Goel, R. K. (2004) Experiences of tunnelling in fragile Himalayan rocks. International Journal of Rock Mechanics and Mining Sciences , 41 (3). pp. 499-500. ISSN 1365-1609

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The total hydro-electric potential of India is 84,044MW at 60 per cent load factor, out of which 65,623MW lies in the Himalayan ranges. The Himalayan region is characterized by high ridges, deep gorges, vulnerable hill slopes, complex geological and tectonic features. The complexity of the Himalayan range is attributed to superimposition and modification of the earlier tectonic phases by the last Himalayan tectonic phase. The poly-phase deformations in Himalaya has resulted in the development of numerous tectonic dislocations and structural discontinuities such as faults, thrusts, shears, joints, etc. which have a direct influence on the geomechanical properties of the rock masses at different project sites in the Himalayan region. Therefore, no two sites are exactly similar in their geological and tectonic settings. It has been experienced that tunnelling through weak, jointed, faulted and sheared rock masses in the Himalayan range is a challenging task. It becomes more challenging in the absence of detailed investigations because of high overburden, thickly vegetated surface and inaccessible terrain. Geological surprises, therefore, during tunnelling result in various tunnelling problems and failures—such as squeezing, chimney formation, face collapse, water inrush, etc. Many times the original tunnel alignment has been changed during construction because of face collapse. The experience of the TBM in the Dulhasti project tunnel of the Himalaya is also not very encouraging where, because of inadequate geological information ahead of the tunnel face and water ingress, the tunnel boring has been suspended many times. As a result, the desired progress could not be achieved. All such experiences have resulted in time and cost over-runs. The problems and the failures may be regarded as challenges and opportunities for generating a new knowledge base and thereby increasing the reliability of tunnelling methods. Information from geo-mechanical and instrumentation studies at various hydroelectric project tunnels has helped in generating information on rock mass behaviour and management of tunnelling problems. For example, the lesson obtained from the effect of tunnel size on squeezing ground conditions in tunnels at two projects has helped in developing a criterion for estimating the ground condition. In Fig. 1, the rock mass number N is defined as Barton’s Q with SRF = 1, H is the tunnel depth in metres and B is the tunnel span or diameter in metres. The tunnelling problems encountered in two Himalayan projects, along with the possible solutions of such problems, are presented in the paper. The steps to be taken to avoid such problems in future tunnelling projects in the highly varying and fragile rock masses such as in the Himalaya are also highlighted.

Item Type: Article
Uncontrolled Keywords: Himalayan tunnelling; Fragile rocks; Squeezing; Water in rush; Shear zones
Subjects: Blasting
Depositing User: Dr. Satyendra Kumar Singh
Date Deposited: 16 Feb 2012 07:16
Last Modified: 16 Feb 2012 07:16
URI: http://cimfr.csircentral.net/id/eprint/949

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