Dam Safety

India’s CEA issues guidelines for slope stability in hydro power projects

India’s CEA issues guidelines for slope stability in hydro power projects

The chairperson of the Central Electricity Authority in India has approved and released Guidelines for Slope Stability in Hydro Power Projects.

This eight-page document was developed after the Minister for Power and New & Renewable Energy directed CEA, in January 2023, to develop “a comprehensive technical manual/guidelines … about aspects to be kept in view before and during construction of hydro project including the mandatory aspects like building retaining wall wherever slope is interfered, reinforcement/strengthening of any identified geological fault, etc.” The Minister said the project proponent for projects above a certain threshold level (such as 400 MW) “may be made responsible to examine upper reaches including reservoir area, dam site and identify faults/slides and take remedial measures for stabilization.”

An expert committee was convened, with members from CEA, the Central Water Commission, Geological Survey of India and hydro central public sector undertakings (NHPC, NTPC, THDC, SJVN, CVPPL, NEEPCO and NHDC).

The guidelines say that “the design, construction and maintenance of the slopes is one of the major challenges during planning, construction and operation of hydropower projects.” Slope instabilities are caused when the force/load equilibrium of the stable slope is disturbed by change in geometry, hydrogeological regime, deforestation and/or weathering effect.

To stabilize an unstable slope, the factor of safety — the ratio of the rock/soil’s in situ shear strength to the shear strength required for equilibrium along a given potential failure surface — must be increased. Slopes can be stabilized by adding a surface cover, excavating and changing (or regrading) the slope geometry, adding support structures to reinforce the slope or using drainage to control groundwater seepage in the slope material.

As hydropower projects usually involve heavy surface excavation for placing the dam, power intakes, powerhouse and other structures that lead to the formation of excavated rock/soil slope, it is essential to maintain slope stability. A thorough investigation of the project area before excavation, using advance techniques covering all the aspects of slope stability, can mitigate the possibility of slope failure. And effective measures for slope stabilization may be planned in advance, reducing the cost of stabilization.

Site selection for critical components of hydropower projects should be such that the orientation of joint/bedding planes is favorable for a stable excavation. However, it is not always possible to have desirable geological formations for placing the structures due to certain technical requirements leading to instability of slopes. In those cases, slope stabilization techniques should be used to increase the stability of slopes.

Just last week, as Hydro Review reported, Teesta Urja Dam in Sikkim State suffered massive damage due to flash flooding.