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SPECIAL EDITION OF THE DUTCH SCIENTIFIC JOURNAL – MAY 2010

11TH International Geotechnical Challenges Conference in Urban Regeneration

Model ‘forecasts’ design feasibility better than guidelines

Voorbij MV piles into Europe

Terracon ‘Quality is the foundation’

Jetgroutstrut prevents deformation diaphragm-wall

Large diameter cased piles and vibrated VM piles

High Speed Piles for foundations of steel fibre-reinforced concrete floors

Self Installing Platforms and Wind Turbines

A2 Maastricht Tunnel: Geotechnical Risk Analysis

May 26th –28th, 2010 – ExCeL – London


Colophon

Scientific Journal Geotechniek SPECIAL: 11th International Conference Geotechnical Challanges In Urban Regeneration May 26th - 28th, 2010 ExCeL - London Publication Uitgeverij Educom BV Mathenesserlaan 347 3023 GB Rotterdam – The Netherlands Tel. +31(10) 425 6544 E-mail info@uitgeverijeducom.nl www.uitgeverijeducom.nl Publisher Robert Diederiks Editorial Board Alboom, ir. G. van Barends, prof. dr. ir. F.B.J. Brassinga, ing. H.E. Brinkgreve, dr. ir. R.B.J. Brok, ing. C.A.J.M. Brouwer, ir. J.W.R. Calster, ir. P. van Cools, ir. P.M.C.B.M. Dalen, ir. J.H. van Deen, dr. J.K. van Diederiks, R.P.H. Eijgenraam, ir. A.A. Graaf, ing. H.C. van de Haasnoot, ir. J.K. Jonker, ing. A. Kant, ing. M. de Korff, mw. ir. M. Lange, drs. G. de Mathijssen, ir. F.A.J.M. Schippers, ing. R.J. Schouten, ir. C.P. Seters, ir. A.J. van Smienk, ing. E. Steenbrink, ing. R. Storteboom, O. Thooft, dr. ir. K. Vos, mw. ir. M. de Waal, van der Wibbens, G. Editing Brassinga, ing. H.E. Brouwer, ir. J.W.R. Diederiks, R.P.H. Kant, ing. M. de Korff, mw. ir. M. Thooft, dr. ir. K. © Copyright Uitgeverij Educom BV - May 2010 © ISSN 1386 - 2758


Preface For centuries, the Dutch have dealt with foundation issues as a result of the soft soil conditions which are typical for a delta area. Piled foundations, especially in the Western part of The Netherlands, are used since the 15th century. Even from a very young age, the Dutch are all used to the sound of pile hammering when a new structure has to be erected. The map shows an overview of piled foundations throughout The Netherlands (from 1984), as a percentage of all foundations, including the average pile length. In urban centers like Rotterdam and Amsterdam, almost all structures have a piled foundation. On the other hand, The Netherlands shows a diversity in soil conditions. In the southern part, see the article about the A2 project Maastricht, the geotechnical issues are of a totally different kind when compared to the soft soil conditions described above. In this case, a tunnel will be constructed in a subsurface (consisting of e.g. fractured lime stone) which isvery unusual in the Netherlands. As The Netherlands develops to be one of the most densely populated countries of the World (currently 26th on the list – source: Wikipedia), the complexity of building projects grows, especially in urban areas. This special edition of ‘Geotechniek’ is linked to the Deep Foundation Institute conference and shows some examples of the difficulties that one can encounter when building in an urban environment. But also some techniques are described when working under totally different conditions, like near- and onshore projects. Furthermore, some fine example are given of new techniques for pile installation where reduction of noise and vibration is frequently demanded, experiences with (Statnamic) pile testing and the use of soil improvement to enhance stability for deep excavations. All projects have in common that risks associated with subsoil conditions may lead to enormous failures in cost and time when not addressed properly. The use of experiences gained at other projects helps minimizing these risks. Since 1997, the periodical ‘Geotechniek’ issued by Educom Publishers, appears quarterly. Formerly only papers in the Dutch language and dealing with Dutch projects were printed. Due to the more international work field of Dutch geotechnical engineers there is a growing number of international papers in the English language. The 11th International Conference on Geotechnical Challenges in Urban Regeneration in London is an extraordinary occasion for a special edition of ‘Geotechniek’ which is facilitated by the Dutch geotechnical industry. The papers in this special edition are presented in the English language and give an overview of challenges and difficulties where Dutch geotechnical engineers nowadays have to deal with. On behalf of the editorial board of ‘Geotechniek’, Roel Brouwer, Msc. ir. J.W.R. Brouwer


Sponsors

This special edition of Geotechniek has been made possible by:

Piet Mondriaanlaan 26, 3812 GV Amersfoort P.O. Box 220, 3800 AE Amersfoort Tel. +31 (0)33 477 1000 The Netherlands www.arcadis.nl

IJzerweg 4, 8445 PK Heerenveen P.O.Box 68, 8440 AB Heerenveen The Netherlands Tel. +31 (0)513 631355 info@apvandenberg.com www.apvandenberg.com

®

Stieltjesweg 2, 2628 CK Delft The Netherlands Tel. +31 (0)88 335 7200 info@deltares.nl www.deltares.nl

Stieltjesweg 2, 2628 CK Delft The Netherlands Tel. +31 (0)88 335 7200 info@deltares.nl www.geobrain.nl

Korenmolenlaan 2, 3447 GG Woerden The Netherlands Tel. +31 (0)348 435260 www.suctionpile.com

Vierlinghstraat 17, 4251 LC Werkendam P.O.Box 49, 4250 DB Werkendam The Netherlands Tel. +31 (0)183 401311 info@terracon.nl www.terracon.nl

Springwell Road, Springwell Gateshead - Tyne & Wear NE9 7SP United Kingdom Tel. +44 (0)191 417 3545 info.vsf@volkerstevin.co.uk www.volkersteelfoundations.co.uk

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Korenmolenlaan 2, 3447 GG Woerden P.O. Box 525, 3440 AM Woerden Tel. +31 (0)348 435254 The Netherlands info@vwsg.nl www.vwsg.nl

Europalaan 16, 2408 BG Alphen a/d Rijn P.O.Box 757, 2400 AT Alphen a/d Rijn The Netherlands Tel. +31 (0)172 471798 info@smet-keller.nl www.smet-keller.nl

P.O.Box 54548, 3008 KA Rotterdam The Netherlands Tel. +31 (0)10 2992288 info@vsf.nl www.vsf.nl

Siciliëweg 61, 1045 AX Amsterdam P.O. Box 20701, 1001 NS Amsterdam The Netherlands Tel. +31 (0)20 4077100 marketing@voorbijfunderingstechniek.nl www.voorbijfunderingstechniek.nl www.voton-hsp.com


Contents

1

Preface

2

Sponsors

4

Model ‘forecasts’ design feasibility better than guidelines Thomas Bles Deltares

6

Voorbij MV piles into Europe Carlo van Klarenbosch Voorbij Funderingstechniek

8

Terracon ‘Quality is the foundation’ Sikko Doornbos Terracon Piling Companies

10

Jetgroutstrut prevents deformation diaphragm-wall Henk Dekker Smet-Keller Funderingstechnieken VOF Rob M. van der Ploeg Projectbureau Noord/Zuidlijn Patrick van Holten Combinatie Strukton Betonbouw / Van Oord

14

Large diameter cased piles and vibrated VM piles Erwin de Jong VWS Geotechniek BV Chris England VolkerSteel Foundations Ltd. Laurent van Mansfeld Volker Staal en Funderingen BV

18

High Speed Piles for foundations of steel fibre-reinforced concrete floors Håkan Bredenberg Bredenberg Teknik Peter Oscarsson AB Consila

20

Self Installing Platforms and Wind Turbines Mark Riemers SPT Offshore

22

A2 Maastricht Tunnel: Geotechnical Risk Analysis Paulien Kouwenberg Arcadis Bjorn Vink A2 Projectbureau

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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Thomas J. Bles MSc Deltares

Summary In addition to the well-known database, GeoBrain Foundation Technics also has a forecasting model. Making use of expert knowledge and 2,400 practical experiences, the model is able to provide a judgment about feasibility and the risk of damage. The model for sheet piling has recently been positively validated. It seems that it can indeed help designers improve designs. Use of the tool is now

Positive validation of GeoBrain Foundation Technics forecasting model

on the rise. ‘Principals will increasingly insist that designers use this type of practical tool.’ Figure 1 Precast concrete tension piles in a deep excavation.

