Levee Rehabilitation, Lower Wood River Phase II - East Alton Il. Deep Cutoff Wall-Paper

Paper

Pdf Summary

The Lower Wood River Phase II project constructed a 1,000-foot cutoff wall beside the Mississippi River levee near East Alton, Illinois, to reduce longstanding underseepage. The wall extended to depths of up to 140 feet through fill, sands, gravels, cobbles, and sandy clay, terminating in glacial till or competent bedrock.<br /><br />TREVIICOS used a hydromill and clamshell to excavate overlapping panels under self-hardening slurry (SHS) made with Portland cement, slag cement, and water. The wall was designed to be at least 2 feet thick, with hydraulic conductivity no greater than 1 × 10⁻⁶ cm/s and specified 28-day compressive strength of 50–180 psi. A test section was completed before production. Construction of the remaining panels was completed in December 2018, following a delay caused by flooding of the work platform.<br /><br />Extensive quality testing found the wall met specification requirements. Automated piezometers and in-place inclinometers monitored groundwater pressures and ground movement during excavation. Pore pressures rose temporarily when excavation reached roughly 90–100 feet, then returned quickly to prior levels as slurry permeated the ground. During installation of the final panel, readings showed the cutoff wall’s effect: groundwater levels fell on the river side and rose on the landside, where river-driven fluctuations were subsequently reduced. Inclinometer measurements showed generally limited movement, including minor displacement in cobble and loose-sand zones.<br /><br />The project demonstrated that hydromill excavation under SHS can safely produce a continuous, low-permeability cutoff wall through difficult soils at exceptional depths. Instrumentation confirmed reduced seepage paths after completion.

Keywords

cutoff wall

Mississippi River levee

underseepage reduction

hydromill excavation

self-hardening slurry

piezometer monitoring

inclinometer measurements

groundwater control

low-permeability barrier

East Alton Illinois