Nonlinear Dynamic Response of Reinforced Concrete Covered Canal under Strong Ground Motions

Abstract

Underground structures have been considered to be relatively safer during the event of earthquakes. This belief has continued to make its roots in the engineers’ mind until the 1995 Hanshin-Awaji earthquake (Kobe earthquake). The Kobe earthquake witnessed severe damage and complete collapse of several subway stations belonging to Kobe metropolitan subway line. Similarly, recent 1999 Chi-Chi earthquake and 1999 Kocaeli earthquake also witnessed severe damages. These events have raised the serious concerns regarding the safety of the underground structures during earthquake. In Nepal, some of the underground structures have been constructed and some are underway to construction. In light of the damages that occurred in underground structures in recent times around the various parts of the world, detailed investigation of the seismic performance of the structures that is currently underway construction and the structures that are to be constructed in future have to be made. It is intended to study the performance of the to be constructed three-chambered reinforced concrete Covered Canal under severe ground motion due to earthquakes, which is a component of SIKTA Irrigation project. For accessing the performance of the covered canal, six different conditions of water levels have been considered. The soil investigation has not been carried out in the region where this structure is going to be constructed. So, for the purpose of the research, soil database of the head works have been utilized. The analysis showed that the covered canal is safer in the event of earthquakes. But, as the soil data used in the analysis is not the one found at the covered canal vicinity, it could not be generalized that the structure is safe in the event of earthquakes. So, it is deemed to be necessary to access the performance of the covered canal in various kinds of multi layered soil profiles. For this purpose, eleven models have been developed. These eleven models are grouped into three sets. First set consists of the three models having only one layer of soil each. Second set consists of six models with thickness and number of soil layers identical to original base case and varying the profiles by combination of soil properties. Third set consists of two models apart from base case with soil properties and number of soil layers identical to the base case and varying the thickness of the soil layers. These studies have revealed that the different types of soil profiles have got profound effect on the performance of the underground structures.