markus muttray - Academia.edu (original) (raw)

Papers by markus muttray

Das Hauptziel dieser Arbeit ist eine umfassende Beschreibung der Wellenbewegung und Ausbreitung a... more Das Hauptziel dieser Arbeit ist eine umfassende Beschreibung der Wellenbewegung und Ausbreitung an und in einem geschütteten Wellenbrecher auf der Grundlage großmaßstäblicher Modellversuche im Großen Wellenkanal, Hannover und einfacher theoretischer Modelle. Der Wellenbrecher wurde in fünf Bereiche unterteilt. In jedem Bereich wurden die Wasserspiegelauslenkungen und ggf. die Porenwasserdruckoszillationen untersucht. Deren Beschreibung setzt sich zusammen aus einem linearen theoretischen Modell und einem empirischen Ansatz für die nichtlinearen Einflüsse. Darüber hinaus wurden die Unsicherheiten dieser halbempirischen Ansätze und deren Übertragbarkeit bestimmt. Es wurden lineare theoretische Modelle zur Beschreibung (a) der Wellenbewegung über rauhen teildurchlässigen Böschungen, (b) der Wellenausbreitung in homogenen, porösen Medien und (c) der gesamten Energiedissipation am und im Bauwerk entwickelt. Die wichtigsten hydraulischen Prozesse, die in den 5 Bereichen des Wellenbrechers...

Presented at: Coastal Structures Conference 2019, Hannover, Germany, September 30th – October 2nd... more Presented at: Coastal Structures Conference 2019, Hannover, Germany, September 30th – October 2nd, 2019

Journal of Coastal Research, 1994

Rundown velocity along the slope of a breakwater is quite an important parameter in breakwater de... more Rundown velocity along the slope of a breakwater is quite an important parameter in breakwater design. Literature review on rundown velocity measurements indicates that a few small scale studies have been attempted in the past, mostly along beach slopes. This paper details the experimental investigations conducted at large wave flume (GWK), Franzius Institute, Hannover, Germany, in regard to rundown velocity along the slope of a rubble mound breakwater with an accropode armour layer. As the wave flume facilitates generation of wave heights in the range of 0.20 to 2.0 m with wave period ranging between 3.0 and 12.0 seconds, measurements on rundown velocity for the near prototype conditions were possible. Two methods were adopted to determine rundown velocity viz., (i) with a float and (ii) with a wave gauge. The results on the variation of rundown velocity with Iribarren Number and wave steepness are presented in the form of non-dimensional graphs and discussed. The studies indicated...

Coastal Engineering Proceedings, 2018

The XblocPlus is a new type of interlocking single layer armour units that is placed with uniform... more The XblocPlus is a new type of interlocking single layer armour units that is placed with uniform orientation. This is novel and different from all other single layer, interlocking armouring systems. The hydraulic stability of the XblocPlus breakwater armour unit was tested in 2D and 3D hydraulic model tests. Wave overtopping tests were performed to determine the roughness coefficients of the EurOtop overtopping formula for the XblocPlus. Model tests on a rubble mound breakwater with XblocPlus armour included 2D tests with a 1:30 seabed slope and with 1:2 and 3:4 breakwater slopes and 3D model tests with a flat seabed and with a 3:4 breakwater slope. Wave heights up to 150% of the design wave height were tested in the 2D tests and up to 200% with wave directions 0° to 60° in the 3D tests. No armour unit displacements were observed in 2D tests with 1:2 slope. In the 2D tests with 3:4 slope one armour unit was displaced when the wave height reached 159% of the design wave height. No d...

Coastal Engineering 1992, 1993

Coastal Engineering 1998, 1999

The hydraulic performance of an innovative structure based on the concept of a high mound composi... more The hydraulic performance of an innovative structure based on the concept of a high mound composite breakwater has been investigated in large-scale hydraulic model tests in the Large Wave Flume (GWK) of the Coastal Research Center (FZK), Germany. The experimental results concerning wave breaking, wave transmission and wave reflection are presented.

