Delineation of Cavity in Downstream Surge Chamber at Punatsangchhu-II Hydroelectric Project, Bhutan

Abstract

On 3rd March, 2016, there occurred a massive roof fall incidence in one of the major caverns of Punatsangchhu-II Hydroelectric Project (PHEP-II), Bhutan which halted the operations in the major caverns and required additional strengthening measures. Prior to concluding anything on the treatment measures for the muck flown into the cavern and the cavity formed over the crown of Downstream Surge Chamber, there was a strong need to determine the extents of cavity. Even to understand the influence of cavity formation on adjacent caverns, the cavity needs to be delineated. Therefore, the management of PHEP-II adopted several techniques to decipher the shape and dimensions of the cavity like, surveying, geophysical, cross-hole seismic surveys, borehole scanning, and exploratory drilling. The tentative shape of the cavity could finally be established. The findings from each method are explained in this paper.

Importance of Instrumentation in Hydropower Projects vis-à-vis Quality Control

“…A typical longitudinal section along the dam axis, maximum sluice section and the maximum non-overflowing section showing the location of different instruments at are shown in Figures 5,6…”