IMPROVING THE DYNAMIC PERFORMANCE OF PRELOADED AND PRESTRESSED MECHANICALLY REINFORCED BACKFILL BY USING A RATCHET CONNECTION

Abstract

A series of laboratory model shaking table tests were performed to evaluate improvement of the dynamic performance of mechanically reinforced soil structures that are vertically preloaded and prestressed by using a ratchet connection for the tie rods. The preloading and prestressing (PLPS) procedure was originally developed to substantially decrease the residual settlement at the top of backfill subjected to long-term live load such as traffic load. It is shown that the maintenance of high prestress in the backfill is also essential to substantially reduce the shear and bending deformation as well as vertical compression of reinforced backfill subjected to dynamic load. For relatively slender reinforced backfill structures, the maintenance of high prestress is particularly important to restrain the occurrence of large bending deformation of backfill. For these purposes, it is proposed that the top end of the tie rods be fixed to the crest of the structure by using a ratchet connection, which allows free compression of backfill at nearly constant prestress while mechanically not allowing any expansion of backfill. It is suggested that, to avoid a resonant or nearresonant state during seismic loading, the initial value of the natural frequency fn of a given structure be designed to be sufficiently higher than the anticipated predominant frequency fp of given seismic load, while the fn value during dynamic loadine is maintained at a higher valve than the fp value by using a ratchet connection.