Page - 155 - in Book of Full Papers - Symposium Hydro Engineering

indicated that cracks appeared above herringbone drains during slab concrete curing, within one month after concrete placement. These cracks provided pathways for leakage through the slab at times when there was water flowing down the chute. Over time, joint filler was removed from joints by the high velocity flows in the spillway. Loss of the joint filler would have resulted in increased leakage through joints when water was flowing down the chute. Spalling occurred almost entirely in delaminated concrete at joints and cracks and at patches from previous repairs, generally in the concrete above the level of the reinforcing steel and dowels. Delamination led to spalling of the slabs near the joints and cracks. The spalling exposed the reinforcing steel in the chute slabs and the dowel bars at the joints to corrosion, leading to reinforcing bar failure (see Fig. 7) when subjected to tension during the winter contraction cycle. Depending on the magnitude and orientation of the spalls, vertical faces that result in stagnation pressures during spillway discharge could have been created. Fig. 7 Corroded and ruptured steel reinforcing bars at a slab crack The chute repairs were generally shallow, involving removal of damaged concrete and patching of spalls to restore the flow surface. In some cases, the chute repairs also involved replacing the joint filler, reconnecting broken reinforcing bars with couplers, and grouting of cracks. In at least one of the repair efforts, the dowels in some of the formed lateral joints were cut in order to place joint-filler material. Although much of the damage resulted from temperature related stresses, there is no evidence that temperature studies were part of any repair design effort. Based on reports of repair efforts and interviews with DWR personnel, the IFT understands that spalling both recurred in previously patched areas and occurred in areas that had not exhibited spalling before. 155