Column-Supported Embankment: Failure and Remedy

The design and construction of an 800-m segment of an embankment over nonhomogeneous soils, including a layer of organic clay, is presented in this paper. The embankment was constructed over 13,670 controlled modulus columns that were designed to transfer loads to deeper, more competent soil layers. The combined length of the columns was about 210 km. The length of individual columns varied from 8.8 m to 22.8 m. A geosynthetic-reinforced load transfer platform was designed to aid in transferring the embankment loads to the columns. Settlements of 30 cm were detected during embankment construction. A correlation was observed between the extreme settlements and the locations of culverts. Efficacy of the column supporting system was estimated through back calculations using the settlement measured data. Analysis and observations of the settlements' distribution led to the conclusion that the major cause of low efficacy was suppressed arching in the fill layer above the columns in the vicinity of culverts. Remedial action included reducing the loads through replacement of natural fill with lightweight expanded polystyrene blocks, and drilled shafts in one location. After the project conclusion, pavement settlements between 8 and 14 mm were observed within eight months, and no distress was reported in the following two years.