Performance of gabion revetments for stabilizing beach profile
Sapporo

Ayumi SARUWATARI, Masanori KOBAYASHI, and Nobutaka TAKASUKA (Hokkaido University), Hirofumi KOYAMA and Mikio TAKAHASHI (Fudo Tetra Co.),
Takayuki YAMASHITA (Hokkaido Kawasaki Tetsumo Co.), Ekimori HIGUCHI (Towaron Co.), Yasunori WATANABE (Hokkaido University)

Introduction■ Gabion revetment
 Dissipating wave energy

Deformation /destruction ofthe basket

Short lifetime of the revetment

Kanagawa, Japan (Towaron Co.)

Wave gauges

Wave gauge

2.5cm

h0 = 43.0cm

Laser ranger

Camera40.2cm

Mound0.3m

0.3m

1m

Revetment model

5.0cm

1/10

1/204m 1m5m

h01m

Model scale (1/50)

Real scaleSignificant wave height H S

2.8 - 11.2 cm

1.4 - 5.6 m

Significant wave period T S

1.5 - 4.8 s

10.6 - 33.9 s

Wave type

Irregular waves (Modified B-M spectrum)

Number of the generated waves

800 - 1800

Initial water level h 0

Bottom of the 1st layer-Middle of the 2ndlayer
Varied from 40.0 cm - 43.7 cm

Application : Add geotextile

Guide rail

d50 = 0.1mm

1/50.5m

1.0m

Round gabions
Rectangulargabions

Sand fill

0.4m
7.5m

10cm
Impermeableblocks
Regular waves
Assuming the risein the sea level
due to high tideand storm surge

Wave generator

Wave gauges

Rectangulargabions

Model scale (1/50)

Real scale

Wave height H

4.0 cm

2.0 m

Wave period T

1.0 s

7.1 s

Wave type

Regular waves

Number of
the generated waves～1000

Beach scarp

Round gabions Round gabions＋geotextile

Gabions revetment installedin front of the scarp

Round gabions
with geotextile

Sand fill behind
the revetment

 Results

Safety number: NS, Kd value

The typical photos recorded from the top of the wave tank

𝐷𝑎𝑟𝑢𝑚𝑎−𝑘𝑎𝑔𝑜 𝑡ℎ𝑎𝑡 𝑚𝑜𝑣𝑒𝑑 𝑚𝑜𝑟𝑒 𝑡ℎ𝑎𝑛 𝑟𝑎𝑑𝑖𝑢𝑠 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑖𝑛𝑖𝑡𝑖𝑎𝑙
N0 =𝑇𝑜𝑡𝑎𝑙 𝑜𝑓 𝐷𝑎𝑟𝑢𝑚𝑎−𝑘𝑎𝑔𝑜

1-2-3 arrangement

N

HS = 5.0cm, TS = 2.0s

Takahashi et al. (1998)
NS = 𝐶𝐻 𝑎(𝑁0 /𝑁 0.5 )0.2 +𝑏
1.4
𝐻1 20 𝐻𝑆

N=0100

200

300

400

2-3-4 arrangement
HS = 5.0cm, TS = 2.0s

c = 𝑁0 /𝑁 0.5

NS’ = 𝐻𝑆 (𝑆𝑟 − 1)(𝑊𝑟 𝜌𝑟 )1/3

CH =Revetment modelzx
Sandy beach11.4m

 Results

N0 = 𝑐 𝑁

Round gabion models used in this study Stabilization of the beach profile

Wave generator

0.3m

h0 = 43.7cm

 Stabilization of the round-gabion revetment

 High flexibility of thearrangement

1/50-scale Experimental setup

2-3-4 arrangement

To assess the characteristics of the roundgabion revetment by performing two kindsof laboratory experiments:

Beach profile around the gabions

 Experimental setup

39.5cm

5.0cm
2.5cm

Stability of the round-gabion revetment

1-2-3 arrangement

 Efficiently packed rockfills
Possibly achieve longer lifetime
than the rectangular ones

0.2m

Coasts along the sea of Okhotsk, JapanObjectiveDestruction

 Protecting eroded beach
until its natural recovery
to an equilibrium beachprofileFormation of beach scarp

 Displacement of the rockfills

 Round-shaped gabion‘Daruma-Kago’

Initial shoreline

Beach erosion due to wave action

 Rectangular gabion

0N0 : Damage level
N : Number of the waves
HS : Significant wave height
Sr : Specific gravity of gabions
Wr : Weight of gabions
𝜌𝑟 : Density of gabions
NS : Safety numbera, b : Coefficient
CH : Coefficient representing breaking
H1/20 : Highest 5% wave height

Beach scarp

200010203040

Beach scarp

Beach scarp

Round and rectangulargabions slowed down
the development of
the beach scarp

50

Scale (cm)NoneRound gabions
Impermeable blocks
Rectangular gabions800

 Results of application caseh01-2-3 arrangement

2-3-4 arrangement

Mid. of 2nd

0.7 (0.3)

1.7-2.0 (4.9-8.1)

Mid. 1/4 of 2nd

1.0 (1.0)―

Bot. of 2nd

1.4 (2.9)

N0 < 0.3

Mid. of 1st

1.5-1.8 (3.6-5.9)

N0 < 0.3

Bot. of 1st

N0 < 0.3―

The sufficient performance ofthe gabion revetment can beachieved by optimizing thearrangement of the gabions byconsidering the various conditionat the construction site

Round gabions
Sand fill

Initial beach scarp

Revetment

Rectangular gabions
Sand fill

Initial beach scarp

Revetment

Round gabions + geotextile
Sand fill

Initial beach scarp

Revetment

N = 350
N = 650
N = 950

Conclusions
 In this study, we evaluated the wave stability of the round-gabion revetment and the performance as a countermeasure against beach scarp retreat through two kinds of laboratory experiments.
 When there is no significant water level rises, the revetment exhibits high stability. Although the stability of the revetment decreases as the water level rises, it was clarified that increasing the arrangement of gabions can increase the stability.
 The round-gabion revetments have the effect of suppressing the formation of the beach scarp. The sand retention function can be improved by using geotextile together.