Model ‘forecasts’ design feasibility better than guidelines Until recently, construction knowledge was mainly in the heads of people. GeoBrain Foundation Technics (GBF) enables this specialist know-how to be accessed centrally, in a structured way. GBF now contains some 2,400 ‘experiences’. And the number increases daily. More and more designers draw on the knowledge of this ‘collective brain’ each day via Internet. As a result, construction problems can be prevented: the failure costs fall, the quality increases.

Milestone The recent positive evaluation of the GBF forecasting model is an important milestone in the tool’s development. Annemieke Mens MSc (TU Delft) validated the model as part of her doctoral research into the application of artificial intelligence in foundation technology in order to reduce failure costs. “A designer can indeed use the GBF model to make a more accurate forecast of

the risk of failure while executing the foundation design than with the current formulas in the Dutch CUR design guideline 166. Validating the model was more problematic than originally thought. The accuracy of negative forecasts in particular is difficult to control. The likelihood that they are actually executed is small.’ GBF was developed to improve the quality of foundations, says Thomas Bles MSc, project leader of GeoBrain Foundation Technics at Deltares: ‘A great deal still goes wrong during construction. Some 13 per cent of all sheet piling experiences in the database are described as ‘poor’. This figure even rises to 20 percent when sheet piles longer than 20 metres are used. And construction using precast piles is evaluated as poor in 8 percent of cases. These problems not only lead to extra costs, but result in serious delays and damage to reputations as well. The most important reason is that insufficient consideration is

Figure 2 A typical Dutch deep excavation (Delft).

Figure 3 Example of construction risk when driving a sheet pile.

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given to feasibility during the design phase. Most problems can easily be prevented by making use of available construction knowledge in the design. GBF provides access to this knowledge. The amount of knowledge from hundreds of experts is simply larger than that of just one. That’s the thinking behind GeoBrain.’

‘Missing link’ Links to design software MSheet and MFoundation have recently been introduced. With ‘a single click of the button’, designers can see an overview of similar experiences and the forecasting model gives insight into the risk profile. It then becomes very easy to complete the design by carrying out a feasibility check. An interactive link has been made between the design software and the Internet application in order to improve accessibility to the information. More and more designers and foundation specia-


lists are discovering the advantages of the ‘missing link’ that GBF actually is. The majority of top-10 engineering consultancies in The Netherlands, such as Arcadis, Oranjewoud and Witteveen+Bos now use GBF. And increasingly larger numbers of specialised construction companies are also working with the tool. A study by the EIB (Economic Institute for the Construction Industry) shows that GBF can lead to savings in direct costs: it is expected that the gain from reducing delays, claims, and damage to reputation is much greater. Nonetheless, the economic value has not been the deciding factor up to now. The most important obstacle to its use has been the segmentation of the construction industry. Bles: ‘Designers have little contact with foundation construction companies. The principal or main contractor often sit in between. As a result, it’s not always obvious which problems play a role. In the worst case, those involved often hide behind their own responsibility. Construction risks are often incorrectly pushed along to the construction phase, although they can in fact be managed effectively in the design phase.’

New types of contract An important stimulus behind the current commotion is the introduction of new, integrated forms of contracts. This is also the opinion of Peter Schouten MSc, geotechnical specialist at Arcadis. ‘Timely understanding of the risks therefore becomes more important. This has also meant a greater need to carefully consider the feasibility of designs. GBF is ideally suited to

Figure 4 Example of construction risk when driving a precast pile.

‘It should be standard practice to check the feasibility for each design. We often estimate this based on our own experience. It’s far better though to make use of earlier experience, particularly in the case of complex projects. In this respect, the Geobrain Foundation Technics database is an important source we can use, for example to analyse the feasibility of piling.’ – Brenda Berkhout MSc, senior geotechnical consultant, Witteveen+Bos ‘Imagine that I’m considering the use of sheet piling, and then search the database for similar situations and find out what the experiences were in those cases. I can easily evaluate the feasibility of different variations using a single method.’ – Peter Schouten MSc, geotechnical specialist at Arcadis

quickly give a picture of the risks involved, and to obtain information about feasibility.’ Principals also now see the value of GBF, says Bles: ‘Certainly in complex projects, there are not only delays and costs to consider but loss of prestige and damage to reputations as well. Local governments in particular do everything possible to prevent this. Nobody wants their name associated with a “Schouwburg Middelburg”.’ He expects that principals will increasingly demand that designers use tools such as GBF. Your story for the principal becomes much more difficult if you later have to admit that you’ve not made use of that knowledge.’ And finally, insurers see the benefits too, according to Alfa Falconi MSc, risk expert for construction projects at Achmea Insurance. ‘We advise our clients, especially municipalities, water boards, and provinces, to take the performance of building contractors and engineering consultancies into account when contracting out construction projects. A great deal can go wrong with sheet piling, for example. GBF is a good tool for estimating the risks.’

Thomas Bles MSc: ‘That’s the great thing about a learning system. It becomes “smarter” and more valuable with every new experience. Or in other words: engineers can develop better, smarter foundation designs. The designer will always remain central in this. We try to help by developing better tools.’ Click on www.geobrain.nl if you would like more information. If you wish to use GBF, you can also request a user name and password here. An English language version is available, although it should be noted that the experiences are from The Netherlands and Belgium. Parties from abroad who are interested in developing their own version should contact Thomas Bles MSc (thomas.bles@deltares.nl). 

Principal

Designer

Main contractor

Sub-contractor

GeoBrain Foundation Technics has become a basic tool for designers. It will never replace them, however. And it is also never ‘finished.

Figure 5 Forecasting.

Figure 6 Position of GeoBrain in the construction process.

Figure 7 Map in experiences database. It is possible to search with a map in the experiences database.

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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Carlo van Klarenbosch Managing Director Voorbij Funderingstechniek

Summary Voorbij Funderingstechniek (Amsterdam the Netherlands) specializes in foundation work of all kinds and is leading in the supply of bearing capacity for infrastructure, residential, and nonresidential applications. We offer our clients solutions for the challenges they face. Our earth and water retaining steel structures are frequently used in construction pits, underground car parks, quay walls and cofferdams. Our approach is to identify the best technical and commercial solutions in consultation with our customers. This partnership is the basis for creative and innovative solutions with a no-nonsense approach.

Figure 1 E-ON MPP3 Rotterdam (NL).

