Geosynthetics for Coastal and Marine EngineeringGeosynthetics for Coastal and Marine Engineering 3. The conventional solutions A revetment is a facial or veneer layer applied to the

Geosynthetics for Coastal and Marine Engineering

TenCate Geosynthetics – how it all beganTenCate 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 Scheldtdischarge 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.

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TenCate Geosynthetics – how it worksCoastal and marine environments are susceptible to 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:

Geometrical measures, where the shape of the structure and adjacent profile is altered in order to reduce the water forces below a minimum threshold.Stabilisation measures, where the exposed structure is protected from erosion by stabilising the susceptible soil. Examples include the provision of revetments, etc.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 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. TenCateGeosynthetics are easy to install beneath the water surface, in difficult conditions, and once in place provide continued performance.

TenCate Nonwovens

TenCate Wovens

TenCate Geosystems

Geosynthetics for Coastal and Marine Engineering 3

The conventional solutionsA 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 armourlayer 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 indesign 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 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 landreclamation 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.

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Revetment

Dyke and related structures

Dyke for reclamation

Solutions incorporating Geosystems

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 TenCateGeotube® 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.


‘Step ladder’ reclamation dykes

TenCate Geobag® Systems

Dyke core replacement

TenCate Geocontainer® SystemsTenCate Geotube® Systems

‘Pyramid stack’ reclamation dykes

Coastal Revetmentspreventing 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 design, are economical, easy to install and robust.

Natural sand dunes may be found at the landward extent of an active beach and can offer some form of protection against wave attack under extreme tidal or surge conditions. When natural dunes do not exist or when they do not provide sufficient protection, rock revetment structures may be built hidden withincovered sand for beach aesthetics and recreation purposes. During a storm event, the front sand cover may be eroded but theexposed revetment would prevent further damage from occurring. After the storm event, the sand cover is then replaced. TenCate® Geotube Systems are commonly used as a very cost effective alternative to hidden revetments in the sand dune zone.

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Coastal Revetment,CT, USA

The town of East Lyme in CT, USA wanted to connect two separate beaches facing the Atlantic Ocean with a new elevated pedestrian and bike path. This elevated pedestrian and bike path would also serve as a buffer to an existing high speed train line that was located beside it.

A coastal revetment was constructed to protect the new coastline. The armourlayer 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

Scour & Capping Layerspreventing seabed erosion

Scour is the removal of granular bed material by hydrodynamic forces in the vicinity of hydraulic and marine structures. Scouroccurs 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. which causes reduction of project owner confidence and results in costly repairs or replacement of structures. Scour can occur 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 cause scour problems are as follows:-

Breaking waves that impact bottomsLocalised increase in orbital velocity due to reflected wavesAccelerated flows due to flow constrictions or structure alignment induced currentsFlow separation and creation of vorticesTransitions from hard bottoms to erodible beds

To prevent erosion of the seabed TenCate Geosynthetics are used as geotextile filters placed on the bed prior to placement of the armour layers.


San Diego Bay Capping,CA, USA

The Campbell Shipyard site in San Diego left behind a basin with contaminated sediments that required extensive environmental remediation to clean up the site for development. As part of the environmental remediation works, an engineered capping structure was placed over a contaminated sea bed area of more than 3 hectares.

The engineered capping structure composed of TenCate geotextilesoverlaid by 0.6 m of sand for isolation of pollutants in existing sediments, which is then overlaid with 0.3 m of well graded gravelly aggregates and a final layer of 0.6 m armouring stones.

There are many reasons for sea levels to rise above inland areas. Tides result in regular rise and fall in sea levels. Although the typical tidal range in the open ocean is about 0.6 m, coastal tidal ranges can vary between zero to over 10 m in height, depending on the coastal geography and location. Due to global warming, the mean sea level is expected to gradually rise with time. Water levels can also rise as a result of waves and surges.

To protect flooding of low lying areas flood control dykes or levees are constructed along estuaries and coastlines. The top of floodcontrol dykes or levees should be higher than the design high water level plus a safety freeboard. In addition the levees should be designed to prevent seepage through the core structure. As such the levee is either constructed with earth or consists of at least one zone of fine-grained soil to act as a hydraulic barrier to seepage water.

TenCate geotextiles are used as a filter layer to revetment associated with protecting the sea facing part of the levee. As such levee structures are often constructed over soft coastal areas, TenCate geotextiles are also used as basal reinforcement of the structure.

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Levees & Flood Control Dykespreventing rising sea levels from flooding inland areas

Flood Control Dykes,Germany

The Big Flood of 1953 that affected the Netherlands also caused flooding and severe damages to land and property in northern Germany. As a result, a 7 km long flood control coastal dyke was constructed beginning in 1992. The 8.8 m high dykes facing the North Sea at Leybucht would keep inland areas of up to 31 km from flooding during extreme events.

TenCate geotextiles were used as filtration layer beneath the rock armourprotection for the dyke as well as for the bed protection in the inlet-outlet channel. Geotube® systems were used as reclamation dyke to raise the earthworks platform above high water levels.

