4-12-03-1-E...bearing sand strata. 7.5 to 9.0 m A second imperme-able, slightly cohesive layer. 9.0 to 13 m The second permanent water bearing sand strata. 13 to 16 m Finally, an imperme-able

Steel Sheet Piling

Underground Car Park

The Hague

4-12-03-1-E

Sheet Piling

66, rue de LuxembourgL - 4221 Esch-sur-Alzette (Luxembourg)

Tel.: (+352) 5313 3105Fax: (+352) 5313 3290

E-mail: [email protected]: www.sheet-piling.arcelor.com

Introduction 1.

Fig. 1

sand

solid sand

precast concrete column

precast prestressed concrete beams

in situ concrete columin sheet pile

concrete floor in situ

permanent drainage

sheet pile

clay impermeable to water

stairwell entrance / exit

precast prestressedconcrete beams

EXISTING BUILDING

ground water level

precast concrete pile foundatoin

sheet pile

clay/peat

clay

sand

average height of the water

This case study considers thedesign and construction of a multi-storey car park in which steel sheetpiling was used as an integral partof the load bearing structure.

The car park was built as anextension of the head office ofSiemens Nederlands N.V. in TheHague and lies adjacent to therailway linking The Hague toAmsterdam. The complex compris-es 12,000 m2 of office space and

an underground car park for morethan 550 cars.

The car park is constructed partiallybelow ground level. The partabove ground consists of theground floor, first floor and roofpark. The underground part com-prises two levels of parking whichextend beneath the upper levelsand the adjacent road. The designis rectangular in shape, being138 m long by 16 m wide on the

surface and 32 m wide belowground. The deepest basementlevel is approximately 5.4 m belowground level, whilst the top level isapproximately 5.4 m above groundlevel. The vertical distance betweeneach level is 2.7 m but the usableheight is 2.2 m due to the thicknessof the floor members. (Fig. 1)

Vehicular access to each level is bymeans of two carousels, one ateach end of the car park.

3

Fig. 4

Fig. 5

Introduction 1.

Fig. 1

sand

solid sand

precast prestressed concrete beams

in situ concrete columin sheet pile

concrete floor in situ

permanent drainage

sheet pile

clay impermeable to water

stairwell entrance / exit

precast prestressedconcrete beams

EXISTING BUILDING

ground water level

precast concrete pile foundatoin

sheet pile

clay/peat

clay

sand

average height of the water

This case study considers thedesign and construction of a multi-storey car park in which steel sheetpiling was used as an integral partof the load bearing structure.

The car park was built as anextension of the head office ofSiemens Nederlands N.V. in TheHague and lies adjacent to therailway linking The Hague toAmsterdam. The complex compris-es 12,000 m2 of office space and

an underground car park for morethan 550 cars.

The car park is constructed partiallybelow ground level. The partabove ground consists of theground floor, first floor and roofpark. The underground part com-prises two levels of parking whichextend beneath the upper levelsand the adjacent road. The designis rectangular in shape, being138 m long by 16 m wide on the

surface and 32 m wide belowground. The deepest basementlevel is approximately 5.4 m belowground level, whilst the top level isapproximately 5.4 m above groundlevel. The vertical distance betweeneach level is 2.7 m but the usableheight is 2.2 m due to the thicknessof the floor members. (Fig. 1)

Vehicular access to each level is bymeans of two carousels, one ateach end of the car park.

3

Fig. 4

Fig. 5

Fig. 2

2.Cone resistance in MPa

sand

TYPE OF SOIL

clay/peat

sand

clay

sand

clay

solid

sand

Cone resistance in MPa Friction value (%)

4 5

2.1. Location

Since existing buildings were closeto the proposed site it was neces-sary to take measures to limit thenoise during pile installation.

Railway embankment

The design requirements specifiedthat the subsidence of the railshad to be minimised as far as pos-sible. Special care was taken withregard to subsidence of the rail-way embankment during the con-struction phase, particularly when

driving the piles and when dig-ging and draining the excavation.It was necessary to phase the pil-ing work and use low vibrationinstallation methods togetherwith an extremely rigid piling sys-tem in order to minimise theeffects on the railway.

