DYWI® Drill Hollow Bar Installation
The DYWI® Drill Hollow Bar offers high rates of installation, as drilling and grouting can be combined as a single cycle. To achieve these benefits, it is important that the correct equipment is selected to ensure efficient drilling.
The three main drilling functions are:
- Rotation: 120-150 RPM. This is the key drilling function to ensure the full diameter of the borehole is cut as drilling advances
- Percussion: 300-600 BPM, for directional stability and drilling efficiency
- Fine Feed: Feed pressures should be regulated to match the achievable drilling rate
Rotary Percussive Top Hammer
This is the essential piece of equipment for hollow bar drilling. Rotary percussive drilling ensures efficiency in most ground conditions, provides good directional stability for the drilled bar and helps consolidate the placed grout. The hammer should have sufficient torque and rotation speed.
Although it may be desirable to maximise the size of the drill bit, it should always be compatible to the bar used to drill.
Simultaneous Drilling and Grouting
This method ensures grout is placed at all points of the borehole as drilling is advanced, permeating the local soil strata and producing bulbing in the softer sections of the borehole.
Reaming (extracting and re-inserting whilst under rotation) of the bottom rod section at full depth will further enhance bond performance, as the ground strength is typically highest at this point due to overburden pressure.