65. Rock Mass Classification System Used in Pir-Panjal Railway Tunnel

Rock mass characterization is an integral part of all rock engineering practices and it is the most important factor for an economical tunnel design. For design of under ground structures, there are several rock classification systems in use. In the past, tunnel design was heavily based on the experience, some simple calculations and standardized rock mass classification. In India, particularly in Himalayan region any substantial deviations in the behaviour of Rock mass during construction leading to collapses, cavity formations were termed as Geological surprises. These so called Geological surprises in tunneling have taken heavy toll on the Projects involving underground structures in terms of Time and cost overruns. Over the years of underground experience in Alps, Austrian engineers have developed a tunneling method called New Austrian Tunneling Method (NATM). The Geological conditions in Alps are rapidly changing and complex. Similar complex conditions exist in Himalayan region necessitating use of more rational Rock mass classification system and for arriving at required excavation and support measures. In this system, instead of only depending on standardized formulas and set classification system, an attempt is made to observe the Rock Mass behaviour and relate to it to the support requirements of the Tunnel under construction. During construction, Geological face mapping, Geotechnical monitoring along with displacement monitoring and face behaviour determine the modification in the support and excavation method decide during designing. This paper deals with rock mass classification used in Pir-Panjal tunnel a part of Jammu and Kashmir Rail Link Project and its usefulness for design and construction.