Influence of armour porosity on the hydraulic stability of cube armour layers

Abstract

Armour placement and packing density directly affect construction costs and hydraulic performance of mound breakwaters. In this paper, the literature concerning the influence of armour porosity on the hydraulic stability of single-and double-layer armours is discussed.Qualitative and quantitative estimations for the influence of armour porosity and packing density on the hydraulic stability are given for the most common concrete armour units. The analysis focuses on specific 2D hydraulic stability tests of double-layer cube armours with different armour porosities and permeable core. The packing density showed a 1.2-power relationship with the stability number for cube units. The literature review and experimental results with small-scale breakwater models protected with a variety of armour units clearly indicate that a significant increase in armour porosity above the recommended values substantially decreases armour hydraulic stability. To avoid uncontrolled model effects, packing density should be routinely measured in small-scale tests, and armour placement techniques should be monitored at prototype scale. The actual packing density obtained in small-scale models and prototypes has to be explicitly reported, because packing density significantly affects hydraulic stability during service time. Key words:Breakwater, Heterogeneous Packing, Armour porosity, Packing density, Armour damage, Hydraulic stability, Armour unit, Cubic block. Highlights:(1) Armour porosity affects the hydraulic stability of armour layers. 1(2) Armour porosity or packing density is rarely included in armour stability formulae.(3) Packing density of randomly-placed double-layer cube armours is a relevant design factor affecting hydraulic stability and construction costs.(4) A significant 1.2-power relationship has been found between the stability number and packing density for double-layer cube armours.(5) The packing density of the armour layer has to be explicitly reported in small-scale tests and monitored at prototype scale.

Calibration of overtopping roughness factors for concrete armor units in non-breaking conditions using the CLASH database

“…Given an armor unit, an armor porosity above recommended values decreases the concrete consumption but also decreases the hydraulic stability (see Medina et al, 2014), affecting the breakwater performance during lifetime.…”

Mound Breakwater Design in Depth-Limited Breaking Wave Conditions

“…The specific placement technique is directly related to armor porosity (p%) and interlocking, which significantly affects armor stability. Van der Meer (1999), Yagci and Kapdasli (2003), Bakker et al (2005), and Medina et al (2014) among others, analyzed a variety of CAUs and reported a significant influence of armor porosity on hydraulic stability. Porosity is also directly related to the number of units in the armor, material consumption and hence the construction cost.…”

“…Frens (2007) summarized problems caused by different researchers using different criteria regarding the layer coefficient and the porosity concept. To prevent misunderstandings, Medina et al (2014) suggested referring armor porosity p(%)=(1-Φ/n) to a layer coefficient of kΔ=1.00 using the dimensionless placing density Φ=φDn 2 . Different criteria can be used to classify armor units depending on the placement technique.…”

“…IV.15. Although cube armor hydraulic stability is significantly affected by armor porosity (see Medina et al, 2014), no clear differences were found when considering armor placement technique.…”

“…Using the virtual net method, armor damage was measured after each test conducted with cubes randomly-and uniformly-placed. Since the armor unit placement technique is a critical consideration in the design phase (see Medina et al, 2014), the influence of the placement technique on armor stability was analyzed using artificial neural networks.…”