Page - 79 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 8 Design measures included in 2017 structural concrete for FCO Spillway chute The 3 m (10 ft) thick RCC apron was founded on rock, requiring substantial removal of surface soils, fills, and temporary armoring. The foundations for the RCC buttress and the 2-m-high concrete crest were specified to be of moderately-weathered rock, or better, and to be thoroughly cleaned. The purpose of the downstream secant pile wall is to support and protect the RCC apron from head-cutting erosion. Using the results of the geologic explorations, an alignment was chosen for the secant pile wall approximately 227 m (746 ft) downstream of the existing monoliths/weir sections. Along this alignment, the depth to slightly weathered or fresh rock is only about 6 m (20 ft) or less. This allows for the bottoms of the piles to be keyed into slightly weathered or fresh rock to depths of at least 4.5 m (15 ft) or more, with total pile depths ranging between 11 and 20 m (35 and 65 ft). As shown in Fig. 9, the piles were designed to be a minimum 91 cm (3 ft) in diameter with centers spaced at 61 cm (2 ft), and to be constructed in 5-pile panels with a 30 cm (1 ft) gap between panels to allow for drainage and to avoid the buildup of groundwater pressure against the wall. Two of the five concrete secant piles in each 5-pile panel were reinforced, while the other three were unreinforced (see Fig. 9). A reinforced concrete grade beam will be constructed across the tops of the piles and anchored back into the RCC apron to a minimum distance of 40 feet (12 meters). (a) 79