The wave transmission at low crested rubble mound breakwaters due to wave overtopping and wave pe... more The wave transmission at low crested rubble mound breakwaters due to wave overtopping and wave penetration through the structure is addressed in this paper. Wave transmission past rubble mound breakwaters was investigated experimentally in 2D hydraulic model tests. The transmission at low crested structures is primarily determined by wave overtopping. The incident wave height, the freeboard and the crest width have been identified as governing parameters for the wave transmission. The effect of breakwater slope and wave steepness is insignificant for contemporary rubble mound breakwaters with interlocking armour. The fictitious run-up height (a function of incident wave height) and the equivalent freeboard (combining actual freeboard and crest width) have been applied for predicting the wave transmission by wave overtopping. A new wave transmission formula has been developed, which is applicable for low crested and submerged rubble mound breakwaters with relatively steep slopes (steeper than 1:2) and various crest geometries (crest width 0.5 < B/Hs,i < 5).

A large variety of concrete breakwater armour units has been developed in the past. Today design ... more A large variety of concrete breakwater armour units has been developed in the past. Today design engineers have the choice between a number of completely different breakwater armour concepts. The most commonly applied types of armour units are presented and classified. The strong and weak points of the various concepts as well as possible applications are discussed. Demands for future improvements are specified with respect to hydraulic and structural stability, placement and casting. Finally a concept for an improved armour unit with a simple bulky shape and two different front faces is outlined, which is easy to cast and easy to place. This block shall be capable to find easily a stable position on the slope. The structural stability shall be similar to Accropodes in order to minimise the risk of breakage and subsequent progressive failure. The optimum interlocking capability has to be balanced between hydraulic stability and the ease of fabrication, placement and strength of the ...

A new interlocking breakwater armour unit has been developed by Delta Marine Consultants during t... more A new interlocking breakwater armour unit has been developed by Delta Marine Consultants during the past two years. The development is based on extensive review of existing breakwater armour concepts, consulting of contractors and designers, desk studies and physical model tests. A randomly placed single layer interlocking armour unit turned out to be the best technique for breakwater protection under severe environmental conditions. The new armour unit is called Xbloc ® and has a simple, bulky shape. Hydraulic model tests (2-D and 3-D), a numerical structural strength analysis (FE calculations) and prototype drop test have been performed. The test results demonstrated the large hydraulic stability and the easily achieved interlocking (automatic interlocking) of the Xbloc ® as well as its very high structural stability. Therefore the Xbloc ® is a promising alternative for conventional single layer armour units. Significant cost savings can be achieved due to easy fabrication, fast p...

Ports 2010, 2010

Port@Lekki (located about 70 km East of Lagos, Nigeria) is a port development for chemical tanker... more Port@Lekki (located about 70 km East of Lagos, Nigeria) is a port development for chemical tankers (160,000 DWT) and container vessels (8,000 TEU). The layout of the new port, including the layout of approach channel, turning circle and harbour basins has been derived from optimisations based on port operations, construction costs and possible future extensions. Two different breakwater concepts were applied for the main breakwater: A rubble mound with geo-bag core for the near-shore sections and a composite breakwater for the more exposed sections. The secondary breakwater was replaced by a barrier. The barrier consists of a core from sand, internally fortified by a protective geo-bag layer, a revetment on the harbour side and an artificial beach on the seaward side. The proposed layout of the new port and the design of main breakwater and barrier are described in this paper.

Coastal Engineering 2004 - Proceedings of the 29th International Conference, 2005

The wave damping in a rubble mound breakwater has been studied theoretically and experimentally. ... more The wave damping in a rubble mound breakwater has been studied theoretically and experimentally. Various types of damping functions (linear, quadratic and polynomial) have been derived and checked against experimental results from large scale model tests. Damping coefficients have been derived from the hydraulic resistance of the breakwater core material. The result is a general approach for the wave decay inside a rubble mound breakwater that clearly reflects the flow processes inside the structure.

Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007

From 2001 to 2003 Delta Marine Consultants developed a new breakwater armour unit, named Xbloc ®.... more From 2001 to 2003 Delta Marine Consultants developed a new breakwater armour unit, named Xbloc ®. Extensive testing and studies were carried out, and the new armour unit has proved to be reliable and easy to use. Port Oriel, an existing fishing port on the East coast of Ireland has been rehabilitated in order to upgrade the port. For the protection of the breakwater Xbloc armour units were used, which is the first Xbloc application in Europe. The design was prepared by RPS Kirk McClure Morton in Belfast and the construction of the project was awarded to Lagan Construction. This paper describes the project, the design and the construction works of the Port Oriel reconstruction. The works started in May 2005, and the breakwater was completed in December 2006.

Ocean Wave Measurement and Analysis (2001), 2002

Based on extensive hydraulic model testing, the uncertainties of available "standard" models used... more Based on extensive hydraulic model testing, the uncertainties of available "standard" models used to predict wave heights on shallow foreshores of coastal structures are quantified. Both wave transformation on the foreshore and at the structure are taken into account. Finally, improvements of the prediction models are proposed and recommendations on the selection of the models to be used are provided.

Coastal Engineering 2004 - Proceedings of the 29th International Conference, 2005

The structural integrity of the single layer armour unit Xbloc ® has been investigated by means o... more The structural integrity of the single layer armour unit Xbloc ® has been investigated by means of an extensive program comprising dynamic prototype tests and dynamic and static numerical tests. The prototype test series comprised overturning and free fall tests with in total over 150 individual drops. The numerical test series comprised 9 cases. Comparing the prototype and numerical results of Xbloc ® with Accropode and Core-Loc ® it can be concluded that the Xbloc ® has a better structural performance than the Core-Loc ® and that Xbloc ® has a strength that is comparable to Accropode.

Coastal Engineering 2008, 2009

ABSTRACT The permeability of a breakwater core affects the stability of the breakwater armour. No... more ABSTRACT The permeability of a breakwater core affects the stability of the breakwater armour. No design guidelines are available to account for the effect of a geotextile container core on armour stability. This paper discusses the present knowledge on the effect of core permeability on armour layer stability, both for rock and concrete armour units. Results are presented from project specific model tests on Xbloc armoured breakwaters with geotextile container cores. A prototype case is presented where damage has occurred, which may be attributed to low core permeability. Recommendations are given for the design of breakwaters and seawalls with low permeability cores. Rubble mound breakwaters generally consist of a permeable core, under layer and armour layer. When a wave impacts on a rubble mound breakwater, the wave penetrates into the rubble mound and energy is dissipated by turbulent flow. If the core is less permeable, increased reflection occurs, leading to higher loads on the armour layer. Therefore a core with low permeability requires larger armour than a core with high permeability. This effect is often not addressed adequately during design and construction. For a breakwater core, generally quarry run is applied as this is an economical construction material. During the design stage the core is normally assumed to be permeable. When the breakwater design is verified with physical model testing, the core is scaled in such a way that turbulent flow is also maintained in the scale model. This implies that the core in the physical model has a different length scale than the armour and under layer. When the design has been verified by model testing, breakwater construction can take place. Normally an existing quarry is used or a quarry is opened. The majority of the production will yield quarry run. A certain percentage will be under layer and armour layer stone. Depending on the rock quality and the production method, large quantities of fines may be present in the quarry run. These fines will affect the core permeability. Removing these fines means running the quarry run through a grizzly, as shown in Figure 1. As this is an extra effort, contractors want to avoid this. If the quarry run includes fines, the core permeability of the constructed breakwater may differ substantially from the value assumed by the designer.

Coastal Engineering 2008, 2009

2 The effect of wave breaking on a steep foreshore on the stability of a rubble mound breakwater ... more 2 The effect of wave breaking on a steep foreshore on the stability of a rubble mound breakwater is addressed in this paper. Results from stability tests with a rock armoured breakwater and two different foreshore slopes (1:8 and 1:30) were reanalysed. The wave conditions at the toe of the breakwater were investigated by a surf-zone model. The damage to the armour layer was larger in tests with steep foreshore than in tests with a gentle foreshore slope. The occurrence of plunging breakers and the uncertainties of the wave height measurements were analysed. Plunging breakers on the foreshore could have an adverse influence on the armour layer stability and should be considered in the design.

