Design Relationship for Filters in Bed Protection

2012

Rubble mound coastal structures typically contain granular filters in one or more layers. These filters are normally geometrically tight (to prevent material washout), often difficult to realize in the field, and expensive. An alternative is a geometrically open filter (i.e. a large ratio of the size of toplayer material and underlayer material), designed in such a way that it fulfills its filter functions with only minimal base material loss or settlement. Potential applications of open filters include bed protections and toe & slope configurations of coastal structures. Proper guidelines on the design of open filters under wave and current loading could lead to significant cost and material savings, and to a more practical application of filters in the field. The physical model tests conducted in this study focus on granular open filters on a horizontal sand bed under wave and combined wave & current loading.

Section: Previous Researchmentioning

confidence: 99%

Granular Open Filters on a Horizontal Bed Under Wave and Current Loading

2012

“…Geometrically open filters in which no transport of material of the filter layer (base material) occurs because the hydraulic load is smaller than the threshold value for incipient motion (hydraulically closed filter), can be applied as alternative to geometrically tight filters. For the onset of base material removal reference is made to De Graauw et al (1983), Bakker et al (1994) and Klein Breteler et al (1992), CUR Report 161 (1993), CUR Report 233 (2010), Sumer et al (2001Sumer et al ( , 2013, Dixen et al (2008), Stevanato et al (2010), Van de Sande et al (2014) and Jacobsen et al (2017).…”

Section: Introductionmentioning

confidence: 99%

Rock Slopes With Open Filters Under Wave Loading: Effects of Storm Duration and Water Level Variations

Werf

2017

Rubble mound breakwaters and revetments typically contain granular filters in one or more layers. The transition from the armour layer to the filter layer, and transitions between other layers within the structure, are normally geometrically tight to prevent material washout. This requires a limited ratio of the material size of the upper layer and neighbouring layer. An alternative is a geometrically open filter where in principle underlayer material can be transported into the upper layer, but if the hydraulic load at this transition between two layers remains low, the transition can be designed such that no or limited transport occurs, see for instance Van Gent and Wolters (2015), Van Gent et al (2015) and Jacobsen et al, (2017). This allows for larger ratios of material sizes, which can reduce the number of filter layers, and relax the material requirements with respect to the width of gradings. This can lead to considerable cost savings. In Van Gent and Wolters (2015) physical model tests for the transition between a layer of rock and an underlayer that consists of sand have been performed and design guidelines have been derived. Here, additional physical model tests are presented to study the influence of the storm duration and water level variations on the response of sand underneath a layer of rock.

“…In the 1980s and 1990s a large number of tests have been performed by for instance De Graauw et al (1983), Bakker et al (1994) and Klein Breteler et al (1992) to determine criteria for the initiation of motion in granular filters. These criteria are based on estimates of the hydraulic gradients parallel or perpendicular to the interface between sand and the granular filter.…”

Section: Introductionmentioning

confidence: 99%

Sloped Granular Open Filters Under Wave Loading

Olthof

et al. 2014

Rubble mound coastal structures typically contain granular filters in one or more layers. These filters are normally geometrically tight (to prevent material washout), often difficult to realize in the field, and expensive. An alternative is a geometrically open filter. A geometrically open filter has a large ratio of the size of toplayer material and underlayer material and is designed in such a way that it fulfills its filter functions with only minimal base material loss or settlement.Potential applications of open filters include bed protections and toe & slope configurations of coastal structures. Proper guidelines on the design of open filters under wave loading could lead to significant cost and material savings, and to a more practical application of filters in the field. Physical model tests were conducted in a wave flume. These tests focussed on granular open filters on a 1:7 sand slope under wave loading. The analysis of the tests has led to guidelines on the amount of erosion of the sand underneath a granular filter and of the sand accretion within a granular filter.