BTS | SHAFTS/KIDSTON PUMPED STORAGE PROJECT
10m
Right, figure 4: Modelling of transition steel liner
hall cavern; the two tailrace tunnels are 330m long,
conveying the water out to the lower reservoir at Eldridge Pit. For the underground works, Mott MacDonald carried
out the permanent lining design of the two intake shafts, the penstocks, the transition, and the tailrace tunnels. Two smaller shafts were chosen rather than one single larger shaft, enabling them to be excavated by raise bore method. Beyond the construction phase, having two shafts also allows some flexibility for maintenance and continuous operation during the long life of the facility. The geology at the project site comprises
undifferentiated gneiss of the Einasleigh Metamorphics with a UCS of 90MPa. The design is based on Q system with generally good rock conditions with a relatively low permeability (in the order of 2 x 10-8 m/s). The penstocks are to be constructed by drill and blast
method and then the two shafts by raise bore from the end of the penstock tunnel. The shafts will have the
primary lining installed and then a slipformed cast in- situ concrete for the secondary lining. Some of the critical checks for hydroelectric schemes include confinement to ensure the minimum in-situ stress in the rock mass is greater than the internal pressure applied to the structure. This was checked during the design, based on the results of the geotechnical investigation and found to be satisfactory. Another check is the hydraulic gradient, where
minimum distance from any point where the internal water pressure is present to the nearest point of atmospheric pressure is determined. This provided the length requirement for the steel liner (see Figure 3). The primary purpose of the secondary lining is to
provide a smooth surface to minimise head losses and therefore to minimise energy, and so economic, loss for the system. The upper 209m of the intake shafts are reinforced
with 250mm thick concrete lining containing macro- synthetic fibres with no steel reinforcement bars. The
Right, figure 5: Construction in the Main Access Tunnel
12 | September 2023
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33
