The first of two 10m diameter Robbins double shield TBMs was launched last month to begin excavation of a 43.5km water tunnel for the Alimineti Madhava Reddy (AMR) scheme in Andhra Pradesh state, India.
Robbins said the second machine would be assembled later this year at the opposite portal to drive towards the first TBM. Factory pre-assembly is not being employed for the machines. The TBMs are being assembled only onsite, in launch pits along with the back-up system and continuous conveyor assemblies.
Contractor Jaiprakash’s project manager, Anil Khamat, said the assembly work for the first TBM went “quite smoothly” though he said there were “some minor mismatch problems that were worked out”. Robbins commented that onsite assembly saves time for the contractor and money.
Geology along the route comprises half in quartzite zones (up to 450MPa) that are layered and separated by shale, and the other approximately 50% in granite (160MPa-190MPa). Both machines will be fitted with back-loading 20” cutters, and the drive motors are to operate at higher than normal revs/min to optimise penetration rates in the hard rock section.
Following the drives, the TBMs and back-ups are to be removed via a dismantling chamber excavated by drill and blast.
Jaiprakash is building the tunnel for the state government to convey water from Srisailam reservoir for irrigation and other water resources in Nalgonda District by the end of 2012. The entire construction period for the project is about 60 months.
Robbins is also to supply a 10m double shield for another long drive on a different water transfer project that will tap the same reservoir – the Pula Subbaiah Veligonda project, also being developed by the state government. Onsite assembly only is also planned for the TBM and back-up, and excavation is due to start in February 2009. Excavation of a smaller, parallel tunnel has already started on the project by a Herrenknecht machine (T&TI, February, p8).
The first of two Robbins TBMs for India’s AMR water tunnel was launched in March AMR – 1 The first of two Robbins TBMs for India’s AMR water tunnel was launched in March AMR – 2
