Agartala–Bangladesh Railway Embankment Construction Over Soft Soils Incorporated with Prefabricated Vertical Drains: A Case Study

Three embankments of different dimensions for the railway tract at contiguous locations are being constructed over soft soils using prefabricated vertical drains for connecting two cities, Agartala and Dhaka. Prefabricated vertical drains were supplied from Maccaferri and the installation rig machineries were provided by IRCON. PVDs were installed in triangular pattern with three different spacing (0.7, 0.8, and 1.0 m) with according depths (15, 6, and 7.5 m). For conducting physical and engineering properties, soils were collected from different locations as well as from different depths using auguring and wash boring method at suitable intervals along with SPT tests. It has been observed that the natural soil profile was composed of three different layers of different thickness; sandy silty-clay at top, silty-clay in the middle, and sandy silty-clay at bottom, respectively, overlying the hard stratum. A sand layer of thickness 0.2 m is being provided underlain by a strip drains made up of polypropylene, which accelerates and helps sand layer draining off the water from PVDs, over which paralinks were also laid that function as reinforcement to embankment soil deposits. Settlements predictions of the existing soils were made and determined. Different results were obtained at various locations. Without PVD, the settlement of the soil strata at chainage Ch-03 + 900 to Ch-04 + 400 km is observed to be 2305 mm and the corresponding settlement time is 189306 days. While the design was made considering PVD the consolidation settlement and time gave as 1660 mm and 122 days, respectively.