Page - 78 - in Book of Full Papers - Symposium Hydro Engineering

Table 2 Design Measures Included in New FCO Spillway Chute Structural Concrete to Address Areas of Improvement Identified in the Original Design/Construction Areas for Improvement Identified in Original Design/Construction Design Measures in New FCO Spillway Chute Structural Concrete to Address Identified Areas for Improvement Relatively thin concrete slab at 0.38 m (1.25 ft) New concrete slab minimum 0.76 m (2.5 ft) thick Only 1 layer of relatively light steel reinforcement 2 layers of robust steel reinforcement No waterstops Waterstops added at each transverse joint Large variations in slab thickness Use of thick (~1.5 m [5 ft]) layers of leveling concrete Corrosion of reinforcing bars Upper layer of steel reinforcement epoxy coated Placement of underdrains within concrete slabs Underdrains placed beneath concrete slabs Collector pipes drain both underdrain and backfill Separate collector pipes for underdrain and backfill Brittle clay underdrain and collector drain pipes PVC underdrain and collector drain pipes 0.15 m (6 in) I.D. perforated underdrain pipes too small 0.20 m (8 in) I.D. slotted PVC underdrain pipes used No clean-outs for underdrain system Clean-outs added for each underdrain pipe Gravel envelope around drains not filter compatible Granular filter material around new drain pipes Presence of untreated erodible rock foundation Intensely-weathered rock was over-excavated Presence of untreated shears in rock foundation Shear zones over-excavated and treated Less rigorous foundation clean- up Extremely rigorous foundation clean-up Insufficient rock anchorage (only ~1.5 m [5 ft] deep) Deeper rock anchors – 4.6 to 7.6 m (15 to 25 ft) deep Potential corrosion of rock anchors Rock anchors epoxy coated Potential cavitation Aeration added in Phase 1 spillway section [3] 78