Estuarial Barriers & Barragesallow river discharges while holding back rising sea levels


Tides cause sea levels to rise and fall in constant cycles. Tidal effects are experienced in coastal and river delta areas. Although the typical tidal range in the open ocean is about 0.6 m, coastal tidal ranges can vary between zero to over 10 m in height, depending on the coastal geography and location. Due to global warming, the mean sea level is expected to gradually rise with time. Water levels can also rise as a result of waves and surges.

Estuarial barriers and barrages are special dam structures that are designed to hold back the sea during high sea levels while allowing river discharges during normal sea levels. The primary objective of such structures is usually flood prevention. Such constructions are usually extremely challenging and techniques often project specific. TenCate geotextiles are used as components in prefabricated systems for filtration and reinforcement functions.

Eastern Scheldt Barrier,The Netherlands

The Eastern Scheldt Barrier is part of the Delta Project to protect the Netherlands against a repeat of the big flood of 1953. The Eastern ScheldtBarrier with a length of 8 km, seals of an estuary with a tidal volume of 2.2 billion m3.

TenCate geotextiles are supplied for the fabrication of foundation mattresses for the 65 prefabricated reinforced concrete piers, each with the height of a 12-storey building and weighing 18,000 tonnes.

Coastal Groynestrapping littoral drifts to stabilise shorelines

Groynes are finger-like hydraulic structures that jut perpendicularly out of coastlines. Their engineering function is to interrupt or reduce longshore sediment transport. This interruption will produce accretion updrift of the groynes and produce concomitant erosion downdrift of the groynes. Groynesare usually constructed in groups otherwise referred to as groynefields. When constructed in concert with beach restoration, the groyne field will act to reduce future beach maintenance and nourishment requirements.

The sectional requirement of a groyne structure is the same as that of a basic dyke structure. TenCate geotextiles are used as a filter layer to prevent sand beneath from being eroded away. Alternatively, TenCate Geotube® Systems may be used to construct coastal groynes.

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Bald Head Island,NC, USA

The South Beach of Bald Head Island in North Carolina experienced severe coastline erosion. Geotube® systems were used to construct a field 14 coastal groynes for long term protection of 3.7 km of South Beach shoreline. The Geotube® groynes had a circumference of 2.75 m and was underlain with a 7.3 m wide scour protection apron. The Geotube®

groynes were embedded within a trench in the upper beach and extended to approximately -1.2 m mean low water level at the seaward end. The beach restoration project also involved 500,000 m3 of beach sand nourishment. The Geotube® systems survived the passage of Hurricanes Bertha and Fran which occurred within three months of completion of project.

Marinas & JettiesProviding calm water area and maintaining draft

Marinas are areas that are either naturally deep enough for boats to seek shelter within a protected area. They may also be artificially created through dredging a confined are to provide navigation draft. The confined area is usually protected by jetties.

Jetties are also finger-like dykes that jut out of coastlines.Jetties are constructed singularly or in pairs with the purpose of maintaining inlet and channel depth for navigation into and out of the marina. Compared with groynes, jetties extend further offshore into deeper waters. As a result jetties force littoral bypasses in deeper waters thus preventing channels from silting and inlets from closing off.

TenCate geotextiles are used as a filter layer to prevent sand beneath from being eroded away. Alternatively, TenCateGeotube® Systems and TenCate Geobag® Systems may be used to replace the rock fill core of the jetty structures.


Stella Maris Marina,Ecuador

Stella Maris, a luxury resort on the Pacific Coast of Ecuador used Geotube® systems to construct the cores of two jetties because there was not a nearby source for rock. Geotube®

units deployed at site were filled sand dredged form the ocean. The units were stacked in a “pyramid” method to build up the jetty core. A steel positioning frame was used to keep the standard 20 m long Geotube® unit straight during filling (while being pounded by waves). A total of 2 km of Geotube® units of 13.7 m circumference were used. The Geotube® systems were strong enough so that heavy construction machinery could drive on top as the structures were being built.

Land Reclamationsretaining reclamation fill

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The shortage of land along certain coastlines requires land to be reclaimed from the sea. Reclamation dykes are cofferdam units that retain fill while providing protection against wave attack during construction, prior to placement of long term armourprotection cover. Conventionally, the cofferdam units are constructed of rock fill material in much the same way as the rock fill core of groynes, jetties, etc. Depending on the grading of the rock fill material, TenCate geotextiles may be laid on the inner side of the reclamation dyke to prevent washout of sand fill through the rock fill dyke. TenCate geotextiles may also be laid over the sea side of the reclamation dyke prior to placement of the armour protection.

Alternatively, TenCate Geotube® Systems and TenCateGeocontainer® Systems may be used to replace the rock fill reclamation dyke.

Brisbane Port Extension,Australia

The Port of Brisbane is located at the mouth of the Brisbane River. To keep pace with growth 230 hectares of land is reclaimed from the sea for the Future Port Expansion Project. This involved the construction of a 4.6 km long and 7.5 m high perimeter reclamation dyke in soft marine clays in order to contain the reclamation fill in an environmentally friendly and controlled manner.

