# Study on the Influence of File Installation Disturbance on the Settlement of Composite Foundation
## 1 Introduction  
Composite foundation is a practical and effective method for treating soft foundations. However, the pile installation process can cause structural damage to the soil surrounding the pile, resulting in a significant increase in pore pressures, a degradation in the strength and modulus of the soil [1, 2, 3]. Especially in low subgrade, the settlement caused by the load is even less than the settlement caused by the reconsolidation of the soil around the piles. For instance, it was reported that, under a vertical load of 500 kN, the settlementcaused by the reconsolidation of the soft clay around jacked pile accounts for 5/7 of the total settlement [4]. Moreover, the method of pile installation has a significant impact on the settlement [5; 6; 7; 8]. [PERSON] et al. reported that in sandy soil foundations, the settlement response of non-displacement piles under the same load is only 1/10 to 1/2 that of driven piles [9]. Therefore, determining the impact of the pile installation process on settlement is of great significance for subgrade quality control and cost savings. Settlement changes caused by pile installation disturbances are commonly discussed in research on the variations in stress and displacement of the pile and the surrounding soil. Common research methods include analytical solutions, numerical simulations, model tests, and full-scale tests. The analytical solution is to solve the settlement by establishing a coordinated equation of pile-soil interaction. Pile installation causes high pore water pressure around the pile, which, when dissipated, leads to further consolidation of the soil around pile. Under the action of negative skin friction, this results in additional settlement of the pile. Based on the analytical solution method, scholars have studied the characteristics of pile-soil interaction for various types of piles, including jacked piles [4], circular piles [10], and XCC piles [11]. In terms of model testing, strain gauges are attached to the model pile, or stress meters are embedded in the soil layers to record changes in the stress field. Digital image correlation (DIC) was employed to document variations in the displacement field [12]. To enhance visibility of these changes, transparent soil was utilized as an alternative to conventional soil [13]. Through selecting appropriate models and parameters, numerical simulation methods can efficiently implement comparisons of displacement fields and stress fields for different types of piles. For instance, [PERSON] et al. simulated the installation of three pile types, finding that the peak soil horizontal deformation occurs at the surface with normalized values of 15.2 for static pressure piles, 7.5 for bag grouting piles, and 1.1 for bored piles [14]. Additionally, the numerical simulation method is also capable of accounting for the effects of other factors, such as soil layers [15]. In-situ test results excel in authenticity and reliability, and test designs based on standard testing methods are commonly recognized. For example, [PERSON] et al. discovered that the increase in pore-water pressure caused by high-frequency vibratory pile driving extends to a range of approximately 3.6 times the pile diameter [16]. Research by [PERSON] et al. indicates that both the soil pressure and the maximum lateral displacement caused by PGP pile construction are approximately half of those caused by driven piles [17]. [PERSON] et al. measured the base residual stress and found that the installation process of driven precast piles causes greater disturbance compared to driven cast-in-situ piles and screw injection piles [18]. In summary, settlement caused by pile installation should not be overlooked, and the piling method is one of the key factors influencing settlement.