SHAFTS & CAVERNS | TECHNICAL
INCLINED BORE FOR HYDRO TBM
Pingjiang hydropower project, in China, recently saw a CRCHI TBM complete bored inclined tunnelling for a diversion shaft.
A variable diameter TBM manufactured by China Railway Construction Heavy Industry Co (CRCHI) recently completed its drive to finish boring on an inclined shaft for Pingjiang hydropower project, in China. The shaft, bored at an inclination of 50°, CRCHI says,
and is for part of the flow diversion among conveyance tunnels at the underground pumped storage project. The successful excavation completed the first diversion inclined shaft for the project, achieving finish in June. Tunnel boring was performed by a large, variable
diameter TBM from CRCHI. For the inclined boring, the TBM - named ‘Tianyue’ - had its excavation diameter adjusted from 6.5m to 8m, says the manufacturer. CRCHI says the shield is a first in large-inclination,
large-diameter, and adjustable diameter TBMs for hard rock tunnel boring on sloping shafts. The TBM drive up No.1 diversion inclined shaft was
almost 1338m in length. For the inclined drive, the TBM (87m long, 900 tonnes)
was equipped with a triple-gripping hydraulic interlock system, says CRCHI. Three sets of grippers anchored to the shaft wall formed an “anti-slip triangular matrix”.
During boring, the mid and rear grippers provided counter-thrust while alternating re-gripping every 1.5m, it adds. The hydraulic design of the inclined shaft - and
consequent increased tunnel excavation challenge - arose in part from seeking lower water flow velocities at one end when the power plant is in operation. With flow rate reduced the risk of cavitation bubbles being generated was designed out. At the other end of the shaft the design reduced the
steel use by almost a third to handle high hydraulic pressures during the life of the plant. The TBM tunnelling solution for the inclined, variable
diameter shaft also reduced construction risks for such a large excavation. CRCHI says that, in designing the TBM, consideration
was given to both the excavation capabilities and structural design for two large span openings of different diameters. The TBM design for adjustable diameter can use a single set of equipment, which helps to reduce costs - which the manufacturer says is like equipping the machine with an “extendable skeletal structure.”
Above: Variable diameter inclined shaft TBM breaks through on China’s Pingjiang pumped storage hydropower project PHOTO CREDIT: CRCHI
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