Chapter 19 - Settlement Behavior of Embankment on Soft Ground Treated with Stepped Rigid Columns

Abstract

Limiting the differential settlement within a bridge approach embankment is of significant importance, particularly where the embankment is constructed over soft ground. A typical approach embankment consists of three treatment zones: (1) approach slab zone where only limited/stringent postconstruction settlement (PCS) is allowed, (2) transition zone to maintain differential settlement grade between the approach slab and general embankment zone, and (3) general embankment zone where higher PCS can be allowed depending on the adopted road pavement type. The appropriate ground treatment should be adopted for each zone considering several factors such as cost, available construction time, construction constraints, and settlement criteria for each zone. In some instances, such as under limited construction time, it may be necessary to choose hard ground treatment using full depth rigid columns (i.e., installed through the soft soil and founded in stiffer material) at the abutment zone. In this situation, an appropriate transition ground treatment using stepped rigid columns (i.e., installed partially into soft clay) may be required to maintain the differential settlement grade between the abutment zone and general embankment area.