Deformation of the Nam Ngum 2 concrete faced rockfill dam (CFRD) in Laos after construction Warakorn Mairaing Chinoros Thongthumachat Associate Professor Senior Researcher Department of Civil Engineering GERD, Department of Civil Engineering, Faculty of Engineering, Kasetsart University Faculty of Engineering, Kasetsart University Bangkok, Thailand Bangkok, Thailand Nam Ngum 2 is one of the world ranked concrete face rock fill dam (CFRD) in Lao PDR. It is 182 meter high with the dam volume of 9.7 million cu.m. Monitoring of dam behaviour was done by 390 sensors with data acquisition system. The deformation of dam body and face slab were measured by embankment extensometers, hydrostatic settlement cells, electro-level, joint meters, concrete and rebar strain meters and survey stations. The maximum settlement of dam crest during 3 years of reservoir operation was 24.6 cm. or 0.15 % of dam height. The settlement creep rate after the last impounding was =0.10%/cycle time. During first impounding, the maximum deflection of face slab was 486 mm. as compared to the design analysis of 457 mm. Face slab joint movements indicated the local maximum settlement of 80 mm on the left abutment. This joint settlement was still in the allowance of copper water stop and joint sealing. 1. Introduction Nam Ngum 2 Hydroelectric Power Project (NN2PP) was constructed on upstream of existing Nam Ngum 1 reservoir, Lao PDR. The dam is located 90 km. north of capital city of Vientiane or approximately 160 km via route No 13N. The construction was started in 2006 and finished in 2010 with dam volume of 9.7 million cu.m. The dam is concrete faced rock filled dam (CFRD) of 182 m high and crest length of 485 m. The project has the capacity to generate the power of 615 MW or about 2220 GWh a year, mostly for Electricity Generating Authority of Thailand (EGAT). The site is located in a narrow valley with rather steep slopes and complex geology of sandstone interbedded with siltstone and shale. The dam and appurtenant structures layout are as shown in Fig. 1. Fig. 1 NN2 dam project layout NN2 dam is consisting of compacted rockfill found on a rock foundation, plinth, face slab and wave wall as shown in Fig.2. Dam slopes for upstream and downstream are designed as 1V:1.4H to suit with available rockfill materials. The dam zoning was divided into three zones as follows: Zone 1 (1A and 1B) is concrete face slab protection zone