international association of dredging companies...a particular project, we haven’t the time nor...

International Journal on Public Works, Ports & Waterways Developments

Number 60 - September 1995

INTERNATIONAL ASSOCIATION OF DREDGING COMPANIES

Terra et Aqua – Number 60 – September 1995

Terra et Aqua is published quarterly by the IADC, The International Association of Dredging Companies.The journal is available on request to individuals or organisations with a professional interest in thedevelopment of ports and waterways, and in particular, the associated dredging work.The name Terra et Aqua is a registered trademark.

EditorMarsha R. Cohen

Editorial Advisory CommitteeR.C.W. Brouwer, ChairmanJ. Boeter P.J.A. Hamburger E.A.M. StraussH. van Diepen H. de Vlieger P.G. RolandH. Fiers

Editorial AddressTerra et AquaKoninginnegracht 522514 AE The Hague, The NetherlandsTel. 31 (70) 364 0394Fax 31 (70) 356 2861

Please address inquiries to the editor.Articles in Terra et Aqua do not necessarily reflect the opinion of the IADC Board or of individual members.

© 1995 IADC, The NetherlandsAll rights reserved. Electronic storage, reprinting or abstracting of the contents is allowed for non-commercial purposes with permission of the publisher.

ISSN 0376-6411

Typesetting and printing by Opmeer Boekdruk Offset bv, The Hague, The Netherlands.

Front cover:Privatisation of dredging in New Zealand has proven cost efficient and profitable. Trailing suction hopperPelican can be seen at work day and night, everyday, summer and winter in one New Zealand port oranother. Here she is dredging the approach channel at Tauranga (see page 11).

IADCDuinweg 212585 JV The Hague, The NetherlandsTel. 31 (70) 352 3334Fax 31 (70) 351 2654

International Association of Dredging Companies

I A D C

2 Editorial

3 The Wear Sensitive Cutting Principle of a Cutter Suction Dredger

H. Jan Reinhout Deketh

Laboratory experiments demonstrate from a wear point of view the inefficiency of cutting tools on a cutter suction dredger. Recommendations are made to optimise the cutterhead design and cutting process.

8 A Tale of Two Dredgers

Adrian Hunt

A look at the joys of working for a high-tech private dredging company versus the difficulties of an underfunded state-run organisation.

11 Privatisation of Ports in New Zealand

Heini Evers and Roy Weaver

By shifting from port-operated dredging to privatised contract dredging, three New Zealand ports have moved from world-ranked laggards to the top echelon of international ports in terms of profitability and performance.

18 Besòs Long Sea Outfall, Barcelona

Bert Dijkstra and Stuart McIntyre

To satisfy EC bathing water quality directives, a new, longer outfall was needed. Dredgers had to reckon with the recreational importance of Spain’s beaches, plus the existence of an operative gas pipeline.

27 Books/Periodicals Reviewed

As the multi-year $25 million Dredging Research Programme of the US Corps of Army Engineers concludes, several final reports have been published. Four are abstracted here.

29 Seminars/Conferences/Events

Getting ready for the WODCON in November 1995, CATS II in March and Hydro in September 1996, as well as an announcement of the new IADC seminar in Singapore.


CO N T E N T S


2

EDITORIAL

Bridges, roads, harbours, beaches, tunnels, airports -- would these exist if dredg-ers with their trusty “digging” tools were not busy as beavers damming a river?Dredging started long ago and over hundreds of years has played a significant rolein the development of civilisation as we have come to know it. Often, focussed ona particular project, we haven’t the time nor inclination to stop and think of whatthe world would be like if dredgers did not dredge.

The articles in this issue of Terra cover a range of subjects, from the techno-logical to the political. Laboratory research provides important technologicalinformation to the dredging industry (page 3). This in turn provides an essentialservice when applied to a specific problem. For instance, by applying dredgingtechnology, dredgers are able to ensure clean water for recreation – for swimmingand fishing. Such was the case in Barcelona, Spain (page 18).

As the dredging industry prepares to gather at the WODCON in November inAmsterdam, the theme of the conference, “Dredging Benefits”, gives reason topause and take inventory of just how important the contribution of dredging hasbeen and continues to be to our economic and social well-being. And the questionarises: how does the future look?

Governments are being forced to tighten their budgets; cost containment whenconsidering infrastructure projects is becoming an ever greater factor. It is norevelation that IADC is of the opinion that the private dredging industry is betterable to meet this challenge through free market competition than are state-runmonopolies. “A Tale of Two Dredgers” was written tongue-in-cheek to contrastthe differences. “Privatisation of Ports in New Zealand” presents a case studywhich gives concrete support to this point of view. The choice of course lies withthe ports and harbour authorities, but it is certainly worth thinking through.

Marsha R. CohenEditor

Introduction

This article is based on the book Wear of Rock CuttingTools, Laboratory Experiments on the Abrasivity ofRock (Deketh 1995). The book is the result of research which aimed at getting a better understandingof the wear processes acting in rock cutting operationsand to determine which factors control these wearprocesses. An improved understanding of these pro-cesses finally allows for a better basis to predict expec-ted rates of pick-point consumption in rock dredgingpractice. The insight in the wear processes can beuseful to optimise the dredging method or dredgerfrom a wear point-of-view.

In this paper the laboratory test set-up is described andsome experimental results are shown. The relevancyand application of these experimental results to a rockcutter suction dredger is discussed and finally somerecommendations regarding wear prediction and opti-misation of the dredging process are made.

Abstract

The operating principle of a rock cutterhead such asused on cutter suction dredgers is an inefficient exca-vation process from a wear-point of view, because ateach revolution of the cutterhead a pick-point has toenter the rock to make a new cut. Especially in therange of small feed, at the start of each cut, high ratesof wear of the cutting tool are expected.

At least, this is shown by specially designed small scalerock cutting laboratory experiments. In these experi-ments high rates of wear were experienced at smallpenetration rates (feed) of a chisel cutting into rock. Mechanical properties and composition of the rock tobe cut determine the range of feed where the highrates of wear are taking place and they affect the levelof wear in the entire cut. The relevant mechanicalproperties are the unconfined compressive strength(UCS) and the Brazilian tensile strength (BTS). Thecompositional features affecting wear are the grain sizeand the volume percentage of the abrasive minerals inthe rock; abrasive minerals are those minerals whichare harder than the tool material under the conditions(stresses and temperature) of cutting.

Considering that wear occurs mainly at the start of acut, some recommendations can be made to improvethe cutting method or to optimise the cutterheaddesign or the cutting process, for example, by tuningoperational parameters like haulage and rotation veloci-ty of the cutterhead to the type of rock to be cut. Besides, a better understanding of the different wearprocesses and the effect of properties and compositionof the rock on wear provides a better basis to estimatepick-point consumption in advance of a rock dredgingproject.

This research was sponsored by the Technology Foun-dation (STW), The Netherlands.

The Wear Sensitive Cutting Principle of a Cutter Suction Dredger

H.J.R. Deketh

The Wear Sensitive CuttingPrinciple of a Cutter SuctionDredger

3

Jan Reinout Deketh

In 1991 Jan Reinout Deketh receivedhis MSc in Mining and PetroleumEngineering from Technical Universi-ty Delft, The Netherlands, Engineer-ing Geology Department. Since thenhe has been working as a researchofficer at the university, studying thewear of cutting tools on rock excava-tion machines in relation to the rocktypes being excavated. In March 1995he obtained a PhD on this subject atTU Delft. At present he is observingthe working performance of rockcutting trenchers at various construc-tion sites throughout Europe.

LABORATORY ROCK CUTTING WEAR

EXPERIMENTS

Experiments have been designed to investigate wearprocesses resulting from sliding of the wear-flat of atest chisel over the surface of different rock types withthe variation of the feed of a chisel into the rock, insuch a way that the transition from scraping to cuttingof rock by the test chisels could be investigated.

In Figure 1 the rock cutting wear test (named thescraping test to stress the feed range at which theexperiments are carried out ) is illustrated. The test isdisplacement controlled. A lathe is used to carry thetest arrangement. Rotating rock cores are penetratedby steel chisels (steel type Fe60 K, relatively soft steel(Vickers hardness ± 3000 MPa) or steel type SRO 57N,hardened steel from dredger teeth (Vickers hardness ± 6000 MPa)) with a continuous feed. When the chiselmoves to the centre of the disc of rock, the angular

velocity is automatically increased to keep the cuttingvelocity constant. Most experiments are executed at acutting velocity of 0.4 m/s.

Cutting forces, feed (displacement of the chisel into therock per revolution of the rock disc) and cutting velocityare automatically recorded and stored by a data acquisi-tion software package on a personal computer. Loss ofmass of the chisel and amount of cut rock material aremeasured manually and fed into the computer. Finallywear phenomena of the chisel are described and pho-tographed.

About 1000 different tests were carried out. Naturaland artificial rocks were used. Artificial rocks (mortar)allowed for a controllable variation of one rock propertyat a time. The rock strength, the grain size, the volumepercentage and the shape of the abrasive minerals(mostly quartz) have been varied. Experiments onnatural rocks (sandstones and limestones) showed towhich rock types the results of the experiments onartificial rocks could be applied.

Next to the rock properties also the feed, and in someexperiments the cutting velocity, of the test chisel intothe rock has been varied.

The loss of mass of the chisel in one test run per metresliding length is taken as a measure for the rate ofwear. The loss of mass of a chisel in one test run percubic metre of cut rock material, the specific wear(SPW) is taken as a measure of the efficiency of thecutting process with respect to wear specific for thistest.

EXPERIMENTAL RESULTS

The following factors showed to affect the wear pro-cess of the experiments on the mortars and the sand-stones:- the tensile and compressive strength of the rock.- the grain size and volume percentage of abrasive

minerals in the rock.- the feed of the chisel into the rock.

Above a certain value of feed, which was determinedby the properties of the rock to be cut, the type of wearchanged and the rate of wear decreased rapidly.

In Figure 2 the effect of the feed on the rate of wearcan be seen for three mortars, which differ in uncon-fined compressive strength (UCS), other propertieswere approximately the same (the mortars contained ± 60 % of rounded quartz grains with an average grainsize of 1.5 mm). The unconfined compressive strengthof the mortars mc1, mc2 and mc3 was respectively 30,18 and 64 MPa. In the graph each dot represents onetest run in which all parameters were kept constant.


