The Penstock Puzzle

After 40 years of chronic slope movements and several engineering studies, the Sacramento Municipal Utility District in California signed a design-build contract to stabilize the 1,500 ft (460 m) long Camino Penstock, on the bank of the American River. The selected stabilization system consists of a grouted gravity structure along the lower 250 ft (76 m) of the west side of the penstock, constructed by grouting and doweling the in-place bedrock. The toppling movement was stabilized by tying the gravity structure and upslope bedrock with 400 kip (1,800 kN) tendon anchors spaced approximately 10 ft (3 m) apart and reaching about 120 ft (37 m) into the bedrock. Additionally, anchor blocks were added to three of the ring-girder foundations to stabilize downslope sliding movements.