Base Grouting of Bored Cast-in-Situ Piles at the Railway Bridge over the River Rupsha, Bangladesh: A Case Study-Paper

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The Khulna–Mongla railway bridge over Bangladesh’s Rupsha River was founded on bored cast-in-situ piles in weak silt and clay soils. An initial 40 m-long, 1.5 m-diameter pile failed to meet its required 570-ton capacity, carrying only 312 tons. Extending piles and adding more piles were considered, but base grouting was investigated as an alternative.<br /><br />The technique used four steel grout pipes fitted with sleeve-protected outlets, installed with the reinforcement cage. Cement-based grout was injected beneath the pile toe in stages to strengthen the supporting soil and improve pile-base resistance.<br /><br />Load tests compared grouted and ungrouted piles. A 45 m grouted pile carried 593 tons, compared with 312 tons for a 40 m ungrouted pile; this comparison is affected by the difference in pile length. The more reliable comparison was between piles both 52 m long: the grouted pile carried 890 tons versus 480 tons for the ungrouted pile, an increase of about 1.44 times.<br /><br />Based on the test results, base grouting was adopted for working piles across both the approach viaduct and main bridge. Subsequent static and dynamic tests indicated that grouting increased vertical load capacity by approximately 1.4 times. The authors conclude that base grouting can be an effective alternative to substantially lengthening piles or increasing their number. Because the long-term durability of the grout was uncertain, the project applied strict quality-control monitoring.

Keywords

Khulna-Mongla railway bridge

Rupsha River

bored cast-in-situ piles

base grouting

pile load capacity

weak silt and clay soils

cement grout injection

steel grout pipes

static load test

dynamic load test