Koldam Hydropower station (4*200MW) of NTPC Ltd. is an earth and rockfill dam 165m high, having a spillway length of 460m with 6 radial gates and a flip bucket as an energy dissipating structure. Station was commissioned in July 2015 and since then spillage of water during monsoon season is a regular activity. During the 2016 monsoon, a widening of the dilation joint between the spillway and flip bucket was observed. The same was monitored via manual and online Vinchon instruments which were under allowable limits. In 2019 the Joint widening crosses the allowable limits, and it was analyzed that there is some movement in the flip bucket on all axis. The same was monitored and various investigations were carried out to reach the root cause which was geology consisting of basic dyke and sheared phyllite joint below the flip bucket. This movement was locked by using 100 Ton ultimate capacity 70 nos. 60 meters long 150mm dia. cable anchors for a spillway discharge of 3000 Cum. at a time. The anchors were installed from the front face i.e. from the plunge pool side by way of making a steel platform and using 02 numbers drilling machines for timely completion of work during 2020-21. The efficacy of these remedial measures has been checked and validated during monsoon 2022. This technical paper will be beneficial for the hydro projects having analogous present situations or may face in future.
Flip Bucket, Plunge Pool, Vinchon, Cable Anchors, GPR, NIRM
