IMPLEMENTATION OF A SUBSTATION ON A CONCRETE SLAB SUSPENDED BY HELICAL STEEL PILES - AFUÃ CASE STUDY - MARAJÃ“ ISLAND - PARÃ

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The case study presents the foundation solution for a 34 kV substation in Afuá, on Marajó Island, Pará, Brazil. The remote, permanently flooded site has no road access and can be reached only by river or small aircraft, making transport of heavy construction equipment difficult.<br /><br />The ground consists of thick deposits of extremely soft organic clay, with very low strength, high compressibility, and near-zero SPT values. These conditions create substantial risks of settlement, differential movement, and instability. Substation equipment is particularly sensitive to such movement, while wind can also impose significant lateral and uplift forces.<br /><br />The adopted design uses a suspended reinforced-concrete slab supported by 309 steel helical piles. The slab, covering approximately 9,881 square feet, acts as a continuous platform that distributes equipment and structural loads across the piles, reducing the load per pile to about 8 metric tons (16 kips) and helping control differential settlement. Design checks addressed compression, uplift, lateral stability, soil–structure interaction, and serviceability in accordance with Brazil’s ABNT NBR 6122:2022 standard.<br /><br />Helical piles were selected because their small installation equipment, modular transport, low vibration, rapid installation, and torque-based capacity verification suit the site’s logistical and environmental constraints. The presentation concludes that combining helical piles with a suspended slab offers a technically viable foundation approach for substations on very soft soils, particularly where access is limited.

Keywords

34 kV substation

Afuá

Marajó Island

soft organic clay

helical piles

suspended reinforced-concrete slab

foundation design

soil-structure interaction

ABNT NBR 6122:2022

differential settlement