Typical permeability factors Pfor different types of rock construc-
tion are presented in Fig. 15.11 (Van der Meer, 1987). The equations
(15.36) and (15.37) have been arrived at from model testing with the layer
thickness of about 2.0D 50. Van der Meer (1988) has also investigated the
stability of specially formed units such as cubes and tetrapods.
Table 15.5 Variation in damage number for failure conditions
Slope Damage (S)
Initial intermediate Failure
1:1.5 2 – 08
1:2 2 5 08
1:3 2 8 12
1:1.4 3 8 17
P 0.1
(a)
D 50 A/D 50 F 4.5
0.5D 50 A
Filter
Arm
our
2 D^50 A
Impe
rmea
bleL
ayer
P 0.4
(b)
D 50 F/D 50 C 4
Arm
our
2 D^50 A
Filte
r
1.^5 D^5
0 A
D 50 A/D 50 F 2
P 0.5
(c)
A D 50 A/D 50 C 3.2
rmo
ur
2 D^50 A
Core
P 0.6
(d)
A No core
rmo
ur No filter
D 50 A nominal diameter of armour stone
D 50 F nominal diameter of filter material
D 50 C nominal diameter of core
Fig. 15.11 Typical permeability factors (P) for different types of rock
construction
652 COASTAL ENGINEERING
