Overcoming the Challenges Endured by the Quality Assurance and Quality Control Teams during the Construction of a Deep Cutoff Wall in East Alton, Illinois-Paper

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The Lower Wood River Levee in East Alton, Illinois, experienced severe under-seepage that threatened its integrity. To address the problem, a 600-metre (2,000-foot) cutoff wall was built along the Mississippi and Wood Rivers, reaching depths of up to 43 metres (140 feet) and extending into till or bedrock. The project’s variable alluvial geology and unusual depth made construction and quality verification especially demanding.<br /><br />Treviicos used a clamshell and hydromill excavation method under self-hardening slurry. The completed wall comprised 66 primary and 65 secondary panels. A test section confirmed the method’s feasibility before production began; construction was completed in April 2016, despite delays caused by high river levels.<br /><br />The extensive quality-control and quality-assurance program monitored slurry properties, excavation depth and verticality, panel overlap, bottom cleanliness, and wall material strength and permeability. Standard verification techniques were often impractical in the dense slurry and deep excavations, so the teams adopted alternatives, including a weighted graduated cable for depth checks and a plumb-bob method for verticality. Hydromill monitoring data were prioritized when measurements differed.<br /><br />Testing also revealed that core samples often showed lower strength and higher permeability than wet-grab samples, partly due to disturbance during coring. The project team adjusted testing procedures and agreed on criteria for ending exceptionally long permeability tests. Overall, the large sampling program showed that the wall generally met specification requirements and produced a homogeneous, continuous barrier.<br /><br />The authors conclude that the construction method was successful at this depth and that the rigorous QA/QC program was necessary, though challenging. They emphasize that close collaboration among the owner, engineer, contractor, and USACE helped resolve issues, and suggest involving contractors earlier in project design to improve constructability and simplify quality assurance.

Keywords

under-seepage

cutoff wall

levee

Mississippi River

Wood River

hydromill excavation

self-hardening slurry

quality assurance

quality control

East Alton Illinois