Session

Session 9 2022

Start Date

10-27-2022 12:00 AM

Abstract

Beaches in India and elsewhere are getting destroyed at an alarming rate as many small ports are being built and sea walls are coming up on the banks. There is an urgent need to stop it. In 1966, Posey used cylinders of net filled with rock (called rock sausages) underlain by a reverse gravel filter for safety against scour in hydraulic structures. Pillai used a bed of stones enclosed in nets underlain by a reverse filter to allow overflow over a sand embankment. Later it was understood that a Polypropylene Fabric (P.F.) could be effective as a filter, and a bed of polypropylene bag filled with sand (like geo-tubes) can be used to prevent scour. However, the P.F. get weathered when exposed to sunlight. A breakthrough came when porous concrete blocks with high porosity, high strength and seawater resistance were developed and were used underlined by a P.F. An attempt was made in an experimental study on the Cheriathura Beach at Trivandrum. Porous concrete blocks 0.5 m X 0.5m, 10 cm thick were cast and arranged at a time of low tide, covering an area of 10 m x 5 m (with the P.F. underneath). When the waves acted frontally during high tide, this rode smoothly on the pavement, had their run-up, and later receded without displacing the slabs. This showed that porous concrete slabs could be a good armour for protecting the beach. The side slabs got displaced with lateral waves because no sidewall could be provided in the narrow strip of protection. It is felt that the porous concrete slabs can be placed deep in the beach so that during the erosive phase, the slab could function as armour, and when there is accretion, there would be deposition of sand on the slabs maintaining the beach.

Share

COinS
 
Oct 27th, 12:00 AM

Porous Concrete Slabs Underlain by Polypropylene Fabric for Restoration of Beaches

Beaches in India and elsewhere are getting destroyed at an alarming rate as many small ports are being built and sea walls are coming up on the banks. There is an urgent need to stop it. In 1966, Posey used cylinders of net filled with rock (called rock sausages) underlain by a reverse gravel filter for safety against scour in hydraulic structures. Pillai used a bed of stones enclosed in nets underlain by a reverse filter to allow overflow over a sand embankment. Later it was understood that a Polypropylene Fabric (P.F.) could be effective as a filter, and a bed of polypropylene bag filled with sand (like geo-tubes) can be used to prevent scour. However, the P.F. get weathered when exposed to sunlight. A breakthrough came when porous concrete blocks with high porosity, high strength and seawater resistance were developed and were used underlined by a P.F. An attempt was made in an experimental study on the Cheriathura Beach at Trivandrum. Porous concrete blocks 0.5 m X 0.5m, 10 cm thick were cast and arranged at a time of low tide, covering an area of 10 m x 5 m (with the P.F. underneath). When the waves acted frontally during high tide, this rode smoothly on the pavement, had their run-up, and later receded without displacing the slabs. This showed that porous concrete slabs could be a good armour for protecting the beach. The side slabs got displaced with lateral waves because no sidewall could be provided in the narrow strip of protection. It is felt that the porous concrete slabs can be placed deep in the beach so that during the erosive phase, the slab could function as armour, and when there is accretion, there would be deposition of sand on the slabs maintaining the beach.