COASTAL EMBANKMENT PROTECTION AT MAHESHKHALI

Asian Institute of Technology, Thailand (AIT)

January 2022 – June 2022

• Terre Armée India

         (Reinforced Earth India Pvt. Ltd.)

The project is at an upcoming Industrial zone in Bangladesh very close to Cox’s Bazar coastline. The owner is developing the land by reclamation with dredged sand from the sea and also raising an embankment above the surge level (8.5m) throughout the boundary. Here extreme surface water level is at 4.87m. The site gets inundated by water during high tide, so the owner has laid some geotextile tubes as temporary barrier against the tidal water so that the filling works can be carried out seamlessly. The project boundary is the slope of the raised embankment, which was initially proposed to be protected using Cement Concrete (CC) blocks with a slope of 1v:5h. As the working season here is 6-8 months in a year, approximately, 3 years of construction period was estimated with CC blocks.

The project owner was unwilling to have a slope of 1v:5h as that would cause a significant loss ofland.

In view of the client’s requirement of saving land, Terre Armée India promptly made a site visit and prepared a detailed proposal using Reinforced Earth® Wall.

However, due to poor foundation soil condition, cost of ground improvement was significant. At the same time, the client was also unwilling to dismantle the temporary geotextile tubes, which were installed earlier.

Terre Armée India, therefore, proposed TechRevetment® (Grout filled concrete revetment mattress) as an embankment protection solution with a slope of 1v:3h. TechRevetment® Articulating Block (AB) mattress with bi-directional cable was installed in the apron area and TechRevetment® Articulating Block (AB) mattress with uni-directional cable was installed on the slope surface up to High Tide Level. TechRevetment® Filter Point (FP) mattress was installed above High Tide Level up to the top of the embankment. TerraAnchor® of 3m length and 2MT capacity was used as an anchorage system. Special and customized provision of saucer drains to drain out the water from the country side of the embankment was also made on the TechRevetment.

Although the crest design was not in Terre Armée India’s scope, during the design and coastal modeling, Terre Armée India found an overtopping of water @ 0.09 m³/s-m for a section of 300m in length. An increase of 1m crest height was suggested along this section.

The design was vetted by the Asian Institute of Technology, Thailand. The installation work started in January 2022 and was completed in the next six months, offering significant time savings to the project owner.