Voorbij piles drive into Europe Innovative solutions – No-nonsense approach We have many decades of experience in soil mechanics and foundation engineering. Together with you, our qualified staff can provide a comprehensive solution including design, project management and execution. For this we can utilize our extensive and modern equipment fleet. We have our own vessels for water-based works.

Using our domestic market as a starting point, we carry out projects all over the world on a project basis, first and foremost when special skills are required.

Figure 2 Quay wall Scaldia harbour Flushing (NL).

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

mv pile steel sheet pile  combi wall 

Our services Our products







 

Voorbij Funderingstechniek is part of TBI Infra, a collection of companies belonging to TBI Holdings in Rotterdam (the Netherlands). The company has over 100 employees and a turnover of approximately € 40 million.



    

precast prestressed pile vibro pile combi pile High Speed Pile fluïdization pile Displacement Screw Pile Displacement Vibration Pile anchor pile

engineering cofferdam  construction pit  quay wall For more information on our company, products and services: www.voorbijfunderingstechniek.com

Figure 3 MV piles quay wall Antwerp (B).


Figure 4 MV piles quay wall Antwerp (B).

Figure 5 Cofferdam Balearic Gas pipeline, Denia (Esp).

Below a selection of two projects which are representative for our company.

Figure 6 Cofferdam Nord Stream pipeline, Greifswald (Deu).

Voorbij MV piles for Antwerp quay wall Voorbij Funderingstechniek was awarded a contract by Van Laere N.V. to install 262 MV piles for the ‘Kaaimuur kanaaldok B2’ project, for approximately 850 metres of quay wall in Antwerp. The project started July 2009. We have used our own vessels for installation of the MV piles. H-section beams with grout injection were used for the MV piles. They have been tested with an ultimate load of 505 ton whereas the service load is 350 ton. We have finished this project before end of 2009. This project was the third quay wall in a row in which we installed MV piles. In 2008 – 2009 we installed MV piles using tubular elements in the first two projects in Flushing and Moerdijk industrial area (both in the Netherlands). Location Principal Main contractor Execution period Activities

Antwerpen Gemeentelijk Havenbedrijf Antwerpen Van Laere N.V. 2009 MV-piles

Cofferdam construction in Denia, Spain The Spanish government approved the Balearic Gas pipeline project in 2003. The objective was to construct a pipeline linking the Mediterranean Balearic islands, which include Ibiza and Mallorca, with the Spanish mainland. This will provide a connection with the Spanish, and therefore with the European, gas distribution

networks. The pipeline leaves the mainland at Denia and makes landfall in Ibiza, from where a link to Mallorca is made. Location Principal Contracting consortium Subcontractor for dredging and pipeline Execution period Activities

Denia Enegas

that had already been completed. The sheet piles with approximately 10 metre elements were of Spanish origin and supplied by the client. Boskalis Offshore contacted Voorbij following a previous partnership in a similar cofferdam construction from Callantsoog beach in 2006 (Balgzand Bacton pipeline (BBL)).

Saipem – FCC Construction Boskalis b.v. - Tideway January - March 2009 Building and dismantling cofferdam construction

Voorbij Funderingstechniek was engaged by Boskalis for the temporary cofferdam construction for the pipeline landfall at Denia. Voorbij was awarded the contract on 20 December 2008, and started work on 12 January 2009 after an extremely brief mobilization. The cofferdam construction was 140 metres long. No auxiliary construction was used, as the machine ‘proceeded over its own work’ – working from the cofferdam

The cofferdam was completed in February and Voorbij then worked with the client on the strutting frame. 25 February 2009 saw the ‘pipe pull’, when the pipeline was drawn ashore. The pipe-line was then covered with sand and Voorbij dismantled the cofferdam construction in March 2009. This project was yet another fine example of teamwork between dredging companies and a foundation partner that they can rely on. Currently we are working on a cofferdam construction for the Nord Straem pipeline landfall at Greifswald (Germany). We have been awarded this project by Boskalis Rhode Nilsson J.V. (Figure 6) 

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

7


Sikko Doornbos Managing Director Terracon Piling Companies

Summary Terracon is an expert in the field of special foundations, both driven and drilled systems and has extensive know-how, geotechnical engineering capacity, modern equipment but most of all motivated staff and crews to its disposal. The highest priority is given to safety and quality. Terracon operates mainly throughout the Benelux-countries (HQ in the Netherlands) and Germany (subsidiary in Berlin), but has executed piling works for large industrial projects on a hit-and-run basis in Finland, Poland, France, England, Scotland, Portugal, Hungary and even on Sri Lanka and Aruba. All of Terracon’s staff and key personnel are multilingual which enables them to work throughout Europe and with international

Figure 1 Foundation systems till 40 mtrs.

clients. Terracon is able to offer and execute a great number of foundation systems from 4 to 40 m in length!

Terracon ‘Quality is the foundation’ Driven pile systems: Vibro piles, Terra-combi-piles and Tension piles The Vibro pile is a driven cast in situ driven pile which is mainly in the heavier sizes compatible and competitive with a precast concrete pile. If pile lengths are unknown or unsure and a client cannot wait for the production and curing time of the precast piles, Vibro piles can not only offer a solution but also maximum flexibility during the actual execution of the piling works. Furthermore there is no chance for damaging the piles during driving if heavier and more dense layers have to be penetrated. In those cases where pile point levels vary

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

strongly the cast in situ pile provides an excellent solution for piles from 4 to 40 m. Terracon owns technically advanced equipment, like hydraulic Junttan and IHC S-90 type hammers which are friendly for the environment as they produce no exhaust. If necessary, a noise reduction sleeve can be mounted around the casing and the hammer. The whole pile driving process is monitored by computer for further analysis. The Vibro-combi pile is a Vibro-pile with a prestressed and precast core suitable to take tensile

and uplift forces. The Terra-combi pile consists of a prefab prestressed concrete core which is surrounded with grout in the layers where positive skin friction is expected. In the softer upper layers, the pile shaft is covered with bentonite to reduce negative skin friction. MV-tension-piles are applied for example for foundations for overhead transmission lines, quay walls, docks, basements, windmill foundations etc.The piles are steel tubes or H-beams which are surrounded with grout during the driving or drilling procedure. Bearing capacities are granted from 500 kN up


to 2,500 kN. Pile diameters up to Ø 2,200 mm have been installed.

Vibration free pile systems: Terr-Econ-piles The Terr-Econ-pile is a vibration free installed, full-displacement type of pile, mainly used near adjacent constructions in urban areas or in industrial sites with existing installation in operation. Terracon applies drill tables, which have a high torque. Even if high soil resistances have to be passed, the high torque combined with a vertical pressure on the casing (pulldown) cause a minimum amount of spoil. This silent and vibration free pile system can be executed with a retrievable casing or with a permanent casing Terracon has developed the vibration free installed, prefabricated Terra-Son-pile. The prefab pre-stressed concrete core is surrounded by grout in the layers which offer positive skin friction. By using a high grade concrete for the prefab shaft and combining this with a grout cover under high pressure a system can be offered which has a high quality and is attractive for the environment. 

Figure 2 Vibro-piles, installed with a noise reduction sleeve.

Figure 3 Bored displacement piles.

