Installation process of hollow bar system
Hollow bar system is typically installed using rotary percussive drilling. The advanced technique improves the rate of installation, also makes good directional stability and helps to consolidate the grout within the borehole.
Rotation speeds should be sufficient to cut a true borehole, as opposed to displacement of the soil with the drill bit through percussion and heavy feed pressures. Drilled boreholes make enlarged grout bodies possible. It is used together with better permeation of the grout into the surrounding ground.Feed pressures on the hollow bar should be regulated in accordance with the cutting performance of the drill bit.
Hollow bar system features simultaneous drilling and grouting. It is suitable for granular soils and fills. This installation method utilises a grout swivel, grout pump and drilling head. The advanced technique combines drilling and grouting into a single operation, ensuring that grout is placed over the full length of the borehole. Simultaneous drilling and grouting is the prefered solution for ground conditions where subsequent grout injection down the center of the bar is problematical.
Grouting pressures should be regulated to maintain circulation at all times, with a small amount of grout return visible at the mouth of the borehole. Pressures in excess of 100 psi are generally only required for special applications.