Restoration of Railway Embankment – A Case Study-PPT Presentation

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The case study describes the restoration of an approximately 100 m railway embankment in Kolkata, underlain by about 7 m of soft clay. The embankment became unstable because the soil had low undrained shear strength (around 15 kPa). During the rainy season, a rising groundwater table increased the embankment’s weight, causing the soft soil to settle and squeeze. The slope then moved vertically, together with the retaining wall at its toe.<br /><br />The adopted solution combined structural support and ground improvement. An 800 mm-diameter row of contiguous reinforced-concrete piles, fitted with 6 mm liners at the bottom, was installed through the soft strata and tied together with a capping beam. Compaction grouting was also used to improve the soil’s shear strength. Confirmatory ground investigation was recommended to validate design assumptions.<br /><br />Design checks covered pile stresses, reinforcement and head deflection, as well as embankment slope stability under static and seismic conditions. The analyses considered groundwater-level differences across the embankment, pavement and rock-backfill loads, railway live loading, and seismic coefficients. A further local stability check reduced the strength of layers above the groundwater table.<br /><br />Reported pile-design results included a maximum bending moment of 42.4 tm/m, maximum shear force of 10.2 t/m, and pile-head deflection of 76 mm. The design provided 1.76% main reinforcement and 10 mm helical bars at 150 mm spacing. Reported slope-stability factors of safety for four analysis cases were 1.47, 1.1, 2.8 and 2.1.<br /><br />The study highlights the importance of thorough geotechnical investigation, groundwater fluctuations, and the effects of train loading, vibration and seismic conditions in railway embankment design.

Keywords

railway embankment

Kolkata

soft clay

groundwater table

undrained shear strength

contiguous piles

compaction grouting

slope stability

pile design

geotechnical investigation