# Study on Disturbance Mechanism of Squeezed and Non-Squeezed Soil Piles on Soft Soil Foundation
## 1 Introduction  
Soil disturbance caused by pile installation could have significant negative effects on existing engineering structures. High-speed railway, for example, has extremely strict requirements on the deformation of soil foundation. Pile penetration near high-speed rail lines will destabilize the soil mass, thus ruining the subgrade of nearby railways [1]. The characteristics of foundation soil often determine the magnitude of foundation disturbance, with the most severe and complex problems usually occurring in soft soil strata. For instance, in economically developed regions with high-speed railway networks in centraland southern China, soft soil is particularly distributed widely, posing a great threat to the running trains. In this situation, it is essential to conduct an accurate and overall evaluation of the disturbance mechanism of squeezed and non-squeezed soil piles on soft soil foundations. The most prevalent method for reinforcing the soft soil foundation is installing piles [2; 3]. Hydrostatic piles, bag grouting piles, and bored piles are mostly adopted for construction. These piles can be classified based on whether the piles would squeeze the surrounding soil during construction. The former two are classified as squeezed soil piles, while the bored pile is classified as a non-squeezed soil pile. As soft soil is a saturated porous medium, the pile driving process usually occurs in unconsolidated and poorly drained soil conditions. If the volume change of soil around the pile is not evident after being squeezed, significant lateral squeezing effects and excess pore water pressure will be generated, resulting in horizontal displacement and vertical uplift of soil [4; 5]. Non-squeezed piles refer to piles that remove soil of the same volume as the pile body during the driving process while leaving the soil around the pile not compressed. A bored pile is a representative example of such type, whose disturbance to the soil is primarily caused by the radial unloading effect [6; 7; 8]. Despite advances in the study of the individual disturbance impact of squeezed and non-squeezed soil piles, the optimal problem of which pile to choose for construction has been unsolved, especially for the soft soil foundation. Quantification of soil disturbance, such as displacement field, stress field, and disturbance range during pile driving is crucial for a comprehensive investigation of the disturbance effects of pile formation on the soil. On-site experiments [9; 10; 11; 12], model tests [13; 14; 15; 16], analytical solutions [17; 18; 19; 20], and numerical simulations [21; 22; 23; 24] have been carried out to investigate the effect of pile driving on soil disturbance. However, in terms of on-site experiments, current research is limited to the non-visibility of soil and embedded monitoring [9]; the obtained test results are not the entire displacement field, but rather local discrete points, which also affect the accuracy of the results. With the development of image processing technology, some scholars have conducted model tests to visualize and analyze the two-dimensional deformation field of soil during the piling process. Nonetheless, model tests are limited to the surface and boundary of the model and cannot capture the deformation characteristics inside the soil foundation. Visualization technologies, such as X-ray imaging and CT scanning, can observe the disturbance degree from a microscopic view, although the cost is rather high. Additionally, an analytical solution is a significant mathematical method with high accuracy and strong interpretability; however, its applicability is usually limited as the established mathematical models are usually idealized. In contrast, numerical simulation is an effective and economical method that has been widely used for modeling and simulating pile installations. It provides significant advantages in visualizing the spatiotemporal response characteristics of soil displacement and stress fields, as well as quantifying the soil disturbance caused by pile driving.