Geosynthetics for Coastal and Marine Engineering TenCate Geosynthetics – how it all began TenCate Geosynthetics and indeed the geosynthetics industry have its beginnings traced back to the Big Flood of 1953 in the Netherlands. During the weekend that spanned the end of January and beginning of February in 1953, a storm raged across the northwest European shelf. The impact of this storm was particularly severe for the Netherlands for several reasons. Firstly, the storm track made landfall directly on the Netherlands coastline. Secondly, a high storm surge coincided with a spring tide event. This combination of factors easily brought about the overtopping and breaching of then existing coastal dykes. The Netherlands is a low-lying country where River Rhine, River Meuse and River Scheldt discharge into the North Sea. In the delta area, communities lived largely below the high-water mark and even below sea-level, protected from flooding only by dykes built around a certain area or polder. The economic impact was enormous because of the large tracts of populated land that were flooded as a result of the overtopping and breaching of dykes and some remained under water for months before full recovery. Timely dyke closure was crucial because twice daily reversing tidal flows through the breaches would threaten further widening of the breach and erosion of the dyke. When the dykes were closed flooded areas within were then pumped dry. The last remaining area affected by the Big Flood of 1953 was only officially declared dry on 31st December 1953. However, the area was so badly affected by sea salt deposition that it took many years before agricultural yields returned to previous levels before the Big Flood of 1953. This natural disaster triggered the formation of the business division in TenCate that developed the use of synthetic textiles for the construction of bigger and stronger storm surge and flood control dykes in the Netherlands and started the geosynthetics industry. TenCate Geosynthetics continued the development of product and application technology in the coastal and marine engineering sector and remained in the forefront of the industry. 2 TenCate Geosynthetics – how it works Coastal and marine environments are susceptible to TenCate Nonwovens erosion, which is caused by the action of waves, tides, currents and other water motion. The consequence of erosion can range from a simple loss of surface soil to the wholesale undermining and collapse of structures. To positively influence the morphology and prevent erosion at designed locations a variety of measures are used. Generally, these measures fall into one of three categories: ¾ Geometrical measures, where the shape of the structure and adjacent profile is altered in order to reduce the water forces below a minimum threshold. TenCate Wovens ¾ Stabilisation measures, where the exposed structure is protected from erosion by stabilising the susceptible soil. Examples include the provision of revetments, etc. ¾ External measures, where the exposed structure is protected from erosion by the provision of a protection structure, placed at some distance. Examples include breakwaters, etc. TenCate Geosystems TenCate Geosynthetics, with filtration, containment or reinforcement functions, are used as integral components in the design and construction of a variety of coastal and marine structures such as revetments, scour protection layers, levees, dykes, groynes, jetties and breakwaters. TenCate Geosynthetics are easy to install beneath the water surface, in difficult conditions, and once in place provide continued performance. Geosynthetics for Coastal and Marine Engineering 3 The conventional solutions A revetment is a facial or veneer layer applied to the sloping surface of soils to prevent their erosion against wave action and currents. Revetments may be deployed to protect toes of coastal cliffs, bluffs, dunes, etc, and to fortify coastal embankments and flood levees. Functionally, as sloping structures, revetments reduce wave reflection and absorbs wave energy through a combination of energy dissipation within the structure and wave runup over the structure surface. They consist of an outer armour layer designed to resist hydrodynamic energy; a TenCate geotextile filter layer designed to prevent erosion of base soil; and possibly bridging layers in-between. The outer armour Revetment layer is commonly constructed using rock but may also be concrete elements, etc. The revetment structure is provided with a freeboard to extend the protection beyond the runup expected in design. If that is impractical due to site conditions, the top of revetment structure may include a capping detail to deflect away the runup or a protective splash apron covering the bank above may