Terracon designs and executes:

Terracon is also able to offer and execute:



Vibro-piles



Diaphragm walls



Vibro- combi-piles



Secant pile walls



Tension-piles (MV-piles)



Slurry walls



Terr-Econ-piles



Jet grouting



Terra-Son-piles



Piling in limited headroom and space



Fundex- and Tubex-piles



Micro piles and soil anchors



Precast piles



Freezing of soils and soil injections



Sheet piles and combi-walls



Static pile load tests

For activities in the Benelux: Terracon Funderingstechniek B.V.

For our activities in Germany: Terracon Spezialtiefbau GmbH

Outside Benelux and Germany: Terracon International B.V.

P.O. Box 49 4250 DA Werkendam The Netherlands

Tietzstraße 25 D-13509 Berlin Germany

P.O. Box 49 4250 DA Werkendam The Netherlands

Tel. +31.183.401311 Fax +31.183.403583 info@terracon.nl www.terracon.nl

Tel. +49.3041744233 Fax +49.30417442344 info@terracon.nl www.terracon-piling -contractors.com

Tel. +31.183.403529 Fax +31.183.403583 info@terracon.nl www.terracon.nl

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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Henk Dekker Smet-Keller Funderingstechnieken VOF

Rob M. van der Ploeg Projectbureau Noord/Zuidlijn

Patrick van Holten Combinatie Strukton Betonbouw / Van Oord

Summary In order to limit the amount of steel struts in the excavation, a jet grout strut was designed and executed. Just beneath the excavation level a 1 to 3 m thick grout layer resists the horizontal forces to limit deformation of the diaphragm wall. Excessive diameter measurements as well Figure 1 Grouting rigs of Smet-Keller in action. Photo Smet-Keller.

as compressive strength tests have been performed to assure that the design requirements have been met.

Jet grout strut prevents deformation diaphragm-wall Introduction Just in front of the Central Station of Amsterdam, a large excavation was needed, to connect the existing East-metro connection with the new North-South connection. This building pit, roughly 3000 m2 has been build with diaphragm walls of 30 to 60 m length and has been excavated in the dry. In the early stages, 5 layers of concrete struts were planned to prevent the wall from to much deformation. During the contracting phase, these have been replaced by two concrete struts and a jet grout strut, just below the excavation (see figure 2).

Design of the jet grout strut The design and tender documents did not prescribe a specific diameter. The layout of the grout strut should be designed with 5% opening to prevent water pressure building up. The minimum thickness of the grout strut was 1,0 m in the middle, 2,0 m near the diaphragm wall and 3,0 m around some of the steel piles (see figure 3). The layout of the individual jet grout columns was designed by the subcontractor and afterwards approved by the client. In principle a triangular grid was adapted which allowed an average

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

inclination of 0,5 degrees and a minimum overlap of 10 cm. Due to several causes the demand was not met and a smaller grid was required. Furthermore, old sheet piles, old structures, the new piles and a former trial pit had to be taken into account (see figure 4).

Before starting the execution, three trial columns were executed. After fine tuning of the parameters, the third column was perfect.

Column production

Jetgrouting with the DS-system.

Because all traffic at street level should proceed without any blockages, the whole building pit was divided in three parts. After the works of one part was finished (diaphragm wall, piles, grout strut und concrete slab) all traffic was diverted and the whole operation started again. The actual column production started in May 2007 where the last column was finished in October 2008. In total 521 columns were produced.

Jetgrouting is a cement soil stabilisation and applicable in all kinds of soils. With the aid of high pressure cutting jets, the borehole is eroded with the cement suspension. The erosion capability can be enlarged by shrouding the jet with air. In this case Smet-Keller used the DS-system which uses the energy more efficient and allows bigger diameter. This enabled it to use a diameter of 3,2 m which limited the amount of columns drastically. The columns were made in two stages, first cutting the diameter (and measuring it) and afterwards increasing the cement content.

The grouting was performed with two tall rigs which could drill the maximum depth of 26 m in one time (see figure 1). Because of the number of return spoil, two large spoil silos were installed, enabling regular concrete trucks to transport the spoil to an especially prepared site. The silos served as temporary storage facility and limited the interference of traffic problems. The sequence of the columns was determined by two requirements: in a virgin area, at least two

The design value of the compressive strength was 4,5 N/mm2 and was negotiated to an average value of 10 N/mm2. The desired E-modulus was 2500 MPa and both values to be reached after 28 days.


Figure 3 Cross-section over the jet grout strut.

Figure 2 Plaxis cross-section over the diaphragm wall.

Figure 4 Top view of as-built (partly).

columns should be left before the next column could be grouted on the same day. After a column was over 24 hours old, columns on the opposite side could be grouted on the same day.

Diameter measurements During the execution of the so called Sandwich wall (another part of the same project) beneath the Central Station, extensive experience was built up with measuring diameter at large depth (see [1]). For this project, a new challenge was found in the diameter of 3,2 m. The device is screwed on the drilling rig and lowered to the desired depth. The first step is hydraulically opening both arms, like an umbrella. After the full opening of the arms, which was afterwards verified by checking a damaged plastic bolt, both arms where enlarged, like a telescope (see figure 6). The values of the measurements where drawn in a diagram and compared with the calibration of the device, before and after the measurement. In total 38 measurements where successfully executed.

Compressive strength One of the main issues during execution was the

Figure 5 Overview of the building site. Photo Projectbureau Noord/Zuidlijn.

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

11


quality of the grout itself. This was done by performing triple core drillings, which enables getting perfect samples for testing and gives a perfect view through the column itself. The drillings were performed both in the hart of the column and at 1/3 of the radius. Representatives of the clients would choose the desired samples on which unconfined compressive strength tests were performed. In total 30 core drillings and over 200 tests were performed. The average value of all tests landed just over the desired value.

Further quality control Further quality control consisted of the measurement of the inclination of the drilling with a mobile inclinometer (218 measurements), the monitoring (100 %) + sampling (~1 %) of the fresh grout and

the monitoring (100 %) + sampling (~5 %) of the return spoil. Because not every column could be measured or core drilled to prove the diameter or strength, it was inevitable to show the client all production details. In this way birth certificate of a measured column nearby could be compared with the actual column. In case of an anomaly or, for example, a large inclination, appropriate measures were taken.

Conclusions

Behaviour during excavation

Reference

During the excavation excessive deformation measurements have been executed. The measured deformations are less than calculated because the soil reacted stiffer, creep effects are incorporated in the calculation but not yet measured and three dimensional effects were not taken into account in the calculation.

[1] Langhorst O.S., Schat B.J., Wit J.C.W.M. de, Bogaards P.J., Essler R.D., Maertens J., Obladen B.K.J., Bosma C.F., Sleuwaegen Y.J. and Dekker H., Design and validation of jetgrouting for the Amsterdam Central Station, Geotechniek ECSMG in Madrid 2007.

Figure 6 Calibration of the diametermeasurement device. Photo Smet-Keller.

Figure 7 Cores made by triple core drilling.

Figure 8 Deformations during excavation.

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

Despite the large depths, a jet grout strut was successfully executed and measurements have shown that the design requirements have been met. Both the column diameters of 3,2 m and the strength reached the desired values. Deformation measurements showed that the calculated values were on the conservative side. The application of a grout strut proved to be a valuable addition to this building pit.


Erwin de Jong General Manager VWS Geotechniek BV

Chris England VolkerSteel Foundations Ltd.

