Investigation and Measures against Internal Restraint Crack due to Thermal Stress of RCC Dam—Practice at Nam Ngiep 1 Hydropower Project in Lao PDR—

Abstract

During construction of the Roller Compacted Concrete (RCC) dam at the Nam Ngiep 1 hydropower project (NNP1) in Lao PDR, cracks in the direction of the dam axis emerged on the RCC placing surface at the left bank side where RCC placing suspended in order to install the penstock to be embedded in the dam body. The NNP1 conducted the crack investigation and thermal stress analysis by inputting the observed ambient temperature and development of RCC strength into the analysis and it was found that the main cause was the difference of the concrete temperature between inner and surface portions of the RCC according to the sudden larger drop of the ambient temperature compared in the mid December than that of the average year. This report presents the process of the above investigation and analysis for seeking the cause, check of the dam stability, and measures based on hearing from RCC experts.