Coastal Structures 2007, 2009

ABSTRACT In 1995 the Pelangi Beach Resort at Langkawi suffered from severe beach erosion. After s... more ABSTRACT In 1995 the Pelangi Beach Resort at Langkawi suffered from severe beach erosion. After studying the causes of the erosion it was decided to construct two shore parallel pile row breakwaters to be able to restore the beach. This was the first time pile row breakwaters were used for beach protection. Soon after construction late 1995, the beach started to recover, although the planned beach replenishment was not carried out. The accretion of the beach after construction was much further than anticipated on the basis of theories. On December 26, 2004 the tsunami impacted on the pile rows. Both the pile rows and beach survived the tsunami impact without significant damage. The paper discusses the development of the beach over the 10 year period after pile row construction. It is discussed why the pile rows have been more effective in trapping sand than anticipated. A comparison is made with conventional shore parallel breakwaters. Also the interaction of the pile rows with the Tsunami is discussed on the basis of available photographs.

Coastal Engineering Proceedings, 2014

Model test results from four experimental studies have been compiled in a data set with 687 test ... more Model test results from four experimental studies have been compiled in a data set with 687 test results. Three widely used or recently developed toe stability formulae have been validated against these model test results. It was found that all three formulae suffer from a lack of accuracy and general validity. This is caused by shortcomings of the underlying wave flume studies. More precisely, the wave height and the water depth above the toe berm are two main influence parameters for the toe berm stability and they are not independent in these studies. Testing the interdependence of parameters is therefore recommended for wave flume studies. An alternative toe berm stability formula was developed by a step-wise approach starting with a simple case with a minimum number of influencing factors and followed by more complex cases. The new formula is believed to provide a more meaningful description of the toe berm stability than existing formulae; this however requires further substantiation. The new approach is proposed as a working hypothesis for further studies and is recommended as benchmark for toe berm testing and design.

Coastal Engineering Proceedings, 2014

A dynamic mooring analysis is performed for a tanker berth in shallow water over a sloping bathym... more A dynamic mooring analysis is performed for a tanker berth in shallow water over a sloping bathymetry. Two different modelling strategies are applied, (i) including the sloping bottom in the panel model as a second structure and (ii) replacing the sloping bottom by an equivalent horizontal bottom. It was found that panel models that are applied for 3D diffraction analysis cannot describe the wave conditions on a sloping seabed. They are unable to describe wave shoaling and wave refraction and predict instead an unrealistic waffled clapotis. Therefore, a sloping seabed seabed cannot be modelled as a second structure in a panel model. This approach will result in unrealistic RAO's with a strongly oscillating pattern, which are in turn the result of unrealistic partial standing waves on the slope. An oscillating pattern is further observed for added mass and damping coefficients; it is unclear if any aspects of the sloping seabed are captured realistically by this approach. Including a sloping seabed in a panel model is therefore not advisable. The simplified modelling approach with an equivalent horizontal seabed is more robust and is more likely to provide a realistic estimate of the actual line and fender forces.

Coastal Engineering Proceedings, 2012

The hydraulic stability of single layer, interlocking armour units on low crested and submerged b... more The hydraulic stability of single layer, interlocking armour units on low crested and submerged breakwaters was investigated in 2D hydraulic model tests. Displacements of armour units and rocking were monitored and have been applied as indicators for the armour layer stability on the crest, front and rear slope. The effect of freeboard, packing density and wave steepness on the armour layer stability have been investigated. The stability of interlocking concrete armour units on low crested and submerged structures is qualitatively different from rock armour. About 40% to 50% larger armour units are required on the seaward slope and crest of low crested structures (as compared to conventional high crested breakwaters). About 35% larger armour units are required on the rear slope. Larger armour units are not required on submerged breakwaters if the water depth on the crest exceeds 50% of design wave height.

