Chapter 29 Bridge abutment made of cement-mixed gravel back-fill

Abstract

This report describes a new type bridge abutment consisting of the backfill of geogrid-reinforced, cement-mixed gravely soil and a thin RC parapet structure (i.e., a parapet) supporting a bridge girder, which was completed in 2003 for a new bullet train line in Kyushu, Japan. The backfill and the parapet are firmly fixed to each other with geogrid layers embedded in the cement-mixed backfill. This structure is very unique in that the backfill supports laterally the RC parapet, rather than exerting static and dynamic earth pressure on the back face of the parapet in comparison with the conventional-type bridge abutment consisting of a relatively massive reinforced concrete structure supporting the backfill of uncemented soil. It is shown that the new type bridge abutment is very cost-effective. A series of model shaking table tests were performed to evaluate the seismic stability of conventional-type bridge abutments as well as several new type bridge abutments including the one that was actually employed to construct the prototype one. Results from a series of drained triaxial compression tests on cement-mixed gravely soil are reported. It is shown that cement-mixed gravely soil should be mixed at the optimum water content for compaction energy used to construct the backfill. It is shown that the compressive strength of cement-mixed gravely soil increases considerably with compacted dry density. The design, in comparison to the one of the conventional-type bridge abutment, and the staged construction procedure of the prototype bridge abutment are described. Results from field full-scale lateral loading tests on the abutment performed to ensure the design conditions are reported. The prototype bridge abutment performed very well showing highly integrated behaviour with very high connection strength between the backfill and the parapet.