Unusual situations are those where the soil load-bearing capacity does not fall within the parameters of the local building control guidance for ‘standard’ foundations. These instances will require the services of a structural engineer to design the foundation and he or she can engage a geotechnical engineer to ascertain the soil characteristics.
Many piling types can be encountered depending on the site and its environment, but the following alternatives are limited to the most common types of piling foundation used for domestic-scale buildings in the UK:
RING BEAM FOUNDATION
by Alternative Piling Solutions UK
Ring beam foundations are better for new builds and extensions. In this case, a trench will be drilled to a depth of about 500mm before the piles are built. After that, the piles are pushed to the proper depth and REBAR PLATES are mounted on top of each pile. The RING BEAM base is then formed by installing a supporting cage in the trench over the piles and pouring concrete.
Screw pile foundations are a type of pile foundation with a helix near the pile toe so that the piles can be screwed into the ground. The process and concept is similar to screwing into wood.
A screw pile may have more than one helix (also called a screw), depending on the usage and the ground conditions. Generally, more helices are specified if a higher load is required or softer ground in encountered.
CFA (Continuous Flight Auger) Piling
CFA piles are constructed by spinning a hollow stem continuous flight auger into the soil until it reaches the desired depth. As the auger is slowly withdrawn, concrete or grout is pumped through the hollow stem at a constant head pressure to fill the cylindrical cavity formed.
To build a continuous pile with no flaws, the grout pressure and volume must be carefully managed. The reinforcing cage is inserted into the newly poured concrete.
Rotary bored piling
Bored piles are installed using high torque piling rigs where structural requirements dictate higher bearing loads and or pile lengths need to penetrate hard rock layers, boulders and overcome underground obstructions.