Design and Construction of the Sutong Bridge Foundations-PDF

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The Sutong Bridge’s two main pylons were built in the lower Yangtze River, where deep water, currents exceeding 3 m/s, heavy sediment transport, and highly variable riverbed levels made foundation construction especially difficult.<br /><br />Each pylon is supported by 131 drilled shafts, approximately 2.5 m in diameter and 114–117 m long, with permanent 2.8 m steel casings extending through the upper soil layers. The shafts support a massive pile cap measuring 113.8 by 48.1 m and 13.3 m deep. Because the deep alluvial soils and drilling-related disturbance made shaft-tip bearing capacity uncertain, the team used post-grouting to improve it. Grout was injected through pipes attached to the reinforcement cages, compacting soil and debris beneath the shafts. Osterberg-cell tests showed that tip grouting increased ultimate shaft capacity by about 20%; the improved tip also exhibited stiffer load–settlement behavior.<br /><br />Scour protection was designed for both construction and long-term riverbed changes. It combined temporary sandbag layers near the piles, quarry-run and rock armour farther out, and a flexible “falling apron” at the outer edge. The apron’s material can move down into developing scour, helping limit erosion near the pylons.<br /><br />The pile caps were constructed inside large double-walled steel caissons. These served as stiffening frames, buoyancy tanks during lowering, temporary cofferdams, permanent forms, and ship-impact protection. Strand-jack systems lowered the caissons into position; after installation, a tremie-concrete seal allowed the interiors to be dewatered so the caps could be completed in the dry.<br /><br />The project demonstrated how coordinated foundation design and construction—including post-grouted shafts, adaptable scour protection, and controlled caisson lowering—could meet demanding structural requirements in an exceptionally challenging river environment.

Keywords

Sutong Bridge

main pylons

drilled shafts

post-grouting

shaft capacity

Yangtze River

scour protection

pile cap

steel caissons

strand-jack lowering