Research on Bearing Mechanism and Key Construction Technologies of Bag-Encased Cast-in-Place Pile Foundations for Overhead Transmission Lines in Hard Rock and Highly Corrosive Regions

Jun Zuo; Yadong Ju; Wenshu Li; Xueyuan Bai

doi:10.54097/tvc6p630

Authors

Jun Zuo
Yadong Ju
Wenshu Li
Xueyuan Bai

DOI:

https://doi.org/10.54097/tvc6p630

Keywords:

Bag-encased cast-in-place pile; hard rock stratum; highly corrosive environment; physical isolation anti-corrosion; water injection and slurry discharge method; bearing characteristics.

Abstract

Overhead collector line projects for renewable energy frequently encounter special geological conditions where hard rock strata coexist with highly corrosive environments. Traditional foundation solutions exhibit significant limitations in construction efficiency, anti-corrosion durability, and economic viability. This paper systematically presents the technological principles of bag-encased cast-in-place pile foundations, revealing the bearing capacity and durability mechanisms arising from the synergistic integration of physical isolation anti-corrosion and efficient hole-forming and grouting. By analyzing the hydraulic expansion principle of the "water (slurry) injection and slurry discharge method," the key controlling factors for uniform expansion and tight adherence of the anti-corrosion bag against the borehole wall are elucidated. Based on engineering measurement data, pile bearing performance was verified through self-balanced load tests and low-strain integrity testing, with the ultimate vertical compressive capacity of single piles satisfying design requirements and all tested piles classified as Class I. Comparative economic analysis demonstrates that, compared with large open-cut foundations with anti-corrosion coating, rock-anchored pile foundations, and driven steel pipe pile solutions, the comprehensive cost of the proposed method is reduced by approximately 25%–39%, 35%–44%, and 72%, respectively, while the earthwork volume per foundation is reduced by over 90%. The research results indicate that bag-encased cast-in-place pile foundation technology effectively resolves the dual technical challenges of rapid hole-forming in hard rock strata and foundation anti-corrosion in highly corrosive environments, offering significant economic and environmental benefits. This technology provides a reliable technical solution for transmission line foundation engineering under similar geological conditions.

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