Pile foundation in Batumi: bored piles and ground beams

Why a house needs piles

A pile foundation is needed when weak ground lies on top and the dense layer is deep: fill over an old gully, wet sand by the sea, silt in river valleys, weathered rock on a slope. Piles pass through the weak part and bear on ground that carries the load, and at the top they are tied together by cast-in-place ground beams. The columns and walls of the house stand on those beams.

Piles are not an expensive whim but a way to avoid digging out and replacing metres of poor ground. Where they beat a slab on cost and on dealing with water is covered in the comparison of pile and slab foundations.

Which piles we use for a house

Under a masonry house in Batumi we almost always use bored piles: a hole is drilled to the required depth, a reinforcement cage is lowered in and it is filled with concrete. They do not shake neighbouring houses during the work, and they hold sideways load in an earthquake if they are reinforced over their full length.

We do not use driven piles in dense housing: vibration from the pile driver travels into the neighbours' foundations. We put screw piles under terraces, gazebos, carports and light timber-frame buildings, but we do not raise a masonry house by the sea on them: a thin steel shaft rusts in salty wet ground and resists sideways movement in an earthquake worse than a concrete pile.

Pile foundation in Batumi: ground beams and crawl space

Ground beams tie the pile heads into one frame and spread the weight of the house onto them. We make them cast-in-place, reinforced to the calculation, with starter bars for the frame columns. There are two options. Low ground beams sit on or slightly into the ground, and the ground floor is built on them. Raised ground beams stand above the ground, leaving a ventilated crawl space under the house where pipes run and damp does not linger.

On damp plots by the sea and on slopes we more often recommend the crawl space. The underside of the house stays dry, the sewer and water pipes stay accessible for repairs, and storm water flows freely under the house along its own course. We close the crawl space round the edge with a grille or a plinth wall with vents so animals cannot get in.

How the piles are laid out

The engineer places piles under columns, corners and wall junctions and calculates their spacing from the load. The ground survey sets the length of each pile: on a slope the piles on the downhill side come out longer than those uphill. If dense ground turns out at a different depth from the survey during drilling, the site foreman stops work and calls the engineer rather than drilling by eye.

Before the ground beams are concreted we photograph the pile heads with their starter bars, the beam cage and the service sleeves. You get these photos in the report and later find them in the handover file.

What the plot needs for piling

A drilling rig needs access and a level pad at each drilling point. On a narrow street or a steep slope this is sorted out in advance: sometimes we bring a compact rig, sometimes we build a temporary track. Spoil from the holes is taken away, and in wet ground the holes are lined with a casing tube. All of this shows up at the site visit before the estimate, which is why we do not quote a pile price without seeing the plot.

How much a pile foundation costs

A pile and ground beam foundation costs from 300 ₾ per m² of house footprint: bored piles to the calculation, reinforced ground beams, service sleeves. A single reinforced bored pile is from 540 ₾, a screw pile with head plate from 300 ₾, and a pier foundation for a light building from 205 ₾ per m² of footprint. The ground survey, from 3,000 ₾, and waterproofing of the ground beams, from 78 ₾ per m², are extra. The final cost is set from the engineer's calculation and the ground survey, after a site visit and agreement on the estimate.