There are two parallel tunnels, is prone to collapse because of water pressure difference between the tunnels. As the pressure variation would show impact along the faces and transfer to the invert and crown part which may lead instability. As this eventually falls under seismic zone V chances of rain occurrence frequency is high, thus stability has to be ensured and this task was entrusted to Spar Geo Infra Pvt Ltd as we have already had wonderful past work experience in slope stabilization.
Solution suggested by us:
The collapsing of wall of tunnel can be avoided by stitching of busduct at power house with horizontal anchor of 100 ton load. For the anchoring a hole of 125mm diameter is drilled with 17.5 m depth was done and rock bolt coming in between is cut down.
Difficulties faced while execution:
The presence of rock bolt in between the anchoring direction lead to repeated changing of drill bits.
Extra Technology used for execution:
New technology were used for locating the direction and depth at which rock bolts are present. Tools for recovery of stuck bits during the process of drilling are imported.
Drilling through the side face of the tunnel which causing instability due to generation of tangential stress at the crown were successfully eliminated which were praised by the Client