DW
D. Weij
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Breaching is an important production mechanism for stationary suction dredgers. It is a process occurring in submerged sandy slopes, which mostly occurs in dense sandy soils with a low permeability. The process is initiated by the formation of a slope under water, whose angle is steeper than the internal friction angle, called the breach face. For dredging related breaching, this steep slope is created by a suction dredger, but it can also be formed after initial shear failure, caused by over steepening due to erosion, an earthquake, or an outwardly directed water flow. During breaching process, this steep slope is semi-stable due to negative pore pressure. Instead of a shear failure, particles are released one by one from the breach face, making it seem like the breach face is slowly moving backwards. The released particles form a density current that flows away from the breach face, and can be collected by a stationary suction dredger. When the size of the breach face increases over time, we have an unstable breach.
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Breaching is an important production mechanism for stationary suction dredgers. It is a process occurring in submerged sandy slopes, which mostly occurs in dense sandy soils with a low permeability. The process is initiated by the formation of a slope under water, whose angle is steeper than the internal friction angle, called the breach face. For dredging related breaching, this steep slope is created by a suction dredger, but it can also be formed after initial shear failure, caused by over steepening due to erosion, an earthquake, or an outwardly directed water flow. During breaching process, this steep slope is semi-stable due to negative pore pressure. Instead of a shear failure, particles are released one by one from the breach face, making it seem like the breach face is slowly moving backwards. The released particles form a density current that flows away from the breach face, and can be collected by a stationary suction dredger. When the size of the breach face increases over time, we have an unstable breach.
To model submarine flows of granular materials we propose an extension of the drift-flux approach. The extended model is able to represent dilute suspensions as well as dense granular flows. The dense granwular flow is modelled as a Herschel–Bulkley fluid, with a yield stress that depends on the dispersed phase pressure. Qualitative numerical experiments show that the model is able to correctly reproduce the stability of submerged sand heaps with different internal angles of friction and initial slopes. When initially starting with heaps with an angle smaller than the internal angle of friction, the heaps are stable. When starting with heaps with angles larger than the internal angle of friction, a flow of solid material is initiated. The flow later stops when the bed is at an angle smaller than the internal angle of friction.
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To model submarine flows of granular materials we propose an extension of the drift-flux approach. The extended model is able to represent dilute suspensions as well as dense granular flows. The dense granwular flow is modelled as a Herschel–Bulkley fluid, with a yield stress that depends on the dispersed phase pressure. Qualitative numerical experiments show that the model is able to correctly reproduce the stability of submerged sand heaps with different internal angles of friction and initial slopes. When initially starting with heaps with an angle smaller than the internal angle of friction, the heaps are stable. When starting with heaps with angles larger than the internal angle of friction, a flow of solid material is initiated. The flow later stops when the bed is at an angle smaller than the internal angle of friction.
Breaching has been an important mechanism for sand suction dredging for a long time. A special kind of breaching, unstable breaching, has recently been identified as a possible failure mechanism for sandy submerged slopes. This has increased the interest into the breaching process. At the Delft University of Technology we have started a research project on the subject of unstable breaching. In this paper we discuss the results obtained so far. First, we discuss a concept for laboratory experiments into the phenomena. Second, we propose a new numerical model, designed to investigate unstable breaching.
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Breaching has been an important mechanism for sand suction dredging for a long time. A special kind of breaching, unstable breaching, has recently been identified as a possible failure mechanism for sandy submerged slopes. This has increased the interest into the breaching process. At the Delft University of Technology we have started a research project on the subject of unstable breaching. In this paper we discuss the results obtained so far. First, we discuss a concept for laboratory experiments into the phenomena. Second, we propose a new numerical model, designed to investigate unstable breaching.