7/23/2019 Initial Equation

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Initial equation[edit]

The equation itself is:

where:

• W  is the design weight of the riprap armour (Newton)

•  is the specific weight of the armour blocks (N/m3)

• H  is the design wae height at the toe of the structure (m)

• K D is a dimensionless stabilit! coefficient" deduced from laborator! e#periments for different kinds of armour blocks and for er! small

damage (a few blocks remoed from the armour la!er) ($):

• K D % around 3 for natural quarr! rock

• K D % around &' for artificial interlocking concrete blocks

•  Δ is the dimensionless relatie buo!ant densit! of rock" ie (ρr  / ρw  - 1) % around &* for granite in sea water 

•  ρr  and ρw  are the densities of rock and (sea)water ($)

• θ  is the angle of reetment with the hori+ontal

Updated equation[edit]

This equation was rewritten as follows in the nineties:

where:

• H s is the design significant wae height at the toe of the structure (m)

•  Δ is the dimensionless relatie buo!ant densit! of rock" ie (ρr  / ρw  - 1) % around &* for granite in sea water 

•  ρr  and ρw  are the densities of rock and (sea)water ($)

• Dn50  is the nominal median diameter of armour blocks % (W 50  /ρr  )1/3 (m)

• K D is a dimensionless stabilit! coefficient" deduced from laborator! e#periments for different kinds of armour blocks and for

er! small damage (a few blocks remoed from the armour la!er) ($):

• K D % around 3 for natural quarr! rock

• K D % around &' for artificial interlocking concrete blocks

7/23/2019 Initial Equation

http://slidepdf.com/reader/full/initial-equation 2/2

• θ  is the angle of reetment with the hori+ontal

The armour blocks ma! be considered stable if the stability number  N s = H s / Δ Dn50  , & to -" with damage rapidl! increasing

for Ns . 3

biousl!" these equations ma! be used for preliminar! design" but scale model testing (-0 in wae flume" and 30 in wae

basin) is absolutel! needed before construction is undertaken