This study investigates into the challenges of widening the “D-shaped” 3.342 km-long Barcem tunnel of Konkan Railway, where limited clearances and under-cuts posed operational issues of goods trains. The paper documents a careful approach to remove these under-cuts without damaging the peripheral rock mass and ensuring uninterrupted train movements. The methodology involved precise drilling of holes of 34 mm diameter using a rolling platform and firing these holes with matching 25 mm diameter emulsion cartridge explosives and detonating cords. Specialized blast patterns having shot holes inclined at 60–75° were designed, having a maximum depth of 0.4 m. In total, ninety-five blasts were conducted to remove all the undercut portions causing infringement to the train movement. Strict safety measures were implemented, including wire-mesh fixation on entire blasting patches to restrict the extent of flyrock during blasting and muffling of rail structures (rail line, slippers, joint boxes, electrical cables) by used rubber tyres of heavy vehicles. The results of blasts indicated that a designed charge factor of 0.05–0.4 kg/m3 effectively removed the hard rock under-cuts, maintaining structural integrity without generating fresh cracks. The magnitude of ground vibration monitored at 1 m distance was 53.3 mm/s ensuring compliance of safety limits.