TAI Journal (A Half Yearly Technical Journal of Indian Chapter of TAI)
Year : 2018, Volume : 7, Issue : 2
First page : ( 84) Last page : ( 91)
Print ISSN : 2277-2820. Online ISSN : 2278-4713.

Engineering Geological Evaluation of Rock Mass of the Transformer Cavern-A Case Study from Lift Irrigation Project, India

Rawat D.S.¹, Naithani A.K.¹, Rao G. Srinivasa¹, Singh Khilap², Babu R.N.S.³

¹National Institute of Rock Mechanics, Bengaluru

²Navayuga Engineering Co. Ltd., Hyderabad

³Aarvee Associates, Hyderabad

Online published on 20 April, 2019.

Abstract

Engineering geological investigations were carried out for 203.4 m long 16 m wide and 27 m high transformer cavern to setup 7 electrical transformers of 150 MVA capacities each. The purposes of transformers are to supply electricity for 7 mechanical pumps. Generally, large underground caverns are preferably excavated by pilot tunnel method to identify the adverse geological features and estimation of rock support requirement. Pilot tunnel method is helpful to avoid any kind of geological surprises. The transformer cavern was excavated with full face excavation methodology which adopted from the heading excavation experience of pump house cavern for 210.6 m long, 25 m wide and 50.3 m high in the similar geological terrain. Full face excavation is more economical in comparison of a pilot tunnel but rock mass needs to support timely. Based on face mapping on 1: 100 scale the excavation methodology for critical tunnel reaches and an immediate rock support was installed. Tunneling was done in dry media and encountered rock was medium to coarse grained grey and pink granite. Critical joints and problematic tunnel reaches were supported immediately with temporary and design rock support which also include sealing shotcrete during the excavation of heading portion. The Unwedge analysis was carried out to provide evaluation for additional rock support in view of persistence joints.

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