Engineering geological evaluation of the spillway of dam (II-B) of Bunakha Hydroelectric Project, Chukha Dzong, Bhutan

Abstract

The 200m long and 106.2m wide spillway of Bunakha Hydroelectric Project is proposed at the centre of the dam to pass the flood discharge. The spillway area was investigated through detailed engineering geological mapping, geophysical survey, exploratory drilling and laboratory testing. The rock mass properties, i.e. joint sets, weathering grade, RQD, RMR, permeability, P-wave velocity etc. of the rock masses to be encountered during the excavation of spillway have been analyzed in detail. Core samples from the exploratory drill hole drilled at the spillway alignment were tested for physico-mechanical properties of rocks in the laboratory. The mapping details indicated that the major rock types which are exposed to the surface and cover the entire spillway area are foliated gneisses with bands of banded gneisses. On the basis of detailed investigations and laboratory testing, inferences and recommendations have been made which will be helpful during the construction of the project.