OBJECTIVE
In the Biobío Region, in the municipality of Negrete, 35 km from the city of Los Ángeles, the construction of a wind farm is planned. This farm will consist of 25 wind turbines connected via 33 kV underground feeders to the new Rihue 220/33 kV substation. The plan is to transmit electrical energy from the Rihue substation to the Renaico substation, and finally to the Mulchén substation. Therefore, a bypass is required to allow for a conductor change in the existing structure. Additionally, the capacity of the existing 1×220 kV PER – Mulchén transmission line will be increased, and its connection will be upgraded to a new bay at the existing Mulchén substation.
AXIATECH was contracted by EIFFAGE, the company responsible for the project’s development, to carry out the engineering, supply, and construction of the structural foundations and connection elements between the foundations and anchor cables.
Given the technical challenges posed by the project’s typology and geographic location, a state-of-the-art and best practice investigation into foundation design was conducted. This resulted in the selection of helical piles as the most advantageous technical and economic option for constructing the project’s foundations.
Project Overview
- Location: Mulchén, Region X – Chile
- Application: Conduit relocation project
- Pile Length: 1331 linear meters – OD3.5X0.3-YS80
- Scope: Design, Supply, and Installation
- Soil: Sedimentary and alluvial deposits
- Installation Time: 90 Working Days
Helical Piles as Anchorage for Guy Wires on Retaining Posts: A Conventional Solution
The geological context of the project area is located on the transition between an igneous rock weathering profile and sedimentary deposits of sandstone and siltstone. Additionally, there are alluvial deposits associated with paleochannels with erratic rock boulders (conglomerates). This condition complicated the implementation of a conventional anchorage system for the guy wires that contribute to the stability of the posts, due to construction time, access challenges, and the need to reuse materials in different sections. Based on the specific needs of the project, a practical, efficient, and economical anchorage system was required that would allow for easy connection to the previously designed guy wire system for the posts. This had to be achieved without compromising proper tensile performance, given that service loads of approximately 15 tons were present in the direction of the respective guy wire. HELICAL PILE SOLUTION Helical piles were an excellent alternative to overcome the challenges posed by the project and its conditions. The versatility of this foundation system allows for variations in the angle of inclination, achieving collinearity with the tie rods and thus optimizing the reaction. Likewise, the load transfer mechanisms allow for behavior similar to compression and tension, meeting the project requirements with pile lengths between 4 and 6 m per tie rod.
The challenge of the project to implement helical piles holistically lay in the coupling system between the pile head and the tie rod. To overcome this technical obstacle without increasing the project’s schedule and budget, a fastening system was designed, supplied, and installed for both single and double tie rod supports. Ultimately, adherence to the schedule and the piles’ performance, as demonstrated by tensile load tests, validated this foundation alternative as the optimal solution from a technical and economic standpoint.
Helical piles are the ideal solution for transmission line foundations… A.B. CHANCE – Hubbell Foundation, a world-leading manufacturer of helical piles, with over 100 years of experience and a proven track record in foundation engineering solutions using helical pile technology.