Finally, it was necessary to includemeasures to avoid increased corro-sion of the piles as a result of anystray currents in the ground comingfrom the adjacent electric railway.

Existing public road

A public road existed on the sitebefore construction started andonce the car park was completedthe road would be re-installed onthe top of the underground partof the car park. The road was notin use during the constructionphase but would be used foraccess on completion. The design,therefore, had to take account ofthe normal urban traffic loadexpected to use this road.

2.2. Ground conditions (Fig. 2)

The nature and the characteristicsof the soils are of great impor-tance when designing a founda-tion. During the initial designprocess the ground conditionswere determined on the basis ofearlier soil analysis carried out forthe adjacent building. The resultswere subsequently confirmed bysoil analysis at the site location.This consisted of a permeabilitystudy and a geotechnical study ofthe excavation, together with abearing capacity study of bothbearing and sheet piles. Theground consists of a post glacialsequence approximately 16 mthick, overlying a Pleistocene sandsequence. The post glacialsequence consists of the following:

0 to 3.5 m An impermeable layerwith fine sand on top and clayand peat below.3.5 to 7.5 m A permanent waterbearing sand strata.7.5 to 9.0 m A second imperme-able, slightly cohesive layer.9.0 to 13 m The second permanentwater bearing sand strata.13 to 16 m Finally, an imperme-able clay which varies in thicknessfrom 3.0 to 3.5 m.

Below this post glacial layer, thepleistocene sequence consists of avery compact sand. The groundwater level is 1.5 m below theground surface.

2.3. Groundwater drainage

The aquifer below the deepestimpermeable clay is used as adrinking water reservoir for TheHague and must not be affected bydrainage. The regional and localauthorities have stipulated thatdrainage of groundwater must notexceed 1.5 m3/h for this project.Thus, it was necessary to ensurethat the car park was made asimpermeable as possible. Duringthe hydrogeological study an esti-mate was prepared of the expectedseepage into the sheet pile sup-ported excavation. It becameapparent that to ensure that thegroundwater seepage remainedbelow the stipulated levels it wouldbe necessary to take additional pre-cautionary measures.

Since the aquifer would be underhydrostatic pressure, the designneeded to take into account thepossibility of ground heave in thelower impermeable layers. The excavation was limited to 6 mbelow ground to provide sufficientvertical stability.Heavy drainage of the upper layers,which are prone to subsidence,would result in subsidence of thebuildings adjacent to the car park.So, for this reason, it would be necessary to use a steel sheet pilingcofferdam in the construction ofthe foundations.

Site conditions

Fig. 2

2.Cone resistance in MPa

sand

TYPE OF SOIL

clay/peat

sand

clay

sand

clay

solid

sand

Cone resistance in MPa Friction value (%)

4 5

2.1. Location

Since existing buildings were closeto the proposed site it was neces-sary to take measures to limit thenoise during pile installation.

Railway embankment

The design requirements specifiedthat the subsidence of the railshad to be minimised as far as pos-sible. Special care was taken withregard to subsidence of the rail-way embankment during the con-struction phase, particularly when

driving the piles and when dig-ging and draining the excavation.It was necessary to phase the pil-ing work and use low vibrationinstallation methods togetherwith an extremely rigid piling sys-tem in order to minimise theeffects on the railway.

Finally, it was necessary to includemeasures to avoid increased corro-sion of the piles as a result of anystray currents in the ground comingfrom the adjacent electric railway.

Existing public road

A public road existed on the sitebefore construction started andonce the car park was completedthe road would be re-installed onthe top of the underground partof the car park. The road was notin use during the constructionphase but would be used foraccess on completion. The design,therefore, had to take account ofthe normal urban traffic loadexpected to use this road.

