The Koyna earthquake of 11th December 1967 caused severe distress in a portion of the Koyna dam, leading to the formation of cracks. With the assumption that the crack had divided the dam portion into two blocks, investigation of the stability of the top block above the crack has been carried out. Under the effect of subsequent earthquakes, or after shocks, toppling of the top block can lead to a disaster downstream of the dam by causing flood, etc. With this objective, possibilities of the sliding and overturning of the top block has been carried out with the utilization of a discontinuum technique known as the Discrete Element Method (DEM). Analysis of the dam with various crack profiles, shear stiffness at the cracked surface, and the effect of vertical motion, is discussed in detail. Results show that the seismic stability of the dam with a horizontal crack is more susceptible to sliding followed by rotation, which is concluded by the effect of shear stiffness at the cracked surface and the increasing reservoir, as recommended by Krishna & Saini [16]. It is observed that the crack profile plays an important role in the stability analysis. A downstream propagating crack with steep angle induces more instability.
