Chapter IV
Design of rubble mounds breakwater
58
Table IV-6 The formulas and variables used to calculate the dimensions of the under-layer
Formula
variables
The median mass of under-layer blocs: í µí° í µí°¬í µí° =
í µí° í µí¿í µí¿
í µí¿í µí¿
í µí±´ í µí¿í µí¿ : the median mass of armourstone.
í µí» í µí² : the apparent rock density (kg/m³).
n: number of layers.
í µí² ∆ : layer coefficient.
Volume of a block: í µí±½ =
í µí±´ í µí²í µí²
í µí½ í µí²
Nominal diameter of bloc: í µí±« í µí²í µí¿í µí¿ = √í µí±½
í µí¿
Armourstone thickness:
í µí² = í µí²í µí² ∆ í µí±« í µí²
NOTE: the underlayer should normally not exceed 15% of the armour unit mass as accurate
placement of armour units requires a relatively smooth surface of the underlayer.
the underlayer armourstone (in mass) should not be less than 5 per cent of the armour unit
mass in order to prevent armourstone material from being washed out through the pores of the
armour layer. (Rock Manual. CETMEF, 2007)
Design of transition filter and core
In coastal or shoreline structures, the transition filter and core are important components that
play a crucial role in maintaining stability and protecting against erosion. They are typically
placed between the armour layer and the underlying soil or sediment.
The design of the transition filter and core involves determining their masses based on the
median mass of the armourstone.
Table IV-7 The formulas used to calculate the mass of the transition filtre and the core
Formulae
variables
The median mass of transition filter: í µí±´ í µí²í µí²í µí¿í µí¿ =
í µí±´ í µí¿í µí¿
í µí¿í µí¿í µí¿
í µí±´ í µí¿í µí¿ : the median mass of armourstone
Mass of core: í µí±´ í µí²í µí¿í µí¿ =
í µí±´ í µí¿í µí¿
í µí¿í µí¿í µí¿í µí¿
NOTE: For the mass of the core and filter, we take a weight limited to 50% and 150%.
Design of Toe bund:
The design of a toe bund involves careful consideration of various factors to ensure its
effectiveness in protecting against wave forces and erosion. engineers take into account
parameters such as the stability coefficient, slope angle, wave height at the toe, apparent density
of the stone, and apparent water density. These parameters are utilized in specific formulas to
calculate crucial dimensions.
Table IV-8 The formulas used to calculate the median mass, thickness and width of a toe bund
Formulae
variables
The median mass of bloc:
í µí±´ í µí²í µí¿í µí¿ =
í µí¿.í µí¿
í µí² í µí²
(
í µí½ í µí² í µí±¯ í µí²
í µí¿
∆ í µí¿ í µí²í µí²í µí²í µí¼¶
)
í µí±¯ í µí²
í µí²
í µí° í µí² : stability coefficient.
í µí» : the slope angle.
í µí° í µí° : wave height at the toe of the structure.
í µí»¥ =
í µí» í µí°«
í µí» í µí°°
− í µí¿ : the relative density of the stone.
í µí» í µí² : the apparent rock density (kg/m³).
í µí» í µí°° : the apparent water density (kg/m³).
n: number of layers.
í µí² ∆ : layer coefficient.
Thickness and width of the armourstone:
í µí², í µí² = í µí²í µí² ∆ √
í µí±´ í µí²
í µí½ í µí²
í µí¿
Design of rubble mounds breakwater
58
Table IV-6 The formulas and variables used to calculate the dimensions of the under-layer
Formula
variables
The median mass of under-layer blocs: í µí° í µí°¬í µí° =
í µí° í µí¿í µí¿
í µí¿í µí¿
í µí±´ í µí¿í µí¿ : the median mass of armourstone.
í µí» í µí² : the apparent rock density (kg/m³).
n: number of layers.
í µí² ∆ : layer coefficient.
Volume of a block: í µí±½ =
í µí±´ í µí²í µí²
í µí½ í µí²
Nominal diameter of bloc: í µí±« í µí²í µí¿í µí¿ = √í µí±½
í µí¿
Armourstone thickness:
í µí² = í µí²í µí² ∆ í µí±« í µí²
NOTE: the underlayer should normally not exceed 15% of the armour unit mass as accurate
placement of armour units requires a relatively smooth surface of the underlayer.
the underlayer armourstone (in mass) should not be less than 5 per cent of the armour unit
mass in order to prevent armourstone material from being washed out through the pores of the
armour layer. (Rock Manual. CETMEF, 2007)
Design of transition filter and core
In coastal or shoreline structures, the transition filter and core are important components that
play a crucial role in maintaining stability and protecting against erosion. They are typically
placed between the armour layer and the underlying soil or sediment.
The design of the transition filter and core involves determining their masses based on the
median mass of the armourstone.
Table IV-7 The formulas used to calculate the mass of the transition filtre and the core
Formulae
variables
The median mass of transition filter: í µí±´ í µí²í µí²í µí¿í µí¿ =
í µí±´ í µí¿í µí¿
í µí¿í µí¿í µí¿
í µí±´ í µí¿í µí¿ : the median mass of armourstone
Mass of core: í µí±´ í µí²í µí¿í µí¿ =
í µí±´ í µí¿í µí¿
í µí¿í µí¿í µí¿í µí¿
NOTE: For the mass of the core and filter, we take a weight limited to 50% and 150%.
Design of Toe bund:
The design of a toe bund involves careful consideration of various factors to ensure its
effectiveness in protecting against wave forces and erosion. engineers take into account
parameters such as the stability coefficient, slope angle, wave height at the toe, apparent density
of the stone, and apparent water density. These parameters are utilized in specific formulas to
calculate crucial dimensions.
Table IV-8 The formulas used to calculate the median mass, thickness and width of a toe bund
Formulae
variables
The median mass of bloc:
í µí±´ í µí²í µí¿í µí¿ =
í µí¿.í µí¿
í µí² í µí²
(
í µí½ í µí² í µí±¯ í µí²
í µí¿
∆ í µí¿ í µí²í µí²í µí²í µí¼¶
)
í µí±¯ í µí²
í µí²
í µí° í µí² : stability coefficient.
í µí» : the slope angle.
í µí° í µí° : wave height at the toe of the structure.
í µí»¥ =
í µí» í µí°«
í µí» í µí°°
− í µí¿ : the relative density of the stone.
í µí» í µí² : the apparent rock density (kg/m³).
í µí» í µí°° : the apparent water density (kg/m³).
n: number of layers.
í µí² ∆ : layer coefficient.
Thickness and width of the armourstone:
í µí², í µí² = í µí²í µí² ∆ √
í µí±´ í µí²
í µí½ í µí²
í µí¿