Numerical Study on Concrete Gravity Dam Subjected to Fault Motion

Abstract

Lifeline structures like dams should always be designed for highest safety, resisting worst forces of nature. However, events that took place across the world proved how devastating an earthquake could be, particularly near-field. Landers (1992 – Mw 7.3), Northridge (1994 – Mw 6.7), Hyogoken-Nanbu (1995 – Mw 6.8) and few more events with near-field effects caused damage to different range of structures. Notable damage to Koyna dam due to Koyna earthquake (1967 – Mw 6.5), India and Shih-Kang dam due to Chi-Chi earthquake (1999 – MW 7.6), Taiwan, proved effects of near-field earthquakes can cause damage even to dams. In India there are several dams constructed near the active faults, which might suffer moderate to severe damage in an event of near-field earthquake. In this concern, a proper study should be done to understand the behavior of concrete gravity dam subjected to near-field earthquake caused by fault motion near the dam site. In the proposed study, a concrete gravity dam is selected from the National Importance Dams of India. Structure-1(S1) as a concrete gravity dam with foundation and structure-2 (S2) as a concrete gravity dam with foundation and soil strata are numerically modeled using Applied Element Method (AEM). Displacement is given at the base to generate reverse fault effect on the dam. Behavior of dam is studied by direct and sub-structure methods. In the direct method, the effect of fault motion on dam is studied in S2, by modeling dam at different locations on foot wall and hanging wall. In sub-structure method, free-field accelerations are recorded at different locations on foot wall and hanging wall while only the sub-structure is subjected to fault motion. The recorded accelerations on the surface are used as input to analyze super structure S1. Comparison is later drawn between S1 and S2.