4

Figure 1. Scraping test.

Figure 2. The influence of the unconfined compressivestrength on the rate and type of wear for mortars mc1, mc2and mc3 for various feeds.

the chisel cuts continuously, but in practice only forabout 25 % of each revolution of the cutterhead. In theexperiments only wear due to sliding contact betweentool and rock is studied. In dredging also wear due toimpact may play a role. These and other differencesbetween the experiments and wear in practice make aquantitative comparison questionable. Still major trendsand wear phenomena observed in the laboratory ex-periments agree with those experienced in practice ofrock cutting (Giezen 1993).

The pick-points mounted on the cutterhead of a cuttersuction dredger make an arc-shaped cut through therock at each revolution. The feed of each pick-pointduring a cut gradually increases from 0 at the start ofthe cut to a maximum feed at the end of the cut. The scraping test experiments showed that with an in-crease of feed the rate and type of wear changes. Thiscan be applied to a pick-point making a cut in the rock.

At low values of feed, the rock production was relative-ly low (scraping process) and the level of wear high;high temperatures and plastic deformation of the steelat the wear-flat of the chisel occurred, two-body abra-sive wear dominated: wear mode I.

At higher levels of feed the rock production was rela-tively high (cutting process) and the level of wear low;lower temperatures and less plastic deformation tookplace, three body abrasive wear dominated: wearmode III. The feed at which a transition from the firsttype of wear during the scraping process to the lattertype of wear during the cutting process takes place,was also dependant on rock strength (UCS and BTS),grain size and volume percentage of abrasive minerals(quartz) in the rock. The transition from wear mode I towear mode III is called wear mode II. In Figures 4 and 5photographs of chisel wear-flats in wear mode I and inwear mode III are shown.

The chisel worn in wear mode I shows clean parallelcontinuous grooves on the wear-flat, pointing to two-body abrasive wear. High temperatures at the wear-flatresulted in burs, tempering colours and plastic defor-mation of the steel, leading to adhesive wear, additionalto the two-body abrasive wear. The chisel worn in wearmode III shows irregular, sometimes abruptly endinggrooves, which are infilled by crushed rock material,pointing to three-body abrasive wear. The absence ofburs, tempering colours and plastic deformation of thesteel indicates lower temperatures at the wear-flat andtherefore adhesive wear is not likely to occur.

These results hold for mortars as well as for the testedsandstones. Limestones behaved differently, probablydue to the fact that the calcite in the limestone was nothard enough to be abrasive to the tested steel types.

In Figure 3 some scraping test results on a sandstoneare shown. In the left graph both the influence of thefeed and the cutting velocity on the rate of wear isshown. In the right graph the range of feed and cuttingvelocity at which the disadvantageous wear and cuttingmode I is delineated.

RELATING THE EXPERIMENTAL RESULTS TO

DREDGING PRACTICE

Before a comparison is made, first the relevancy of thelaboratory experiments to dredging practice are put intoperspective. Pick-point consumption in practice is dueto damage, which is either failure (breakage) or wear ofthe pick-points. Whereas wear is a surface process,failure concerns the whole body of the cutting tool. Inthis research only wear has been considered.

The experiments in the laboratory are only remotelyrelated to rock dredging in practice; in the experiments


5

Figure 3. Rates of chisel wear in scraping tests on a sandstoneas a function of the feed for different cutting velocities. At ahigher cutting velocity a higher feed is needed for anadvantageous mode of wear.

0.4 cm

At the start of a cut a pick-point rather scrapes the rockthan that it cuts the rock; there is relatively little produc-tion of excavated rock. Moreover, in this range thefriction is high (two-body wear) causing high tempera-tures which in their turn weaken the tool materialwhich then becomes vulnerable to abrasive wear. At a certain feed, the scraping action of the pick-pointschanges gradually into cutting with further increase offeed. At the same feed the mode of wear changesfrom mode I to mode III via mode II; two-body wearchanges to three-body wear with lower temperaturesat the wear-flat and lower rates of wear.

In Figure 6 a cut made by a pick-point mounted on acutter head is shown for three different situations:

- Case A shows a pick-point which reaches at the endof the cut a maximum feed which is lower than thefeed at which a transition from mode I to mode III

occurs (left graph). The rate of wear in this case ishigh in the entire cut.

- In case B, and more profoundly in case C, the maxi-mum feed is larger than the feed at which a transi-tion from mode I to III takes place (left graph). The greater the portion of the cut in mode III thelower the total rate of wear will be as can be seen inthe right graph. The maximum feed value, at the endof a cut, depends on the resistance of the rock tocutting, the ability or power and design of the cuttingmachine (number of blades on the cutterhead) andthe conditions of cutting (haulage and rotation veloci-ty of the cutterhead).

RECOMMENDATIONS TO REDUCE WEAR OF

THE PICK-POINTS

In general the amount of wear can be reduced byminimising or avoiding the time the cutting process istaking place in the disadvantageous wear mode, whichis at small feed of the pick-points. This can be achievedby choosing a type of dredger with a cutting principle inwhich the pick-points do not cut at small feed (e.g. a trailing hopper dredger instead of a cutter suctiondredger).

If we still are dealing with a cutter suction dredger asolution to decrease wear is to increase the maximumfeed reached by a pick-point at the end of each cut by:

1. increasing the power of the dredger. An increase ofpower on the cutterhead and winches results in anincrease of the penetration of the cutterhead (andtherefore also of the pick-points) per revolution ofthe cutterhead.

2. increasing the ratio haulage velocity over rotationvelocity of the cutterhead. This results in a highermaximum feed of the pick-points. An additionaleffect of a lower cutting velocity is that the temper-atures at the tool-rock contact will remain lower,which ensures that the wear resistance of thecutting tool does not drop, by softening of the steel.

3. changing the cutterhead design such that themaximum feed of each pick-point increases. For example a reduction of the number of blades ofa cutterhead would result in a higher maximumfeed per blade (and therefore per pick-point).

A higher feed per pick-point can also be realised bypositioning the pick-points in such a pattern on thecutterhead that the cutting paths of pick-points ondifferent blades are not making a cut in the samegroove made by a pick-point positioned on theprevious blade. This can be achieved by situatingthe pick-points on the odd and even blades instaggered positions.


6

Figure 4. Part of a test chisel wear-flat worn in wear mode I.

Figure 5. Part of a test chisel wear-flat worn in wear mode III.

back edge of the chisel

��

back edge of the chisel 0.4 cm

��

- the magnitude of the wear in wear mode I is deter-mined by the same rock properties and by the sensi-tivity of the tool material to wear.

References

Deketh, H.J.R. Wear of Rock Cutting Tools, Laboratory Experiments on the

Abrasivity of Rock. A.A.Balkema, Rotterdam ISBN

90 5410 620 4, 1995.

Giezen, M. “Rock Properties Relevant for Tool Wear and Production of

Rock Cutting Trenchers”. Memoirs of the Centre for Engineer-

ing Geology in the Netherlands, no 110, Technical University

Delft, Faculty of Mining and Petroleum Engineering, 1993.

Conclusions: Implementation ofResearch Results in Wear Prediction

The experiments showed that wear is mainly occurringat the start of a cut in wear mode I. To predict the rateor amount of wear for a specific dredger it is thereforevery important to determine for what part of the totalcut made by a pick-point this disadvantageous wearmode I will take place.

For that we have to calculate:1. the maximum expected feed per pick-point of the

chosen dredger in the rock to be dredged. This is afunction of the advance (haulage) rate and rotationvelocity of the cutterhead. These dredging param-eters depend in their turn on the dredger characte-ristics like power on the cutterhead and the win-ches, cutterhead design etc. and the resistance ofthe rock to cutting.

2. the feed at which a transition (mode II) from wearmode I to III takes place. The transition is a functionof the UCS, BTS, the content (vol.%) and the grainsize of the abrasive minerals in the rock.

The total expected wear is approximated by:- the percentage of the cut at which wear mode I

takes place multiplied by the magnitude of wear inwear mode I.


7

Figure 6. Wear at low feed (start of a cut) is higher than at higher feed (end of a cut). The wear during a cut is determined by themagnitude of the contribution of wear mode I.

This is a story about two men, two dredgermen. Oneworks in the private sector; the other in the publicsector. Eric Van GATT, he’s the private sector man; andBarri ER, he’s from the public sector.

Eric Van GATT is employed by the “World DredgingCompany” which has an international spread of officesand operations covering more than 30 countries. Its fleet is substantial and multi-functional, and it isbacked by state-of-the-art R&D, Technical and Logisti-cal Departments.

Barri ER works for the “State Legislature of Water-ways” (SLOW for short). It has responsibility for themaintenance of one principal port and several minorports in a faraway country somewhere. Very littlecapital dredging is ever carried out, the work is mostlymaintenance. The small fleet is dated and frequently in dock.

The Tale

We take up the story one morning quite recently.

“Damn”, said Barri ER as he nicked himself shaving infront of his hotel mirror. He was rarely in a good moodthese days. Almost two decades with his SLOWemployer had taken their toll. There was little to inte-rest him any more. One cubic metre seemed much likethe other. The same routine, day in day out. Oh, butthere was that one occasion, when was it? six or sevenyears ago, when he thought he’d found live ammuni-tion in the hopper. As it happened, the bomb turnedout to be the end of a suction pipe that SLOW’s princi-pal trailer, the Elderly Statesman, had lost some yearsearlier. Was it his fault that the thing had dropped offbecause of rust? He had been saying for years that areplacement trailer was needed.

SLOW agreed that it was needed and had appointed acommittee to look into it. Good progress had beenmade in the first 18 months. Several sub-committeeshad been formed and these were due to report backwithin the year. But then the whole process began toslow down. The committee members couldn’t agreeon the vessel’s specification. Ideally, two or even threedifferent types of dredgers were needed. But, therewere only sufficient funds to build one. With all thebickering and disagreement the replacement ship,code-named New Statesman, was still not commis-sioned.

“May I join you?”’ said Barri ER fifteen minutes later ashe arrived for breakfast in the busy hotel dining room.The question was addressed to a man whose bright,alert expression belied his real age. Eric Van GATTbeckoned the newcomer to sit down.

He had been deep in thought, scribbling notes andsketches on his paper napkin. He was intrigued by atechnical problem on his current dredging project.


