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.