2.2. Ground conditions (Fig. 2)

The nature and the characteristicsof the soils are of great impor-tance when designing a founda-tion. During the initial designprocess the ground conditionswere determined on the basis ofearlier soil analysis carried out forthe adjacent building. The resultswere subsequently confirmed bysoil analysis at the site location.This consisted of a permeabilitystudy and a geotechnical study ofthe excavation, together with abearing capacity study of bothbearing and sheet piles. Theground consists of a post glacialsequence approximately 16 mthick, overlying a Pleistocene sandsequence. The post glacialsequence consists of the following:

0 to 3.5 m An impermeable layerwith fine sand on top and clayand peat below.3.5 to 7.5 m A permanent waterbearing sand strata.7.5 to 9.0 m A second imperme-able, slightly cohesive layer.9.0 to 13 m The second permanentwater bearing sand strata.13 to 16 m Finally, an imperme-able clay which varies in thicknessfrom 3.0 to 3.5 m.

Below this post glacial layer, thepleistocene sequence consists of avery compact sand. The groundwater level is 1.5 m below theground surface.

2.3. Groundwater drainage

The aquifer below the deepestimpermeable clay is used as adrinking water reservoir for TheHague and must not be affected bydrainage. The regional and localauthorities have stipulated thatdrainage of groundwater must notexceed 1.5 m3/h for this project.Thus, it was necessary to ensurethat the car park was made asimpermeable as possible. Duringthe hydrogeological study an esti-mate was prepared of the expectedseepage into the sheet pile sup-ported excavation. It becameapparent that to ensure that thegroundwater seepage remainedbelow the stipulated levels it wouldbe necessary to take additional pre-cautionary measures.

Since the aquifer would be underhydrostatic pressure, the designneeded to take into account thepossibility of ground heave in thelower impermeable layers. The excavation was limited to 6 mbelow ground to provide sufficientvertical stability.Heavy drainage of the upper layers,which are prone to subsidence,would result in subsidence of thebuildings adjacent to the car park.So, for this reason, it would be necessary to use a steel sheet pilingcofferdam in the construction ofthe foundations.

Site conditions

3.

Fig. 3

air duct air duct

air flue

precast prestressed concrete beams precast prestressed concrete beams

stairwell stairwell

air flue

Fig

. 1

EXISTING BUILDING

7

Design considerations

6

Two alternative designs were con-sidered when designing the carpark. A closed concrete structureand the chosen option, an opensteel piling structure. (Fig. 3)

3.1. Closed concrete structure

A conventional closed concretestructure would consist of a con-crete basement cast in-situ. Thethick concrete floor would be set onconcrete bearing piles and provisionwould be made at the bottom ofthe structure to prevent lifting.A variant of the same structure

with only one level below groundwas not an attractive propositionbecause of the increased floorarea needed.

Both of these concrete solutionswould also require extensive useof sheet piling in the form of tem-porary cofferdams.

3.2. Open structure constructed using steel sheet piling

Since an impermeable clay layer3.5 m thick exists above the verydense sand, an open structure was

considered as a viable option. Thisstructure consists of a car park sup-ported on all sides by steel sheetpiling that had been driventhrough the clay into the sand. Inthe middle, a separate system ofbearing piles is also driven into thedense sand.

In this case, the clay layer and thepiling form a near watertight sealto the basement of the garageand have sufficient vertical stabili-ty to resist heave due to hydraulicuplift. As there is the possibility of

a slight amount of leakage alongthe interface between the pilesand the clay, a permanentdrainage system has been installedapproximately 0.5 m below thedeepest car park level.

The floor for the deepest level wasdesigned as a thin concrete strut.This floor has a series of openingsin it, in the form of small pave-ment sections set on sand. Theseallow water to pass through in theevent of the car park flooding andprevent the floor becoming dis-

torted due to water pressure in aflood situation.

When comparing the two alterna-tives on the basis of cost andspeed of construction, the openstructure, employing steel sheetpiling, proved to be approximately15% cheaper than the convention-al concrete option.

The clients’ design consultants hadrecommended that considerationbe given to remedial measuresneeded in the event of higher

water inflow than expected. Thiswould only become apparent dur-ing excavation and could originatefrom the piling interlocks or fromthe pile to clay interface. If need-ed, the remedial measures fore-seen are grouting behind the pilesor into the floor.

3.