Adrian Hunt

A Tale of Two Dredgers

8

A freelance technical journalist spe-cialising in the construction sector,Adrian Hunt has been writing for andabout the dredging industry for almost20 years. He is involved in the editingand production of several periodicalspublished by leading contractors inthe dredging and construction fileds.He is a past winner of the WoodrowWyatt Award presented by the BritishAssociation of Industrial Editors.

Adrian Hunt

Figure 1. Introducing Eric Van GATT from the private sectorand Barri ER from the public sector.

This article was originally part of the IADC presentationat the Dredging ‘94 Conference in Orlando, Florida,USA in November 1994.

cies cannot hope to equip themselves other than forthe day-to-day operational duties.

COMPETITION IS THE DRIVING FORCE

Competition is the driving force in the private sector.Everything is geared toward dredging that cubic metremore efficiently and at less cost than the competition.Overheads and administration are kept to a minimum;research and development are on-going; personneltraining is fundamental. The independence to reactquickly and positively to market requirements is ofparamount importance.

As the benefits of a competitive trading environmentbecome better understood, the world dredging marketis steadily becoming more open, more accessible.

He liked nothing better than a challenge. The time hehad spent at head office, working in the various projectsupport offices, and his wide operational experiencehad equipped him to deal with most problems that facetoday’s busy project managers working for internationaldredging contractors. There was never time to getbored, moving from one project to another, from onecountry to another and from one dredger to another.There was real variety to his working life. He wasfascinated by the technological advances that werebeing made.

Take, for example, the vessel he was currently workingwith, the trailer Free Trader. She is a powerful, bigcapacity ship full of sophisticated electronics and gad-getry. It had taken just 18 months from the time thatthe Board of Directors decided to invest in a newdredger, to the time that Free Trader took to the water.Eric Van GATT was only too aware that to be competi-tive you need to have modern and efficient equipment.

Eric Van GATT and Barri ER chatted happily over break-fast. After all, they had much in common -- dredging.Eric explained that he had just flown in from the FarEast where he was working on a new petro-chemicalport. He was then scheduled to go to South Americafor port maintenance work combined with reclamation.

Barri ER listened enviously in the knowledge that hewould shortly be returning to the same dredger, to thesame port work and to the same old routine. But, forthe time being at least, he had a few days in which tobroaden his mind and to see what was happening inthe “real” world of dredging. Looking at his conferenceprogramme, he said to Eric Van GATT: “Which of thepapers are you most looking forward to hearing?”

“Why, the IADC presentation of course”, came thereply. Outside, the sun shone on the Buena VistaPalace grounds.

The Conclusion

Eric Van GATT and his counterpart from the statedredging sector, Barri ER, are of course purely fictitious.The problems faced by the equally fictitious SLOWorganisation, whilst being greatly exaggerated, dodemonstrate some of the difficulties facing state dredg-ing agencies. The lack of public funds is the principalone. Without a proper investment programme, dredg-ing operations must inevitably suffer which in turn willaffect port efficiency and productivity. For it to survive,the private sector must be properly equipped withmodern, efficient plant. The range of plant must also besufficiently wide and versatile to deal with the widevariety of dredging challenges facing today’s interna-tional contractors. The right dredger for the right job isvital for efficient production. Cash-strapped state agen-

A Tale of Two Dredgers

9

Figure 3. Eric Van GATT, intrigued by his currentdredging project.

Figure 2. Barri ER in despair awaits the commission of anew dredger.

Admittedly there are still notable exceptions, wherecertain countries still cast a “protective net” aroundtheir markets and refuse to permit “foreign” contrac-tors -- outsiders -- to compete for work openly andfairly. We trust that more and more such countries willsoon see the error of their ways.

Last year, for instance, we witnessed the sale of thebulk of the Mexican state-owned fleet and the transferof maintenance dredging to the private sector. Thiswinding-down process is being repeated in Argentina,and Brazil intends to phase out its state fleet too. As long ago as the mid-1970s a multi-million dollardredger investment plan in the Federal Republic ofGermany was abandoned in the wake of an officialinvestigation which concluded that it would be lessexpensive to delegate part of the annual dredgingprogramme to the private sector. Not only was thestate relieved of the initial investment burden but theoperational savings amounted to 10 percent. The introduction of competition was also responsiblefor the state-owned dredgers improving performancesubstantially.

OPEN DOOR POLICY IS THE TREND

The trend towards increased competition throughprivatisation and opening the door on so-called protec-ted markets is worldwide. There are numerous otherexamples, such as India and New Zealand, that onecould draw upon.

Cost-efficiency is of course not the only considerationof those countries evaluating a more laissez-faire ap-proach. There are also social implications which needto be carefully evaluated. Some people in the statesector would also point to other barriers, such as theimplications for national security, but practice hasproved these to be unfounded worries. Often there isresistance to abandoning state involvement simply forhistorical reasons, because dredging has always beenhandled in this way and always with local suppliers.

This attitude cannot continue. As the demands onpublic funds become ever greater, so the need forgreater cost-efficiency increases. Specifiers of dredgingservices are looking for the least-cost, least-time andmost technically sound solution, and that can only beprovided if there is a competitive, open market.


10

Figure 4. Private sector investments in research andequipment vs. a lack of public funds for state dredgers.

Figure 6. Despite obstacles, when it comes to least-cost,least-time and most technically sound solutions, the winner isthe private sector dredger.

Figure 5. Legal obstacles are the protective net that statedredging agencies use to limit competition.

options open to them collectively and individually, andfinally settled on contract dredging as the most cost-effective solution.

HISTORICAL BACKGROUND

New Zealand ports, where they had significant on-goingmaintenance or capital development programmes,historically owned their own dredgers. This stems from the geographic isolation of New Zealand with theconsequent very high mobilisation costs of bringingdredgers from even the closest neighbour, Australia.Until 1970 dredgers owned by individual harbourboards were designed, manned and set up for work attheir home port only, and there was no real sharing ofequipment or contracting out of work to other harbourboards.

Abstract

The New Zealand economy has undergone significantchange in the last ten years. The Ports Industry is oneof the many areas affected by changed Governmentpolicy since the mid-1980s. This paper sets out howthree ports -- Tauranga, Taranaki and Timaru -- respon-ded to the changing political and economic climate inone aspect of their business operation: port dredging. It describes the shift from port-operated dredgers tocontract dredging.The dredging situation in New Zealand until 1986 ispresented, followed by a summary of the investigationconducted by the three ports of all options open tothem. Financial and engineering analyses carried out byindependent consultants are reported. The conclusionof these analyses was that the most cost-effectiveoption was clearly to pool their dredging workloads andenter into term contracts with an international dredgingcontractor. This was effectuated in 1988.The contract operation is discussed from the perspec-tives of the contractor and the port companies inclu-ding: dredging programme flexibility; plant utilisation;human resources and industrial relations; long-termplanning of operations; utilisation of port companyresources; and contract benefits and problems. Thepaper concludes with an update on the present situ-ation of this cooperative dredging arrangement.The paper was first presented at the Australasian Portand Harbour Conference in 1990. The authors wish toacknowledge the contributions to the original paper ofJohn Palmer, who was then Engineering Manager ofthe Port of Tauranga Ltd. and is presently a consultantfor port planning and development based in of Tauran-ga; of Peter Atkinson who continues to be TechnicalServices Manager of Westgate-Taranaki Port as it isnow known; and of Hadyn Pike, who was ContractsManager of Australian Dredging & General Works Pty.Ltd. at the time the contract was signed.

Introduction

Many ports find the costs of dredging to be one of themajor annual operating costs of the port. Such was thecase of three New Zealand ports -- Tauranga, Taranakiand Timaru (Figure 1). They investigated in detail the

Privatisation of Ports in New Zealand

Heini Evers and Roy Weaver


11

Heini Evers

Roy Weaver

Heini Evers worked for Volker Stevinfor more than 30 years and was theManaging Director of both AustralianDredging & General Works and NewZealand Dredging from 1982 until1992. At that time both companieswere part of the Volker Stevin Groupof The Netherlands. He is presentlyan independent consultant with hisresident office in Australia.

Roy Weaver is a member of theInstitution of Professional EngineersNew Zealand and has a Master’sDegree in Business Administration.He joined the Port of Timaru Ltd. in1985 and is presently its Deputy ChiefExecutive and Manager of Port Operations.

If a port required capital dredging the practice was toinvite tenders from overseas-based companies andenter into a contract. Upon arrival of that contractdredger in New Zealand, it succeeded in picking upother work around the coast and there was somesharing of the overall mobilisation costs to NewZealand.

Port-owned Dredgers In 1976 the Port of Timaru concluded that the era ofbucket dredging at its port was finished and decided toconvert the bucket dredger W.H. Orbell to a trailersuction dredger. The conversion was carried out recog-nising that ports such as Tauranga, Napier, Otago andothers would intermittently require some on-goingtrailer dredging work.

In 1985 the Port of Otago constructed the 600 m3hopper trailer dredger New Era designed for workparticularly in the Port of Otago. During the 1970s andearly 1980s the Port of Tauranga had been undertakinga major reclamation using material from capital dredg-ing, primarily from its own cutter suction dredger but

also with some pump-ashore from trailer dredgingcontracts. Using the New Era as a model of the type ofequipment that could be built, the Port compared theoption of building and owning a similar dredger, andcontracting with the W.H. Orbell. This investigationshowed that, given a reasonable on-going annual vol-ume and even allowing for the fact that the Port ofTimaru had been successful in achieving some reduc-tions in the crewing of the W.H. Orbell, ownership wasa more economic option than retaining the services ofthe W.H. Orbell.

Since 1959 the Port of Taranaki had owned the 560 m3

trailer suction dredger Ngamotu. In the early 1980s thisvessel was upgraded, first with new dredging equip-ment, and then with the replacement of the steamengines with diesel.

In 1983 the Government expressed their concern atthe high cost of getting goods from farm to market-place and began what became known as the “OnshoreCosts Study”. This study focussed particularly on portsand highlighted the need for structural change within theindustry to achieve lower costs and greater efficiency.

Port CompaniesIn 1984 the Government immediately set about elimi-nating subsidies wherever they were and freeing upthe New Zealand economy from many of the controlsthat it had traditionally been under. All industries wereaffected in many ways by the changes and the Govern-ment took up the Onshore Costs Study and progressedit vigorously. This eventually led to the formation of PortCompanies to manage the commercial port operationsand probably had the effect, as far as dredging wasconcerned, of making all ports more aware of theirdredging costs and more receptive to looking at alterna-tive or new means of reducing them.

