Desiree Willis, Technical Writer, The Robbins Company
- A remote location 200km from the nearest city, two fault zones, difficult ground conditions and a succession of power cuts - but still a 4.3m diameter Robbins double shield TBM has emerged triumphant and on schedule to complete a 9.3km headrace tunnel in Turkey's mountainous Adana Province.
4.3m Robbins double shield TBM breaks through
- The hard rock TBM - operated by contractor NTF Construction for the Yamanli II hydro scheme - broke through on time as a result of excellent advance rates and minimal downtime throughout the 14-month excavation period.
- Monthly progress on the 6.6km-long reach of TBM bored alignment averaged 472.7m, with a best month of 782.8m, in spite of high rock strength averaging 60-70 MPa and up to a maximum of 120 MPa. The first 2.7km of heading was excavated by drill+blast prior to TBM launch. Rates were achieved in ground conditions of mainly limestone with some clay-filled fissures.
- Despite the hard ground, cutter expenses were extremely low. "The 28th gauge cutter ran more than 8km throughout the bore in limestone up to 120 MPa without any change," said Mustafa Akgül, Tunnel Chief at NTF Construction.
- The machine also passed through two fault zones with clay inflows; at machine launch only one had been anticipated. Probing and pre-grouting allowed crews to prepare in advance for the additional fault zone and other difficult ground conditions encountered along the alignment.
Construction and field crews celebrate breakthrough
- In addition to challenging ground, the machine also experienced unexpected power cuts. This led to delays resulting in long machine and PLC startups. Extended day and night shifts allowed the machine to catch up: "The TBM performed very well with minimal downtime and made up the initial delays, finishing right on time," said Dursun Yildiz, Machinery Manager of NTF Construction.
- Some modifications were required during machine operation, specifically the pea gravel conveyor system, bridge-front supporting legs, and the surveying system. Akgül said: "Three modifications were undertaken during the bore, and Robbins Field Service conducted them smoothly. Their cooperation with NTF personnel was strong and continuous."
- The project took place at a remote jobsite roughly 200km from the city of Adana. The mountainous region features a valley in which many civil works projects are currently taking place; the Yamanli II project is the third hydroelectric project in the area. The completed tunnel will source water from the Göksun River, with an annual generating capacity of 78 MW, to power up to 78,000 homes.
Can you check the numbers? Excavating a 9.3km tunnel in 14 months does not result in an average monthly advance rate of 470m (quite apart from the fact that 60MPa is not really hard rock).
There were sections with up to 120 MPa limestone formations in the tunnel alignment. We also passed through five fault zones with crushed limestone and clay layers, of thickness ranging between 1m and 6m. We used universal type segments with cement grout injection for lining of the tunnel.
Mustafa Akgül, Tunnel Chief at NTF Construction
Double shield taking on tough work in Turkey - TunnelTalk, August 2012
Dynamic Robbins will adapt mid-bore - TunnelTalk, February 2009
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