Time-Dependent Deformation of Dredged Harbor Mud Used as Backfilling Material

Abstract

Dredged harbor mud is being increasingly used as backfilling and construction material in harbor development or reorganization to gain financial and operative advantages compared to disposal or ex situ treatment of the often contaminated material. However, the suitability of such soft organic sediments as construction material is unclear. This study presents geotechnical parameters for describing the one-dimensional consolidation based on large-scale long-term and standard oedometer tests using organic harbor mud from the Osthafen (East Harbor) reorganization project in Bremerhaven, Germany. Determined compression indices Cc are in the range of peat, whereas the water permeabilities resemble those of clay. The coefficients of consolidation cv vary between 10−9 and 10−8m2∕s and large coefficients of secondary compression Cα between 0.065 and 0.14 are observed. Differences in parameters from large-scale and standard tests can be explained by volume and time effects likely linked to biogeochemical degredation of organic carbon and the resulting methane degassing. A curve fit based on the Levenberg–Marquardt nonlinear least-squares optimization method confirmed the applicability of the Terzaghi theory in combination with a creep term.