In 1986 the question arose as to whether it was eco-nomic to have three dredgers in New Zealand doingwork which could be performed by one or perhaps twoof the existing dredgers or by contract. As a result, theports of Tauranga, Taranaki and Timaru held a meetingat which the idea of carrying out a detailed study intothe best option for dredging the three ports in combina-tion was explored. Thus in December 1986 the studyinto the optimal dredging method for the three portswas initiated in a political and economic environmentwhich encouraged a fresh and more stringently eco-nomic approach to dredging policies.

EVALUATION OF DREDGING OPTIONS

The study canvassed the following options:1. Contract dredging by international companies;2. Replacement vessel, size of the W.H. Orbell

(1200 m3);


12

Figure 1. The North and South Islands which form NewZealand, with the three ports involved in contract dredgingindicated -- Tauranga, Taranaki and Timaru.

Tauranga

Taranaki

Timaru

Tasman

Sea

Pacific

Ocean

..

.

The total costs of the joint venture for the period 1988-2000 under each option was established, and afterdiscussions with the engineers from the three partici-pating ports, Option 1 “Contract Dredging” was selec-ted as the most favourable. The total dredging bill forthe three ports was slashed by over $1,000,000 perannum as a result of the change to contract dredging.

THE CONTRACTOR

The contract was awarded to New Zealand Dredging &General Works, which at the time in 1988 was a whollyowned subsidiary of Royal Volker Stevin of The Nether-lands. Since 1992 New Zealand Dredging & GeneralWorks is owned by WestHam of Sydney, Australia.The contract is for a period of fifteen years with areview every five years.

To execute the work a 1,000 m3 trailer suction split-hopper dredger, Pelican, was mobilised from Europe(Figure 2). The Pelican is basically stationed in NewZealand but also makes the occasional side trip toAustralia. Work for third parties is only undertaken after consultation with the three main client PortCompanies.

3. Replacement vessel, size of the New Era (900 m3);4. W.H. Orbell in a joint venture; and5. Ngamotu in a joint venture.

Responsibility for the investigation was awarded toDeloitte Haskins & Sells, Financial Consultants, withBecca Carter Hollings & Ferner acting as EngineeringSub-consultants.

Their proposal was to undertake the study in threeparts:- Data collection, port investigations, discussions,

creation of financial models.- Evaluation of the options, using financial and non-

financial criteria.- Establishment of the joint venture, including the

selection of vessel, management, industrial consid-erations.

Stage 2 was completed in April 1987 at a cost of$65,000. It clearly showed that the operation of a jointventure brought about significant reductions in the totalcost of dredging operations at the three ports. Eachoption was considered by using the “most likely”,“maximum”, and “minimum” volumes to be dredgedas well as three inflation and interest rate scenarios.


13

Figure 2. The Pelican is a split-hopper trailing dredger, equipped with a suction installation allowing the dredged spoil to bedischarged ashore. The dredge pump has been mounted halfway along the suction pipe enabling the vessel to dredge highlyconcentrated mixtures at great depths.

THE INTERPORT AGREEMENT AND

DREDGING CONTRACT

A contract had to be negotiated which would bind thefour parties together. The most practical way toachieve this was for the three ports to formulate anagreement to use a common contractor, and under thisHeads of Agreement enter into individual contractswith the dredging contractor for the work at each port.

Heads of AgreementThis document set out the intention of the three portsto employ a common contractor for trailer suctiondredging work. It also set out such matters as theestablishment of separate contracts, cross-liability, thesharing of establishment costs, refunds, contract intelli-gence and cooperation in dealing with the program-ming of dredging and urgent dredging.

Dredging ContractsEach individual contract between the Port Companyand the Dredging Contractor is divided into three parts:Part A, Special Conditions of Contract; Part B, Specifica-tion; and Part C, Schedule.

Part A, Special Conditions of ContractIn this part the most significant section is clause 7,Payment, which is commerically sensitive and cantherefore not be elaborated upon in depth. Clause 7g isthe market fluctuations clause and contains two ele-ments that merit further comment.

The first element is the labour adjustment factor. At thenegotiating stages of the contract, the manning for thevessel was not known so the contractor was requiredto make the initial offer subject to eventual outcomes ofthe labour negotiations. The three ports were obviously reluctant to enter into acontract which was open ended in regard to a majorcost component. Eventually both sides agreed to sharea degree of the risk associated with the labour negotia-tions. For the purposes of the unit rates in the dredgingcontract, a nominal manning level was agreed and anotional gang rate reflecting the cost of manning thedredger was calculated.

It was then agreed that any variations to the anticipatedmanning levels be carried by the ports to a limitedextent and thereafter by the dredging contractor. It wasalso agreed that the maximum variation from theexpected cost per crew member that the ports wouldmeet by way of the adjustment to the notional gangrate, and hence the unit rate, would be +/- 15 percent.If the final rate negotiated varied more than thisamount, the cost or savings would be borne by thecontractor.

Thus at the point of contract negotiations, the maxi-mum risk resulting from labour cost variations was

prescribed and an incentive to the contractor to holdthese costs was provided.

The second element worth noting is that after two anda half years of operation of the market fluctuationsformula, a re-assessment of the notional gang rate wasmade from base data and substituted in the formulareplacing the value derived by reference to the move-ment of the wage rate index. This was done to ensurethat actual rates are not overly influenced by statisticaldata not directly related to the operation of a dredger.

Clause 9, The Term of Contract, sets out the procedurefor extending the contract beyond the initial period offive years.

Part B, SpecificationIn Part B the contract details the work to be carried outat each port and specifies an annual volume of dredg-ing that each port has contracted to provide to thedredging company. The rates for this work are speci-fied along with adjustments ot be made if the contractvolume increases or decreases. The contract allows aport to defer or cancel its dredging, but it must pay aminimum sum to the contractor in so doing.

Sections 5 and 6 of Part B deal with the measure of thework and the planning and control of dredging. Toleran-ces on minimum areas of dredging are presented asguides.

CONTRACT OPERATION

Dredging Programme FlexibilityControl of the dredging programme essentially lies withthe Port Companies and is driven by their needs. Thelong-term programme of the contractor is reviewed byall parties on a biannual basis where each Port Com-pany’s individual forecast of dredging needs is pro-grammed with other work the contractor may have orconsiders likely together with other requirements suchas vessel maintenance.

The Port Companies are able to take advantage of thecontractor’s ability to be flexible in dredging operationsand programming campaigns. This can enable the portto be confidently operated with some tolerance orvariation to the port operating parameters, e.g.,draught, channel, width, and so on.

There are no physical limits as to the volume dredgedeach year, therefore each Port Company is able tochoose whether to bring forward, defer or combinedredging campaigns to meet their own shipping orcash flow needs. Instead of slavishly following a “cleardepth over a clear toeline” concept essential for “oneoff” contracts, the Port Companies can tailor eachdredging campaign and time a campaign for a better


14

- The contractor has broader experience in dealingwith different dredging problems.

- “The creation of work” is eliminated.

Human Resources and Industrial RelationsIntroduction of a dredging contractor working on a long-term basis on the New Zealand coast necessitated thenegotiation of new industrial agreements with theMaritime Union. Existing industrial agreeements gene-rally only covered vessels working in their home port.Negotiation of these agreements was not made anyeasier by the fact that all facets of port operations inNew Zealand were undergoing dramatic change at thedirection of the Government.

The emergence of the new industrial agreements andthe fact that the contractor has now taken over the rollof the employer with all its responsibilities meant thatthe Port Companies could either free up their ownpersonnel for other duties or reduce their static work-force and management.

By using the contractor’s dredger and crew the follow-ing benefits are forthcoming:- Labour costs are reduced in maintenance dredging,

reflected through lower unit contract rates.- A pool of dredging personnel with a greater diversity

of dredging experience is established.

Long-term Planning of OperationsThe long-term contract enables the contractor to viewthe employment of the dredger from a more “stable”

overall return for the Port. Any urgent or unexpectedneed for dredging can be accommodated under thecontract by a variation to the long-term programme.Co-operative programming between the Ports alsoenables the cost of mobilisation and demobilisation tobe kept to a minimum by minimising the inter-portvoyages of the dredger.

Plant UtilisationBy virtue of their co-operation the three Port Compa-nies have:- eliminated future capital spending on plant for main-

tenance dredging;- eliminated a significant part of the operation cost of

the dredging.

By employing a contractor with a modern dredger witha capacity matching typical dredging needs the PortCompanies do not need to invest in new equipment,keep existing equipment in operation or modify equip-ment for specific purposes. In the long-term this meansthat capital potential is able to be utilised for otherrevenue earning activities.

The benefits to the Port Companies from sharing thecontractor’s dredger are many:- The dredging contract is based on working 24 hours

per day 6 1/2 days per week.- Greater plant utilisation by the contractor reflects in

lower contract prices.- Port Companies can do away with maintenance and

supervision systems of their own.


15

Figure 3. The Pelican at work in the evening, dredging the harbour of Timaru. Dredging takes place 24 hours a day, 6 1/2 days perweek.

position, particularly when considering:- long-term maintenance and slippings;- investment in new technology;- investment in modifications or improvements;- investment for diverse operations.

Long-term maintenance can now be carried out in themost preferred manner and location rather trying to fit itin between projects or for the sake of expediencywhen passing a slipway or drydock. This enables therepair costs to be better controlled and overall cheaper.

Upgrading the technology in the vessel to maintain itscompetitiveness can be viewed more rationally know-ing its occupancy more accurately for the long-termcontracts.

Modifications or improvements can be more readilymade knowing the expected increased return from themodification and the pay back period for that return.

Should changing materials or disposal methods berequired by the client, the investment in the dredger tomeet those needs can be explored more rationally thanfor the “one off” situation. All of the above factorscontribute to keeping the maintenance costs to aminimum and enable the vessel to be kept in competi-tive condition.

The benefits of the long-term contract to the contractorultimately flow to the Port Companies by resulting inlower contract rates and from the decision-makingprocess available through the flexibility in programmingdredging campaigns. Conversely the contract term of 5 years is not so long as to remove the incentive offuture renewals.

Utilisation of Port Company ResourcesTypically dredging contracts require the contractor to be

self-sufficient in all facets of the execution of a contract.This ensures that the areas of responsibility are clearlydefined. Also, contractors operate with different priori-ties with regard to time.

