Challenges of Tunnelling in Mixed Geological Condition

Among the modern transport systems in cities, the construction of metrorails has gained exponential momentum as it provides a safe, quick, reliable, environment-friendly, clean, and comfortable public transport system. The majority of the Bangalore region is covered by the Peninsular Gneissic Complex, which represents remobilized parts of an older crust with abundant additions of newer granitic material. The rocks essentially consist of granites and gneisses intruded by a number of basic dykes. The selection of each TBM was decided by the geological conditions along the tunnel alignments. Tunneling through the complex geology of Bangalore is the toughest task for engineers and geologists. Tunneling in mixed ground conditions with the presence of boulders like gabbro or dolerite below densely populated areas and busy roads was a challenging endeavor. These issues impact the delay in progress as well as heavy damages to cutting tools. Based on site conditions, corrective measures are to be adopted on a case-by-case basis to carry out tunneling in a trouble-free manner. This paper presents a comprehensive summary of the hindrances faced during tunneling due to the presence of boulders along the alignment and suitable corrective measures adopted according to the site conditions.