Helical Piles – Renaico – Mulchén Transmission Line
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, consisting of 25 wind turbines that will be connected via 33 kV underground feeders to the new Rihue 220/33 kV substation.
Objective
From the SE Rihue, the projection of electrical energy transmission to SE Renaico is planned, eventually leading to SE Mulchén. Therefore, the construction of a variant is required to enable a conductor change in the existing structure. Additionally, the capacity of the existing transmission line 1×220 kV PER – Mulchén will be increased, and its connection to a new section at the existing Mulchén Substation will be reconfigured.
AXIATECH was requested by EIFFAGE, responsible for the construction development of the project, to execute the engineering, supply, and construction of the foundations for structures and the connection elements between the foundation and anchor tendons.
Given the technical challenges that the project typology and geographical location required, it was necessary to conduct a state-of-the-art research and best practices review in foundation engineering. This resulted in the selection of helical piles as the most advantageous technical and economic choice for the foundation construction of the project.
Project Overview
• Location: Mulchén, X Region – Chile
• Application: Conductor change variant
• Pile: 1331 linear meters – OD3.5X0.3-YS80
• Scope: Design, Supply, and Installation
• Soil: Sedimentary and alluvial deposits.
• Installation: 90 Business Days
Helical piles as anchorage of stay cables on retaining posts
CONVENTIONAL SOLUTION
The geological context of the project area is located on the transition of a weathering profile of igneous rock and sedimentary deposits of sandstone and siltstone. Additionally, there is the presence of alluvial deposits associated with paleochannels with erratic arrangement of rock balls (Conglomerates). This condition made it difficult to implement a conventional anchoring system for the stays (winds) that contribute to the stability of the posts that make up the variant, due to the execution times, complexity of the accesses and reuse of the material in different sections. Based on the particular needs of the project, a practical, efficient and economical anchoring system was required that would allow easy coupling with the brace system previously designed for the posts. This without neglecting the correct tension performance, given that service loads of the order of 15 Ton were presented in the direction of the respective tie rod.
SOLUTION WITH HELICOIDAL PILES
Helical piles were an excellent alternative to overcome the challenges imposed by the project and its conditions. The versatility of this foundation system allows variations in the angle of inclination, achieving collinearity with the ties and thus optimizing the reactions. Likewise, the load transfer mechanisms allow a behavior similar to compression and traction, managing to meet the project requests with pile lengths between 4 and 6 m per tie rod.
The challenge of the project to implement helical piles holistically was in the coupling system of the pile head and the tie rod. To technically overcome this obstacle without increasing the project schedule and budget, a fixing system was designed, supplied and installed for both the single and double brace supports. Finally, compliance with the schedule and the performance of the piles through the execution of tension load tests validate this foundation alternative as the optimal solution from the technical-economic point of view of the project.
Helical Piles are the appropriate solution for foundations in transmission lines… A.B. CHANCE – Hubbell Foundation World leading manufacturers in the manufacture of helical piles, with more than 100 years of experience and history in foundation engineering solutions applying helical pile technology.
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