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Self drilling anchor for Dagachhu Project

Self drilling anchor system, an advanced anchoring system, is a kind of bolt integrated with the functions of drilling, grouting and anchoring. Self drilling anchor was successfully utilized for an exciting Bhutan project- Dagachhu Hydroelectric Project.

The Dagachhu project is the first hydropower project managed by a Bhutanese team, and the team worked with an Austrian consultant. The 126 (2x63) MW Dagachhu Hydroelectric Project is located at Dagana in the south-western part of Bhutan. The run-of-the-river project is designed for an estimated mean annual generation of 515 GWh and in a 90% dependable year to generate 360 GWh.

The surge shaft location is underlain by loose overburden/highly weathered rock mass (mica schist/gneiss). Surprisingly, Self drilling anchors coupled with shotcrete and lattice girders have been provided in the loose ground area around surge shaft. The back slopes are protected by shotcreting.

The excavation at the adit to HRT (SOUTH) was taken up without constructing any portal, though the rock mass is highly weathered poor and loose. It was opined that the initial section of the tunnel should have been done with a proper portal and steel rib supported section. NATM(new Austrian tunneling method) should be used only where it is found suitable. Under complex geological and tectonic setting of the Himalayas, only combination of different stabilization measures work effectively.

The main access tunnel to the underground power house location has mainly thinly foliated gneisses. Here self drilling rock anchors have been installed irrespective of the orientation/attitude of the foliations and other joints. Further the width of the underground power house cavern is 25 m which is perhaps the biggest span in the Himalayan region. Hence it was advised to exercise caution in view of the site conditions and adopt controlled blasting techniques.