Effect of composition on the compressibility and shear strength of dredged cohesive sediment

Progressively, more dredged sediments are being reused for engineering projects. For
example, the Marker Wadden is a new wetland constructed in lake Markermeer, the
Netherlands, with dredged cohesive sediments originating from the bed of the lake. Such
dredged sediments are often dominated by cohesive sediment particles with varying
amounts of sand and organic matter. In addition, during and after the construction
process, the material consolidates and is often compressed from a very loose state
into a significantly denser condition. To assess the mechanical behavior of this material, the
compressibility of the Markermeer dredged sediment samples with various sand and
organic matter contents was analyzed with incremental loading oedometer tests, whereas
the undrained shear strength was studied using the fall cone test. The behavior was
theoretically analyzed assuming a fractal structure of the sediment and applying power law
constitutive equations for effective stress, hydraulic conductivity, and undrained shear
strength. These constitutive equations, usually used at low initial sediment densities,
worked well at the relatively high initial densities studied and proved to be a useful tool to
identify the transition fines content TFC. The constitutive equations were put in context with
indicators traditionally used in soil mechanics. Samples, each with an identical composition
of the fines fraction (particles< 63 μm), but with a sand content varying from 9 to 40%,
showed the same compressibility and undrained shear strength behavior when
considering the sand a filler material. For a natural sand content of 70%, the behavior
was dominated by sand. The organic matter oxidation was observed to drastically
decrease the compressibility and the shear strength, and even to decrease the
amount of sand needed to exhibit sand-dominated behavior, showing the importance
of the reactivity or state of organic matter on the TFC