When cutting water saturated sand, as is done in dredging, agriculture and soil movement in general, the process is dominated by the phenomenon of dilatancy. Based on pore pressure calculations and the equilibrium of horizontal and vertical forces, equations can be derived to predict the cutting forces. The derivation of this model has been described extensively in previous papers by Miedema et all (1983-2005). In the equations derived, the denominator contains the sine of the sum of the 4 angles involved, the cutting angle α, the shear angle β, the angle of internal friction ψ and the soil interface friction angle δ. So when the sum of these 4 angles approaches 180° the sine will become zero and the cutting forces become infinite. When the sum of these 4 angles is greater then 180° the sine becomes negative and so do the cutting forces. Since this does not occur in reality, nature must have chosen a different mechanism for the case where the sum of these 4 angles approaches 180°. Hettiaratchi and Reece, (1975) found a mechanism which they called boundary wedges for dry soil. At large cutting angles a triangular wedge will exist in front of the blade, not moving relative to the blade. This wedge acts as a blade with a smaller blade angle. In fact, this reduces the sum of the 4 angles involved to a value much smaller than 180°. The existence of a dead zone (wedge) in front of the blade when cutting at large cutting angles will affect the value and distribution of vacuum water pressure on the interface. He, (1998), proved experimentally that also in water saturated sand at large cutting angles a wedge will occur. The main questions however are; at which blade angle does a wedge start to occur, how does this depend on the soil mechanical, geometrical and operational parameters and what will be the geometry of the wedge. Based on the equilibrium of moments a solution is found to answer these questions.
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