Abstract:
The paper presents the case study of repetitive dam failure of Morasuab dam, a homogeneous dam in Thailand, occurred in 2016, 2017 and 2019 after the appearance of a sink hole in 2012. The dam has failed at the same section, regardless of its rehabilitation. The geotechnical investigation like boreholes, electro resistivity test (ERT) and Kunzelstab penetrometer test (KPT) showed the presence of permeable sandy foundation and shallow deep bedrock at downstream section. However, the two-dimensional (2D) seepage analysis of the affected section (Station 0 + 450 km) showed no failure due to uplift or exit hydraulic gradient. This suggested that sandy foundation and shallow bed rock is not solely responsible for dam breach. When further investigation was carried out, dispersive soil was identified in embankment fill zone during dam excavation. This suggests that dispersive soil is the major cause of piping that led to repetitive dam failure since 2012 and the presence of sandy foundation and shallow bedrock could have accelerated the piping mechanism. Moreover, the post breaching survey of affected section suggested that piping occurred through the embankment section and erupted through the filter.
