PSI - Issue 72

G. Gusev et al. / Procedia Structural Integrity 72 (2025) 464–469

465

Many structures are built on pile foundations, which also experience the effects of seasonal soil freezing and thawing, as shown by Guan et al. (2022). The element of such a foundation is the single pile, provides contact with the soil. A considerable number of works is devoted to studying the interactions in the pile – soil system. For example, certain analytical solutions are presented by Gao et al. (2017), Cui et al. (2023), Wu et al. (2022), and Lu et al. (2014). Numerical methods are also used to estimate the dynamic response of the pile in the works by Ai and Li (2015), Liu et al. (2021), and Ma et al. (2022). Furthermore, analyzing the natural oscillations of a pile with various attached masses can be used to estimate properties of the surrounding soil, as shown by Gusev et al. (2024). Studies of pile behavior in frozen soils can be found in works by Chen et al. (2012), Xiao et al. (2018), and Yang et al. (2023). The study of the performance characteristics of boring piles is presented in the article by Aksenov (2014). Investigation of deformation processes in the pile –soil system during the soil’s transition from the frozen state and back again (the freezing or thawing process) is of considerable interest. This work is devoted to field experiments on the dynamic response of a pile installed in soil that is undergoing natural freezing. It should be noted that, because of the nonlinear behavior of soils over a wide range of parameters, the response of the pile – soil system can also be nonlinear, which creates additional challenges.

Nomenclature f

frequency

ω f n

angular frequency natural frequency

ω n

natural angular frequency

α ς

decay rate

damping ratio

2. Experimental setup The subject of this study was a single pile embedded in a soil mass that freezes under natural environmental conditions. The soil is a sandy loam. The experiment consisted of periodically measuring the dynamic response of the “pile–soil” system to both amb ient background excitations and impact excitations from an actuator, and then estimation of evolutionary changes in the system’s dynamic parameters. In autumn, while the ambient temperature was above 0 degrees Celsius, a 1.5-meter screw pile was installed in the soil at a depth of about 1.15 m. The pile is a steel tube with the following dimensions: length 1.5 m, outer diameter 0.057 m, wall thickness about 3 mm, and a total mass of approximately 6 kg. The portion of the pile extending above the ground surface was about 0.35 m high. A steel plate measuring 0.2 × 0.2 m was rigidly attached to the pile head. Three metal disks (masses) were fastened to this plate, with diameters of 0.285, 0.250, and 0.205 m; heights of 0.067, 0.057, and 0.055 m; and masses of 9.3, 5.9, and 3.7 kg, respectively. The top of the pile, along with the on masses and equipment, was sealed off to protect against moisture (rain and snow). During the winter experiment, the above- mentioned parameters of the “load–pile” system were mainta ined: the soil around the pile was cleared of snow and ice, and the protective shell over the load was in place. Thus, the mass of the load and the geometry of the system did not change over time. Fig. 1(a) shows the schematic of the object, indicating the location where the impulse force (Fact) from the actuator was applied, as well as the location of the accelerometer, which was mounted at the top of the structure. The location of the applied force was chosen so as to excite bending modes of vibration, and the direction of the applied force coincides with the sensor’s x -axis. The actuator is a DC electromagnetic solenoid with a spring-loaded plunger that imparts an impact to the pile. The impulse load was generated by briefly passing current through the solenoid coil via a relay connected to a power supply. The relay was driven by a Raspberry Pi 3b+ single-board computer, which also recorded the signals from temperature and vibration sensors.