Laurent van Mansfeld Volker Staal en Funderingen BV

Summary

VolkerWessels: we present solutions for every geotechnical challenge

VolkerWessels is a close-knit group of companies, working in construction and related fields. Its 100 operating companies trade as independent entities with their own profit and market responsibility. VolkerWessels has a turnover in excess of € 4.4 billion (2009). The operating companies form part of a strong internal network, within which they cooperate in the areas of business development, staff development and communications. Both in the UK and the Netherlands VolkerWessels has operating companies in the field of foundation construction and engineering. These companies operate worldwide and are capable of fulfilling all your construction requirements when dealing with challenging ground conditions. This paper will present both general information of our companies and some of the special techniques that are available from VolkerSteel Foundations Ltd., Volker Staal en Funderingen B.V. and VolkerWessels Stevin Geotechniek B.V., all part of the VolkerWessels group. At the 11th DFI conference VolkerWessels will present two papers about the foundation techniques that the companies have developed, executed and tested in recent years. The introduction of large diameter cased piles and vibrated VM piles has been a success in the Netherlands and we consider these techniques to be interesting for the UK market as well.

Figure 1 Floating barge with piling equipment.

Large diameter bored casing piles The railway extension project between three major Dutch cities, The Hague, Rotterdam and Utrecht, was commissioned by the Dutch railway authority, Prorail, in 2005. Near the city of Utrecht the extension includes the construction of a new embankment for four railroad tracks and a total of 20 new railway viaducts. These viaducts will provide a safe passage for the people living in the new residential area of Leidsche Rijn.

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

In the original client design all bridges had piled foundations. The foundations of abutments and footings consisted of thick concrete slabs with a large number of driven prefabricated concrete piles, which are commonly used in the Netherlands. Since the bridges themselves were supported by columns of 1.2m in diameter an alternative design was made to use bored casing piles with a diameter of 1.65m, one pile below each column. Instead of using 80 prefabricated concrete piles, columns could be constructed on

six of these casing piles. Also the heavy concrete slab (for which dewatering and additional temporary facilities were necessary) could be omitted. The alternative foundation had to meet strict client requirements. The piles have a design pile load of 12.000kN, but should also have a vertical deformation less than 10mm during train passage. Since bored piles normally have a flexible loaddisplacement behaviour, it was deemed necessary to equip the piles with a grouting device at the pile tip.


The casing piles were bored without a stabilising fluid such as bentonite. During drilling and removing the ground inside the casing, it was therefore essential that a higher water level was maintained in the casing than the actual groundwater head at the pile tip. To minimise the risk of disruption of the ground at the pile tip the piles were equipped with a grouting device that was injected after hardening of the concrete of the piles. By filling the grouting device under high pressure it was possible to pre-stress the pile tip (and hence the entire pile) to guarantee a stiffer load-settlement behaviour. The execution method of the bored casing piles is presented in figure 2. The use of bored, large diameter casing piles with base grouting, was a first time application in the Netherlands. Therefore it was decided to use Cone Penetration Tests (CPT’s) as a way of checking the influence of the installation of the pile on the surrounding soil. A total of three piles were instrumented and tested on site by means of a static load suitability test and the deformations of all piles were monitored during construction up to the actual completion of the works. In order to get information on the pile behaviour under even larger loads two extra piles were tested by means of a statnamic load test with a 16MN device. The statnamic load test results were interpreted according to international standards and have been analysed using numerical modelling with the finite element program Plaxis. Based on the CPT results, pile load tests (both static and statnamic) and the monitoring results of the deformations of all piles during construction, a very good understanding was reached regarding the ultimate bearing capacity and the load-settlement characteristics of these piles.

Figure 2 Pile execution method.

Vibrated VM piles Part of the North/South line metro extension in Amsterdam, the Netherlands, is the construction of the RAI - Europaplein station. This station is situated in front of the RAI complex, the most important exhibition and congress centre of the Netherlands. The metro tunnel and station were constructed in a building pit with sheet piling, underwater excavation and underwater concrete. Due to the high groundwater levels tension piles are necessary during construction. Once the station is completed a number of piles will remain in tension, while others become compression piles. The station floor is situated at 11m below

Figure 3 Pile execution.

ground level. The design pile loads vary from 1.100 kN compression load to 700 kN tension load. As a result pile tip levels varied from 28 to 31m below ground level, approximately 20 m below the bottom of the excavation. Since a stiff load-settlement behaviour of the piles was required by the design, both in tension and compression, and the impact on the RAI congress centre should be as minimal as possible,

Figure 4 16 MN Statnamic load test.

the client decided to use Rüttel-Injectionspfahle which are commonly used in parts of Germany. These piles, that can be described as vibrated Hbeams with grout injection along the shaft, were new to Dutch foundation practise and had to be tested both prior to the installation (design investigation tests) and after installation (acceptance tests) in order to meet the demands of the building authority.

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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Cone Penetration Tests (CPTs) were carried out before and after excavation and again after installation of the piles. The piles where installed from a piling rig that was placed on a working platform on top of the sheet piles (figure 4). Six piles were monitored with strain gauges at different locations along the shaft. The continuous monitoring started directly after the underwater concrete was in place and lasted until most of the inner structure of the station was completed. The pile design was based on the results of static load tests and on the results of Cone Penetration Tests (CPTs) carried out at various stages of the works. The performance of the piles was validated by monitoring results that were obtained during construction. Subsequently the results were interpreted to increase the understanding of the behaviour of pile groups subject to

Figure 5 Piling rig.

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

tension forces. The choice for vibrated VM piles for this project proved to be an excellent one. Not only did the piles meet the construction requirements, the installation of the piles resulted in very limited noise and vibrations exposure to the surrounding municipal area. Further information on both foundation techniques can be found in the conference proceedings.

VolkerSteel Foundations is a specialist in the design, supply and installation of all forms of steel sheet and bearing piles. Our in house team make the company what it is today. All experienced construction professionals, we are passionate about our work and

our company and pride ourselves on finding tailored solutions for complex projects. Our aim is to achieve best practice in all works that we undertake, completing them to the highest quality, within time and budget constraints. We will undertake projects ranging in value from £20,000 to large scale multi-million pound contracts. We are able to offer a complete service from conceptual design through to supply and installation, using where possible our own fleet of ABI Mobilram Leader Rigs. We can also tailor make a solution to suit our clients needs which may include any of the following:  Concept design including costing  Detailed design  Construction advice  Pile supply and buy back


VolkerWessels: we present solutions for every geotechnical challenge



Pile installation – vibration free/ leader driven/ conventional  Supply and installation of associated temporary works Through association with our sister companies VWS Geotechniek and Volker Staal en Funderingen in the Netherlands we can also offer other leading edge alternative foundation techniques including soil improvement and impermeable/ low permeability cut-off walls. VolkerSteel Foundations Ltd. Springwell Road, Springwell Gateshead Tyne & Wear NE9 7SP Tel. +44 (0)191 - 417 3545 Fax +44 (0)191 - 416 2894 info.vsf@volkerstevin.co.uk www.volkersteelfoundations.co.uk Contact: Chris England General Manager

Volker Staal en Funderingen (VSF) is an innovative contractor in the Dutch foundation and steel fabrication industry, specialized in heavy and complex foundation techniques and steel structures. VSF is a subsidiary of VolkerWessels and together with its mother company Van Hattum & Blankevoort, the infrastructural expert within the Volker Wessels group. VSF is located at the Quarantaineweg in the port area of Rotterdam, located directly at the Nieuwe Waterweg. VSF services a wide range of foundation techniques varying from piling to retaining walls and soil improvement. For more detailed information you are invited to visit our website or contact us directly. A few examples of our expertise and capabilities are presented here:

Waterworks VSF has a great deal of in-house experience and expertise in floating piling techniques. Coupled with an extensive fleet of marine equipment including floating crane barges, VSF can provide a full projects service to clients including design, engineering and delivery in near or offshore waters.

