Development and Application of Methodology for Quantification of Overbreaks in Hard Rock Tunnel Construction

A methodology for determining overbreaks in hard rock tunnel construction using the drill-and-blast technique is presented this paper. The was developed and applied to crystalline medium- thick-bedded limestone, but it can be used any jointed mass. Overbreaks are inevitable tunnelling a low-confinement environment (shallow tunnels up several hundred meters deep) as result of wedge failures along unfavourably oriented discontinuities caused by blasting. It widely accepted engineering practise that will even if smooth contour blasting applied. If not controlled, extreme financial time costs; determining, predicting, mitigating them key successful rock. Technological overbreaks, which inappropriate use excavation, easily distinguished from dictated geological conditions with they interfere overlap. aim distinguishing two causes phase evaluation or mitigation. analysis inputs, including face mapping, shear strength tests mass, their spatial orientation relative advancement survey overbreak measurements, Due stochastic statistical nature problem, probabilistic concept also part method so probability failure around unprotected sections could determined. so-called stability criterion introduced distinguish between stable unstable terms safety factor. quantification threshold value technological proposed. application methodology, demonstrated on an 8.1 km long section 12 pressure rock,