During the initial stage of construction of a 23 m high composite dam across the Guhai river, the downstream dipping sedimentary rock sequence of conglomerate, sandstone and shale resting unconformably over quartzite and schist was encountered as a surprise during the excavation of the foundation. Besides, an 8 to 8.5 m wide major fault zone along with three minor faults running across the dam axis were also noticed. Extensive subsurface investigations to study the nature and characteristics of sedimentary rocks, fault zones, etc. met with in the foundations were undertaken concurrently with the construction activity. As a result, the construction schedule was greatly affected. The paper discusses the detailed evaluation of the geological flaws by thorough investigation and foundation treatment evolved to safeguard the structure