Fig. 3

air duct air duct

air flue

precast prestressed concrete beams precast prestressed concrete beams

stairwell stairwell

air flue

Fig

. 1

EXISTING BUILDING

7

Design considerations

6

Two alternative designs were con-sidered when designing the carpark. A closed concrete structureand the chosen option, an opensteel piling structure. (Fig. 3)

3.1. Closed concrete structure

A conventional closed concretestructure would consist of a con-crete basement cast in-situ. Thethick concrete floor would be set onconcrete bearing piles and provisionwould be made at the bottom ofthe structure to prevent lifting.A variant of the same structure

with only one level below groundwas not an attractive propositionbecause of the increased floorarea needed.

Both of these concrete solutionswould also require extensive useof sheet piling in the form of tem-porary cofferdams.

3.2. Open structure constructed using steel sheet piling

Since an impermeable clay layer3.5 m thick exists above the verydense sand, an open structure was

considered as a viable option. Thisstructure consists of a car park sup-ported on all sides by steel sheetpiling that had been driventhrough the clay into the sand. Inthe middle, a separate system ofbearing piles is also driven into thedense sand.

In this case, the clay layer and thepiling form a near watertight sealto the basement of the garageand have sufficient vertical stabili-ty to resist heave due to hydraulicuplift. As there is the possibility of

a slight amount of leakage alongthe interface between the pilesand the clay, a permanentdrainage system has been installedapproximately 0.5 m below thedeepest car park level.

The floor for the deepest level wasdesigned as a thin concrete strut.This floor has a series of openingsin it, in the form of small pave-ment sections set on sand. Theseallow water to pass through in theevent of the car park flooding andprevent the floor becoming dis-

torted due to water pressure in aflood situation.

When comparing the two alterna-tives on the basis of cost andspeed of construction, the openstructure, employing steel sheetpiling, proved to be approximately15% cheaper than the convention-al concrete option.

The clients’ design consultants hadrecommended that considerationbe given to remedial measuresneeded in the event of higher

water inflow than expected. Thiswould only become apparent dur-ing excavation and could originatefrom the piling interlocks or fromthe pile to clay interface. If need-ed, the remedial measures fore-seen are grouting behind the pilesor into the floor.

4.

air flue

concrete column (in situ)

column reinforcement

column

concrete

column

concrete

column

sheet pile

variable traffic load

air flue

sheet pile

air flue

precast prestressedconcrete beam

Loads to be considered

8 9

Horizontal loads

The horizontal loads on the structureinclude:• Wind load on the superstructure in

accordance with NEN 3850.• Soil pressure against the substructure.• Lateral pressure from the railway

embankment.

Vertical loads

The vertical loads consist of:• Self weight.• Live load on the floors in the garage.• Live load on the garage roof.

Load transmission

These loads are transmitted to thefoundations in the following way:

4.1. Vertical load transmission

On the railway side (Y16)

The vertical load of the superstructureis transmitted through the floor beamsonto precast concrete columns whichare sited at 7.2 m centres. The columnsin turn rest on a capping beam castonto the sheet piling which redistrib-utes the point loads of the columnsinto the sheet pile wall. (Fig. 4)

The underground floors of the car parkare supported directly by beams thatbear directly onto the sheet piling. Thedeepest floor of the car park is found-ed directly on the subsoil and is notsupported by the sheet piling.

On the central axis

A double row of columns on thecentral axis of the structure is supported on bearing piles, whichare founded in the dense sand 18 m below the surface level.

On the office side (Y12)

The vertical load due to traffic onthe office side of the garage istransmitted to the supportingsheet piling as an evenly distrib-uted load. The roof comprises16 m long girders which rest on acapping beam cast onto the sheetpiling. The basement floors areconstructed adopting the samemethod used on the railway sideof the building. (Fig. 5+7)

4.2. Horizontal load transmission

Horizontal load transmission of the superstructure (Fig. 6)

The design of the structure is suchthat the horizontal wind load isnot transmitted directly to thesheet piling, but is transmitted tothe ground floor and the base-ment floor beneath it, formingtogether with the in-situ concretecolumns a stiff frame and soabsorbing this additional moment.

The load bearing system of the lower structure

The sheet piling supports theground pressures in both the con-struction and working phases ofthe structure. During the tempo-rary stages, ground anchors andwallings were used for support,where as the floors of the com-pleted structure supported thewalls in the long term.