be provided in design. Scour protection and capping layers are similar to revetments in design except they are generally laid horizontal. Dykes and related structures typically consist of a general rock fill core and an outer armour protection for long term design against wave and Dyke and related structures current attacks. TenCate geotextiles are placed over the rock fill core to act as filters prior to the construction of the revetment structure. TenCate geotextiles prevent fines in the rock fill core from being washed out through the porous external revetment cover. For land reclamation works in marine environment, dykes are used as cofferdams to retain fill material. TenCate geotextiles are placed over the reclamation dykes to act as filters prior to filling. When dykes and other marine structures are constructed over soft foundations, TenCate geotextiles can also be used as basal reinforcing layers to provide stability. Dyke for reclamation 4 Solutions incorporating Geosystems TenCate Geotube® Systems TenCate Geocontainer® Systems TenCate Geobag® Systems TenCate Geosystems are systems of geotextile encapsulated granular soils that may be used to replace rock as conventional building blocks in coastal and marine engineering structures. They include TenCate Geotube® Systems, TenCate Geocontainer® Systems and TenCate Geobag® Systems. TenCate Geotube® Systems involve tubular units that are typically hydraulically filled. TenCate Geocontainer® Systems involve units that are tailor made to match split bottom barges; within which the units are filled, sealed and dropped into position. TenCate Geobag® Systems involve a wide array of bag designs and geometry, and are typically dry filled on site, sealed and deployed. TenCate Geobag® Systems units tend to be smaller in size as they need to be handled with and deployed using conventional construction machinery like loaders and lifting cranes. Dyke core replacement ‘Pyramid stack’ reclamation dykes ‘Step ladder’ reclamation dykes Geosynthetics for Coastal and Marine Engineering 5 Coastal Revetments preventing shoreline erosion Revetments are often used to protect coastlines. Coastal revetments may be deployed to protect toes of coastal cliffs, bluffs, dunes, etc, They may also serve other purposes such as limiting wave overtopping or wave reflections. TenCate offers a wide range of filter geotextiles to satisfy different conditions in Coastal Revetment, design, are economical, easy to install and robust. CT, USA Natural sand dunes may be found at the landward extent of an active beach and can offer some form of protection against wave The town of East Lyme in CT, USA attack under extreme tidal or surge conditions. When natural wanted to connect two separate dunes do not exist or when they do not provide sufficient beaches facing the Atlantic Ocean with protection, rock revetment structures may be built hidden within a new elevated pedestrian and bike covered sand for beach aesthetics and recreation purposes. path. This elevated pedestrian and bike During a storm event, the front sand cover may be eroded but the path would also serve as a buffer to an exposed revetment would prevent further damage from existing high speed train line that was occurring. After the storm event, the sand cover is then replaced. located beside it. TenCate® Geotube Systems are commonly used as a very cost effective alternative to hidden revetments in the sand dune zone. A coastal revetment was constructed to protect the new coastline. The armour layer of the coastal revetment consists of approximately 1.8 m of large heavy rip rap. TenCate geotextiles were used as filter layer underneath the rip rap. Exposed after storm event Replaced sand cover 6 Scour & Capping Layers preventing seabed erosion Scour is the removal of granular bed material by hydrodynamic forces in the vicinity of hydraulic and marine structures. Scour occurs when the hydrodynamic bottom shear stresses exceed the sediment critical shear stress. Scour problems can lead to damage of structures e.g. revetments, dykes, seawalls, etc. San Diego Bay Capping, which causes reduction of project owner confidence and results in costly repairs or replacement of structures. Scour can occur CA, USA around bridge piers, in front of seawalls and revetments, at specific locations and tips of breakwaters and jetties, along and around bottom laid pipelines, etc. The conditions that likely will The Campbell Shipyard site in San cause scour problems are as follows:- Diego left behind a basin with ¾ Breaking waves that impact bottoms contaminated sediments that required extensive environmental remediation to ¾ Localised increase in orbital velocity due to reflected clean up the site for development. As waves part of the environmental remediation