APPLICATION OF THE ELASTIC BOUNDARY INDUCED BY SHEAR HISTORY ON SATURATED COHESIVE SOIL

A new construction procedure applying a large preload to a mechanically reinforced backfill structure and keeping a large prestress while the structure is in service is described. This construction procedure was developed to substantially decrease transient and residual compression of reinforced backfill by long-term vertical cyclic loading, such as traffic load. A very high performance for about four and a half years of a prototype railway bridge pier of preloaded and prestressed geogridreinforced gravel backfill, which validated the advantages of this construction procedure, is described. A series of model loading tests performed in the laboratory to find the relevant preloading and prestressing procedure are described. It is shown that the transient and residual compression of reinforced backfill by vertical cyclic loading can be made very small by preloading the reinforced backfill and then decreasing the load level to a prestress level that is about a half of the preload level, while keeping the difference between the preload and prestress levels sufficiently larger than the amplitude of subsequently applied cyclic load. Effects of different combinations of backfill soil type and reinforcement material, the use of tie rods and the application of pre-cyclic preloading are reported. Negative effects of the swelling of backfill during unloading are discussed.