Cyclic loads induced by environmental factors such as wind, waves, and currents can lead to degradation in pile performance, affecting settlement accumulation and bearing capacity evolution. This paper presents a comprehensive investigation through model tests focusing on a single pile subjected to static and cyclic loading in medium-dense sands. The influence of installation method, diameter, cyclic load amplitude, and loading frequency on pile response was explored, particularly emphasizing the accumulation pattern of pile head settlement and the evolving laws governing pile shaft and end resistance. The findings illustrate that the radial stress at the pile shaft 400 mm away from the pile end increases to 3.27 times its initial stress after pile jacking. As pile diameter increases, the accumulative settlement rate decreases, highlighting the soil-squeezing effect on cyclic stability. Small cyclic loads gradually densify soil around the pile end, increasing pile end resistance, while larger cyclic loads rapidly reduce both pile end and shaft resistance. Under high-amplitude, low-frequency cyclic loading, the load-settlement hysteresis characteristics of model piles intensify, with the hysteresis loops moving more rapidly in the deformation direction.

Shield tunneling adjacent to existing piles is common occurrence in subway construction. This study proposes a novel tunnel model capable of simultaneously simulating ground loss, unloading effects, and void grouting under in-flight conditions. Several three-dimensional (3D) centrifugal scale model tests are implemented in a silty-silty clay composite to investigate the response of a single pile (Test SP) and pile group (Test GP) with a sinking low cap subject to adjacent tunneling. The results indicate a critical influence area, i.e., 0.75D in front and 0.25D behind the centerline of the existing piles, is observed for the pile head settlement, in each test, and the induced bending moment in the piles above the tunnel spring line is more sensitive to tunneling than that below it. A decreasing trend in axial force along the pile shaft is observed in Test SP, whereas Test GP shows the opposite behavior. The maximum variations in axial force and bending moment occur near the tunnel invert and crown in Test SP, respectively, however, they all appear near the tunnel spring line in Test GP. There is a law of load transfer for downward migration in Test SP. In Test GP, however, the load on the upper part of pile P1 decreases and shifts to the lower of pile P1 and the whole pile P2. Subsequently, the load on the upper part of pile P2 reduces and transfers to the lower part of pile P2 and the whole pile P1. A significant increment in the earth pressure near the pile toe is observed. The pore water pressure increases slightly at first and then dissipates. Digital image correlation (DIC) has been preliminarily demonstrated as a valuable tool for visually capturing the progressive behavior of pile-soil interactions during in-flight tunneling, proving advantageous for analyzing tunnel-soil-pile interaction issues under centrifugation conditions.

Investigating the dynamic response and damage condition of variable- single pile in seismic subsidence site, taking Xiang'an Bridge as the engineering background, the dynamic response of variable- single pile under 0.10g-0.45g ground vibration intensity was investigated through large shaking table tests, and the damage degree was evaluated and analyzed. Results are as follows: Influenced by the seismic subsidence characteristics of the soil layer, the top horizontal displacement, acceleration, and bending moment of the variable- single pile tend to increase with the increase of vibration intensity, while the base frequency of the variable- single pile gradually decreases. The maximum bending moment of the variable- single pile occurs at the seismic subsidence soil stratum demarcation, where the ground shaking strength of 0.30g exceeds its flexural capacity. At a ground vibration intensity of 0.20g, the top horizontal displacement, acceleration, bending moment of the variable- single pile increase significantly, and the base frequency of the pile decreases abruptly. Based on the system damage theory, the damage condition of variable- single piles in seismic subsidence sites can be divided into three stages: stable stage, intensified damage stage, and plastic failure stage. At the end of the test, bending plastic damage occurred at the location of the variable section.

The scouring effect is widely acknowledged as a primary contributor to the weakening in the bearing performance of offshore piles; it often results in asymmetric scour patterns around the pile. To meticulously examine the impact of three-dimensional asymmetric local scour on the lateral bearing performance of a single pile, the Boussinesq solution is employed to determine the effective stress within the soil encompassing the pile, considering the presence of a three-dimensional asymmetric local scour hole. Utilizing the strain wedge model, the calculation method for the lateral bearing performance of a single pile under the condition of three-dimensional asymmetric local scour is established. The validity of this approach is established, and parameter analysis unveils the effect of varying sizes of three-dimensional asymmetric scour holes on the mechanical properties and displacement performance of a single pile. The analysis reveals that, as scouring dimensions around the pile escalate, the impact of scouring on single-pile lateral displacement and internal forces intensifies, leading to a decrease in the lateral bearing performance of a single pile. At a constant scour depth, the bottom area of the upstream scour hole significantly influences the displacement performance of a single pile. When the bottom length Swb1 of the upstream scour hole grows by 1 time, 4 times, and 8 times, the lateral displacement of a single pile at a buried depth of 6 m is augmented by approximately 0.41%, 1.65%, and 2.06%, respectively. The simplified model obtained via the modified strain wedge model and Boussinesq solution can provide a theoretical basis for the preliminary design of a single pile under asymmetric scour hole conditions.