Deformation Response of Dam-Foundation System of Concrete Gravity Dam Due to Presence of Shear Seams in Rock Foundation

Abstract

The paper describes the influence of shear seam on the equivalent continuum dam-foundation system of a concrete gravity dam, as observed through elasto-plastic analyses. Discrete element analyses have been carried out using UDEC by idealizing the foundation as an equivalent continuum. Multiple scenarios for analyses have been simulated under varying magnitudes of seam width, seam location and seam orientation $(\theta_{s} )$. Analysis has been carried out for two specific static load combinations as per IS: 6512 (1984), viz., (i) Loading condition ‘A’ (construction condition), $LCA$, and (ii) Modified loading condition ‘B’ (normal operation condition), LCB. It is observed that due to the presence of a seam, the stresses and displacements are affected in the dam and foundation in the vicinity of the seam. The vertical deformation at the mid-point of the seam, $\delta_{ys}$, at the dam base is compared with the vertical deformation at the same location in the absence of the seam, $\delta_{y}$. A seam influence factor ($I_{f}$), defined as the ratio of $\delta_{ys}$ to $\delta_{y}$, is calculated for each case, to study the impact of the seam. Relative assessment of seam influence factors across different scenarios has been performed to arrive at the design implications emerging from the study. It is observed that the seam influence factor increases with increase in the seam width, under all simulation conditions, hence implying that wider seams are more critical. Further, it is concluded that seams at certain locations and seams of certain orientations are more critical than the others-seam orientations of 90 and 120° are the most critical for $LCA$ and $LCB$ respectively, and, seam location at the heel of the dam is most critical for both loading conditions.