Fig. 4 - Vertical load transmission

Fig. 5 - Steel sheet pile/concrete connection

Fig. 6 - Sheet pile bending at Y16 due to wind load Fig. 7 - Sheet pile bending at Y12 due to variable traffic load

in situ casted concrete beam withreinforcing bars welded to steel

sheet pile; Anchorage

4.

air flue

concrete column (in situ)

column reinforcement

column

concrete

column

concrete

column

sheet pile

variable traffic load

air flue

sheet pile

air flue

precast prestressedconcrete beam

Loads to be considered

8 9

Horizontal loads

The horizontal loads on the structureinclude:• Wind load on the superstructure in

accordance with NEN 3850.• Soil pressure against the substructure.• Lateral pressure from the railway

embankment.

Vertical loads

The vertical loads consist of:• Self weight.• Live load on the floors in the garage.• Live load on the garage roof.

Load transmission

These loads are transmitted to thefoundations in the following way:

4.1. Vertical load transmission

On the railway side (Y16)

The vertical load of the superstructureis transmitted through the floor beamsonto precast concrete columns whichare sited at 7.2 m centres. The columnsin turn rest on a capping beam castonto the sheet piling which redistrib-utes the point loads of the columnsinto the sheet pile wall. (Fig. 4)

The underground floors of the car parkare supported directly by beams thatbear directly onto the sheet piling. Thedeepest floor of the car park is found-ed directly on the subsoil and is notsupported by the sheet piling.

On the central axis

A double row of columns on thecentral axis of the structure is supported on bearing piles, whichare founded in the dense sand 18 m below the surface level.

On the office side (Y12)

The vertical load due to traffic onthe office side of the garage istransmitted to the supportingsheet piling as an evenly distrib-uted load. The roof comprises16 m long girders which rest on acapping beam cast onto the sheetpiling. The basement floors areconstructed adopting the samemethod used on the railway sideof the building. (Fig. 5+7)

4.2. Horizontal load transmission

Horizontal load transmission of the superstructure (Fig. 6)

The design of the structure is suchthat the horizontal wind load isnot transmitted directly to thesheet piling, but is transmitted tothe ground floor and the base-ment floor beneath it, formingtogether with the in-situ concretecolumns a stiff frame and soabsorbing this additional moment.

The load bearing system of the lower structure

The sheet piling supports theground pressures in both the con-struction and working phases ofthe structure. During the tempo-rary stages, ground anchors andwallings were used for support,where as the floors of the com-pleted structure supported thewalls in the long term.

Fig. 4 - Vertical load transmission

Fig. 5 - Steel sheet pile/concrete connection

Fig. 6 - Sheet pile bending at Y16 due to wind load Fig. 7 - Sheet pile bending at Y12 due to variable traffic load

in situ casted concrete beam withreinforcing bars welded to steel

sheet pile; Anchorage

6.5.

Soil pressure (kN/M2) Bending moment (kNM) Displacements [MM] Soil pressure (kN/M2) Bending moment (kNM) Displacements [MM]gauchedroite

gauchedroite

11

Specific aspectsCalculations

10

6.1. Surface treatment

The exposed parts of the steelsheet piling were treated with alayer of zinc-rich primer, then acoat of epoxy primer and finally acoat of epoxy paint.

6.2. Fire protection

No specific measures were takenwith respect to fire protection ofthe steel since the exposed sur-faces were backed by saturatedsoil, which would act as goodthermal conductor.In use, the steel stress in the sheetpiling is very low at 40 N/mm2,which is approximately half of themaximum value.

A slight decrease in the yield pointof the steel due to the effects oftemperature would not affect thebearing capacity of the sheet pil-ing significantly.

6.3. Corrosion of steel sheet pilingby stray electrical currents

In view of the location of thegarage, with its steel sheet pilingclose to an electrified railway line,a study of the possible effects ofstray currents was undertaken.Stray currents occur as a result ofusing the rails as the return forthe electricity used by the trains.The voltage of these stray currentsdepends on the proximity of sub-stations and the type of ground.The corrosion effects can be min-imised by ensuring good conduc-tivity between the individual pilesand by welding on steel rods atcertain points to act as electricalearth pathways, which lead thestray current back to the rails.

