Minimum invasive drill‐and‐blast designs for optimizing pull efficiency and minimizing overbreaks/underbreaks in varying rock masses

In tunneling and underground projects, the drill‐and‐blast method is most commonly utilized for rock excavation. It is notable for cost‐effectiveness and versatility in achieving different tunnel profiles. Though the technique has advantages, it also has challenges such as overbreak, undercut, and occasional poor advances, which can increase project costs and delays. The outcome of blast results is also associated with the competency of driller in effectively drilling the planned holes. Hence, frequent and substantial modifications in the blast designs to attain good profile and pull can adversely affect the driller's performance, thereby reducing the desired outcome. This article presents a case study of the Sivok‐Rangpo tunnels passing through different classes of rock mass (class III–VI). Minimum changes in cut pattern and periphery holes design were incorporated and found efficient in increasing the tunnel advance rate to 90–92 % of the drill hole length. The processes also reduced the overbreak and underbreak considerably.