Drilled & Grouted Hollow Bar Micropiles
Drilled micropiles are constructed using bespoke hollow-threaded steel bars that are simultaneously drilled and grouted. These piles are generally between 150 mm and 300 mm in diameter and installed using powerful minipiling rigs weighing between 2.5 and 10 tonnes. These piles can be installed in restricted-access areas and very-low-headroom environments, depending on the rig and loading requirements.
They are installed using rotary percussive drilling techniques. The bore’s stability is maintained by the grout flush, which is pumped through the centre of the steel bar as the pile is progressed. The steel bar is advanced into the ground using sacrificial drill bits selected to suit the ground conditions. The steel bar forms the structural element of the pile; the grout acts as the load transfer mechanism from the steel bar to the ground to achieve the geotechnical capacity. These micropiles can also be enhanced at the head with circular hollow sections to provide modest shear capacity. This technique requires comprehensive ground investigation information to design the pile for the prescribed loads.