Stability of Layered Dredged Sediment Deposits at Subaqueous Sites

Covering, or capping, dredged-sediment deposits at subaqueous disposal sites is a technique to isolate contaminated sediment from the aqueous environment and to contain it on the site. After deposition, the sediments will consolidate with the expulsion of pore water and the layers may deform. If the deformation is extensive, the cap may be disrupted. Two conditions must be met for internal instability in the deposit; (1) the upper layer must be more dense than the lower and (2) the shear stress along the interface between the layers must exceed the strength of the deposit. Mathematically, the second condition is Δpgh>;(ατ) where Δp is the difference in density between the layers, h is the height of irregularities in the interface between the layers and (ατ) is the creep limit stress of the deposit. The creep limit stress is some fraction, α, of the shear strength τ. A deposit of dredged mud under a one-meter thick cap of sand might be expected to support irregularities about 1 m high.