Print Email Facebook Twitter Stability of open filter structures Title Stability of open filter structures Author Van de Sande, S.A.H. Contributor Uijttewaal, W.S.J. (mentor) Verheij, H.J. (mentor) Verhagen, H.J. (mentor) Van den Bos, J.P. (mentor) Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 2012-06-27 Abstract Granular filters are used for protection against scour and erosion. For a proper functioning it is necessary that interfaces between the filter structure, the subsoil and the water flowing above the filter structure are stable. Stability means that there is no transport of subsoil material through the filter to the water above the filter, and that no filter material is removed by currents above the filter. Three types of granular filters can be distinguished; 1) Geometrically closed filter structures, 2) Stable geometrically open filter structures, 3) Unstable geometrically open filter structures. This research is focusing on stable geometrically open filter structures. Recently, a desk study has been carried out by Deltares resulting in a new theoretical formula for single layered geometrically open filter structures (CUR, 2010). Hoffmans improved the theoretical formula that had been founded by Deltares (Hoffmans G. , 2012) The goal of this research was to verify the formula found by Hoffmans [2012] for structures loaded by currents (flow parallel to the filter construction). As part of the verification of the design formula ten flume experiments were performed in the Environmental Fluid Mechanic Laboratory at Delft University of Technology. After the execution of the model tests an extensive analysis was made based on the performed model tests and model tests performed in the past (Bakker [1960], Haverhoek [1968], Wouters [1982], Konter et al. [1990], Van Huijstee and Verheij [1991] and Van Velzen [2012]). The analysis showed that the formula is valid for single layered geometrically open filter structures loaded by currents. Two adjustments to the design formula are proposed: 1. The relative layer thickness fits better when related to the nominal diameter of the filter material; 2. The alpha value proposed by Hoffmans [2012] is too high (new alpha values are 30% to 60% lower). The original formula as proposed by Hoffmans [2012] gives unrealistic values for situations with wide graded filter material. Model tests showed that the relative layer thickness is better represented when related to the nominal diameter of the filter material. The design formula can be used for design purposes. The design of a single layered geometrically open filter structure can be schematized in two steps; 1. Firstly, determination of the material that should be used for the top-layer; 2. Secondly, determination of the layer-thickness of the filter/top-layer taking into account filter and base material characteristics. Subject bed protectionopen filterfilter structuregranular filtergeometrically opendesign formulamodel testflume experiment To reference this document use: http://resolver.tudelft.nl/uuid:832e1f8f-23d0-4f72-9998-b02c2e003503 Related item https://doi.org/10.4121/uuid:963e9fae-e50d-403d-90c7-a273aeb730f7 Part of collection Student theses Document type master thesis Rights (c) 2012 Van de Sande, S.A.H. Files PDF van de Sande 2012_MSc The ... e_2013.pdf 6.39 MB Close viewer /islandora/object/uuid:832e1f8f-23d0-4f72-9998-b02c2e003503/datastream/OBJ/view