Groynes are built to stabilize a stretch of natural or artificially nourished beach against erosion that is due to primarily to a net longshore loss of beach material. Groynes function only when longshore transport occurs. Groynes are narrow structures, usually straight and perpendicular to the preproject shoreline. The effect of a single groyne is accretion of beach material on the updrift side and erosion on the downdrift side; both effects extend some distance from the structure. Consequently, a groyne system (series of groynes) results in a saw-tooth-shaped shoreline within the groyne field and a differential in beach level on either side of the groynes.
Labuan Blocks are concrete mass blocks. They are cast insitu, often with locally available material and therefore have a relatively low capital cost. Because they are portable and removable they can be easily transported to any places, reducing the cost of coastal erosion control project. Labuan Blocks can be placed as sloping “mattresses” or as near vertical cubic blocks. The latter are intended for bank or cliff stabilisation and are not normally suitable for use in shoreline situations.
Labuan Blocks (backshore) are generally preferred to rock revetment (foreshore) in coastal environments being less reflective of wave energy and more stable. Sand is also better able to accumulate on Labuan Blocks, potentially softening their appearance.
The purpose of Labuan Blocks is to provide short term (3-5 years) protection from backshore erosion by absorbing wave energy along the dune face. Their application is restricted to the upper part of sandy beaches, since they are not sufficiently durable to withstand regular direct wave action. As they are concrete structures placed at backshore, they will tend to trap wind blown sand and sediment transport and allow the growth of vegetation under favourable conditions. This only applies to sloping structures.
Description Of Drawings
The moulds for the Labuan Blocks are made locally. Ready-mixed concrete is then delivered to site. The ready-mixed concrete is then discharge from the mixer-truck and placed inside the moulds. The next process is the vibration of concrete. This is essential to eliminate the entrapped air and forcing the particles into a closer configuration. Internal vibrator like poker vibrator is used. Some admixtures can also be used to accelerate the hardening or the development of early strength of concrete.
The most common cement used in this case is the Ordinary Portland (Type I) cement with a Grade of 35. As to avoid sulphate attack (sea water attack), Sulphate-Resisting (Type V) cement is recommeded.
The next step in this process is curing at normal temperature; that is to keep concrete saturated, or as nearly saturated as possible, until the originally water filled space in the fresh cement paste has been occupied to the desired extent by the products of hydration of cement. Curing may be aided by wetting the moulds before casting. The blocks must be wetted during hardening. The concrete should be sprayed with water or covered with suitable covering to avoid drying out.
Methods Of Placement
Concrete Blocks should be placed as a sloping revetment as shown in pictures. Near vertical walls are more likely to suffer toe scour and structural collapse as they are less able to dissipate wave energy during storm wave attack. They are also much more obtrusive to the dune landscape and will not become buried by new foredunes.
SAUH Revetment, Haji Sirat, Selangor.
Basalton Revetment, Pulau Besar, Melaka
Flex-Slab Revetment, Pantai Klebang, Melaka
Rock Revetment, Kg Pasir Pandak, Kuching, Sarawak
Last Updated 2017-05-18 13:23:55 by Administrator