The main calculations used in thedesign of the steel sheet piling

The sheet piling serves as both thesupport to the ground and thevertical loads from the structureabove.The profile chosen was the PU 16type of sheet piling (in steel quali-ty PAE 250 in accordance withEuronorm quality Fe340 B).

Stresses as a result of vertical load

The stresses in the sheet pilingresulting from vertical loads com-prise a normal compressive stressand a local bending stress wherethe capping beams are formed atthe top of the piling and wherethe underground floors are fixedto the walls.

Normal vertical force

This consists of the vertical compo-nent of the ground anchor forcein the temporary case and theload of the structure and its con-tents in the permanent case.

The bending stress in the steel

This falls into two parts:• The localised bending in thepiles due to the connection of thefloor members and the transmis-sion of the vertical load.• The bending moment due to theground pressure.

Bending of the railway side wallon line Y 16 (Fig. 8)

The sheet piling showed little orno bending due to the vertical orfloor connection loads transmittedto it.

Bending of the office side sheetpiling line Y12, due to verticalload (Fig. 9)

The ground floor caused majorbending moments at the head ofthe sheet piling. During the con-struction phase this was due tothe load of the garage roof and,in the permanent condition, fromthe heavier load from traffic onthe road on top of the garageroof.

Deflection of the sheet piling dueto the soil loading on the railwayside

The deflection of the sheet pilingdue to soil loading has been calcu-lated using a programme which isbased on bi-linear ground springsagainst the sheet piling.

The railway load has been calcu-lated as an additional horizontalload using the Culmann method.The ground pressure coefficientshave been based on assumed fail-ure surfaces.

By welding on rods in certainspots, it was possible to perform acontrolling measurement after-wards. The location of the garagewas so favourable that no risk ofcorrosion due to stray currentswas found.

6.4. Impermeability

A sealing product was applied tothe interlocks at the factory andthe piles were driven into pre-drilled holes filled with bentonitecement slurry, down to the claylayer. This pre-drilling was carriedout to reduce the vibration andsubsidence effects on the sur-rounding ground and structures.However it was thought that pil-ing into bentonite cement slurrywould have a beneficial effect onsealing the interlocks. Once theexcavation was complete thesheet piling wall was grouted tocomplete the sealing process.

6.5. Ventilation provisions

The ventilation of the under-ground part of the garage wasdealt with in two ways:• On the office side of the struc-ture, 5 ventilation shafts wereformed using sheet piling. Eachshaft was 2.5 m x 2.5 m andextended down to the under-ground levels from ground level.The top of each shaft is protectedwith a grill• On the railway side, mechanicalventilation was provided via smallvertical ducts made as part of thevertical columns. (Fig. 10)

Fig. 8 - Sheet pile bending at Y16 due to soil andwater pressure

Fig. 9 - Sheet pile bending at Y12 due to soil andwater pressure Fig. 10 - Ventilation shaft

6.5.

Soil pressure (kN/M2) Bending moment (kNM) Displacements [MM] Soil pressure (kN/M2) Bending moment (kNM) Displacements [MM]gauchedroite

gauchedroite

11

Specific aspectsCalculations

10

6.1. Surface treatment

The exposed parts of the steelsheet piling were treated with alayer of zinc-rich primer, then acoat of epoxy primer and finally acoat of epoxy paint.

6.2. Fire protection

No specific measures were takenwith respect to fire protection ofthe steel since the exposed sur-faces were backed by saturatedsoil, which would act as goodthermal conductor.In use, the steel stress in the sheetpiling is very low at 40 N/mm2,which is approximately half of themaximum value.

A slight decrease in the yield pointof the steel due to the effects oftemperature would not affect thebearing capacity of the sheet pil-ing significantly.

6.3. Corrosion of steel sheet pilingby stray electrical currents

In view of the location of thegarage, with its steel sheet pilingclose to an electrified railway line,a study of the possible effects ofstray currents was undertaken.Stray currents occur as a result ofusing the rails as the return forthe electricity used by the trains.The voltage of these stray currentsdepends on the proximity of sub-stations and the type of ground.The corrosion effects can be min-imised by ensuring good conduc-tivity between the individual pilesand by welding on steel rods atcertain points to act as electricalearth pathways, which lead thestray current back to the rails.