Quite often this results in a contractor duplicating re-sources that already exist within a port’s infrastructure.Therefore whilst such duplication may be necessary fora single contract, the contractor proposed that if it werepossible for the Port Companies to provide support tothe contractor as a condition of the contract therewould be multiple effects:

1. Direct reduction of the contract price resulting fromreduced capital investment or hire by the contrac-tor.

2. Reduction in the contractor’s site staff, again provi-ding a reduction in the contract price.

3. Greater utilisation and hence cost benefit of thePort Companies’ own personnel, plant and equip-ment.

4. Reduced mobilisation and demobilsation costs asthe contractor does not have to set up/end dis-mantle a site infrastructure for each campaign.

Under the long-term contracts the Port Companies arerequired to provide all hydrographic surveying supportnecessary for both the administration of the contractand also for the day-to-day operation needs of thecontractor. The Port Companies are also required toprovide a service vessel to support the dredger forcrew changes and day-to-day requirements.

Contract BenefitsThe benefits of the long-term contract are for bothparties and are summarised below.

Benefits for the Port Companies are:- free to tailor maintenance dredging needs and pro-

grammes to suit shipping requirments;- instead of ports having to create additional work or

obtain work outside of the ports to keep personneland plant viably occupied the contractor can be usedonly as required;

- reduced direct expenditure for maintenance dredg-ing;

- fixed term unit rate contract is an incentive for thecontractor to remain competitive.

Benefits for the contractor are:- stabilisation of vessel occupancy in the long term;- smooth regulation of cash flow in the long term;- increased efficiency from working in the same

environments on a regular basis.

Contract ProblemsSome difficulties can be met in the execution of thelong-term contracts, and these are summarisedbelow.


16

Figure 4. The general layout of the Port of Timaru.

New Zealand. Port Companies, with a considerablydifferent focus, were established. The need for struc-tural change in the industry became apparent immedi-ately, and in several ports the new approach resulted ina shift from port-owned and -operated dredgers tocontract dredging.

In the ports of Tauranga, Taranaki and Timaru this wasthe case, and this re-appraisal resulted in a contract fora period of fifteen years, with a review every five years.

The contract is now in its eighth year and is without adoubt of great benefit to the three Port Companies. In less than ten years time since the study into theoptimal dredging method was made, New Zealandports have moved from world-ranked laggards to thetop echelon of international ports in terms of profitabil-ity and performance. They have become customerfocussed and flexible. It seems therefore quite likelythat a similar arrangement will continue in the future.

References

Deloitte Haskins & Sells. Financial Evaluation of the Joint Venture Dredging Options.

Report for the Ports of Tauranga, Taranaki and Timaru.

June 1987.

Problems which can arise for the Port Companies are:- digression from the original concept or intent of the

actual dredging to any large extent that does noteasily fit in with the exisiting unit rate price structure;

- adopting variations to their own dredging pro-grammes should the contractor obtain other workoutside of long-term contracts.

Problems which can arise for the Contractor are:- logistical problems of short campaigns in personnel

and spare parts;- short-term peaks and troughs can create difficulties

in manning the vessel and deploying site staff.

OVERVIEW

Since the implementation of this contract in 1988, thePort of Timaru has dredged 160,000 m3 per annum(Figures 3 and 4), Westgate-Taranaki 120,000 m3 perannum, and Tauranga (Figure 5) approximately 350,000m3. During 1993 Timaru gained ISO 9002 Certificationfor a key customer interface, its container yard andfreight station area. It was the first port in Australia orNew Zealand to do so.

Conclusions

The waterfront reform in the mid-1980s in NewZealand resulted in the privatisation of all the ports in


17

Figure 5. The Pelican dredging the approach channel at Tauranga in 1990. Its modest size and high manoeuvrability make the vesselideally suited for operations in smaller harbours as well as for dredging pipeline and cable trenches in shallow coastal waters.

Abstract

Besòs Long Sea Outfall, Barcelona, Spain, is one ofEurope’s largest long sea outfalls installed by the bot-tom pull method. The outfall consists of a cementmortar lined 19 mm thick steel liner pipe with a struc-tural reinforced concrete coating and a total length of2900 m. This paper provides a brief overview of theproject and discusses in greater detail the somewhatunusual dredging activities carried out which allowed itssuccessful installation. Dredging activities included soil improvement by remo-val of soft clay and its replacement by compacted sand,the dredging of a 7 m deep trench beneath a highpressure gas pipeline located approximately 1 kmoffshore and the dredging of a 2900 m long trench inwater up to 55 m deep.

Introduction

In the light of recent EC legislation, EMSSA (the Barce-lona sewerage disposal authority) had been reviewing

the performance of the sewerage disposal system toBarcelona. They had identified a need for a substantiallyimproved outfall system to the north of Barcelona thatwould replace the existing outfall which was leakingbadly and not long enough to satisfy EC bathing waterquality directives.

An EPIC (Engineer, Procure, Install Commission) con-tract for the outfall and associated pumping station wasthen drafted, and ultimately awarded to a joint venturecompany comprising two Spanish contractors, SATO,and Cubiertas y Mzov, and two Dutch contractors, SmitTak and Ballast Nedam Dredging. Two British consul-tants were engaged; Andrew Palmer and Associateswere responsible for the detail design of the outfall,and Watson España provided engineering support tothe client. A truly pan-European venture.

The contract was awarded in January of 1994 and byJanuary of 1995 the outfall had been designed, builtand installed. The final part of the project, Pump StationCommissioning, was completed in May 1995. Figure 1shows the outfall location.


Bert Dijkstra and Stuart McIntyre

Besòs Long Sea Outfall,Barcelona

18

En

viro

nm

ent

Figure 1. Location of the outfall at Sant Adrià de Besòs.

The strings were then moved sideways into stock andthe joints between pipes completed with the concretecoating. The temporary works required to allow thehandling of such large pipe strings was one of themajor investments onshore; its successful operationdetermines whether welding is completed on time.Figure 2 shows the partially completed string numberone about to be moved sideways into stock. During the welding and fabrication process, the off-shore trench was being dredged. The dredging of thetrench is the primary focus of this paper.

DREDGING ACTIVITIES

PlanningThe dredging works consisted of dredging the 4-mdeep, 2900-m long trench and, after installation of thepipe, backfilling of the trench with sand. The overall

OUTFALL DESCRIPTION

The outfall consists of a cement mortar lined 19 mmthick steel liner pipe with a structural reinforced con-crete coating to produce the following overall dimensions:

Bore 2.10 mOutside Diameter 2.62 mStructural Concrete 222 mm thickTotal length 2900 mDiffuser section(with 15 diffusers) 840 mTotal dry weight empty 16,800 TSubmerged weight 150 kg/mMaximum flow rate 12.4 m3/ s.

The outfall was installed to a maximum water depth of55 m using the bottom pull method. Installation to this,in the context of outfalls, extreme water depth, withsuch a large diameter pipe, required state-of-the-artpipeline analysis using finite element analysis.

The large diameter of this pipe is considered close tothe practical limits for the bottom pull method of instal-lation because with a submerged weight of only 2 to 3 per cent of its dry weight, factors such as concretedensity, water absorption and construction tolerancesmay determine whether the pipe floats or is too heavyto pull. Recognition of this led to the somewhat un-usual step of concrete coating the individual 9 m steelpipes off site. This ensured that the concrete coatingwas of the highest quality.

The high concrete quality achieved will help ensure thatthe outfall fulfils its 100-year design life. Further mea-sures used to maximise longevity included coating theconcrete reinforcement with fusion bonded epoxy, andthe liner pipe with a two pack epoxy paint and connec-ting the liner to an impressed current CP system.Although the pipe is enormously heavy when dry (5800 kg/m), because of its large displacement, thepipe has a low submerged weight (150 kg/m) whenempty. Traditional two-dimensional stability modelsindicated that the pipe was only stable in very smallwaves, and more sophisticated three-dimensionalanalysis was required to determine the limiting instal-lation weather conditions.

LAND-BASED CONSTRUCTION

This part of the work was undertaken by SATO andCubiertas. The outfall is made up of 9 m long steelpipes, fabricated near Barcelona. These pipes wereindividually concrete coated in a specialist factory, again near Barcelona. When the pipes were delivered to site they werewelded together to form strings 117 m long.

Besòs Long Sea Outfall, Barcelona

19

Bert Dijkstra

Stuart McIntyre

Bert Dijkstra holds a BSc in CivilEngineering and a BBA in BusinessAdministration. Since 1964 he haswork all over the world for VolkerStevin and Ballast Nedam. He ispresently Area Manager Europe atBallast Nedam Dredging.

Stuart McIntyre holds a BSc in CivilEngineering and is a Charter CivilEngineer. He works as a Senior Engi-neer with Andrew Palmer and Asso-ciates, and was posted to Spain bythem for the duration of the outfalldesign and installation as AssistantProject Manager.

programme was for construction to begin in Februaryof 1994, with completion in May 1995.

The critical path for the project lay through:- welding of the pipe strings on site; - trench dredging;- pipe pulling; - testing;- backfilling; and - pumping station construction.

Because of the client’s extreme concern that dredgingactivities should not cause turbulence which couldarrive on the beaches during the holiday periods, strictcontrols were enforced. These included limiting thedates during which dredging could take place, andrequiring the suction hopper dredger to work withoutoverflow.The above restrictions effectively resulted intwo periods of dredging activity: a period in the springof 1994, prior to the peak summer holiday period, and aperiod after summer and into the autumn/winter of1994.

The first season of dredging work comprised thedredging, backfilling and compaction of a soil improve-ment area designed to support a future breakwatercrossing of the outfall. The second season of workcomprised the dredging of the main trench. The activi-ties in these two seasons are discussed below.


20

Figure 2. The first pipe string being moved from the welding area to the stock area. The structures on top of the pipe are thestarters for the diffusers.

Figure 3. Cutter dredger Rozenburg, 160 m from cofferdamand hopper dredger Lelystad, 600 m from cofferdam,launching preparations on shore side.

carefully designed and executed, particularly throughsag curves and at the end of the ‘launch ramp’. Theanalysis ensures that if the pipe is very stiff and light, itwill not ‘lift off’ in sag bends, particularly underneaththe gas line. Similarly, when soils are very soft and thepipe is not able to lift, at the end of the launch ramp forexample, it does not plough-in and become embedded.

