7. Scour Around Marine Structures
229
the common failure modes. The location of the structure in relation to
the wave breakpoint, form of structure with respect to reflectivity and
nature of the seabed are crucial in deciding the nature of toe protection
required. The action of scour is often catalyzed with changes in alignaient,
downdrift of groins, channels and structural roundheads. The purpose of
providing flexible toe is to ensure that the foundation materials remains
in its place beneath the structure until the depth of maximum limit of
scour.
The methods available for the protection of scour and also to increase
the stability of the structure are, (1) rip rap rock fill (2) protective mattress
and (3) buried toe (4) sand bags or grout filled bags (5) concrète grout and
(6) soil and structural improvement.
7.9.2
Rip rap rock fill
Deploying rip raps is the most convenient and cost effective methods of
scour protection. This method involves fixing of apron or collar around
the base of the structure in a rip-rap manner which serves as a protective
layer.
7.9.3
Protective mattress
Scour protection by providing mattress is often used for pipelines, but it
can also be embraced for other sea bed structures. Because of its flexible
nature and installation in controlled manner, protection by mattress has
an advantage over rock fill. There are different types of mattress such as
fascine mattress, block mattress, cell mattress, concrète mattress and ballast mattress. Soil pins or anchors are provided to hold the mattress in
its place. The soil pins or anchors has to be designed to resist the uplift
and drag due to hydrodynamic forces. Filters made up of geo-textiles or
geo-synthetic materials can also be used to prevent érosion underneath the
hydraulic structures.
7.9.4
Buried toe
Where construction conditions permit, the cover layer is extended by burying the toe in an excavated trench to the depth of predicted scour. It may
be appropriate to backfill the trench with granular fill or rock, depending
on natural conditions.
229
the common failure modes. The location of the structure in relation to
the wave breakpoint, form of structure with respect to reflectivity and
nature of the seabed are crucial in deciding the nature of toe protection
required. The action of scour is often catalyzed with changes in alignaient,
downdrift of groins, channels and structural roundheads. The purpose of
providing flexible toe is to ensure that the foundation materials remains
in its place beneath the structure until the depth of maximum limit of
scour.
The methods available for the protection of scour and also to increase
the stability of the structure are, (1) rip rap rock fill (2) protective mattress
and (3) buried toe (4) sand bags or grout filled bags (5) concrète grout and
(6) soil and structural improvement.
7.9.2
Rip rap rock fill
Deploying rip raps is the most convenient and cost effective methods of
scour protection. This method involves fixing of apron or collar around
the base of the structure in a rip-rap manner which serves as a protective
layer.
7.9.3
Protective mattress
Scour protection by providing mattress is often used for pipelines, but it
can also be embraced for other sea bed structures. Because of its flexible
nature and installation in controlled manner, protection by mattress has
an advantage over rock fill. There are different types of mattress such as
fascine mattress, block mattress, cell mattress, concrète mattress and ballast mattress. Soil pins or anchors are provided to hold the mattress in
its place. The soil pins or anchors has to be designed to resist the uplift
and drag due to hydrodynamic forces. Filters made up of geo-textiles or
geo-synthetic materials can also be used to prevent érosion underneath the
hydraulic structures.
7.9.4
Buried toe
Where construction conditions permit, the cover layer is extended by burying the toe in an excavated trench to the depth of predicted scour. It may
be appropriate to backfill the trench with granular fill or rock, depending
on natural conditions.