Das Hauptziel dieser Arbeit ist eine umfassende Beschreibung der Wellenbewegung und Ausbreitung a... more Das Hauptziel dieser Arbeit ist eine umfassende Beschreibung der Wellenbewegung und Ausbreitung an und in einem geschütteten Wellenbrecher auf der Grundlage großmaßstäblicher Modellversuche im Großen Wellenkanal, Hannover und einfacher theoretischer Modelle. Der Wellenbrecher wurde in fünf Bereiche unterteilt. In jedem Bereich wurden die Wasserspiegelauslenkungen und ggf. die Porenwasserdruckoszillationen untersucht. Deren Beschreibung setzt sich zusammen aus einem linearen theoretischen Modell und einem empirischen Ansatz für die nichtlinearen Einflüsse. Darüber hinaus wurden die Unsicherheiten dieser halbempirischen Ansätze und deren Übertragbarkeit bestimmt. Es wurden lineare theoretische Modelle zur Beschreibung (a) der Wellenbewegung über rauhen teildurchlässigen Böschungen, (b) der Wellenausbreitung in homogenen, porösen Medien und (c) der gesamten Energiedissipation am und im Bauwerk entwickelt. Die wichtigsten hydraulischen Prozesse, die in den 5 Bereichen des Wellenbrechers...

Presented at: Coastal Structures Conference 2019, Hannover, Germany, September 30th – October 2nd... more Presented at: Coastal Structures Conference 2019, Hannover, Germany, September 30th – October 2nd, 2019

Journal of Coastal Research, 1994

Rundown velocity along the slope of a breakwater is quite an important parameter in breakwater de... more Rundown velocity along the slope of a breakwater is quite an important parameter in breakwater design. Literature review on rundown velocity measurements indicates that a few small scale studies have been attempted in the past, mostly along beach slopes. This paper details the experimental investigations conducted at large wave flume (GWK), Franzius Institute, Hannover, Germany, in regard to rundown velocity along the slope of a rubble mound breakwater with an accropode armour layer. As the wave flume facilitates generation of wave heights in the range of 0.20 to 2.0 m with wave period ranging between 3.0 and 12.0 seconds, measurements on rundown velocity for the near prototype conditions were possible. Two methods were adopted to determine rundown velocity viz., (i) with a float and (ii) with a wave gauge. The results on the variation of rundown velocity with Iribarren Number and wave steepness are presented in the form of non-dimensional graphs and discussed. The studies indicated...

Coastal Engineering Proceedings, 2018

The XblocPlus is a new type of interlocking single layer armour units that is placed with uniform... more The XblocPlus is a new type of interlocking single layer armour units that is placed with uniform orientation. This is novel and different from all other single layer, interlocking armouring systems. The hydraulic stability of the XblocPlus breakwater armour unit was tested in 2D and 3D hydraulic model tests. Wave overtopping tests were performed to determine the roughness coefficients of the EurOtop overtopping formula for the XblocPlus. Model tests on a rubble mound breakwater with XblocPlus armour included 2D tests with a 1:30 seabed slope and with 1:2 and 3:4 breakwater slopes and 3D model tests with a flat seabed and with a 3:4 breakwater slope. Wave heights up to 150% of the design wave height were tested in the 2D tests and up to 200% with wave directions 0° to 60° in the 3D tests. No armour unit displacements were observed in 2D tests with 1:2 slope. In the 2D tests with 3:4 slope one armour unit was displaced when the wave height reached 159% of the design wave height. No d...

Coastal Engineering 1992, 1993

Coastal Engineering 1998, 1999

The hydraulic performance of an innovative structure based on the concept of a high mound composi... more The hydraulic performance of an innovative structure based on the concept of a high mound composite breakwater has been investigated in large-scale hydraulic model tests in the Large Wave Flume (GWK) of the Coastal Research Center (FZK), Germany. The experimental results concerning wave breaking, wave transmission and wave reflection are presented.