The high stiffness of the pipe determines that changesin the longitudinal profile must occur slowly. This meantthat, although the target trench depth was 3.6 m beloworiginal seabed, the trench was frequently deeper thanthis in areas of profile change. A major part of theprofile design process was therefore the optimisationof stresses within the pipe to minimise dredge quanti-ties and ensure that the pipe would follow the designprofile. The trench profile adopted is shown in Figure 5.

To allow accurate dredging of the trench to a maximumwater depth of 55 metres required a large trailingsuction hopper dredger, Lelystad. This vessel usesextremely sophisticated positioning and control equip-ment which allows very tight dredge tolerances andensured that the position of the suction head wasexactly known at all times.

Trench Section 3: Gas Line CrossingThe first item of work to be started on the dredging ofthe main trench was the offshore crossing of a 20 inchoutside diameter high pressure gas pipeline. This waslocated 1 km offshore in approximately 26 m of water.Because of its arterial role in the distribution of gas

Four different dredgers were utilised (Figure 3):- trailing suction hopper dredger Lelystad to dredge up

to 55 m below seabed;- trailing suction hopper dredger Poseidon to facilitate

backfilling of the trench through one of the suctionpipes;

- cutter suction dredger Rozenburg to make thetrench in the nearshore shallow waters; and

- submerged jetpump in combination with FLYGTpump (2 cutter system) operated from the pontoonKutxa to allow for very accurate dredging near theexisting pipeline.

SPRING 1994

Breakwater Soil ImprovementThe future harbour breakwater will be constructed overthe outfall, in approximately 20 metres of water. Tosupport this massive construction so that it does notdamage the outfall required the removal of 200,000 m3

of soft clay and mud.The soft material was removed by the suction dredgerPoseidon, and on acceptance of the dredged area bythe client, was backfilled by the same vessel with sandwith a D50 of 400 µm. The borrowing of sand for this purpose is controversial,as sand is particularly valuable in Spain for the forma-tion and maintenance of beaches.After backfilling, the area was compacted using twintorpedo vibro-compactors supported from the cranepontoon Kutxa (Figure 4), in a pattern that compacted 5m2 per point. Design of the soil improvement area tosupport the breakwater and protect the outfall, evenduring earthquakes, used specialist three-dimensionalconsolidation, finite element models developed byCambridge University, followed by finite element dy-namic earthquake analysis using real earthquake re-cordings, scaled appropriately to the design criteria atBarcelona.

AUTUMN /WINTER 1994

Main Trench DredgingThis season of work comprised dredging of the outfalltrench and was divided into four sections:1. Beach cofferdam to water depth 15 m (chainage

CH 40 m to 430 m).2. Water depth 15 m to gasline crossing (chainage

CH 430 m to 1125 m).3. Gasline crossing (chainage CH 1120 m to 1165 m)

at 35 m water depth.4. Gasline crossing to end of trench (chainage

CH 1165 m to 2920 m)

Longitudinal ProfileBecause of the very high longitudinal stiffness of thepipe, the trench longitudinal profile had to be very


21

Figure 4. After backfilling, the area was compacted using twintorpedo vibro-compactors supported from the crane bargeKutxa. Kutxa is seen here dredging under the gas line, with apull barge behind.

around Barcelona, the gas line could not be shut downto allow dredging of the trench. It was therefore sup-ported on a lattice ‘bridge’ with a length of 60 m and aclear central span of 40 m. The bridge was designed inaccordance with API RP2A (Figure 6). Although thissolution worked well, considerable restrictions wereplaced on dredging activities.

Before dredging could begin, the owner of the gaspipeline, Gas Natural SA was provided with detailedmethod statements and work procedures. Theseprocedures considered contingencies and were devel-oped in conjunction with Gas Natural so that risks tothe pipeline were minimised. In this way, should anunfortunate event have occurred, the dangers to crew


22

Figure 5. Basic design, longitudinal profile. Minimum radius at gasline crossing: 4500 m.

Figure 6. The gas pipeline bridge is lowered into the harbour in preparation for towing out to site. This support bridge is 60 m overall length.

Survey was carried out by survey launch, supported bydivers when necessary. The divers were also requiredto manually remove the small amount of material lyingdirectly underneath the pipe bridge.

Trench Section 1: Cofferdam to 15 m Water DepthThis section of trench was dredged by the cutter dredg-er Rozenburg on a box cut of 40 m width. The bottomwidth required before pipe pulling was 10 m. As theprevailing wind direction is from the northwest, andbecause of a slight coastal drift and the close proximityto shore and the surf zone, a small amount of trenchmaintenance was expected. In the event however, nomaintenance dredging was required. Dredged materialwas dumped via a floating pipeline 450 m to the southof the trench.

Trench Sections 2 and 4: 15 m Water Depth to GasCrossing, Gas Crossing to End of TrenchThese sections were dredged by the hopper dredgerLelystad. Bottom width was set at 15 m while the sideslopes were expected to be stable with slopes of 1:4.Dredge tolerances were determined by the pipe, withcomputer analysis on site to verify that the profile wasacceptable. Tolerances were typically plus 10 cm tominus 40 cm per cross-section.

Difficulties encountered in the dredging of section 4 ofthe main trench included the material being very soft,the requirement for very tight tolerances at greatdepths, and being restricted to dredge without over-

were minimised, and the pipeline could have beenreturned to service as quickly as possible.

The procedures also placed restrictions on the move-ment of vessels and required that the suction heads ofthe dredger were always at surface when crossing thegas pipeline (Figure 7). After the pipe bridge had beeninstalled and the procedures agreed, dredging to re-move the 30,000 m3 of material underneath and closeto the pipeline could begin.

The dredging of this gas line crossing section hadoriginally been planned for an underwater, remotelycontrolled vehicle carrying a jet pump. Unfortunately,production targets could not be met and the workmethod was changed to two cutter FLYGT pumpsmounted on a vertical steel tube, supported by a craneaboard the pontoon Kutxa. High pressure water jetswere also mounted around the pumps to help dislodgematerial around the pumps. Figure 8 shows the dredg-ing system used at the gas line crossing.

Because of the nature of the sandy clay encountered,excavation slopes were steep (approximately 1:1). This had the advantage of reducing the overall amountof material to dredge, but as the material was not freerunning towards the pump and cutters, every part ofthe required trench area had to be thoroughly coveredby the cutters. Figure 9 shows the trench cross-sectionnear the gas line. It makes clear just how steep thetrench slopes were.


23

Figure 7. Situation at the pipeline crossing. Window of suction pipe of Lelystad.

flow. Overcoming these difficulties required a greatdeal of skill and attention.

A difficulty encountered in dredging section 2 was thepresence of a “hard spot” in the trench at CH 480(Figure 10). The difficulty with dredging such hard spotsis that the suction head follows the path of least resis-tance, and the danger arises of overdredging one sideof the trench and leaving the other side high. This againcalls for experience and skill from the crew and thedredging engineer on the bridge.

PIPE PULL

When dredging of the trench was complete and accep-ted by the client, the outfall could be pulled out. Thepull out went very smoothly, with the outfall beingpulled into the trench using the Taklift 8 pull barge withan installed winch capacity of 600 tonne reactingagainst four huge anchors placed further offshore (13Tonne Stevpris type). One 117 metre string was fullywelded, wrapped, concrete coated and pulled outevery 24 hours (Figure 11).The pull barge was initially anchored 1.5 km offshorewith the pull pennant passing underneath the gas lineonly 400 m away. Considerable detailed engineeringand monitoring was required to ensure that the pullwires did not lift off close to the gas line, threateningcontact with it.During the pull, continuous survey was carried out todetermine that the pipe was following the correctprofile and monitoring the cable touchdown point.Installation of the diffusers, traditionally a very weather-sensitive and timeconsuming activity also went verysmoothly. All 15 diffusers were installed within 30hours. This is all the more remarkable considering thatthis was carried out by divers in 50 metre water depthwith one metre visibility. The diffusers were installedusing the deck crane aboard the pull barge.

BACKFILLING

After the pipe and diffusers had been installed andapproved, backfilling could begin. Unfortunately, thequantity of sand available in the contractual sand bor-


24

Figure 8. General arrangement of the steel pump; insert: onepump unit and two cutter units, hydraulic driven.

Figure 9. CH 1120 cross-section. Progress bridge 19November 1994.

row area was very limited and alternative borrow areashad to be located. The alternative sand source providedmaterial of the grading shown in Figure 12.

Backfilling was done in two parts because of the draftrestrictions of the suction hopper dredger Poseidonmobilised to backfill the trench. The first section wasfrom the beach cofferdam to CH 400, and the secondfrom CH 400 offshore.

The shallower section was backfilled using the pontoonKutxa supporting a T-shaped fall-pipe which, whenconnected with the Poseidon via a floating pipeline,allowed discharge of the 3000 m3 load over the outfall.

The offshore section was backfilled by the hopperdredger directly. This was done by pumping the hoppercontents down one of the suction pipes and allowing itto discharge 5 to 10 m above the outfall.

Unfortunately, because of the fine content of the back-fill material and cross-currents, there was a significantloss of backfill material.


25

Figure 11. In the foreground, the pipeline is awaiting the pull.In the background is the pull barge and the pontoon dredgingunderneath the gas line. In the middle ground is a sewerdiversion pipe crossing the pipe trench.

Figure 10. CH 480 cross-section. Preliminary outsurvey Kp 60-500, 15 November 1994, showing “hard spot”.

SURVEY

The key to the successful accurate dredging of thetrench was survey. The control system for the surveycomprised two DGPS reference stations, seven micro-fix stations and an automatic tide gauge. Survey sta-tions were installed on the survey launch La Restinga,crane pontoon Kutxa, suction hoppers Poseidon andLelystad and the cutter dredger Rozenburg. In the laterstages, a station was set up on the pull barge Taklift 8and another on the anchor handling tug Smit Lloyd 31.

Conclusion

The dredging activities necessary to ensure the success-ful construction of the new longer outfall at Besòs inBarcelona were defined by several strict requirements.For instance, dredging activities were not allowed tocause turbulence which would disturb beaches duringholiday seasons. Therefore work took place duringrestricted periods (spring and autumn) and suctionhopper dredgers had to work mostly without overflow.

