Design Of Anchoring System for Spillway-stilling Basin Junction (Gulpur Hydropower Project)

Abstract

Dams are important structures for reservation of the water and hydroelectric power generation. A dam is a combination of several structural elements including a stilling basin. Stilling basin is an important part of a dam structure and is used to dissipate the energy carried by high-velocity water falling from the height. Usually, the magnitude of the energy that needed to be dissipated is enormous for the discharge of the spillway. This can result in scouring and damage to the stilling basin slabs. Spillways exhibit a tendency of sliding during the seismic events, and it can have a damaging impact on stilling basin slabs. This is because stilling basins relate to the spillway at the foundation level. This introduces slope failure in the slab of the stilling basin. This study would provide the necessary anchorage system to stilling basin slab which would resist the thrust of the spillway during seismic actions. This report presents the stability analysis for the rock mass at the Spillway-Stilling Basin Junction for the Gulpur Hydropower Project. Previous dynamic analysis of the spillway structure indicated that the spillway structure exhibits some sliding tendency during a Maximum Credible Earthquake (MCE) Event, which has a Return Period of 10,000 years associated with it. The Spillway Structure thus exerts a thrust at the Spillway-stilling basin junction, which has to be resisted by the rock mass at this junction. The rock mass at the Spillway- Stilling Basin has to be reinforced by the provision of anchors to enable it to withstand the expected thrust from the Spillway Structure during an MCE Event. For the purpose of evaluation of the rock mass, manual computations are presented in this document. The problem has also been solved in the software Plaxis 2D V-8. Pl 2D, is a powerful and user- friendly finite element package intended for two-dimensional analysis of geotechnical engineering and rock mechanics. The software has the features of non-linear material modeling and interfaces modeling between different material surfaces. The software has the capability of performing analysis with different types of anchoring systems, using which suitable anchoring systems can be designed to assure a safe design.