Figure 5 Monitoring results pile shaft.

A wide range of structures are constructed, welded and transported from these facilities including steel bridges, jettys, suction anchors, barges and mooring dolphins. The company’s riverside location provides a wide range of transportation opportunities.

Pneumatic caissons and other air pressure techniques VSF has more then 30 years of international experience sinking all kind of structures such as cellars, bridge foundations and TBM receiving structures. Ten years ago we expanded our scope for building underground structures with air pressure facilities. One of our present projects is the excavation and the concrete works at 25 m depth for the Underground station Ceintuurbaan in the North South line in Amsterdam. VSF has its own specialized equipment and expertise available for clients and other contracting companies. Volker Staal en Funderingen B.V. P.O. Box 54548, 3008 KA Rotterdam The Netherlands info@vsf.nl www.vsf.nl Contact: Laurent van Mansfeld Manager International Operations

Steel fabrication Next to its office in Rotterdam, VSF has well equipped workshops, storage and assembly facilities for its steel fabrication business.

mechanics and foundation engineering. Moreover, it is the only company that connects theoretical knowledge directly to the know-how of construction. The office is located near the city of Utrecht. Our work focuses mainly on the Netherlands, but designs and advice are also given on regular basis for international projects. Our project engineers and consultants are employed in an efficient and flexible way for our clients. Secondment to a project location is always a possibility. Within the field of geotechnical engineering our scope is very wide. In our work we deal with almost every type of construction, technology and engineering method. By means of working at construction sites, contacts with contractors and participation in courses, committees, and international congresses, we continually raise our level of competence. Based on a solid knowledge of theory as well as actual construction, we are able to advise about risks and problems during construction. Drawing up construction plans or quotations are also services we can offer. VolkerWessels Stevin Geotechniek B.V. P.O. Box 525, 3440 AM Woerden The Netherlands info@vwsg.nl www.vwsg.nl Contact: Erwin de Jong General Manager 

VWS Geotechniek is one of the leading Dutch engineering companies in the field of soil

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

17


Håkan Bredenberg Bredenberg Teknik

Peter Oscarsson AB Consila*

Summary For warehouse buildings, a steel fibrereinforced concrete floor is often used as floor construction. Where pile foundations are required for this type of floor, the piles must be placed relatively close together, depending on the limited bending moment capacity of the floor. Close spacing of piles implies that the pile load is relatively low in most cases, e.g. in comparison with heavily loaded piles under columns and facades. This article describes a recent project where, for the foundations of a 12,000 m2 fibre-reinforced concrete floor, a type of pile was used that is new to Sweden: the Dutch Voton HSP pile (HSP = High Speed Pile).

Figure 1 Voton HSP installation.

High Speed Piles for foundations of steel fibre-reinforced concrete floors Central warehouse FMCL

Soilconditions – design with Voton HSP

The Swedish government wanted to change the basic structure of the Swedish defence into a modern operations-oriented force. This implies tougher requirements concerning controls of storage, handling and distribution of the equipment. One stage of this transformation was to build a new central warehouse (FMCL) for the Swedish Armed Forces in Arboga.

The subsoil consists of:  upper layer 1 m – 1.5 m of dry crust clay.  3 – 14 m uncompacted clay (shear resistance 10 – 20 kPa ), resting on friction material (gravel, sand), or moraine on rock.  average ground water level: 1 m below existing grade, varying appr. 0.5 m up or down depending on the season and rainfall conditions.

Project / Site supervision

AB Consila

Design

Structor AB

Geotechnical engineering

Bredenberg Teknik

After various comparisons, the decision was made to establish the lower loaded section of the fibre-reinforced floor on HSP piles. This solution had never before been used in Sweden, but there were good references from the domestic market, the Netherlands. In order to ensure the intended quality and bearing capacity, a test programme was conducted at the Arboga works site. The programme involved static test-loading as well as excavation of a number of piles after the test.

Foundation works Voton HSP Voorbij Funderingstechniek (The Netherlands) Earthworks

Skanska Sverige AB

Steel structure

Ruukki OY (Finland)

Building costs

Appr. SEK 500 million

Construction period

2007 - 2009

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

The total floor space of the FMCL is 40,000 m2. The floor is made of 200 mm fibre-reinforced concrete. The floor foundation for the cold storage area (12,000 m2) was designed with HSP piles:  diameter 180 mm  pile length 7 – 14 m  pile distance 1,20 m square grid  altogether appr. 8,000 piles  dimensioned load effect in the flexural strength state 150 kN  concrete grade C20/25.

High Speed Piles The piles can be characterised as cast in situ concrete piles. The manufacturing process is shown in figure 3. Pile production is very quick – a 10 m pile produced using the above method takes some 2 minutes. Capacity for the project in question amounted to 350 to 400 piles per 12-hour shift, compared to about 20 – 30 for


conventional pile driving. Available pile diameters: 180 mm - 220 mm and 273. Last two types in combination with reinforcing cages (upto 10 m in length). The equipment used can produce piles 25 m in length.

Verification and inspection Pump pressure, flow and other relevant production data were recorded in the computerised documentation and presentation system in the cab of the pile crane. All data were stored locally and also transmitted in real-time to the database server in the Netherlands. If there is any disruption the driver intervenes, but in normal production the processes are largely automated. Once the piles had hardened for about 2 weeks, they are inspected by means of integrity testing, to make sure no cracks or the like have occurred.

Test percentage of 10% is a standard value for this type of test. At Arboga 800 HSP piles were tested without any defective piles being found. Two piles were exposed down to a depth of some 4 m. It was noted that the surface of the piles was very smooth and appr. 20 cm in diameter (nominal 180 mm).

Test-loading As referred to above, static test loading was carried out on several HSP piles. An excavator was driven up onto a 25 mm steel plate so that the centre of gravity was directly above the jack on top of the pile. The testing up to 285 kN was carried out without any significant tendency to crumpling. Loads were applied in increments of 50 kN. Each load increment was maintained for 16 minutes, with movements recorded after 1, 4, 9 and 16 minutes. The load was removed incremen-

tally. The greatest remaining movement measured was appr. 5 mm (total station, accuracy +/- 1 mm).

Conclusion Altogether the use of Voton HSP piles can be seen as successful in this project. Besides the use as pile foundations for concrete warehouse floors, HSP piles are also used in road and railway embankments (LTP constructions) and piled raft foundations. It is therefore considered that HSP piles could be a useful method of restricting settlement and increasing the subsoil bearing capacity. Dutch contractor Voorbij Funderingstechniek, which undertook the work, has four sets of equipment for the installation of HSP piles besides some 30 conventional pile cranes.  *Peter Oscarsson has moved earlier this year to company C&M Projekt AB.

Figure 2 Test loading and over 4 m exposed HSP pile.

Figure 3 Schematic view of the installation of HSP piles (www.voton-hsp.com).

Figure 4 The machinery used consisted of a pile crane and concrete pump. Both items are on caterpillar tracks, with relatively low ground pressure. The crane weighs some 60 tonnes. Photo: Andre de Lange, Voorbij Funderingstechniek.

