Piling Contractors

Your structural engineer will recommend piles when traditional strip or trench-fill foundations would be too deep, unsafe to dig or unreliable. Common reasons are:

• Clay near trees: London Clay shrinks and swells with the seasons, and tree roots make it worse. Foundations must go below the zone of movement, which can be deep near large trees.
• Soft or made ground: Fill, old rubble, peat or soft soils that cannot carry the load.
• High water table: Deep trenches that would fill with water.
• Heavy loads: Blocks of flats and larger new builds.
• Next to existing buildings, drains or sewers: Where a deep trench would undermine neighbouring foundations.
• Heave risk: Where trees have been removed and the clay may swell back.

As a general guide, many engineers start to consider piles once traditional foundations would need to go deeper than about 2.5 metres, because piling then often becomes the safer and more economical option.

Mini piling uses small-diameter piles installed with compact rigs. The rigs are small enough to reach back gardens through side passages or narrow access, which suits London terraces and semi-detached houses. Mini piles are used for extensions, new houses, small blocks of flats, garden buildings and as a method of underpinning. The main types are:

• Bored mini piles: A hole is drilled with an auger, then filled with reinforced concrete. They produce little vibration, which suits sites close to neighbours.
• Driven mini piles: Steel tubes driven into the ground, then filled with concrete. There is no spoil to remove, but there is more noise and vibration.
• Screw piles: See below.

On larger sites, bigger rigs can install continuous flight auger (CFA) piles, where concrete is pumped down the auger as it is withdrawn.

Screw piles are steel shafts with helical plates that are screwed into the ground by a rig. They produce no spoil and little noise or vibration, and they can usually carry load as soon as they are installed, with no concrete curing time for the piles themselves. They suit garden rooms, small extensions, decking, lightweight structures and sites where muck-away is difficult. Very hard or obstructed ground may not suit them, so the engineer decides whether they are right for your site.

Piles alone do not support walls. On top of the piles, reinforced concrete pile caps and ground beams are cast to carry the walls and spread the load between the piles. On clay, the engineer may specify heave protection: compressible material under the beams and floor slab, so that if the clay swells it does not lift the building. The floor may be a suspended slab that spans between the beams rather than resting on the ground.

It depends on the ground and the load. The engineer sets the depth so that each pile reaches enough resistance from the soil, and on clay near trees, so that it goes well below the zone affected by roots and seasonal movement. Mini piles for houses and extensions commonly go several metres deep, and deeper where trees are close or the soil is weak. Ground investigation, such as trial pits or boreholes, gives the engineer the soil information needed, and some projects include pile testing to confirm the design.

• Ground investigation: Trial pits, boreholes and soil testing to inform the pile design.
• Structural design: The number, type, size and depth of piles, and the pile caps and ground beams.
• Building regulations: Approval of the design and inspections during the work.
• Party wall notices: Piles within 3 or 6 metres of a neighbour's building, depending on the depth, can need notice under the Party Wall etc. Act 1996.
• Drains and sewers: Locating existing drains, often with a CCTV drain survey. Building within 3 metres of a public sewer usually needs a build over agreement from the water company.
• Access and spoil: Planning how the rig gets in and how spoil is removed.

• House extensions on clay near trees, or next to existing drains.
• New build homes and building flats on poor ground or with heavier loads.
• Garden buildings such as garden offices and summer houses, often on screw piles.
• Existing buildings, where mini piles are used as a method of underpinning. See our underpinning contractors service.