The problem arises with the grouting operation is that the quality of the borehole filling can not be controlled since unstable borehole walls can collapse and prevent a complete filling of the annulus resulting in a reduced function of the stress transfer to the SDA bar and furthermore reducing the grout to act as a layer of corrosion protection.
A more advanced installation method which can only be utilized with self-drilling anchors is the installation by “Simultaneous Drilling and Grouting”, which although not new is being adopted by many contractors today in the industry. This method requires a grouting swivel providing the drilling operator the option to use the grout mix directly as a flushing media.
The percussive force of the hammer should be balanced with rotation of the drill bit, as advancing the drill string with excessive percussion and feed pressure, but limited rotation, will restrict the formation of a true hole resulting in inconsistent grout cover. The flushing and grouting efficiency of the drill bit will also be reduced. Normal rotation is between 40 and 100 RPM.
Grouting pressure should be sufficient to maintain circulation at all times, with a small amount of grout return visible at the collar of the hole. A constant rotation should be maintained.
Grouting Swivel consists of a body with inlet for flushing medium/grout and a female-female Swivel shaft which connects the Rock drill/Drifter shank adapter with the bar at the other end.
Mounting of the grout swivel shall be in a way to keep the Body and the Shaft always aligned and also to prevent the body from rotating during drilling. For this a steel bracket is being used, which is fabricated in accordance with drill rig and drifter specifications.