## 1 Introduction  
The limited land available for construction in northwest China has constrained the sustainable development of the region. In order to solve the problem of insufficient land for construction, the development and expansion of underground space has become an effective way to solve the problem, but this has also given rise to many complex foundation pit projects at the same time. [1]. A deep foundation pit is a complex high-risk system, the engineering of which is performed in a multi-phase and multi-field manner, composed of structure, soil and groundwater. It involves the stress path during excavation and unloading of soil, which is closely related to the nature of the soil body [2, 3]. However, the current theories and methods of foundation pit design are only based on component design, and the experimental research is also based on field test. Restricted by the factors such as site construction conditions and project attributes, field tests sometimes failed to comprehensively test and analyze the stress characteristics of the support structure. Therefore, the indoor model test research can make up for the insufficiency of the field test and can qualitatively analyze the mechanical characteristics of the support structure. There are many scholars who have carried out a lot of research on the model test of foundation pits. [PERSON] [4] studied the bending moment and earth pressure of passive piles subjected to horizontal force through model tests, believing that the bending moment curve of passive piles changes with the distance between the pile and the load boundary and intersects at the lower part of the pile. [PERSON] [5] simulated the excavation process of the foundation pit through the photoelastic test and studied the force chain and its variation characteristics of the soil around the foundation pit. [PERSON] [6] conducted a 1:30 indoor model test of foundation pit excavation. He obtained the earth pressure distribution, the horizontal displacement of the wall and the settlement law behind the wall, which were verified by finite element method. [PERSON] [7] derived the generalized effective stress principle, which differs from the classical effective stress principle in that the model can automatically take into account the effects of stress paths, temperature paths, and soil structure. [PERSON] [8] studied the influence of foundation pit excavation and construction on adjacent existing buildings and surrounding soil through model tests; he discussed the horizontal and vertical displacements of the adjacent buildings, the earth pressure around the foundation pit and the variation law of the existing building foundation under different parameters. [PERSON] [9] used a large model box to simulate the whole process of underground space excavation and studied the influence of several parameters on the h-shaped support system with double-row piles. The test results showed that significant load transfer effects were generated between the rows of piles and that increasing the row spacing within a certain range could result in a more reasonable distribution of bending moments and pile forces. [PERSON] [10,11] studied the influence of local anchor failure on the soldier pile support system through an indoor model test system. They clarified the mechanism of the continuous failure of the foundation pit and proposed an active, real-time, targeted deformation control method. [PERSON] [12] studied the evolution of supporting structure performance and earth pressure through large-scale model tests. [PERSON] [13] studied the synergistic deformation of a combined structure of high-fill slopes through model tests, which was composed of a pile-anchor and reinforced soil. [PERSON] [14], [PERSON] [15] and [PERSON] [16] studied the bearing and deformation characteristics of axially loaded piles and horizontally loaded piles, respectively, through indoor model tests.