Pile foundation design

The pile type follows the ground, the loads and the access. Continuous flight auger piles are fast, quiet and clean and suit most medium sites. Bored cast-in-place piles handle large loads and can be taken through obstructions. Driven precast or steel piles suit softer ground and give a tested capacity as they go in, but the noise and vibration can rule them out near neighbours. On tight domestic plots, underpinning and sites with headroom limits, restricted-access mini piles are often the only rig that can physically get in.

Group effects and lateral loads matter as much as vertical capacity. Piles in a close group interact, so the group can settle more than a single pile carrying the same average load, and we account for that efficiency in the design. Where wind, retained ground or crane loads push sideways, we check the piles for bending and lateral soil resistance, and where uplift can occur we design for tension along the shaft. Each of these can change the pile length or reinforcement.

Piles rarely land exactly under the load, so a pile cap or ground beam spreads the wall or column load onto them. A cap over two or more piles is designed as a strut and tie, with the load spreading down inclined concrete struts to the piles and horizontal tension ties resisting the spread, which sets the bottom reinforcement and the cap depth. Ground beams span between caps or single piles to carry the walls, and we design them for the wall load plus any heave acting on the underside where clay can swell against them.

Piling only works when it is coordinated with everyone else. We set out the piles to clear drains and boundaries, allow for the specialist contractor's positional tolerance so the caps still work if a pile is slightly off, and tie the reinforcement between piles, caps, ground beams and the ground floor into one load path. The calculations and drawings are prepared to Eurocode 7 and 2 and delivered to clients across the UK, with the site works staged around the region.