Embankment Behavior over the Soft Soil in Southwestern Part of Bangladesh-Paper

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The study evaluates Class-A predictions of railway embankment settlement over soft, organic soils along the Khulna–Mongla Port railway in southwestern Bangladesh. The embankment, built in stages over more than 1,000 days, is supported by prefabricated vertical drains (PVDs) and surcharge.<br /><br />Researchers modelled the actual construction sequence and compared predictions with settlement-plate measurements at Chainage 11,540. PLAXIS 2D analyses used the Soft Soil Creep model for organic clay, the Soft Soil model for soft clay, and the Mohr–Coulomb model for sand and embankment fill. Soil parameters were derived from laboratory and field tests, established correlations, and two geotechnical investigations: IRCON’s 2017 data and KUET’s 2022 data.<br /><br />After 1,243 days, with approximately 7.5 m of fill, measured settlement was 1.72 m. The model based on KUET’s 2022 investigation predicted 1.973 m—a discrepancy of about 13%. By contrast, the 2017-data model predicted only 0.736 m. The authors attribute the improved agreement to more detailed soil stratigraphy, better characterization of organic layers, and suitable constitutive models and parameter correlations. They also note that poor or disturbed samples and inadequate stratigraphic detail can undermine predictions.<br /><br />The findings indicate that reliable settlement forecasting depends on high-quality undisturbed samples, detailed soil profiling, and appropriate soil models. The results also support using established laboratory correlations for consolidation parameters and adopting a smear-zone parameter ratio of approximately 2 for PVD applications in Bangladesh.

Keywords

railway embankment settlement

soft organic soils

Khulna–Mongla Port railway

prefabricated vertical drains

PLAXIS 2D

Soft Soil Creep model

settlement prediction

geotechnical investigation

consolidation parameters

PVD smear zone