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Influence of the slurry initial conditions on the dewatering process evaluated by falling-head column test

Geotextiles Closed Systems, GCS, has been used to dewatering a variety of high-water content sediments aiming to reduce the final volume of the residue at disposal. The geotextile retention capability to form a filter-cake that does not involve an excessive reduction of the hydraulic conductivity of the system is determinant to the success of the dewatering process. In addition, the grain size distribution of the solid phase, GSD, is tightly related to this success. There are two distinguishable phases in the process: the initial phase in which geotextile permeability controls the flow rate, and the postfilter- cake formation phase in which the retained sediments start to control the flow rate. The GSD play an important role in the retention of particles with a diameter smaller than the characteristic geotextile opening size by interlocking small particles between the bigger ones retained by the geotextile. However, it is difficult to determine how sensitive the dewatering process is to GSD variation. This work presented a discussion on how the increment in the coarse fraction of the GSD affects the filter-cake formation. The paper discusses the results of the falling-head column test performed to evaluate the behavior of a woven geotextile in the dewatering process of sediment with different GSD, in a turbulent flow condition at low initial solids content. The tests also evaluated the solids concentration in the effluent and water content in retained material. The obtained results indicate that a small amount of coarse material is sufficient to initiate the filter cake formation and has a greater impact on the effluent quality.