San Francisco HEP Headrace Tunnel

The San Francisco Hydroelectric Project in Equador is utilizing hydropower from the Rio Pastaza in a 230 MW plant. 8.4 km of the 11.2 km long HRT have been excavated by a double shield (DS) TBM. After 4.950m TBM excavation in metamorphic rock series of the Cordillera Real, the TBM was trapped by a block failure of the rock under high water ingress and the TBM shield was demolished. A rescue program was undertaken immediately on the TBM in order to stabilize the region of the event, to get control about the water ingress, to make free and to repair the TBM and to continue excavation under controlled conditions. Concurrently an alternative rescue program was investigated and started in order not to waste time if the rescue of the TBM should fail or if further events should occur. The TBM stoppage lasted for about 5 month and the rescue program enabled the repair of the TBM and a controlled restart of the TBM without any accident. After the restart the TBM again reached a sufficient daily progress of more than 20m/day and the tunnel could be finalized with success.