The wave transmission at low crested rubble mound breakwaters due to wave overtopping and wave pe... more The wave transmission at low crested rubble mound breakwaters due to wave overtopping and wave penetration through the structure is addressed in this paper. Wave transmission past rubble mound breakwaters was investigated experimentally in 2D hydraulic model tests. The transmission at low crested structures is primarily determined by wave overtopping. The incident wave height, the freeboard and the crest width have been identified as governing parameters for the wave transmission. The effect of breakwater slope and wave steepness is insignificant for contemporary rubble mound breakwaters with interlocking armour. The fictitious run-up height (a function of incident wave height) and the equivalent freeboard (combining actual freeboard and crest width) have been applied for predicting the wave transmission by wave overtopping. A new wave transmission formula has been developed, which is applicable for low crested and submerged rubble mound breakwaters with relatively steep slopes (steeper than 1:2) and various crest geometries (crest width 0.5 < B/Hs,i < 5).

A large variety of concrete breakwater armour units has been developed in the past. Today design ... more A large variety of concrete breakwater armour units has been developed in the past. Today design engineers have the choice between a number of completely different breakwater armour concepts. The most commonly applied types of armour units are presented and classified. The strong and weak points of the various concepts as well as possible applications are discussed. Demands for future improvements are specified with respect to hydraulic and structural stability, placement and casting. Finally a concept for an improved armour unit with a simple bulky shape and two different front faces is outlined, which is easy to cast and easy to place. This block shall be capable to find easily a stable position on the slope. The structural stability shall be similar to Accropodes in order to minimise the risk of breakage and subsequent progressive failure. The optimum interlocking capability has to be balanced between hydraulic stability and the ease of fabrication, placement and strength of the ...

A new interlocking breakwater armour unit has been developed by Delta Marine Consultants during t... more A new interlocking breakwater armour unit has been developed by Delta Marine Consultants during the past two years. The development is based on extensive review of existing breakwater armour concepts, consulting of contractors and designers, desk studies and physical model tests. A randomly placed single layer interlocking armour unit turned out to be the best technique for breakwater protection under severe environmental conditions. The new armour unit is called Xbloc ® and has a simple, bulky shape. Hydraulic model tests (2-D and 3-D), a numerical structural strength analysis (FE calculations) and prototype drop test have been performed. The test results demonstrated the large hydraulic stability and the easily achieved interlocking (automatic interlocking) of the Xbloc ® as well as its very high structural stability. Therefore the Xbloc ® is a promising alternative for conventional single layer armour units. Significant cost savings can be achieved due to easy fabrication, fast p...

Ports 2010, 2010

Port@Lekki (located about 70 km East of Lagos, Nigeria) is a port development for chemical tanker... more Port@Lekki (located about 70 km East of Lagos, Nigeria) is a port development for chemical tankers (160,000 DWT) and container vessels (8,000 TEU). The layout of the new port, including the layout of approach channel, turning circle and harbour basins has been derived from optimisations based on port operations, construction costs and possible future extensions. Two different breakwater concepts were applied for the main breakwater: A rubble mound with geo-bag core for the near-shore sections and a composite breakwater for the more exposed sections. The secondary breakwater was replaced by a barrier. The barrier consists of a core from sand, internally fortified by a protective geo-bag layer, a revetment on the harbour side and an artificial beach on the seaward side. The proposed layout of the new port and the design of main breakwater and barrier are described in this paper.

Coastal Engineering 2004 - Proceedings of the 29th International Conference, 2005

The wave damping in a rubble mound breakwater has been studied theoretically and experimentally. ... more The wave damping in a rubble mound breakwater has been studied theoretically and experimentally. Various types of damping functions (linear, quadratic and polynomial) have been derived and checked against experimental results from large scale model tests. Damping coefficients have been derived from the hydraulic resistance of the breakwater core material. The result is a general approach for the wave decay inside a rubble mound breakwater that clearly reflects the flow processes inside the structure.

Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007

From 2001 to 2003 Delta Marine Consultants developed a new breakwater armour unit, named Xbloc ®.... more From 2001 to 2003 Delta Marine Consultants developed a new breakwater armour unit, named Xbloc ®. Extensive testing and studies were carried out, and the new armour unit has proved to be reliable and easy to use. Port Oriel, an existing fishing port on the East coast of Ireland has been rehabilitated in order to upgrade the port. For the protection of the breakwater Xbloc armour units were used, which is the first Xbloc application in Europe. The design was prepared by RPS Kirk McClure Morton in Belfast and the construction of the project was awarded to Lagan Construction. This paper describes the project, the design and the construction works of the Port Oriel reconstruction. The works started in May 2005, and the breakwater was completed in December 2006.

Ocean Wave Measurement and Analysis (2001), 2002

Based on extensive hydraulic model testing, the uncertainties of available "standard" models used... more Based on extensive hydraulic model testing, the uncertainties of available "standard" models used to predict wave heights on shallow foreshores of coastal structures are quantified. Both wave transformation on the foreshore and at the structure are taken into account. Finally, improvements of the prediction models are proposed and recommendations on the selection of the models to be used are provided.

Coastal Engineering 2004 - Proceedings of the 29th International Conference, 2005

The structural integrity of the single layer armour unit Xbloc ® has been investigated by means o... more The structural integrity of the single layer armour unit Xbloc ® has been investigated by means of an extensive program comprising dynamic prototype tests and dynamic and static numerical tests. The prototype test series comprised overturning and free fall tests with in total over 150 individual drops. The numerical test series comprised 9 cases. Comparing the prototype and numerical results of Xbloc ® with Accropode and Core-Loc ® it can be concluded that the Xbloc ® has a better structural performance than the Core-Loc ® and that Xbloc ® has a strength that is comparable to Accropode.

Coastal Engineering 2008, 2009

ABSTRACT The permeability of a breakwater core affects the stability of the breakwater armour. No... more ABSTRACT The permeability of a breakwater core affects the stability of the breakwater armour. No design guidelines are available to account for the effect of a geotextile container core on armour stability. This paper discusses the present knowledge on the effect of core permeability on armour layer stability, both for rock and concrete armour units. Results are presented from project specific model tests on Xbloc armoured breakwaters with geotextile container cores. A prototype case is presented where damage has occurred, which may be attributed to low core permeability. Recommendations are given for the design of breakwaters and seawalls with low permeability cores. Rubble mound breakwaters generally consist of a permeable core, under layer and armour layer. When a wave impacts on a rubble mound breakwater, the wave penetrates into the rubble mound and energy is dissipated by turbulent flow. If the core is less permeable, increased reflection occurs, leading to higher loads on the armour layer. Therefore a core with low permeability requires larger armour than a core with high permeability. This effect is often not addressed adequately during design and construction. For a breakwater core, generally quarry run is applied as this is an economical construction material. During the design stage the core is normally assumed to be permeable. When the breakwater design is verified with physical model testing, the core is scaled in such a way that turbulent flow is also maintained in the scale model. This implies that the core in the physical model has a different length scale than the armour and under layer. When the design has been verified by model testing, breakwater construction can take place. Normally an existing quarry is used or a quarry is opened. The majority of the production will yield quarry run. A certain percentage will be under layer and armour layer stone. Depending on the rock quality and the production method, large quantities of fines may be present in the quarry run. These fines will affect the core permeability. Removing these fines means running the quarry run through a grizzly, as shown in Figure 1. As this is an extra effort, contractors want to avoid this. If the quarry run includes fines, the core permeability of the constructed breakwater may differ substantially from the value assumed by the designer.

Coastal Engineering 2008, 2009

2 The effect of wave breaking on a steep foreshore on the stability of a rubble mound breakwater ... more 2 The effect of wave breaking on a steep foreshore on the stability of a rubble mound breakwater is addressed in this paper. Results from stability tests with a rock armoured breakwater and two different foreshore slopes (1:8 and 1:30) were reanalysed. The wave conditions at the toe of the breakwater were investigated by a surf-zone model. The damage to the armour layer was larger in tests with steep foreshore than in tests with a gentle foreshore slope. The occurrence of plunging breakers and the uncertainties of the wave height measurements were analysed. Plunging breakers on the foreshore could have an adverse influence on the armour layer stability and should be considered in the design.

