This research aims to provide an understanding of the behaviour of co-disposed coarse (sand) and fine (clay and silt) tailings when discharged into an onshore dredge pond, and the dependence of that behaviour on the sediment composition. This understanding contributes to the ultimate goal of finding a method by which fine tailings can be discharged back into the original dredge pond, while preventing these fines from recirculating through the production process. This would eliminate any need for external tailings dams, thus avoiding the risks traditionally associated with these dams. This study is part of an effort by Royal IHC to make dredge mining a competitive method for mining a wide variety of mineral deposits. To describe the behaviour of co-disposed coarse and fine tailings, an analogue is found in debris flows. From this analogue, four key behavioural aspects of mud in water are defined: erosion of sediment or entrainment of water, hydroplaning, segregation of coarse and fines particles in a slurry, and the strength increase of the material after deposition. Literature on debris flows suggested that the cohesion of the material, in the description of debris flows usually captured in a yield stress, is instrumental in determining if any of the first three behaviours are to be expected. The fourth characteristic, strength increase, depends mainly on material specific relations between void ratio on one hand, and permeability and effective stress supporting capacity of the material on the other. The concept of yield stress shows many similarities with that of the undrained shear strength. Therefore it is investigated if the yield stress can be calculated as a function of a material’s Atterberg limits – as is possible with the undrained shear strength – and thus provide a method of predicting the slurry flow behaviour. This removes the need for relationships between the less easily captured quantities as particle size distribution and clay mineralogy, and the yield stress. Experiments are performed on modelling clay and three mixtures of this modelling clay with a silica flour to determine the relationships of both undrained shear strength and yield stress with the liquidity index. Testing is done on soils with different Atterberg limits to confirm dependence on liquidity index only. The undrained shear strength is measured using a fall cone test. The yield stress is measured using a viscometer. To determine the yield stress, a full rheogram is measured for each sample. A Bingham type rheological model, of which the yield stress is a parameter, is then fitted to this rheogram. The yield stress and the undrained shear strength are plotted together as a function of liquidity index and proved to fit to the same curve, which thus describes the strength of a soil from a liquidity index of 0 up to 4. The relationship between the yield stress and clay content of the tested samples is also investigated. It is found that the concentration of the clay-sized fraction in water correlated well to both the yield stress and undrained shear strength. Hence it is concluded that yield stress is primarily determined by the clay content, and that any other size fraction has negligible effect on the yield stress of slurries. This changes when sand is added to diluted soil, as is suggested with the co-disposal method. At low sand concentrations, the effect of sand on the yield stress is still minor or even negligible. At higher concentration however, the sand noticeably increases the yield stress of the overall fluid. At a certain sand concentration, the sand grains form a network throughout the material, at which point it can no longer be considered a fluid. Silt is found to have a similar influence as sand on the slurry yield stress. The yield stress of the modelling clay in the experiments is plotted as a function of both the fines concentration in water and the sand concentration in the overall mixture. An optimum mixture range is identified based on earlier identified limits: As a minimum, the yield stress should be 35 Pa for a slurry to remain coherent at low slope angles. As a maximum, the pumpability with a centrifugal pump is used. This can be guaranteed up to a value of 200 Pa. However, for different pumps different values apply. It is concluded that the clay fraction of a sediment is the critical mixture component for providing yield stress in when the material is slurried. Sand and silt sized material only have noticeable effects when their concentrations reach such levels that they form the main structure of the mixture. However, as the relationship between the carrier fluid’s clay content and yield stress is heavily dependent on the clay mineralogy, a more convenient method of estimating a slurry’s yield stress, and thus suitability for deposition, uses the liquidity index of the fines fraction.