Type Seawall Research Articles

Wave Flume Experiment on the Settlement of Reclamed Sand behind a Caisson-type Seawall

A model experiment is conducted in a large wave channel to reproduce the settlement failures of caisson type seawalls. Due to wave overtopping and wave transmission through the rubble mound, the reclamed sand is washed down through the back-fill rubble stones. The pore pressure variation in the rubble stones and reclaimed sand can well explain the through-wash of the sand.

GENTLE SLOPE SEAWALLS COVERED WITH ARMOUR UNITS

Since the early 1960's, many seawalls against the beach erosion have been constructed in Japan, most of which were of vertical type. As a result, some of the seawalls even encouraged the beach erosion due to the reflected waves on the steep front of the seawalls. The author then proposed seawalls of new types with gentle front slope(l to 3) covered with armour units in 1981, and over one hundred fieldworks have successfully been carried out. In 1985, the author proposed reforming the existing vertical type seawalls into the gentler front slope (1 to 5 or 6) seawalls. The laboratory test on the gentle slope seawall was made, and some experimental fieldworks were carried out. At this time, these new type gentler slope seawalls are successful.

MEASUREMENT OF REFLECTION COEFFICIENT OF SEAWALL IN OMORA BAY

Field investigations were performed in order to establish the reflecting characteristics of a steel sheet-piling type seawall and two vertical wave-dissipating type seawalls through directional wave measurements of wave reflection systems. A pre-designed line array of several capacitance-type wave gauges was used to measure the wave field just in front of the seawall, and the MMLM (Modified Maximum Likelifood Method) was applied for the calculation of the directional wave spectrum and the reflection coefficient. The estimated directional spectra demonstrated that the MMLM has high resolution power and can sufficiently separate the incident and the reflected wave energies. As a result , it was found that the reflection coefficient of the vertical steel sheet-piling seawall is about 0.9 and is independent of the incident wave conditions, whereas those of the vertical wave-dissipating type seawalls show considerable change in correlation to the incident wave period or the mean water level.