Time-dependent compression behaviour of dredged clays at high water contents in China

• Vertical yield stresses develop notably during ageing with YSR = 1.2–1.8.
• Ageing volumetric strains are small during ageing with most being less than 2%.
• An equation is proposed for assessing the vertical yield stress developed during ageing.
• Dredged clays aged for short time behave like natural clays with long geological ageing.

Incremental load one-dimensional consolidation tests were performed on dredged clays with and without ageing to investigate their time-dependent compression behaviour. The dredged clays investigated had a wide spectrum of liquid limits within 55.6% to 100% and a predominant clay mineral of illite. It is found that vertical yield stresses develop notably during ageing. The developed vertical yield stresses vary within the range of 1.2 to 1.8 times the specifically assigned vertical effective stress under which ageing is allowed for 15 to 105 days. But the corresponding ageing volumetric strains are small, varying within the range of 0.6% to 3.4% with most being less than 2%. The test results obtained also allow proposing an empirical equation of assessing vertical yield stress. The changing law of vertical yield stress with stress level for ageing, ageing time, soil properties is investigated based on the empirical equation. Moreover, it is found that the structural resistance of dredged clays developed during ageing for a period of consolidation time up to 105 days is weak compared with the sedimentation compression line of natural clays developed during long geological ageing. But the compression curves of dredged clays with ageing converge slowly to the intrinsic compression line over a wide range of stresses, like natural clays subjected to the effect of soil structure developed during long depositional and post-depositional processes.