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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Mark Riemers Managing Director SPT Offshore

Summary SPT Offshore, a company within the Royal

Self Installing Platforms and Wind Turbines

Volker Wessels Stevin group, is a leading independent offshore contractor that specialises in the development and production of innovative suction pile foundations and self-installing platforms (SIPs), for use in offshore oil and gas developments and wind farms. Based in the Netherlands, the business serves customers on a global basis, collaborating closely with many of the industry’s leading contractors. Aside from its established self-installing and suction pile products, the company has recently developed an innovative suction embedded anchor (SEA) and is looking to move into the wind energy field using its proprietary Self Installing Wind Turbine (SIWT) concept. There is really no other company quite like SPT Offshore, in that we specialise completely in the development and manufacture of self-installing platforms and suction pile foundations. We have developed our own, in-house concepts in these fields that really set us apart and allow us to offer considerable benefits to our customers.

The company’s range of products includes selfinstalling platforms, suction pile clusters, suction piles, suction embedded anchors (SEA), and suction pile foundations. SPT has developed five proprietary self-installing platform concepts - unique designs that are installed without the use of heavy lift vessels or the need for pile driving, and are ideally suited to marginal field developments. The platforms are either self-floating using their own buoyancy, or we use our own barges to float them out and install them. This is an extremely useful solution that means that we do not have to rely on anyone else to float or install our products, but can complete the whole operation quickly and smoothly by ourselves. The Self Installing Wind Turbine (SIWT) is a concept in which the complete wind turbine (ranging from 3 to 10 MW) including tripod foundation is assembled in port, subsequently transported and installed using a standard flat top barge or alternatively a DP vessel. Recently we completed a study for Carbon Trust together with support from Wood Group, Volker Construction International and Boskalis. The study focuses on the UK 3rd round of wind farm licences in with water depths ranging from 30 to 60m. See below some sketches of the SIWT concept.

Key benefits of the SIWT are: 

Resources required to enable the offshore

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

installation are relatively cheap and widely available. The main components of the offshore installation spread are typically a 120m long x 36m wide flat top barge, tugs (or alternatively 36m wide DP vessel), strand jacks (for lowering) and suction pumps 

Light weight tripod structure, weighing 500 tons (primary steel) excluding suction piles  Commissioning the wind turbine is performed in port prior to installation. Traditionally, this activity is carried out offshore resulting in several months downtime before the wind farm is operational.  Concrete acting as structural top of the suction piles pre-installed prior to load-out above the two braced suction piles in order to a) move the COG away from the mono-column and make it possible to lift and install the complete turbine in one piece and b) to reduce tension on the foundation. Concrete is relatively inexpensive compared to using steel and serves the same purpose.  Suction pile foundation allows for a speedy and simultaneous installation (4-6 hours suction time); suction installation is a silent and vibration free method and does not disturb the marine wildlife and the sea bed.  Suction pile foundation is able to cope with an uneven sea bed; hence dredging is not required.



Installation from a flat top barge using an inexpensive marine spread, whereby offshore jack-up or heavylift vessels are not required. Alternatively a DP vessel may be cost efficient too and would accelerate the offshore program and, hence return on investment.  Short installation time offshore while installing the foundation and wind turbine in one go.  Flexible planning as marine equipment is plenty available compared to scarce availability of expensive HLVs and jack-up lifting vessels;  Decommissioning is easy by simply reversing all installation steps; the suction piles can be pressed out using the same suction pump spreads, leaving no trace behind after removal; The barge installed platform concept uses a flat top barge to transport and install the platform to the offshore site. It is particularly suited for the heavier decks, say from 1,000 ton up to 5,000 ton. Four legs are used to support the deck and each leg is founded on a single suction pile. Strand jacks are used to lower the legs and to lift the deck. Our suction pumps are used to install the suction piles. The concept works in water depths up to 50m with some additional strengthening of the legs near the suction piles. The whole offshore installation operation takes no more than 2 days, so the weather dependency is quite small. We design for transport wave heights up to Hs of 4m


and for installation wave heights up to Hs of 1.5m. The advantages of the self-installation concept are easily apparent. The product offers significant cost and time savings in comparison with the more conventional heavy lift barge installed and piled platforms, and can be re-used. The combination of the platform and suction piles works excellently together because you only need a pump to install them rather than heavy pile driving equipment. Also, the suction piles are versatile, easy to use and decommission and simple to move to other locations when the field is depleted. SPT together with Heerema and IV Oil & Gas are currently building a large SIP platform destined for the Dutch F3 field. The platform is planned for installation in August this year. Pictures of the concept and the completed suction piles are shown above. More recently, SPT has been developing an innovative anchor technology that is installed using a suction pile follower. We are in the process of testing the SEA anchor, which is an umbrella anchor, in collaboration with Petrobras off the coast of Brazil. Unique in its approach, the anchor is pushed into the soil using a suction pile, in a process that leaves a relatively small amount of steel behind. Once the anchor is pushed in at the required depth, the suction pile flow is reversed, detaching it and leaving the anchor behind. We see great potential for this solution as it provides a very effective anchor, and is up to 50 per cent cheaper than current suction pile technology. Another successful achievement was the installation of the Ithaca Jacky platform in January 2009 next to the Beatrice field. The jacket and deck were built by our client HSM in Schiedam. We design, built and installed the 3 suction piles, see also below Much of SPT’s success is founded on the extensive experience within the business, which allows it to design, develop, test and market innovative solutions in-house. Its skilled and professional personnel includes project managers and engineers, geotechnical, structural and marine engineers, naval architects and experienced offshore installation crews. We have our own extensive design department that develops all of our concepts totally in-house. Furthermore, we operate our own fabrication yard (VSF in Rotterdam) to manufacture the products and take care of the installation of the products. In doing this, we work closely with our clients carrying out FEED studies to develop solutions for their specific needs.

Figure 2 Transport and installation of SPT's self installing wind turbine and foundation concept.

Figure 3 SIP2 barge installed platform at Calder field Morecambe Bay.

SPT Offshore

Korenmolenlaan 2 3447 GG Woerden The Netherlands Tel. +31 348 435260 www.sptoffshore.com Contact: Mark Riemers Managing Director

Figure 4 Suction Embedded Anchor (SEA).

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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Ir. Paulien Kouwenberg currently Junior Geotechnical Specialist at ARCADIS Supervision: Ing. Bjorn Vink A2 Projectbureau

Summary

A2 Maastricht Tunnel: Geotechnical Risk Analysis

This article summarizes the conclusions of the MSc thesis of the author, based on research done under supervision of the A2 Projectbureau. The A2 Maastricht Project’s goal is the design and construction of a tunnel for the busy A2 motorway, which runs right through the city of Maastricht. The A2 tunnel shall greatly reduce current daily traffic problems which negatively impact Maastricht’s living conditions.

Figure 1 Overview of the project location. The site investigation locations are indicated.

be about 2300 m, roughly between junctions Geusselt and Europaplein (see figure 1). The main goal of the research and subject of this article has been to get a better insight in geotechnical risks involved, by linking geology to different physical properties of the local limestone; which were obtained by geological, geotechnical and geophysical surveys.

