law of piles and soil in composite foundations under vertical loads, a deformation coordination equation was derived for composite foundations, and the stress of the piles and soil was iteratively obtained [3]. [PERSON] considered the deformation coordination relationship between piles and soil in the tangential and vertical directions, and analyzed the consolidation deformation of three-dimensional composite foundations using the effective stress method [4]. However, it is undeniable that theoretical analysis methods have certain limitations, such as difficulties in considering the effects of seismic factors on the additional settlement of composite foundations and the seismic response of composite foundations. The use of numerical simulation methods can effectively address these issues [5; 6]. This is because the use of a limited number of correlated elements to simulate the geometric model of composite foundations simplifies complex engineering problems, shows significant advantages in solving problems with complex boundary conditions, and makes conducting a sensitivity analysis of the load-carrying capacity characteristics and parameters of composite foundation piles more convenient and reliable [7; 8; 9]. In addition, by considering the interaction model between piles and soil and analyzing the settlement characteristics of internal piles in composite foundations, the finite element method can provide good solutions [10]. Often, in order to control the main target parameters and facilitate comparative experiments, model tests on composite foundations are necessary. Through model tests, we can not only understand the working mechanism of different types of composite foundations, including the working mechanism of long- and short-pile composite foundations [11; 12], but also analyze the load transfer mechanism, deformation, and settlement laws of different types of composite foundations [13; 14; 15; 16]. In some cases, the combined use of numerical simulations and experiments can provide a more comprehensive study of composite foundations. For example, [PERSON] et al. first calculated the corresponding pile material parameters through a numerical simulation and then studied the settlement and stress of lightweight composite foundations through model tests in order to explore feasible solutions for treating soft soil foundations with lightweight piles [17]. Existing studies have shown that, under upper loading and due to the influence of group pile effects, the stress characteristics of the central pile differ from those of other pile locations. Specifically, the axial force and displacement of the central pile are most affected by other piles, while piles farther away from the central pile are least affected by others [18; 19].