Monitoring of an Embankment Project Using Rigid Inclusions and Vacuum Consolidation during and after Construction-Paper

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The paper examines ground improvement for access roads at a gas-fired power station in Bang Bo, Thailand, built on very soft, compressible marine clay near the Gulf of Thailand. To raise the roads above flood levels and limit long-term settlement, the design combined prefabricated vertical drains at two depths and spacings, vacuum consolidation, surcharge embankments, and rigid Controlled Modulus Columns.<br /><br />Vacuum treatment lasted 202–221 days. Construction monitoring indicated that the treatment had achieved its settlement targets and predicted future settlement of 95–355 mm, within the contractual 400 mm limit over 25 years. However, surveys conducted from 2002 to 2010 recorded roughly 600–800 mm of additional settlement after treatment. The resulting loss of road elevation increased the risk of flooding, prompting remediation with lightweight concrete blocks.<br /><br />Hand calculations and 3D finite-element modelling were used to reassess the performance. The analyses broadly matched measured settlement and suggested that primary consolidation was largely complete when the vacuum was stopped. Instead, ongoing secondary compression, or creep, was the main cause of the unexpectedly large post-treatment settlement. The modelling showed creep affecting settlement from the start of construction and continuing over time. The authors conclude that the soil’s creep behavior—and especially an underestimated secondary compression parameter—was central to the failed long-term settlement prediction.

Keywords

ground improvement

access roads

gas-fired power station

marine clay

vacuum consolidation

prefabricated vertical drains

Controlled Modulus Columns

secondary compression

creep settlement

finite-element modelling