Case Study: Slope Stabilization using Deep Soil Mix (DSM) Columns – Strategic Petroleum Reserve, Bayou Choctaw Facility-Paper

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At a U.S. Department of Energy facility in Plaquemine, Louisiana, roadway cracking beside Cavern Lake worsened from 2018 until a partial slope failure in March 2020 forced the road to close. Inclinometer readings recorded substantial lateral movement, and geotechnical analyses found factors of safety below 1.0 for both shallow and deep failure surfaces. Soft, organic clays were a key contributor.<br /><br />Several stabilization options were rejected because of site-access and property constraints, cost, or the risk that construction vibrations could further destabilize the slope. The team selected deep soil mixing (DSM), which creates reinforced soil columns with relatively low vibration and limited displacement. Before construction, removing three feet of roadway and stone fill reduced the load enough to improve construction safety. Lake levels and slope movement were monitored throughout the work.<br /><br />The design used 20-foot-long DSM shear panels, spaced 10 feet apart, with a front row of columns to retain soil in case of shallow sloughing. Laboratory mix testing informed the cement dosage, and the installation sequence was staggered to limit short-term instability. Analyses predicted a factor of safety above 1.3 for the improved slope.<br /><br />Some movement occurred during mixing close to inclinometers, but it generally stopped once equipment moved away. After treatment, monitored lateral movement remained small through September 2021. A new shallow failure occurred in front of the DSM panels without significant movement detected within or beyond the treated zone.<br /><br />Durability tests could not establish how exposed DSM columns would withstand long-term weathering. The team therefore recommended periodic inspections and future remediation if further failures occur. The case highlights the importance of monitoring, construction sequencing, and close coordination when stabilizing an actively moving slope under tight constraints.

Keywords

deep soil mixing

slope stabilization

roadway cracking

inclinometer readings

partial slope failure

geotechnical analysis

factor of safety

soft organic clays

lateral movement

Cavern Lake