280
Coastal Engineering: Theory and Practice
is 620 kN/m and the résultant force acts at 6.5 m above the seabed. The
maximum run up is given as 4.2 m. The friction (/z) between the concrète
and the soil is 0.6.
Solution
The crest élévation is designed such that wave would not overtop.
Crest élévation = d+ HTL + run-up + free board = 15 m with a
freeboard of 0.3 m.
Adopt a crest élévation of 15 m from the seabed.
The concrète caisson is designed as mass concrète structure and thus,
the structure should be designed to take only compressive loads to minimize
the tensile stresses.
W
M
Le'’ Â" ~ T’
where, W is the weight of caisson; A (= width of the caisson, Bx lengthof
the caisson breakwater) is the area of cross-section at the based and Z is the
section modulus of the base section with reference to the wave direction.
The moment (M) induced on the breakwater due to wave is
(620 x 6.5) kN-m/m.
Since the breakwater is generally of long structure, the stability of one
meter long breakwater is considered. For zéro tension requirement, the
required width of the caisson (B) is 8.2 m.
In order that the caisson to be stable against sliding and overturning, the
following design checks should be made.
Check for sliding
A factor of safety of 1.5 or higher against sliding should be maintained.
uW
- =2.85 > 1.5
r
Hence the structure is safe against sliding.
Check for Overturning
To avoid overturning, a minimum factor of safety of 1.5 for resisting moment
(AIr) induced by the self-weight of the structure to induced moment (M)
Coastal Engineering: Theory and Practice
is 620 kN/m and the résultant force acts at 6.5 m above the seabed. The
maximum run up is given as 4.2 m. The friction (/z) between the concrète
and the soil is 0.6.
Solution
The crest élévation is designed such that wave would not overtop.
Crest élévation = d+ HTL + run-up + free board = 15 m with a
freeboard of 0.3 m.
Adopt a crest élévation of 15 m from the seabed.
The concrète caisson is designed as mass concrète structure and thus,
the structure should be designed to take only compressive loads to minimize
the tensile stresses.
W
M
Le'’ Â" ~ T’
where, W is the weight of caisson; A (= width of the caisson, Bx lengthof
the caisson breakwater) is the area of cross-section at the based and Z is the
section modulus of the base section with reference to the wave direction.
The moment (M) induced on the breakwater due to wave is
(620 x 6.5) kN-m/m.
Since the breakwater is generally of long structure, the stability of one
meter long breakwater is considered. For zéro tension requirement, the
required width of the caisson (B) is 8.2 m.
In order that the caisson to be stable against sliding and overturning, the
following design checks should be made.
Check for sliding
A factor of safety of 1.5 or higher against sliding should be maintained.
uW
- =2.85 > 1.5
r
Hence the structure is safe against sliding.
Check for Overturning
To avoid overturning, a minimum factor of safety of 1.5 for resisting moment
(AIr) induced by the self-weight of the structure to induced moment (M)