Deep Excavation by Controlled Rock Blasting in UG Metro Station near by a Strutures

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The case study examines controlled blasting for deep excavation of an underground metro station in densely developed Bengaluru. The site comprises soil over Precambrian granitic gneiss, with rock grades ranging from I to V, weak shear zones, and water seepage. Excavation beneath or near sensitive buildings, heritage sites, utilities, and electrical equipment required careful control of vibration, flyrock, and overbreak.<br /><br />The project team used geological and geotechnical data to develop blast designs, including peripheral line drilling to limit damage to the final rock face and reduce vibration transfer. Nonel initiation, rubber mats for blast-hole muffling, and field vibration monitoring were also used. A site-specific attenuation relationship linking peak particle velocity (PPV), distance, and maximum charge per delay was developed from comparable metro sites. It informed charge limits and highlighted that alternative mechanical excavation may be needed where structures are less than 10 m from blasting. Preliminary vibration thresholds were set according to structure type and sensitivity.<br /><br />A two-dimensional finite-element model was used to assess slope stability during blasting; most modeled areas had a factor of safety above 1.25, although the slope face required attention. Field monitoring recorded a maximum PPV of 1.3 mm/s, below the 5 mm/s limit adopted for the project. The authors recommend maintaining stricter vibration limits near particularly sensitive structures and conclude that line drilling, appropriate blast design, and instrumentation can support safe rock excavation in congested urban settings. Further work is proposed to compare measured vibration data with numerical predictions.

Keywords

controlled blasting

deep excavation

metro station

Bengaluru

peak particle velocity

vibration monitoring

line drilling

granitic gneiss

slope stability

urban excavation