Helical Piles – Renaico – Mulchén transmission line.

Goals
In the Biobío region, in the Negrete commune 35 km from the city of Los Angeles, the construction of a wind farm consisting of 25 wind turbines is planned, which will be connected by 33 kV underground feeders to the new Rihue 220/33 kV substation. From the Rihue SE, the electric power will be conduction to the Renaico SE, to finally conduct it to the Mulchén SE, for which reason, the construction of a variant that allows a change of the conductor in the existing structure is necessary. Additionally, the capacity of the existing 1×220 kV PER – Mulchén transmission line will be increased and its arrival will be readjusted by connecting to a new panel in the existing Mulchén Substation.

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 for stay 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 an erratic arrangement of rock boulders (conglomerates). This condition made it difficult to implement a conventional anchoring system for the stay cables (winds) that contribute to the stability of the posts that constitute the variant, due to the execution times, complexity in the accesses and reuse of the material in different sections. Based on the particular needs of the project, a practical, efficient and economic anchoring system was required that would allow easy coupling with the stay cable system previously designed for the posts. This without neglecting the correct performance under tension, given that service loads of the order of 15 tons were presented in the direction of the respective stay cable. SOLUTION IN HELICAL PILE The helical piles were an excellent alternative to overcome the challenges imposed by the project and its conditions. The versatility of this foundation system allows for variations in the angle of inclination, achieving a collinearity with the ties and thus optimizing the reaction. 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.

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.