Where boreholes give you a 75 mm window into the rock mass, a drift lets a geologist walk into it. Adits expose joint sets, shear zones and weathering at full scale, which is why they remain standard practice on major hydro and tunnel investigations.
Drift length and section are set by the rock encountered — advance rates, support requirements and pull recovery all vary with hardness and jointing.
Drifts and adits already completed include the Malari–Jhelum and Jhelum–Tamak schemes, Badrinath, Chhatru in Lahaul & Spiti, Maneri-Bhali, and Shikariabyol for UJVNL.
