Bored piles in Batumi: drilling, cage, concrete

Bored piles in Batumi: how one pile is made

A drilling rig bores a hole of the required diameter down to the dense ground from the survey report. A reinforcement cage on spacers is then lowered into the hole so it stays centred and does not touch the sides. Concrete is placed from the bottom through a pipe that is raised as the hole fills, pushing out water and slurry. Once the pile has gained strength its top is cut back to sound concrete and the starter bars are taken into the ground beams.

The work involves no impacts, so these piles can be made a metre from a neighbour's house or next to an old wall that must not be shaken. That is what sets them apart from driven piles, and from screw piles in that they carry both the heavy weight of a masonry house and the sideways load in an earthquake.

Wet ground and the casing tube

By the sea and in river valleys the hole often fills with water while it is still being drilled, and sandy sides collapse. Then the hole is lined with a casing tube: it goes down with the drilling and is pulled out once the concrete is in. Concreting such ground without a casing leaves necks and voids in the body of the pile, and that is almost impossible to check later.

So we place concrete continuously, without gaps between trucks, and each pile is concreted in one go. On wet plots we drill no more piles per shift than we can concrete the same day: a hole left open overnight has slumped by morning.

Diameter, length and reinforcement

The engineer sets the diameter, length and reinforcement of each pile from the load, the ground survey and seismic loads. In private houses these are usually small-diameter piles, but reinforced over their full length: in an earthquake a pile works not only under vertical load but also in bending near the top. We do not put a short cage only in the top part of a pile under a home.

If dense ground turns out deeper than in the report, we do not shorten the pile. The site foreman records the depth of every hole in a log, and the engineer decides whether to lengthen the piles or change the layout. This log, together with photos of the cages, goes into the handover file.

Where else bored piles are needed

Besides houses, we use these piles under retaining walls, heavy terraces on a slope, a pool on filled ground and an extension to an old house that cannot rest on the existing foundation. Strengthening an existing foundation can call for smaller drilled and grouted mini piles: they are drilled straight through the old strip, as described on the page about foundation underpinning.

What we check on every pile

• the position of the drilling point against the surveyor's setting out;
• the depth of the hole and the ground at its base compared with the survey;
• the cage: bar diameters, length, spacers;
• continuous concrete placement and the level of the pile top;
• the pile head after trimming: concrete without honeycombing, starter bars intact.

All of this goes into the pile log and is photographed. If you are running the build from abroad, on request the site foreman shows the drilling and concreting on a video call.

How much bored piles cost

One reinforced bored pile costs from 540 ₾: drilling, a casing tube if needed, the cage and concrete. Ground beams are priced separately, and a complete pile foundation with ground beams comes to from 300 ₾ per m² of house footprint. A drilled and grouted mini pile for underpinning costs from 810 ₾, soil removal from 39 ₾ per m³, the ground survey from 3,000 ₾. The final cost is set from the engineer's calculation, after a site visit and agreement on the estimate.