Completion of the heading excavation for the headrace at Uri II and the pilot bore for the surgeshaft at Rampur, and also advancing ground treatment ahead of the recovered TBM at Parbati II, mark a series of milestones achieved in tunnelling works on hydro projects in India (hydels).
Project developer National Hydroelectric Power Corp (NHPC) has reported that the heading of the 4,233m long headrace tunnel at Uri II was finished at the end of June, and bench excavation of the 8.4m wide horseshoe shaped tube is 60% completed. The 240MW project is being built in Jammu & Kashmir.
More than 80% of the heading for the 3,615m long tailrace tunnel has been bored. NHPC said that almost a quarter of the bench excavation has been completed.
Other underground works on the project that have been completed include pressure shafts and the 133m long by 15m wide by 40m high powerhouse cavern. The project’s transformer cavern is two-thirds complete.
At the Rampur project, which is being developed in Himachal Pradesh state by Satluj Jal Vidyut Nigam (SJVN), the 7.15m diameter pilot bore for the surgeshaft has been completed. The 149.4m pilot was excavated over 11 months and is to be widened to 38m diameter for the main surgeshaft by the end of the year. Works are being undertaken by the Patel Gammon JV.
Headrace drives are underway on multiple faces and progress has been slow due to poor ground. The circular, concrete-lined tunnel will be 10.5m i.d. and almost 15.1km long. Half of the heading was excavated by the end of June, and the target completion is late March 2009.
The heading for the 68m long, 10.5m diameter tailrace tunnel is to be completed a month earlier. Rampur also calls for a total of 3,300m of excavation for five adits.
Rampur is being built downstream of the Nathpa Jhakri plant on the Satluj river, and obtained US$400M in World Bank financing earlier this year. SJVN is developing the project with the state government, which has a 30% stake.
NHPC also reports that ground treatment was being finalised ahead of the recovered TBM on the Parbati II project in Himachal Pradesh state. The shield was excavating Face 4 on the headrace when, in November 2006, it was buried a heavy ingress of ground and water. Following months of recovery and repair, NHPC said the ground ahead of the TBM was almost ready for excavation to resume.
The 31.5km long headrace tunnel at Parbati II is being driven by both TBM and drill and blast, and by the end of June was just over 80% excavated. Almost 15% of the 6m diameter tunnel has been concrete lined. Both inclined pressure shafts have been completed (T&TI, January 2007, p9).
