Bottom Driven Minipiles

Bottom driven minipiles are a cost-effective, low-noise, low-vibration installation technique that requires minimal attendance and minimal site enabling work. They can be installed using lightweight, restricted access minipiling rigs. These rigs can weigh as little as 2.5 tonnes, fit through standard double doors and are either diesel or electrically powered. With either rubber or plastic tracks, these rigs can operate on most surfaces without causing damage.

Regarding the installation, the piles are formed by driving a crimped, closed-end, sacrificial thin wall steel casing into the ground using an internal drop hammer. This drop hammer drives onto a dry concrete plug/packer at the toe of the casing and additional casing sections are added as the pile is advanced. These casings are joined using full filleted welds. When the casing has been advanced to its predetermined design length, or more common design set, the steel reinforcement is placed, and the pile bore is filled with concrete or grout. As the permanent casings provide a dry and stable pile bore, there is no requirement for constant concreting/grouting work. The concrete/grout placement can be scheduled and planned around other site activities.

As this is a displacement technique, no spoil is produced, making it beneficial on brownfield sites. This method is a low-noise and low-vibration technique compared with more conventional driven precast or steel tube techniques. It can be used in sensitive environments where the use of driven techniques is generally precluded. Piles installed using this method can also be positioned in very close proximity to walls and structures.

Bottom driven minipiles

Depending on the ground conditions and diameter, these piles can be installed for loads of up to 750 kN in compression (safe working loads/characteristic) and can carry modest lateral loads and tension. They are installed to a predetermined set resistance in the anticipated founding that would be identified/indicated using the ground investigation borehole or cone penetration test logs. Dynamic or maintained load testing can be used with this technique for design verification purposes.

This installation technique is well suited to city-centre developments when working close to sensitive historic buildings. It is also beneficial when working inside occupied buildings. Where the ground conditions permit, this is the favoured option for piling new mezzanine foundations in distribution facilities or retail parks.