Solar foundation testing, Ireland.

The challenge

The test area sat across agricultural fields and bog. Ground varied row by row. Some areas were sandy and till-like, with stones close to surface. Others were thick, loose peat and clay. The desk study wouldn't carry a confident foundation tender.

The developer needed measured pile capacity figures, not estimates, before committing to a design.

What we found in the field

The defining feature was a stony layer at roughly 1.5 to 2.5 m depth. Above and below it the profile changed. In the sand-and-till parts, the stone layer was a usable bearing horizon for piles. In the peat-and-clay parts, the same stones were a refusal risk for the wrong pile geometry: you can hit them before the helix is in soil that gives you the capacity you need.

That single observation shaped the design. Two helical-pile geometries were required to cover the workable area, one for each sub-profile.

The test programme

Three working days, 46 GPS-tagged measurements:

• 12 tension tests for tracker uplift and wind-load resistance.
• 6 lateral tests for sideways-load behaviour, particularly in soft-ground zones.
• 3 compression tests for vertical capacity at design depth.
• 25 torque measurements to map installed-capacity behaviour and zone boundaries.

The result: three foundation zones

The helical-pile solution covered approximately 80 % of the area, but not as a single product. The workable area split further into two helical sub-zones with different pile sizes:

• Sand-and-till zone (helical, geometry A). Pile geometry sized to seat above and within the stony layer, taking advantage of the bearing it offered.
• Peat-and-clay zone (helical, geometry B). Different geometry, longer shafts and helix sizing matched to the softer profile, designed around the stony layer rather than relying on it.
• Alternative-foundation zone. The remaining area, where local conditions made helical piles the wrong answer, designated for an alternative foundation.

The detailed design uses measured data. Pile geometry differs between sub-zones. The same measurement framework will carry through to installation-stage QA.