Two 12.4m diameter TBMs – a Robbins main beam and a Herrenknecht hard rock gripper – were launched last month on parallel 16.7km long headrace drives at the Jinping II hydropower scheme in Sichuan province, China.
The project developer – Ertan Hydropower Development Co Ltd (EHDC) – has two of the project’s four headrace tunnels being driven by TBM and the others by drill and blast.
Separate contractors are using the shields – China Railway 18th Bureau (Group) Co Ltd driving the Robbins TBM, and China Railway 13th Bureau (Group) Co Ltd the Herrenknecht machine (S-405). Each contractor also has a drill and blast bore to drive.
Earlier this year, a refurbished and rebuilt 7.2m diameter Robbins TBM, from the Karahnjukar project in Iceland, began excavating the single dewatering tunnel for the project. The tunnel is being excavated in advance of the parallel headrace tunnels on the project and is needed due to high inflows expected in the headrace bores, possibly up to 4,000l/s.
Herrenknecht has noted that the geology along the alignment of the bores comprises mostly (86%) limestone and the balance is sandstone. Its TBM has cutterhead power and torque of 4,900kW and 19,750kNm, respectively, and total thrust is 24,885kN.
Snow storms and transport logistics proved a challenge to the entire project over recent months, including the wider, knock-on effects of the Sichuan earthquake. There were also delays in cavern excavation for the assembly. In addition, limited space on site required most TBM components to be staged 80km away.
Robbins erected the main beam TBM using its Onsite First Time Assembly (OFTA) method (T&TI, September, p29-31).
Following assembly, the TBM and the first three back-up gantries were walked forward approximately 200m to the launch chamber. A further six gantries and the conveyor were added, and the shield was launched on 18 September to begin driving for the final commissioning phase involving a 1,000m long test bore.
The contract requires that the shield achieves an average advance rate of at least 800m per month. The TBM’s own two feeder conveyors have been designed to cope with wet conditions.
Steve Smading, Robbins’ project manager, in noting that assembly was completed on schedule, said: ‘Everything has gone remarkably well in retrospect. Of course we had problems, but our onsite assembly team was able to manage them as they occurred without adversely affecting the assembly process.’
Robbins TBM set for launch at Jinping II, China Herrenknecht TBM at formal launch ceremony for Jinping II shields