In addition, utmost care was needed to cross a highpressure operational gas pipeline. This included devisingcontingency plans which had to be approved by Gas

Natural SA. Movement of vessels was restricted andcontingency plans required that suction heads werealways on the surface when crossing the gas line.

Although modern engineering works are increasinglydominated by highly sophisticated technical systems,the type of precision involved in this project also reliedheavily upon the close cooperation of a large number ofindividuals. The collective skills of the crew, the engi-neers and the divers allowed for the successful com-pletion of this a significant contract within a limited timespan.


26

Figure 12. Particle size distribution of sand for backfilling.

5

approach for computing the bottom surge and compu-tations that make the model more applicable at disper-sive disposal sites.

STFATE has been applied to simulate disposal testsconducted at a 1:50 scale in a large laboratory facility atthe US Army Engineer Waterways Experiment Station.Comparison of computed and measured results ondecent and bottom surge speeds, bottom deposition,and suspended sediment concentrations have beenmade. The results show that STFATE can be used toreliably predict the fate of material disposed at openwater disposal sites. However, an uncertainty analysisis needed to place accuracy bounds on model results.

Key words: barge, disposal, dredged material, hopperdredge, mixing zone, numerical model, sediment.

Plume Measurement System (PLUMES), TechnicalManual and Data Analysis Procedures: Final Report.Technical Report DRP-95-1. US Army Corps of Engineers. February 1995. Bibliographic references. 94 pp. Illustrated.

M.W. Tubman

The PLUmes MEasurement System (PLUMES) wasdeveloped under the Measurement of Entrainment andTransport research work unit of the DRP TechnicalArea 1 to monitor the transport of suspended sedimentfrom dredging and dredged material disposal opera-tions. This system can monitor the transport nearlysynoptically, both horizontally and vertically. The reportprovides technical information on the overall system,guidance on locating specific information in the stan-dard technical manuals provided by the manufacturersof the individual system components, technical infor-mation on special features of the system componentsnot included in the manufacturers’ manuals, informa-tion on system operation and deployment procedures,

The US Army Corps of Engineers is concluding a multi-year $25 million dredging research programme. Manyfine interim technical reports have been producedperiodically during the course of the programme. Presently a number of final reports are being publishedwhich are of prime interest, and four of these areabstracted below. The Dredging Research Programme(DRP) is organised into five technical areas:

Area 1 Analysis of Dredged Material Placed in OpenWaters

Area 2 Material Properties Related to Navigation andDredging

Area 3 Dredge Plant Equipment and Systems Proces-ses

Area 4 Vessel Positioning, Survey Controls and Dredge Monitoring Systems

Area 5 Management of Dredging Projects

Development and Verification of Numerical Modelsfor Predicting the Initial Fate of Dredged MaterialDisposed in Open Water, Report 2. TheoreticalDevelopments and Verifications Results. TechnicalReport DRP 93-1.US Army Corps of Engineers. February 1995. Bibliographic references. 74 pp. Illustrated.

B.H. Johnson and M.T. Fong

This research was conducted under the DRP TechnicalArea 1. A numerical model called STFATE (Short TermFATE) for computing the short-term fate of dredgedmaterial disposed in open water has been developed.STFATE builds upon work of earlier researchers toprovide a more realistic simulation of actual disposaloperations from split-hull barges and multi-bin hopperdredges. New developments allow for multiple-connec-ting clouds and stripping of solids fluid from thoseclouds to better represent water column effects. Other developments include the use of the total energy

Books/Periodicals Reviewed

Charles W. Hummer, Jr.

Books/PeriodicalsReviewed

27

descriptions of the PLUMES software, and informationon the data analyses procedures.

Key words: acoustic, dredged material, monitoring,PLUMES, suspended sediment transport

Technologies for Hopper Dredge Production andProcess Monitoring - Laboratory and FieldInvestigations: Final Report. Technical Report DRP-95-2.US Army Corps of Engineers. February 1995. Bibliographic references. 95 pp. Illustrated.

S.H. Scott, J.D. Jorgeson, M.B. Savage and C.B. Cox

This work unit, which falls under DRP Technical Area 3,was initiated to investigate methods for monitoringhopper dredge production and operation. Hopperdredging accounts for a significant portion of the totalamount of material dredging in the United States.Operating costs for a hopper dredge are significant.Costs may vary from approximately $30,000 to$75,000 per 24 hour day, depending on the size of thedredge and support requirements. Typically, the cost ofefficiency of a dredge is judged by its ability to movesediments from the project area to disposal with aminimum of pumping and travelling time. The idealhopper load for accomplishing this is referred to as the“economic load”. Better methods are needed to moni-tor dredge processes which will reveal the optimaloperation for achieving the goal of economic load.Under this work unit, two methods were designed,fabricated, tested and evaluated for effectiveness inproviding data to dredge personnel for the purpose ofincreasing dredge efficiency:- A resistivity probe was developed to directly mea-

sure the vertical density profile of dredge material inthe hopper.

- An instrumentation package which included acousticand pressure sensors was developed to monitor thereal time dredge displacement and hopper volumeand indirectly measure the density of dredged mate-rial in the hopper.

The data resulting from the application of both systemscan be used for calculating dredge production on a loadby load basis. The report presents the description andmethod of the testing programmes and the studyfindings. The concept of uncertainty analysis for deter-mining the error potential in hopper dredge productioncalculations is presented and discussed with an exam-ple calculation.

Key words: dredges, hopper dredge, dredge investiga-tions, economic load, excavating machinery

A Technique to Assess the Characteristics of Bottomand Subbottom Marine Sediments: Final Report.Technical Report DRP-95-3. US Army Corps of Engineers. February 1995. Bibliographic references. 174 pp. Illustrated.

R.G. McGee, R.F. Ballard, Jrand D.D. Caulfield

The theoretical concept, assembly and field testing of awaterborne seismic acoustic impedance techniquewhich has been developed to characterise bottom andsubbottom sediments as they relate to removal bydredging are presented in this report. This method,developed under the DRP Technical Area 2, providesestimates of in-situ density and soil type in rapid, cost-effective manner using digital acoustic subbottomprofiling methodology.

In-situ densities obtained by the acoustic impedancetechnique to date, when compared to those obtainedby conventional means at several different sites undera wide varity of marine conditions, have statisticallybeen within 10 percent. However, only marine sedi-ments considered to be fully saturated, inorganic anduncontaminated have been investigated and “groundtruthed”. After comparisons with ground truth informa-tion and laboratory testing, a critical analysis of theacoustic impedance technique reveals it to be a validand useful approach to bottom and subbottom materialand density prediction. Athough some development isstill needed to fully establish advantages and limita-tions, its potential usefulness warrants technologytransfer now provided proper cautions are observed.This supposition is corroborated by the fact that nume-rous reimbursable surveys have been successfullyconducted whilst products were still in the develop-ment stage. Each site surveyed provided valuable inputto the R&D evolutionary processes, and enabledresearchers to fine tune procedures whilst simultane-ously providing a successful and timely service toclients.

Key words: acoustic impedance, acoustic subbottomprofiling, bottom sediments, subbottom sediments

These reports may be obtained at no cost from:Mr E. Clark McNair, JrProgramme Manager, Dredging Research ProgrammeU.S. Army Engineer, Waterways Experiment Station3909 Halls Ferry RoadVicksburg, Mississippi 39180-6199, USA

or at nominal cost from:National Technical Information Service5285 Port Royal RoadSpringfield, Virginia 22161, USA


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1070 MS Amsterdam, The Netherlandstel. +31 (20) 549 1212, fax +31 (20) 646 4469

C.P. WulfRoosens Park 222605 Hamburg, Germanytel. +49 (40) 880 2467, fax +49 (40) 880 7172

RAI Exhibitions London LtdGlen House, Suite 509200/208 Tottenham Court RoadLondon W1P 9LA, U.K.Tel. +44 (71) 436 9774, fax +44 (71) 436 5694

maritime country, and water tranportation is crucial fortrade. Investments are being made in the developmentof port facilities, deep seaports, export processingzones (EPZ), ship repair, dredging, ship and marineequipment and so on.

For further information contact:RAI Exhibitions Singapore Pte Ltd1 Maritime Square, #09-49World Trade Centre, Singapore 0409tel. +65 272 2250, fax +65 272 6744

Amsterdam RAIP.O. Box 77777

Call for Papers

31

PIANC Conference on Inland and MaritimeNavigation and Coastal Problems of East EuropeanCountries

Gdansk, PolandSeptember 1-5 1996

The Marine Civil Engineering Department of the Tech-nical Univesity of Gdansk is the site of the PIANC(Permanent International Association of NavigationCongresses) conference on inland and coastal pro-blems in Eastern Europe.

The focus will be on East European waterways and thetopics which will be discussed are:- inland navigation in East European countries and its

link to other countries;- maritime navigation with particular consideration of

shipping in the Baltic, Black, Adriatic and other seas;- competitiveness of navigable waterways;- pollution of seas due to contaminated rivers in

Eastern Europe;- coastal problems such as sediment, beach and

harbour pollution in Eastern Europe;- rehabilitation and modernistation of existing struc-

tures; and- particular areas of shipping such as from Scandina-

vian ports to Northeast Europe.

Further information is available from:Prof. B.K. MazurkiewiczTechnical University of Gdanskul. G. Narutowicza 11/1280 - 952 Gdansk, Polandtel. +48 58 472611, fax +48 58 471436telex 0512302 plg pl

Hydro 96De Doelen Congress CentreRotterdam, The Netherlands

September 24-26, 1996

The tenth international biennial symposium of TheHydrographic Society is being organised by The Socie-ty’s Benelux Branch and will take place in September1996. The Symposium’s topics will address key hydro-graphic issues affecting port and other applications,including: - port and coastal surveys; - port and coast geodesy and navigation; - dredging surveys; - mapping; and - water management.

The proceedings will be supported by an exhibition ofequipment and services at which the Port of Rotterdamwill be a major participant. Deadline for submission ofabstracts is 1 January 1996. Notification of acceptancefor presentation will be 1 March 1996. Submission offull papers for proceedings must take place by 1 July1996.

