Rotary Bored Minipiles

Rotary bored minipiles are suitable in most ground conditions; therefore, they are the most versatile regarding an engineer’s specification. These components are generally between 300mm and 750mm in diameter and installed using powerful high torque minipiling rigs typically weighing between 4.5 and 18 tonnes. They can be installed in restricted-access locations and low-headroom environments, depending on the rig and diameter requirements.

Rotary/auger bored minipiles are made using segmental augers that are rotated into the ground with the penetrated soil raised to the surface by the auger flights. Where the ground is unstable, a temporary casing can be installed in advance of the augers to maintain the stability of the pile bore and ensure no destabilisation of the surrounding soil occurs. When its predetermined design length has been achieved, the steel reinforcement is placed before it is filled with either concrete or grout. This technique is most effective in cohesive soils where minimal temporary casings are required, resulting in exceptionally quick and cost-effective installation.

Rotary bored minipiles

Rotary bored minipiles are installed with little or no vibration; piles can be positioned as close as 500 mm to adjacent structures (i.e., from its centre to a vertical face). Where piles are required close to underground structures, such as foundations, tunnels or services, permanent sleeves can be used to prevent load transfer from the piles to these structures.

This technique requires comprehensive ground investigation information to design the pile for the prescribed loads. The ground conditions can be verified during the installation process in which the pile bore arisings can be observed and compared with the soil and rock descriptions indicated in the ground investigation boreholes.

Pile load-carrying capacities with this technique vary significantly and depend greatly on the ground conditions. Maintained load tests can be carried out on preliminary or working piles for design verification purposes. Integrity testing can also be carried out on these piles to confirm that there are no construction defects.