The design required the reclamation dyke to be basally reinforced for foundation stability. TenCate geotextileswere used as basal reinforcement geotextiles to ensure the reclamation dykes are constructed without stability failures.

Creating Islandspreventing shoreline erosion


Artificial islands are constructed for a variety of reasons. They may provide land for development of prime residential and commercial properties; create eco-friendly habitats and sanctuaries; act as barrier islands to protect coastal habitats,etc. Reclamation dykes are used to form the shorelines of the islands in very much the same way as land reclamation techniques. TenCate geotextiles may be laid on the inner side of the reclamation dyke to prevent washout of sand fill through the rock fill dyke. TenCate geotextiles may also be laid over the sea side of the reclamation dyke prior to placement of the armour protection.

Alternatively, TenCate Geotube® Systems and TenCateGeocontainer® Systems may be used to replace the rock fill reclamation dyke.

Amwaj Islands Project,Bahrain

As part of a US$1 billion project to create an island and build an exclusive community with upscale residences, luxury apartments and a marina, the developers of Amwaj Islands selected Geotube® systems as a way to literally form islands from the sea.

A total of 30 km of 13.7 m circumference Geotube® units were stacked two layers high to create containment dykes and sand was filled behind them to a height of over 3 m above sea level. Work could be completed so quickly that the shoreline for the islands were created within five months.

Coastal Breakwaterssheltering and preventing erosion of coastal development

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Coastal breakwaters are marine structures that have the primary function of sheltering a coastal development by preventing longshore currents from causing erosion and reducing wave energies impacting a shoreline. They are connected to the shoreline like groynes and jetties but differ in function and massiveness. Like groynes and jetties they impact the littoral functions but coastal breakwaters differ with the additional function of forcing waves to break offshore. Coastal breakwatersalso tend to have special end details in the sea e.g. fishtailed, L-shapes or T-shaped that are designed to eliminate problems of downdrift erosion and promote the formation of beaches.

TenCate geotextiles are used as filter layers for the construction of coastal breakwaters. TenCate geotextiles can also be prefabricated onshore into a large panel of fascine mattress that can be floated out to sea. This panel of fascine mattress can then be ballasted into position on the seabed by dropping rock onto the floating fascine mattress.

Alternatively, TenCate Geotube® Systems, TenCateGeocontainer® Systems and TenCate Geobag® Systems may be used to replace the rock fill core of breakwaters.

Bengkulu Breakwater,Indonesia

The Port of Bengkulu in Indonesia completed in 1985 is protected with two rubble mound breakwaters with approximate crest lengths of 390 m and 420 m. The heads of the breakwaters were constructed with blocks weighing up to 10 tons.

TenCate geotextiles were prefabricated onshore into large panels of fascine mattresses. These large panels of fascine mattresses were then floated offshore and sunk into position by ballasting with bedding stones. The use of such a technique made construction of the breakwaters an easy job. A total of 110,000 m2 of TenCate geotextileswere used for the project.

Offshore Breakwatersreducing wave energies impacting shorelines

Offshore breakwaters are marine structures that have the primary function of reducing wave energies impacting a shoreline. Offshore breakwaters reduce wave energies by partially reflecting some wave energy seawards as well as forcing some wave energies to be expensed through wave breaking on the structure before such destructive waves can reach the shoreline. Offshsore breakwaters are generally constructed parallel to shorelines. Offshore breakwaters are sometimes designed to be permanently submerged and are often designed to retain a perched or artificial beach.

As offshore breakwaters tend to involve construction in relatively deep waters, the installation of geotextiles can often be challenging. TenCate geotextiles can be specially designed to make installation in deep waters a simple and efficient task.TenCate geotextiles can be prefabricated onshore into a large panel of fascine mattress that can be floated out to sea. This panel of fascine mattress can then be ballasted into position onthe seabed by dropping rock onto the floating fascine mattress.

Alternatively, TenCate Geotube® Systems, TenCateGeocontainer® Systems and TenCate Geobag® Systems may be used to replace the rock fill core of breakwaters.


Kerteh Breakwater,Malaysia

The onshore operation base for Peninsular Malaysia’s offshore petroleum production is situated along Kerteh Bay. Coastal erosion threatened the school and housing facilities, as well as a golf course. Offshore breakwaters together with beach nourishment was the solution of choice as this option would allow the recreational beach to be fully accessible without imposing rock structures along the shoreline.

TenCate geotextiles were prefabricated onshore into large panels of fascine mattresses. These large panels of fascine mattresses were then floated offshore and sunk into position by ballasting with bedding stones.

Mirafi®, Polyfelt®, Geolon®, Geotube®, Geocontainer® and Geobag® are registered trademarks of Royal Ten Cate. The information contained herein is to the best of our knowledge accurate, but since the circumstances and conditions in which it may be used are beyond our control we do not accept any liability for any loss or damage, however arising, which results directly or indirectly from use of such information nor do we offer any warranty or immunity against patent infringement.

Documents

Geosynthetics for Coastal and Marine EngineeringGeosynthetics for Coastal and Marine Engineering 3. The conventional solutions A revetment is a facial or veneer layer applied to the