Prospective speakers and organisations wishing toparticipate should contact:

Mrs P.Y. van den BergHydro 96 Organising CommitteeOceanographic Company of The NetherlandsP.O. Box 74292701 AK Zoetermeer, The Netherlandstel. +31 7942 8316fax +31 7941 5084

Call for Papers

11th International Harbour CongressAntwerp, Belgium

June 17-21 1996

Organised by the Royal Flemish Society of Engineers,this five-day congress will be held together with the 8thInternational Harbour Exhibiton.Topics will include all aspects of port and harbourtechnology such as:- port planning: extension, renovation, future policy

making, environment, financing through privatisation;- port infrastructure design: reducing wave agitation;

quality control and care; measurements, instrumen-tion; design in third world situations;

- port construction: innovative techniques, new shiptypes, protection of water bottom;

- port access: approach channels, capital dredging andmaintenance in rivers;

- maintenance: planning, reducing work on piers,breakwaters, etc.; maintenance dredging; emergen-cy intervention; third world ports.

For further information contact:11th International Harbour Congressatt: Ms Rita Peysc/o Ingenieurshuis, Desguinlei 214B-2018 Antwerp 1, Belgiumtel. +32 (3) 216 0996, fax +32 (3) 216 0689


32

Day 1: Why Dredging?The Need for Dredging/Project Phasing

Day 2: What is Dredging?Dredging Equipment/Survey Systems

Day 3: How Dredging?Dredging Projects

Day 4: Preparation of DredgingContract

Day 5: Cost/Pricing and Contracts

Representatives of port authorities, companies, andindividuals interested in attending are requested tocomplete the preliminary registration form below assoon as possible and prior to November 15 1995, andreturn to:

IADC Secretariat, Duinweg 21,2585 JV The Hague, The Netherlandstel. 31 (0)70 352 3334, fax 31 (0)70 351 2654telex 31102 (dune nl)

Place: SingaporeDate: January 15-19, 1996Venue: Concorde Hotel

In cooperation with the National University of Singapore(NUS) and the Applied Research Corporation (ARC),International Association of Dredging Companies ispleased to organise, for the second consecutive year,an intensive, one-week seminar on dredging and recla-mation. Last January’s course met with such enthu-siastic response, that IADC, building on this success,has decided to present this seminar again in 1996. Thecourse will be held at the Concorde Hotel, Singapore. The costs are US$ 2650, which includes six nightsaccommodation at the Concorde Hotel, breakfast andlunch daily, one special participants dinner, and a gener-al insurance for the week.

The seminar includes workshops and a site visit to adredging project. Highlights of the programme are:

International Seminar onDredging and Reclamation

(please print)

Name ..........................................................................................................................................................................

Title ..........................................................................................................................................................................

Company ..........................................................................................................................................................................

Address ..........................................................................................................................................................................

..........................................................................................................................................................................

Tel. ................................................................................... Fax ...............................................................................

Signature ..........................................................................................................................................................................

Do not send payment with this form. Upon receipt of this form, we will send you further detailed informationabout the seminar, final registration forms and an invoice for the correct amount.

AfricaBoskalis Togo Sarl., Lomé, TogoBoskalis Westminster Cameroun Sarl., Douala, CamerounDredging and Construction Finance NV, Libreville, GabonDredging International Services Nigeria Ltd., Lagos, NigeriaHAM Dredging (Nigeria) Ltd., Ikeja, NigeriaNigerian Dredging and Marine Ltd., Apapa, NigeriaWestminster Dredging Nigeria Ltd., Lagos, NigeriaZinkcon Nigeria Ltd., Lagos, Nigeria

The AmericasACZ Marine Contractors Ltd., Brampton, Ont., CanadaBeaver Dredging Company Ltd., Calgary, Alta., CanadaGulf Coast Trailing Company, New Orleans, LA, USAHAM Miami Office, Miami, Florida, USAObras Portuarias de Coatzacoalcos SA de CV., Coatzalcoalcos, MexicoStuyvesant Dredging Company, Metairie, LA, USAUscodi, Wilmington, DE, USA

AsiaBallast Nedam Malaysia Ltd., Kuala Lumpur, MalaysiaBallast Nedam Dredging, Hong Kong Branch, Hong KongBoskalis International BV., Hong KongBoskalis International Far East, SingaporeBoskalis Taiwan Ltd., Hualien, TaiwanDredging International N.V., Hong KongDredging International N.V., SingaporeFar East Dredging Ltd., Hong KongHAM Bangladesh Office, Dhaka, BangladeshHAM Hong Kong Branch, Wanchai, Hong KongHAM Singapore Branch, SingaporeHAM Taiwan Office, Taipei, TaiwanHAM Thai Ltd., Bangkok, ThailandJan De Nul Singapore Pte. Ltd., SingaporePT Penkonindo, Jakarta, IndonesiaTideway DI Sdn. Bhd., Selangor, MalaysiaVan Oord ACZ B.V., Hong KongVan Oord ACZ B.V., SingaporeZinkcon Marine Malaysia Sdn. Bhd., Kuala Lumpur, MalaysiaZinkcon Marine Singapore Pte. Ltd., Singapore

Middle EastBoskalis Westminster Al Rushaid Ltd., Dhahran, Saudi ArabiaBoskalis Westminster M.E. Ltd., Abu Dhabi, UAEDredging International N.V., Middle East, DubaiDredging International N.V., Tehran Branch, Tehran, IranGulf Cobla (Limited Liability Company), DubaiHAM Dredging Company, Abu Dhabi, UAEHAM Saudi Arabia Ltd., Jeddah, Saudi ArabiaJan De Nul Dredging, Abu Dhabi, UAEVan Oord ACZ Overseas BV., Abu Dhabi, UAE

AustraliaCondreco Pty. Ltd., Sydney, NSW, AustraliaDredeco Pty. Ltd., Bulimba, QUE., AustraliaJan De Nul Australia Pty. Ltd., Brisbane, QUE., AustraliaNew Zealand Dredging & General Works Ltd., WellingtonVan Oord ACZ B.V., Victoria, AustraliaWestHam Dredging Co. Pty. Ltd., Sydney, NSW, Australia

EuropeACZ Ingeniører & Entreprenører A/S, Copenhagen, DenmarkAlmagià S.p.A., Rome, ItalyAnglo-Dutch Dredging Company Ltd., Beaconsfield,United KingdomA/S Jebsens ACZ, Bergen, Norway

Atlantique Dragage S.A., Nanterre, FranceBaggermaatschappij Boskalis B.V., Papendrecht, NetherlandsBaggermaatschappij Breejenbout B.V., Rotterdam, NetherlandsBallast Nassbaggergesellschaft, Hamburg, GermanyBallast Nedam Dredging, Zeist, NetherlandsBallast Nedam Dragage, Paris, FranceBoskalis Dolman B.V., Dordrecht, NetherlandsBoskalis International B.V., Papendrecht, NetherlandsBoskalis Oosterwijk B.V., Rotterdam, NetherlandsBoskalis Westminster Aannemers N.V., Antwerp, BelgiumBoskalis Westminster Dredging B.V., Papendrecht, NetherlandsBoskalis Westminster Dredging & Contracting Ltd., CyprusBoskalis Zinkcon B.V., Papendrecht, NetherlandsBrewaba Wasserbaugesellschaft Bremen mbH, Bremen, GermanyCEI, Bagger- en Grondwerken, Zele, BelgiumDelta G.m.b.H., Bremen, GermanyD.O.S. Dredging Company Ltd., Greenock, United KingdomDraflumar SA., Neuville Les Dieppe, FranceDragados y Construcciones S.A., Madrid, SpainDragomar International AG., Vaduz, LiechtensteinDragomar SpA., Rome ItalyDravo S.A., Madrid, SpainDredging International N.V., Madrid, SpainDredging International N.V., Zwijndrecht, BelgiumDredging International Scandinavia NS, Copenhagen, DenmarkDredging International (UK), Ltd., Weybridge, United KingdomEnka-Boskalis, Istanbul, TurkeyEspadraga, Los Alcázares (Murcia), SpainHAM Dredging Danmark Aps, Korsør, DenmarkHAM Dredging Ltd., Camberley, United KingdomHAM, dredging and marine contractors, Capelle a/d IJssel,NetherlandsHAM-Van Oord Werkendam B.V., Werkendam, NetherlandsHeinrich Hirdes G.m.b.H., Hamburg, GermanyHolland Dredging Company, Hardinxveld, NetherlandsHolland Dredging Iberica S.L., Tarragona, SpainHolland Dredging Co. (Irl.) Ltd., Cork, IrelandHolland Dredging Co. (U.K.) Ltd., Farnham, United KingdomImpresa SIDER SpA., Rome, ItalyJan De Nul N.V., Aalst, BelgiumJan De Nul Dredging N.V., Aalst, BelgiumJan De Nul (U.K.) Ltd., Ascot, United KingdomNordsee Nassbagger- und Tiefbau GmbH, Wilhelmshaven,GermanyN.V. Baggerwerken Decloedt & Zoon, Brussels, BelgiumPhilipp Holzmann Aktiengesellschaft, Hamburg, GermanyS.A. Overseas Decloedt & Fils, Brussels, BelgiumSkanska Dredging AB, Gothenborg, SwedenSociedade Portuguesa de Dragagens Lda., Lisbon, PortugalSociedad Española de Dragados SA., Madrid, SpainSocietà Italiana Dragaggi SpA. “SIDRA”, Rome, ItalySociété de Dragage Holland (France) S.A., Bondues, FranceSociété de Dragage International “S.D.I.” S.A., Marly le Roi, FranceSodranord Sarl, Paris, FranceTideway B.V., Breda, NetherlandsVan Oord ACZ B.V., Gorinchem, NetherlandsVan Oord ACZ Ltd., Newbury, United KingdomVan Oord ACZ B.V., Zwijndrecht, BelgiumVolker Stevin Baggermaatschappij Nederland B.V.,Rotterdam,NetherlandsVolker Stevin Dredging B.V., Rotterdam, NetherlandsWasserbau ACZ GmbH, Bremen, GermanyWestminster Dredging Co. Ltd., Fareham, United KingdomZanen Verstoep B.V., Papendrecht, NetherlandsZinkcon Contractors Ltd., Fareham, United KingdomZinkcon Dekker B.V., Rotterdam, NetherlandsZinkcon Dekker Wasserbau GmbH, Bremen, Germany

Membership List IADC 1995Through their regional branches or through representatives, members of IADC operate directly at all locations worldwide.

INTERNATIONAL ASSOCIATION OF DREDGING COMPANIESDuinweg 21 - 2585 JV The Hague - The Netherlands

international association of dredging companies...a particular project, we haven’t the time nor...

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