Field Performance of Prefabricated Vertical Drain to improve soft clay beneath the high railway embankment in Bangladesh-PPT Presentation

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The study evaluates prefabricated vertical drains (PVDs) for improving soft clay beneath high railway embankments on the Khulna–Mongla Port railway line in southwestern Bangladesh. The route crosses waterlogged deltaic deposits with very soft, highly compressible clay; embankments range from about 4 to 12 m high, and reported SPT values are typically 0–1.<br /><br />Subsoil conditions were investigated through 173 boreholes. PVDs were installed at 2.5 m spacing in a triangular pattern, to a length of 7.5 m. Settlement plates, piezometers and inclinometers were used to monitor construction and ground response. Design assumptions included normally consolidated soft deposits, a target consolidation degree of 90%, a 50 kPa surcharge for the railway superstructure, and a design stability factor of safety of 1.1.<br /><br />Field records show substantial settlement beneath the embankments. Predicted and measured settlements differed considerably, which the authors attribute in part to limited subsurface information and strong variation in soil properties along the alignment, despite the use of uniform design parameters. Stability was assessed using Low’s approach; the minimum reported factor of safety for PVD-improved ground was 1.25. No signs of embankment instability were observed during field monitoring.<br /><br />The findings support the use of PVDs to improve the soft clay, while highlighting the need for more detailed, site-specific investigation and design to better predict settlement and assess variable ground conditions.

Keywords

prefabricated vertical drains

soft clay

railway embankment

Khulna-Mongla Port railway

settlement monitoring

ground improvement

piezometers

inclinometers

stability factor of safety

deltaic deposits