1 THE CUTTING MECHANISMS OF WATER SATURATED SAND AT SMALL AND LARGE CUTTING ANGLES. Dr.ir. S.A. Miedema 1 Abstract. In dredging and tunneling there is a strong interaction between the material to be handled and the equipment handling the material. To be able to make an optimal design of the equipment, the physical processes and mechanisms involved in the interaction should be known. In dredging and tunneling processes, the excavation is the first and primary step. In the water saturated sand cutting process, the dilatancy phenomenon plays an important role in determining the cutting forces. As a result of shear in the sand package the pore volume changes. The flowing water which fills the increased volume experiences a certain resistance, causing pore water under pressure. By this reason, grain forces increase and so the required cutting forces. If the volume strain rate is high enough, there is a chance that the pore pressure reaches the saturated water vapor pressure and cavitation occurs. Since the seventies and eighties the cutting process in saturated sand is extensively researched at Delft Hydraulics in Delft[13], at the Delft University of Technology and at the Mineral Technology Institute[19]. Conventional analyses generally assumes that all the soil within the rupture surface, isolated by the outer bounding stress (and velocity) discontinuity, is deforming. This is not always so and dead zones of soil, with no movement relative to the interface, can develop within the rupture surface. These zones, which can be very large, are capable of drastically altering the effective interface geometry. In two-dimensional soil failure problems these zones resemble regular prisms of soil, so can be simply described as ‘wedges’. As these boundary wedges are ‘fixed’ to the interface there is no necessity for the soil interface friction to be fully mobilized(δ<δ f ). A third possibility is a continues deforming wedge, with a flow velocity distribution, starting with a low velocity on the blade and an increasing velocity moving away from the blade. Since in this case the wedge is not fixed to the blade, the soil interface friction will be fully mobilized. 1. Introduction. In the last decennia extensive research has been carried out into the cutting of water saturated sand. In the cutting of water-saturated sand, the phenomenon of dilatation plays an important role. In fact the effects of gravity, inertia, cohesion and adhesion can be neglected at cutting speeds in the range of 0.5 – 10 m/s. In the cutting equations, as published by Miedema, there is a division by the sine of the sum of the blade angle, the shear angle, the angle of internal friction and the soil/interface friction angle. When the sum of these angle approaches 180°, a division by 1 Associate Professor, Delft University of Technology, Mechanical Engineering, Dredging Engineering, Mekelweg 2, 2628 CD Delft, The Netherlands, Tel: +31-15-2788359, Fax: +31-15-2781397, s.a.miedema@wbmt.tudelft.nl , http://www.dredgingengineering.com . Figure 1: Photo of the failure pattern with a rake angle of 120°. Miedema, S.A., "THE CUTTING MECHANISMS OF WATER SATURATED SAND AT SMALL AND LARGE CUTTING ANGLES". International Conference on Coastal Infrastructure Development - Challenges in the 21st Century. HongKong, november 2004. Copyright: Dr.ir. S.A. Miedema