EARTH PRESSURE AND SEISMIC DESIGN OF RETAINING WALLS

Abstract

his dissertation described study into earth retaining cantilever walls with relief shelves behaviour under seismic conditions, using numerical modelling technique. The effects of provision of relief shelves on lateral earth pressure and backfill soil settlement were studied with the help of numerical models using small strain finite element methods available in commercial software ABAQUS. The soil response was simulated using the Mohr-Coulomb’s model. Two seismic events (i.e., 1994 Northridge earthquake and 1983 Trinidad earthquake) were considered for dynamic loading. The results for static surcharge and soil self-weight loading showed that the lateral earth pressure and therefore total thrust on the wall reduces significantly when the cantilever retaining wall is provided with monolithic relief shelves. The backfill-soil-surface settlement also decreased substantially for the wall with one relief shelf, in comparison to the one with no relief shelf. When the number of relief shelves provided increased, the settlement further reduced. However, it was observed that the soil settlement remains almost similar for the cases of the wall with two and three relief shelves. The effect of relief shelf thickness on the lateral earth pressure and the backfill soil settlement were also investigated. The response of the cantilever retaining wall with and without relief shelves were studied for the considered seismic events. The lateral earth pressure decreased for the wall with no relief shelves as the wall tilted towards opposite of the backfill soil. This led to a drastic increase (about 85%) in vertical settlement of the backfill soil. This shows that the cantilever retaining walls without any additional measure for settlement resistance can lead to failure of structures constructed on the backfill soil. However, as expected, the retaining wall with relief shelves resisted the tilting wall due to earthquake. Thus, the lateral earth pressure and the backfill soil settlement remained almost similar to those before the occurrence of earthquake. The importance of the provision of relief shelves with the cantilever retaining wall is clear from this study. Such walls behave better in the time of seismic events.