Undrained shear strength properties of organic harbor mud at low consolidation stress levels

Schlue, Benjamin Friedrich; Mörz, Tobias; Kreiter, Stefan
March 2011
Canadian Geotechnical Journal;Mar2011, Vol. 48 Issue 3, p388
Academic Journal
Dredging operations in European harbors for maintenance of navigable water depth produce vast amounts of harbor mud. Between 2005 and 2007, the second largest harbor construction project in Germany was designed as a pilot study, using dredged harbor mud as backfill material to avoid expensive deposition or ex situ treatment. During this project, strong surface deformations of the backfill highlighted the need for an improved assessment of undrained shear strength of naturally liquid harbor mud. The strength of harbor mud cannot be measured accurately under corresponding low in situ effective stress levels by standard laboratory tests. Therefore, a large-scale oedometer cell with a diameter of 22 cm was designed, providing the opportunity to perform vane shear measurements during consolidation. This study shows that East Harbor mud is a very sensitive, organogenic clay of extremely high plasticity, exhibiting very small undrained shear strength when compared with other cohesive soils. Both the peak and residual undrained shear strengths are shown to increase about 3%-4% per log-cycle increase in secondary compression time (days). Les opérations de dragage dans les ports européens, effectuées pour maintenir la profondeur nécessaire à la navigation, produisent de grandes quantités de boues de port. Entre 2005 et 2007, la construction du deuxième plus grand projet portuaire en Allemagne a été conçu comme une étude pilote sur l'utilisation de boues de dragage comme matériau de remblayage afin d'éviter la déposition coûteuse ou le traitement ex-situ. Durant ce projet, des fortes déformations de la surface du remblai ont fait remarquer le besoin d'une meilleure évaluation de la résistance au cisaillement non drainé des boues, qui sont naturellement liquides. La résistance des boues ne peut pas être mesurée précisément à des faibles niveaux de contrainte effective correspondant aux conditions in situ par des essais de laboratoire standards. Ainsi, une cellule odométrique de grande échelle, avec un diamètre de 22 cm, a été conçue afin d'obtenir des mesures scissométriques pendant la consolidation. Cette étude montre que la boue du port Est est une argile organogénique très sensible avec une plasticité extrêmement élevée, et qui présente une résistance au cisaillement non drainé très faible comparativement aux autres sols fins. Les résistances au cisaillement non drainé maximum et résiduelles ont augmenté de 3-4 % par log-cycle en temps de compression secondaire (jours).


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