The geology at site is defined by a series of en-echelon folds with southerly plunge, which are associated with a dextral transpressive shear zone which runs parallel with the Mekong river course in a North - South direction. The component parts of this structure are the highly sheared zones passing obliquely through the structures, an ‘S’ shaped outcrop pattern of the competent Limestone and series of en-echelon folds indicating relative dextral displacement across this highly sheared zone. The structures seen at dam site are dormant sub-structures to the main alignment which is situated to the West of the dam project. The rock mass has been in the geological past, highly tectonized, resulting in part with a high disturbed rock mass.
The lithologies present at the Navigation Lock comprise essentially a thinly bedded flysch rock type sequence, which has been highly tectonized. The succession at the site of this construction element consists of 4 rock units as follows;