In-situ capping is a method to manage contaminated sediments and minimize dredging for environmental remediation projects. Placement of a cap on soft sediments poses challenges to the geotechnical stability of the cap and underlying sediments.
Failures of insitu caps sliding over subaqueous soft sediments are not uncommon. The current state of practice for the geotechnical design and construction of in-situ caps on soft sediments is based largely on experience. Various construction techniques, such as placing thin lifts of cap materials in stages and allowing sufficient time between each lift, are used in an attempt to prevent cap failures. However, there is a lack of guidance for the evaluation of geotechnical properties of soft sediments and the assessment of stability of the cap and underlying sediments during placement. This paper presents a method that was developed to evaluate the geotechnical stability of an in-situ cap placed on soft sediments. A technical approach is presented to estimate the design lift thickness of the cap and the waiting period between lifts.