Pile Foundation (Ground Mount)

Foundation Types

Key Takeaways

• Pile foundations support solar trackers and fixed-tilt arrays.
• Driven H-beam steel pile is the dominant type.
• Screw piles for sandy/rocky soil; concrete piers for unstable.
• Site-specific geotechnical investigation required.
• ASCE 7-22 and IS 800 govern structural design.

How Pile Depth and Type Get Decided

The pile schedule for a ground-mount site is not a single number applied across the plot — it comes out of the geotechnical investigation described above. A standard penetration test (SPT) at multiple boreholes establishes soil bearing capacity and stratification, and a lateral load (pull-out) test on trial piles confirms how the soil actually resists the overturning moment a tracker row or fixed-tilt table imposes under wind. Where the SPT results show consistent cohesive soil or sand, a driven H-beam or W-flange pile at 1.5–3.5 m depth is usually the lowest-cost option. Where boreholes hit rock close to surface, or the soil is loose sand and gravel that won’t grip a driven pile reliably, a helical screw pile trades a cost premium for installation speed and easier quality control. Concrete piers and micropiles are reserved for the soil conditions — unstable fill, very poor bearing capacity — where neither steel option performs reliably.

Because the pile is the load path between the racking structure and the ground, its design is inseparable from the structural analysis of the row above it. Wind uplift and lateral loads calculated under ASCE 7-22 flow directly into the pile’s required embedment depth and section, and IS 800 governs the steel member design itself for projects following Indian structural codes.

Related Reading

Pile selection is only half of the ground-mount foundation story — the structural loads that size the pile are worked out well before the geotech report is finalized. Our field guide to pile foundation design for solar ground-mount walks through that process end to end, from soil investigation to pull-out testing. For the wind-load inputs that drive embedment depth and section sizing, ASCE 7-22 wind load methodology for solar rooftops is a useful companion read, and for how engineering teams validate the racking-to-pile connection under those loads, SAP2000 vs STAAD Pro vs manual calculations for solar structures compares the analysis approaches in practice. Projects on rooftops or ballast-friendly sites instead of soil-driven piles are usually evaluated against ballasted racking as the alternative foundation strategy.