Design of Cofferdam for Well Foundation Construction

Paper

Pdf Summary

The paper presents a cofferdam method used to construct water-based well foundations for a 1.4 km steel railway bridge over the Narmada River in Gujarat. The bridge has 30 well foundations, 13 of them in the river, where daily tides vary by 3–4.5 m. Instead of using conventional, costly steel caissons, the project created a dry working area so the foundations could be built using land-based methods.<br /><br />Each circular cofferdam was 16.2 m in diameter and formed from 1,500 mm steel liner piles connected by sheet piles. Its design accounted for local soil conditions, water and soil pressures, construction stages, and the surcharge from the well curb and steining. Engineers used WALLAP software to model the system and assess wall forces and deformations, then checked the steel sections for the resulting bending moments and shear forces. The selection of pile toe levels also required consideration of ground conditions and potential scour.<br /><br />Construction involved positioning barges, driving the liner and sheet piles with a vibro hammer, installing the strut and waler system, and filling the cofferdam with sand. Formwork and concrete work for the well foundation followed, after which the well was sunk.<br /><br />The authors report substantial reductions in temporary steel use and faster foundation progress compared with the conventional caisson approach. The cofferdams could also be installed ahead of foundation construction. The study notes that reliable performance depends strongly on soil-stiffness assumptions and on selecting suitable founding levels for the cofferdam.

Keywords

cofferdam

well foundation

steel railway bridge

Narmada River

sheet piles

steel liner piles

WALLAP software

scour

barges

soil stiffness