The A2 Maastricht project is a challenging project indeed, as this tunnel will be constructed using cut-and-cover techniques in a deep building pit, to be dug in a subsurface very unusual in the Netherlands. The tunnel will be built on 2 levels, with on each level 2x2 traffic lanes, separated by a safety tunnel. Total length of the tunnel is to

The surface level along the planned tunnel varies between 46 and 50 m +NAP, and the groundwater table is about 3 m below surface. The subsurface consist of a top soil of about 3 m of sand and clay, and a 10 m thick gravel layer on top of limestone from the Formations of Maastricht and Gulpen, containing flint and hardground layers. The Formation of Maastricht here consists of six members, the material properties of which are presented in Table 1. These members are distinguishable, based on

Figure 2 Adjacent boreholes. Blue represents the top soil, purple the gravel layer, the green colours the different members of the Formation of Maastricht and brown the Formation of Gulpen. The black line indicates the pocket penetrometer readings.

characteristic horizons, hardgrounds and flint content. Vertical displacement of these members between adjacent boreholes revealed the existence of faults. On one location (intersection Voltastraat) a fault was found with a displacement of about 15 m (see figure 2). The chemistry of the groundwater confirmed a connection between the gravel and deep limestone layers. Site investigation data were used for Risk Determination. Descriptions and laboratory tests (UCS and pocket penetrometer tests) of seventeen ‘undisturbed’ cores along the tunnel alignment were available, as were data from some in-situ tests (Menard and Lugeon tests).

Geophysical Techniques To get a better understanding of the (existence of the) fault and to find more information on the local subsurface in general, different downhole geophysical techniques were tested in the fault area. Most of the techniques (gamma ray, sonic logging, electric conductivity logging, borehole penetration radar, crosshole tomography) were alas unsuccessful, due to high groundwater conductivity and/or formation damage due to drilling. Seismic reflection with a low energy airsound source was found to be very useful to develop an adequate image of the shallow subsurface. This revealed the presence of a complex fault zone, rather than a single fault under the Voltastraat (see figure 3). Based on knowledge of normal faults in the neighborhood, it is assumed that the strike of this fault zone will be between 110 140°. To the south of this fault younger members (Meerssen, Nekum and Emael) have been eroded.

Fault Zone Risks The fault zone in question is characterised by very

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GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom


low strength material (carbonate sand, or limestone which degrades easily into sands under mechanical loading). Beside this, they are also expected to have high permeability. Where faults and younger members are encountered, ground improvement techniques (jet grouting columns and grout injection) may have to be used, to limit water ingress into the building pit, to increase the ground bearing capacity and to provide adequate passive resistance to the planned sheet pile walls of the building pit. These techniques themselves have been associated with several risks, and therefore might require an alternative design (like underwater concrete with tension piles) if proven to be inadequate. For example, it is difficult to guarantee adequate quality, shape and overlap of jet grouting columns, since intercalations of hard and weak materials are found. As for the grout injection, it is difficult to control which discontinuities will be sealed. Slurry filled trenches will be used to install the sheetpile walls through the gravel. The high permeability of the gravels and possibly of the fault zones themselves may cause loss of the bentonite slurry during trench construction, and consequently trench instability might occur. This risk can be reduced by thickening the slurry. The presence of large boulders or other obstacles (thick vertical flint layers, sliding blocks in fractured limestone) may also divert and increase locally the groundwater flow and thus cause instabilities. Moreover, there always remains the possibility of local problems emerging during trench and building pit excavation, even when the flint logs derived from the borehole logs do give a reliable estimation of the flint content expected along the tunnel’s planned alignment.

Reducing Risks To minimize these risks, the A2 Maastricht Project decided on a number of interventions and new research projects. It was recommended to perform a large scale pumping test, aimed at determining the permeability of the limestone and gravel. Also, to perform extensive seismic reflection along the total tunnel alignment, in combination with the creation of additional boreholes.

Member UCS (MPa) Average Standard deviation Minimum Maximum Number of tests E50 (MPa) Average Minimum Maximum Number of tests Dry density (mg/m3) Average Standard deviation Minimum Maximum Number of tests Flint content (%)

Primary Secondary

Furthermore, more research into the ground improvement methods is needed. There also is a great need for a method to effectively detect discontinuities. It is also recommended to reconsider the length of each of the planned construction compartments, since smaller compartments can greatly reduce construction risks in zones with a high risk profile, as found along the new A2 Maastricht Tunnel. 

Meerssen

Nekum

Emael

Schiepersberg

Gronsveld

Valkenburg

0.78 0.21 0.56 0.97 3

0.4 0.52 0.03 1.55 32

0.48 0.79 0 2.7 18

1.53 0.77 0.23 2.32 6

1.73 1.06 0.03 3.74 33

1.71 1.16 0.53 2.86 3

173 100 250 3

104 2.2 480 25

109 1.9 640 17

460 39 760 6

387 2.2 1570 31

499 58 750 3

1.25 0.04 1.18 1.29 5

1.37 0.08 1.18 1.5 48

1.31 0.05 1.24 1.43 17

1.4 0.03 1.36 1.46 10

1.46 0.1 1.31 1.67 41

1.6 0.11 1.39 1.73 7

0.1

2.2

4.3

4.6

6.7

4.2

Permeality [Darcy] 0.001 - 10 0.8 - 1.8

Hydraulic conductivity [m/day] 0.001 - 10 0.7 - 1.4

Table 1 Material properties of the members of the Formation of Maastricht Primary permeability is material permeability. Secondary permeability is the mass permeability (including discontinuities).

Figure 3 Seismic reflection profile underneath the Voltastraat. Reflections highlighted in green represent the top of the members of the Formation of Maastricht. The pink line indicates the top of the formation of Gulpen. The red line is the fault with the largest vertical displacement (about 8 m) and the black lines indicate smaller faults.

Figure 4 Dubble stacked tunnel A2 Maastricht. Source: Avenue2.

GEOtechniek – Special 11th DFI/EFFC – London – United Kingdom

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a.p. van den berg We at A.P. van den Berg provide technical solutions in areas that have traditionally been strong Dutch fields of expertise. Against a background of reclaiming Holland from the sea, controlling the water levels in the Low Countries and building an infrastructure on and in soft soils, our industry was and still is forced to develop techniques and standards to meet various challenges. A.P. van den Berg’s contribution consists of designing and supplying advanced soil investigation technology to customers who are in the forefront of their field of expertise.

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Deltares Academy Deltares Academy is Deltares’ educational facility in the field of geo- and hydraulic engineering by means of courses, masterclasses and ICT facilities. One of our courses is:

State-of-the-art design of pile foundations Worldwide buildings and many other constructions are built on pile foundations. Recently, considerable progress has been made in the field of understanding, modelling and testing of pile foundations, leading to the use of more advanced models in pile design. We organize a three-day course presenting the complete scope of pile design and pile behaviour from the principles to state-of-the-art knowledge on modeling and testing. The diff erent aspects of pile design and behaviour will be discussed by selected, wellknown instructors from universities and industrial companies all over the world.

Course date and location: On 21 - 23 June 2010 in Delft , The Netherlands Subjects: šf_b[Z[i_]dWYYehZ_d]je;kheYeZ[1 šf_b[beWZj[iji1    šef[d#[dZ[Zij[[bf_b[i1   šf_b[ikdZ[hlWh_WXb[WdZYoYb_YbeWZi1 šf_b[Z[i_]dm_j^<_d_j[;b[c[djCeZ[bi1

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Deltares is a Dutch independent research institute for water, soil and subsurface issues. We work on innovative solutions that make life in deltas, coastal areas and river basins safe, clean and sustainable www.deltaresacademy.com | sales@deltaresacademy.com | +31 88 3357500

www.deltares.nl | info@deltares.nl | +31 88 3357500

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