The study on the uplift bearing characteristics of variable diameter micro pile foundation for mountain transmission towers

Abstract

[Objective] Due to the complex conditions in deep canyon areas, the pullout capacity of micro-pile foundations configured with small-diameter towers in power grid projects is insufficient. The use of tapered micro-piles, which combine traditional micro-piles with varying diameters, may be an effective solution to enhance pullout resistance. This approach aims to improve the pullout performance while offering greater cost-effectiveness. [Methods] Five groups of indoor model tests were conduceted to comparatively analyze the load-bearing characteristics of traditional micro-piles and tapered micro-piles in sandy silt. It also examined the relationship between tapered arrangements and the load-bearing mechanisms of tapered micro-piles. Furthermore, numerical simulations were employed to reveal how various structural parameters of the tapered design and soil properties affect the vertical load capacity of tapered micro-piles. [Results] The result indicated that the load capacity and material efficiency of tapered micro-piles exceed those of conventional micro-piles by over two times, with displacements under ultimate loads significantly greater than those of traditional micro-piles. Additionally, the group effect of tapered micro-pile groups was enhanced, and under uplift loads, different parts of the pile experienced varying load distributions, with the role of enlarged heads becoming increasingly prominent, carrying more than 50% of the load. [Conclusion] The influence of different tapered structural parameters on the vertical load capacity of the pile foundation varied with changes in the enlarged head and side friction resistance. For practical applications, it is essential to optimize the design parameters rationally, as tapered micro-piles demonstrate greater advantages in the treatment of high-strength foundation soils.

Keywords

load sharing ratio / variable diameter micropiles / model tests / numerical simulations / enlarged head / side friction resistance of piles