Design of Pile Foundation for Tall Railway Bridges in North-East India-Paper

Paper

Pdf Summary

The paper describes the design of pile foundations for five tall railway bridges on a planned 125 km railway linking Imphal, Manipur, with Assam. The route crosses steep, seismically active terrain in Northeast India; the tallest bridge spans a gorge about 140 m deep and is approximately 700 m long.<br /><br />After comparing bridge configurations, designers selected simply supported steel through-girders, up to 103.5 m in span, supported by hollow reinforced-concrete piers. Arch and continuous options were rejected because of geological instability, potential differential settlement, excessive deflection, and construction constraints. Bored, cast-in-place piles were chosen over open or well foundations because they better address steep slopes, weak weathered rock, and large earthquake-induced lateral forces.<br /><br />Ground conditions generally comprise 4–10 m of mixed soil and gravel over highly to moderately weathered shale, sandstone, or siltstone, with very low rock-quality designation. The 1.5 m diameter piles are typically 20–30 m long. Their number and length are governed by vertical and lateral capacity, flexible-pile behavior, tension, and the need to extend below potential slope-failure surfaces. Slope foundations generally use 30 m piles; level-ground foundations use shorter piles. Conservative strength assumptions were adopted, and pile capacities were checked using relevant Indian standards.<br /><br />A site-specific seismic study recommended a peak ground acceleration of 0.372g, slightly above the seismic-zone code value. Dynamic analyses considered soil flexibility and higher vibration modes, which were particularly significant for tall piers. Slope-stability analyses informed pile lengths and used conservative rock-strength parameters. Initial and routine pile load tests reportedly confirmed the design capacity.<br /><br />The study concludes that carefully investigated and conservatively designed pile foundations are a suitable solution for tall bridges in steep, weathered-rock terrain subject to severe seismic loading.

Keywords

pile foundations

tall railway bridges

Northeast India

seismic design

bored cast-in-place piles

hollow reinforced-concrete piers

weathered rock

slope stability

bridge foundation design

peak ground acceleration