Study on Negative Friction of Long Short Pile Foundations in Loess Regions Considering Immersion

In the northwest region of China, collapsible loess is widely distributed, and its special geological characteristics have brought numerous challenges to the construction of foundation engineering. As a new type of foundation form, the research on long and short pile foundations in the collapsible loess area of the northwest is still in the initial and exploratory stage. In-depth exploration of the bearing characteristics of long and short pile foundations in the loess area under the water immersion state is of crucial significance for the safety and stability of engineering construction in this area. This paper adopts the effective stress method, fully considers the important factor of pore water pressure, and combines it with the load transfer method to construct a calculation method for negative skin friction of long and short pile foundations in the collapsible loess area. Through theoretical derivation and analysis, it can be known that the calculation method established has many unique features. It explicitly defines the soil surrounding the pile as unsaturated soil, on the basis of which the effective stress method and the load transfer method are organically integrated, and then a segmented curve model for calculating the negative skin friction of long and short piles under the water immersion state was established. The advantage of this model lies in its comprehensive and in-depth consideration of the influence of multiple factors (including pore water pressure, effective stress, and pile-soil relative displacement) on the mobilization of skin friction. To further verify the accuracy and reliability of this calculation method, the indoor model tests were conducted: the axial force, the lateral friction resistance, and the vertical displacement of pile foundation were compared. The results show that there is a good agreement between the theoretical and experimental results, proving that the calculation method proposed in this paper is reasonable and feasible. The achievement of this research result can provide a valuable reference basis for the pile foundation design work in similar collapsible loess areas, help improve the quality and safety of foundation engineering construction in these areas, and promote the further development and progress of engineering technology in related fields.