TBM's are certainly the best choice for excavation of long tunnels provided geology is favourable or found as anticipated. Roadheaders are also useful equipment for short tunnels, the tunnels with variable dimensions, top down excavation of underground metro stations and at many other places where blasting is either not permitted or restricted. Nevertheless detailed investigations are required; the choice of Roadheader over the other available options of tunneling is also a delicate option. There are many limitations of Roadheaders, the major being – its high cost and risk factor involved in case of variation between the predicted and actual rock conditions. Two Roadheaders AM-75 were inducted for the excavation of Tunnel No.2 and Tunnel No.5 by Konkan Railway Corporation Ltd. at Udhampur-Srinagar-Baramulla Rail Link Project (USBRL) in 2005. The machine from tunnel no. T-2 at Katra face was stuck for a long time,being in Reasi Thrust, encountering ingress of water and later contractor abandoning the job. The second machine at tunnel no. T-5 performed reasonably well but unfortunately the project was suspended in 2008 for some alignment problem and the contractor demobilized.
The execution of Udhampur Srinagar Baramullah Rail Link Project (USBRL) was entrusted to Konkan Railway Corporation Ltd. (KRCL) and IRCON International who are the two Public Section Undertakings under the administrative control of Ministry of Railways. The Project was allotted in Aug 2002 with completion date of Aug’08. The benchmark while fixing this target was completion of 741 km Konkan Railway Project in Western Ghats between Roha and Mangalore, commissioned in 7 years involving about 93 tunnels of 83km length; the longest being 6.5 km Karbude tunnel, near Ratnagiri in Maharashtra. Almost 13 years have passed since inception and the project is still not completed. Some experience gained on this project from the use of Roadheaders is summarized in this article.
