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Preface

  • Page ID
    33160
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    In dredging, trenching, (deep sea) mining, drilling, tunnel boring and many other applications, sand, clay or rock has to be excavated. The productions (and thus the dimensions) of the excavating equipment range from mm3/sec - cm3/sec to m3/sec. In oil drilling layers with a thickness of a magnitude of 0.2 mm are cut, while in dredging this can be of a magnitude of 0.1 m with cutter suction dredges and meters for clamshells and backhoe’s. Someequipment is designed for dry soil, while others operate under water saturated conditions. Installed cutting powers may range up to 10 MW. For both the design, the operation and production estimation of the excavating equipment it is important to be able to predict the cutting forces and powers. After the soil has been excavated it is usually transported hydraulically as a slurry over a short (TSHD’s) or a long distance (CSD’s) or mechanically. Estimating the pressure losses and determining whether or not a bed will occur in the pipeline is of great importance. Fundamental processes of sedimentation, initiation of motion and erosion of the soil particles determine the transport process and the flow regimes. In TSHD’s the soil has to settle during the loading process, where also sedimentation and erosion will be in equilibrium. In all cases we have to deal with soil and high density soil water mixtures and its fundamental behavior.

    This book gives an overview of cutting theories. It starts with a generic model, which is valid for all types of soil (sand, clay and rock) after which the specifics of dry sand, water saturated sand, clay, atmospheric rock and hyperbaric rock are covered. For each soil type small blade angles and large blade angles, resulting in a wedge in front of the blade, are discussed. The failure mechanism of sand, dry and water saturated, is the so called Shear Type. The failure mechanism of clay is the so called Flow Type, but under certain circumstances also the Curling Type and the Tear Type are possible. Rock will usually fail in a brittle way. This can be brittle tensile failure, the Tear Type for small blade angles, but it can also be brittle shear failure, which is of the Shear Type of failure mechanism for larger blade angles. For practical cutting angles in dredging a combination may occur, the Chip Type. Under hyperbaric conditions rock may also fail in a more apparent ductile way according to the Flow Type or Crushed Type of failure mechanism. This is also called cataclastic failure.

    For each case considered, the equations/model for the cutting forces, power and specific energy are given. The models are verified with laboratory research, mainly at the Delft University of Technology, but also with data from literature.

    The model is named The Delft Sand, Clay & Rock Cutting Model. Up to date information (modifications and additions) and high resolution graphs and drawings can be found on the website www.dscrcm.com.

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