Case study of undrained strength stability analysis for dredged material placement areas

This paper describes the stability of the west perimeter dike at the Craney Island Dredged Material Management Area (CIDMMA) using an undrained strength stability analysis. An undrained strength stability analysis expresses the undrained shear strength in terms of the effective overburden stress of the dredged material and the marine clay underlying the dike. An undrained strength stability analysis was used to evaluate the current stability of the west perimeter dike, the possibility of raising the perimeter dike, and the effect of undrained strength increase along with full consolidation by installing vertical strip drains on the current stability and the potential for raising the dike. Vertical strip drains would accelerate consolidation of the confined dredged material and underlying marine clay and thus produce an increase in undrained shear strength and dike stability. The analyses show that installation of vertical strip drains and full consolidation of the dredged material and underlying marine clay should allow the perimeter dike and dredged material to be raised and an increase in CIDMMA service life.