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The nonlinear response of concrete gravity dam-reservoir system has been investigated by conducting experiments on small scale model of Koyna dam on a horizontal shake table using sinusoidal chirp motions. Two dimensional models of non-overflow section of Koyna dam have been prepared in the laboratory with a scale ratio of 1:150. To satisfy the laws of similitude, an appropriate ratio of cement, sand, bentonite and water has been mixed to find the target properties of model dam. Dam models have been casted over a wooden base plate using a wooden mould. After setting and drying process the wooden mould has been removed and each dam model has been assembled with a reservoir model after placing them over a horizontal shake table. The interaction between dam and reservoir model has been made in such a manner, so that it can transmit the hydro dynamic force of reservoir water to the dam model without allowing any seepage of water across it. Experiments have been performed on the dam-reservoir system with empty and full reservoir water by applying horizontal sinusoidal chirp excitations to the shake table to observe the basic behaviour, crack formation, crack opening, sliding along crack planes and stability after crack formation of the dam model. The numerical analysis of the system has been carried out using ABAQUS 6.10 considering damage plasticity model. The effect of foundation has been neglected assuming a rigid dam foundation as the dam is placed on a rigid plate. The eigen frequencies of the dam model have been calculated and compared with experimental values to calibrate the analysis model. The crack propagation due to tensile damages is computed and the results are compared with the experimental results. The outcome of the response results shows the correctness of the developed experimental model of dam-reservoir system. [ABSTRACT FROM AUTHOR]

We report here the salient features of the recently concluded International Continental Scientific Drilling Program (ICDP) workshop in Koyna, India. This workshop was a sequel to the earlier held ICDP workshop in Hyderabad and Koyna in 2011. A total of 49 experts (37 from India and 12 from 8 other countries) spent 3 days reviewing the work carried out during the last 3 years based on the recommendations of the 2011 workshop and suggesting the future course of action, including detailed planning for a full deep drilling proposal in Koyna, India. It was unanimously concluded that Koyna is one of the best sites anywhere in the world to investigate genesis of triggered earthquakes from near-field observations. A broad framework of the activities for the next phase leading to deep drilling has been worked out. [ABSTRACT FROM AUTHOR]

The seismic activity in the Koyna area is clearly related to the water impoundment of the Koyna dam in 1962, and has reached a remarkable level with the occurrence of a major event of magnitude 6.3 in 1967 December 10. We present a homogeneous poroelastic model based on analysis of the first eight years of seismicity, which aims to link the water-level fluctuations of the reservoir with the seismicity. Starting from a discretized lake, we calculate the stress field resulting from the water-level fluctuations and the pore pressure changes due to the undrained and the diffusive responses of the medium. Then, we compare the Coulomb stress variations with a set of relocated seismic events. We find that more than 80 per cent of the relocated events before the M6.3 event are well described by this poroelastic model, leading us to derive a suitable diffusivity . Then, we model the response of the system after the M6.3 event of 1967 December 10, by comparing the variation of the Coulomb stress field with the spatio-temporal characteristics of the relocated post-seismic events and the decay of aftershocks with time. We find that compared to before the main event a tenfold increase in hydraulic diffusivity is required to satisfactorily describe the aftershock decay with the appropriate Omori exponent. Although this increase in diffusivity may be physically related to the main shock we also note that events later than 9 months after the main shock are not well explained. We therefore propose an alternative hydrological model, which involves two compartments of contrasting diffusivities. [ABSTRACT FROM AUTHOR]