Coastal Structures 2007, 2009

ABSTRACT In 1995 the Pelangi Beach Resort at Langkawi suffered from severe beach erosion. After s... more ABSTRACT In 1995 the Pelangi Beach Resort at Langkawi suffered from severe beach erosion. After studying the causes of the erosion it was decided to construct two shore parallel pile row breakwaters to be able to restore the beach. This was the first time pile row breakwaters were used for beach protection. Soon after construction late 1995, the beach started to recover, although the planned beach replenishment was not carried out. The accretion of the beach after construction was much further than anticipated on the basis of theories. On December 26, 2004 the tsunami impacted on the pile rows. Both the pile rows and beach survived the tsunami impact without significant damage. The paper discusses the development of the beach over the 10 year period after pile row construction. It is discussed why the pile rows have been more effective in trapping sand than anticipated. A comparison is made with conventional shore parallel breakwaters. Also the interaction of the pile rows with the Tsunami is discussed on the basis of available photographs.

Coastal Engineering Proceedings, 2014

Model test results from four experimental studies have been compiled in a data set with 687 test ... more Model test results from four experimental studies have been compiled in a data set with 687 test results. Three widely used or recently developed toe stability formulae have been validated against these model test results. It was found that all three formulae suffer from a lack of accuracy and general validity. This is caused by shortcomings of the underlying wave flume studies. More precisely, the wave height and the water depth above the toe berm are two main influence parameters for the toe berm stability and they are not independent in these studies. Testing the interdependence of parameters is therefore recommended for wave flume studies. An alternative toe berm stability formula was developed by a step-wise approach starting with a simple case with a minimum number of influencing factors and followed by more complex cases. The new formula is believed to provide a more meaningful description of the toe berm stability than existing formulae; this however requires further substantiation. The new approach is proposed as a working hypothesis for further studies and is recommended as benchmark for toe berm testing and design.

Coastal Engineering Proceedings, 2014

A dynamic mooring analysis is performed for a tanker berth in shallow water over a sloping bathym... more A dynamic mooring analysis is performed for a tanker berth in shallow water over a sloping bathymetry. Two different modelling strategies are applied, (i) including the sloping bottom in the panel model as a second structure and (ii) replacing the sloping bottom by an equivalent horizontal bottom. It was found that panel models that are applied for 3D diffraction analysis cannot describe the wave conditions on a sloping seabed. They are unable to describe wave shoaling and wave refraction and predict instead an unrealistic waffled clapotis. Therefore, a sloping seabed seabed cannot be modelled as a second structure in a panel model. This approach will result in unrealistic RAO's with a strongly oscillating pattern, which are in turn the result of unrealistic partial standing waves on the slope. An oscillating pattern is further observed for added mass and damping coefficients; it is unclear if any aspects of the sloping seabed are captured realistically by this approach. Including a sloping seabed in a panel model is therefore not advisable. The simplified modelling approach with an equivalent horizontal seabed is more robust and is more likely to provide a realistic estimate of the actual line and fender forces.

Coastal Engineering Proceedings, 2012

The hydraulic stability of single layer, interlocking armour units on low crested and submerged b... more The hydraulic stability of single layer, interlocking armour units on low crested and submerged breakwaters was investigated in 2D hydraulic model tests. Displacements of armour units and rocking were monitored and have been applied as indicators for the armour layer stability on the crest, front and rear slope. The effect of freeboard, packing density and wave steepness on the armour layer stability have been investigated. The stability of interlocking concrete armour units on low crested and submerged structures is qualitatively different from rock armour. About 40% to 50% larger armour units are required on the seaward slope and crest of low crested structures (as compared to conventional high crested breakwaters). About 35% larger armour units are required on the rear slope. Larger armour units are not required on submerged breakwaters if the water depth on the crest exceeds 50% of design wave height.