At Moyna Hydro-electric Project, an 80MW powerhouse is currently proposed at the left dam foot of Moyna river dam in Maharashtra. The underground powerhouse cavern needed for housing the two turbine units of 2 X 40MW is designed using three-dimensional numerical modelling. Three possible geometries for the powerhouse are designed considering the weaker rock mass layers of Volcanic Becca existing in the vicinity of the proposed cavern. These configurations are simulated in FLAC3D software. Their stability is analysed using Hook and Brown rock mass failure criterion. Taking cues from the stability predicted for the three configurations, a final configuration is designed. The final configuration is further subjected to three dimensional modelling and stability analysis. The cavern is expected to have good overall stability. The crown region, since it will be located in stronger Compact Basalt rock layer, will have superior stability. However, the cavern will have weaker sides, where Volcanic Becca will be exposed. A support plan for the entire cavern is also designed incorporating 100mm thick steel fire reinforced shotcrete (SIRS) and 6.0m long full column grouted resin bolts.
Moyna Hydro-electric Project of Maharashtra State Government produces electricity of the order of 2000MW in four stages. This environmental friendly and cheap power generation caters to the energy demands of the neighbouring region. As an extension of Stage IV, an 80 MW (2x40 MW) capacity powerhouse is proposed at the Moyna dam foot at the left bank of the Moyna River. Underground powerhouse chambers are proposed for power generation. From the geological survey conducted by Moyna Project authorities, the rock types existing in this vicinity was found to be Deccan Trap Basalts, viz.
The intact rock properties tested earlier by CAPES (Anon (2004) and Anon (2005)) and rock mass parameters such as RM (Bieniawski (1976)) for compact basalt and volcanic Becca are given in Table 1. The Hook and Brown rock mass parameters are also evaluated (Hook and Brown (1980)) and given in the table since they are to be used in the numerical modelling.
Three optional configurations were initially chosen to comparatively analyze the stability scenario. Depending on their stability, the most stable configuration shall be chosen as the final powerhouse design. The three configurations modelled for their stability analysis has the following salient features.
A powerhouse cavern of 21m width, with crown level at 599m EL and springing level at 592.5m EL A valve house of 10m width, with axis at 600 to that of the powerhouse cavern, with crown level at 595.5m EL and springing level at 592.5m EL
A powerhouse cavern of 21m width, with crown level at 595m EL, and springing level at 588.5m EL A valve house of 10m width, with crown at 591.5m EL and springing level at 588.5m EL
A single powerhouse cavern of 25m width, with crown level at 595m EL and springing level at 588.5m EL, and without a valve house
