Dunes and residential building protection using geotextile tubes

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Ofir Towers - Portugal

TenCate Geosynthetics

This project was realized to protect the dunes against erosion and protect the buildings on top of the dunes. Several attempts were tried but the final solution was using geotextile tubes made from a high UV stabilized sand color fabric called GT 1000MB making use of local available fill material: sand.

The beaches of Portugal that are located at the Atlantic Ocean erode during the storms of the fall and winter. The eroded sand moves offshore then during the spring and summer the sand is pushed back onto the beaches with the gentle waves of summer. Periodically, the fall and winter storms will erode some of the dunes and this sand replenishes the beaches. This is a common cycle that occurs in all coastline communities. When a series of storms occurs in quick succession, the shape of the barrier island changes as Mother Nature moves the sands.

This would not be a problem if the coastline was left in its natural state but humans desire to enjoy the beach and ocean has led to the development and construction of infrastructure on the barrier islands that must be protected. In Ofir all the dunes are eroded to a critical situation that the urban development came into the danger zone.

Different attempts, using heavy sandbags, rocks and wooden piles, had been made to protect the dune area but failed all. The University of Porto-FEUP-IHRH was asked to come up with a suitable solution for two critical areas in Ofir based on the local conditions and to make use of local available sand to build the protection.

The design included the use of a scour apron with a single anchor tube on the ocean side to avoid sinking of the geotextile tube due to erosion underneath the geotextile tube. Based on the wave conditions that were expected the TenCate Geotube® units were designed for a filled height of 2,4 meter. The structure was designed to be stable for significant wave height up to 5 meters.

After completion a severe storm hit the Atlantic Ocean shoreline. The structure was tested directly and proofed its functionality.

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