Page - 953 - in Book of Full Papers - Symposium Hydro Engineering

On the other hand, in case of non-emergency, it's better not to lower down the reservoirs water level too much to avoid excess concrete stress and crack, especially arch dams, to which, the temperature load is a kind of particularly sensitive load. In fact, majority loads of water thrust act on the higher part of arch dams. The total water thrust of Xiaowan arch dam with the height of 294.5m reaches 18 million tons. And half of the thrust act on the top 40m of the dam, while the other half act on the bottom 250m height left. So the integral stability of Xiaowan arch dam is enough safe after discharging to the designed emptying ending water level even if there is still 139.5m water head left. The safety of embankment contains dam slope stability and seepage stability. When the anti-seepage is damaged, the seepage gradient of dam body behind the anti-seepage can be significantly reduced while the downstream slope stability been increased by lower the reservoirs water level, no matter earth core dam or concrete faced rockfill dam (CFRD). DAM OVERHAUL CONDITIONS Foundation galleries are usually set up in concrete dams, especially high dams. So the cracks in the upstream surface of dam body and seepage of dam basement can be handled by grouting in the foundation galleries, without emptying the reservoirs. However, some concrete dams developed cracks penetrating from upstream surface to foundations, which caused dam uplift pressures and leakage increase. In this case, the cracks have to be repaired by emptying the reservoirs instead of grouting only, such as Konbrien arch dam in Austria. The key problem of embankment dams is overhauling conditions of anti-seepage systems. For earth core dams with foundation galleries, the effects of supplementary grouting under high water head are usually not good if the anti-seepage systems are damaged. So it is need to lower the reservoirs water level to reduce the seepage pressure and velocity in order to achieve good grouting effect. For CFRD, the biggest challenge is how to overhaul the broken seepage system. Clay blanket under the emptying ending water level is designed to protect the anti-seepage systems. But there are still some problems. The leakage position of Baiyun CFRD in Hunan province was just below the clay blanket, so the reservoir has to be emptying and clay blanket be dug out to overhaul the broken concrete face. Some research suggest that do not set clay blanket on the concrete face for convenience of overhaul. In the near future, the dam examine and overhauling may not be limited by the water depth along with the development of intelligent robots and detection technologies in deep water. COMBINATION OF EMPTYING AND DISCHARGE FACILITIES Usually, the intakes of emptying facilities are set too low and do not used to discharge flood or silt. Most of them are rarely used and have very few chances to operate and be maintained. So they may not be able to operate in case of emergency. Thus it should be considered to combine the emptying facilities and 953