The main calculations used in thedesign of the steel sheet piling

The sheet piling serves as both thesupport to the ground and thevertical loads from the structureabove.The profile chosen was the PU 16type of sheet piling (in steel quali-ty PAE 250 in accordance withEuronorm quality Fe340 B).

Stresses as a result of vertical load

The stresses in the sheet pilingresulting from vertical loads com-prise a normal compressive stressand a local bending stress wherethe capping beams are formed atthe top of the piling and wherethe underground floors are fixedto the walls.

Normal vertical force

This consists of the vertical compo-nent of the ground anchor forcein the temporary case and theload of the structure and its con-tents in the permanent case.

The bending stress in the steel

This falls into two parts:• The localised bending in thepiles due to the connection of thefloor members and the transmis-sion of the vertical load.• The bending moment due to theground pressure.

Bending of the railway side wallon line Y 16 (Fig. 8)

The sheet piling showed little orno bending due to the vertical orfloor connection loads transmittedto it.

Bending of the office side sheetpiling line Y12, due to verticalload (Fig. 9)

The ground floor caused majorbending moments at the head ofthe sheet piling. During the con-struction phase this was due tothe load of the garage roof and,in the permanent condition, fromthe heavier load from traffic onthe road on top of the garageroof.

Deflection of the sheet piling dueto the soil loading on the railwayside

The deflection of the sheet pilingdue to soil loading has been calcu-lated using a programme which isbased on bi-linear ground springsagainst the sheet piling.

The railway load has been calcu-lated as an additional horizontalload using the Culmann method.The ground pressure coefficientshave been based on assumed fail-ure surfaces.

By welding on rods in certainspots, it was possible to perform acontrolling measurement after-wards. The location of the garagewas so favourable that no risk ofcorrosion due to stray currentswas found.

6.4. Impermeability

A sealing product was applied tothe interlocks at the factory andthe piles were driven into pre-drilled holes filled with bentonitecement slurry, down to the claylayer. This pre-drilling was carriedout to reduce the vibration andsubsidence effects on the sur-rounding ground and structures.However it was thought that pil-ing into bentonite cement slurrywould have a beneficial effect onsealing the interlocks. Once theexcavation was complete thesheet piling wall was grouted tocomplete the sealing process.

6.5. Ventilation provisions

The ventilation of the under-ground part of the garage wasdealt with in two ways:• On the office side of the struc-ture, 5 ventilation shafts wereformed using sheet piling. Eachshaft was 2.5 m x 2.5 m andextended down to the under-ground levels from ground level.The top of each shaft is protectedwith a grill• On the railway side, mechanicalventilation was provided via smallvertical ducts made as part of thevertical columns. (Fig. 10)

Fig. 8 - Sheet pile bending at Y16 due to soil andwater pressure

Fig. 9 - Sheet pile bending at Y12 due to soil andwater pressure Fig. 10 - Ventilation shaft

7.

8.

9.

Phasing of excavation construction

12 13

Evaluation

Parties involved in this project

1st Phase: Pre-Drilling of BentoniteCement filled holes

Holes of 30 cm ø were drilled at1.2 m spacing (driving width ofthe paired piles) and filled with abentonite mix prior to driving thepiles. The pre-drilling was neces-sary to reduce the ground vibra-tions in order to minimise thepotential for subsidence duringpile driving and to improve thequality of the sheet pile installa-tion.

2nd Phase: Pile Driving

The piling was driven using a pil-ing hammer with an impact ener-gy of 120 kN/m per blow. The pil-ing was driven in crimped pairsbetween the pre-drilled holes suchthat each free lock that had notbeen previously treated wasplaced in a bentonite hole. Thecomposition of the bentonitecement mixture was such that itwas considered to be extremelywatertight with respect to the

8.1. Impermeability

The requirements stipulated withregard to permanent drainagewere amply met. However, somemoisture had entered the structurenear the sheet piling interlockswhich made surface treatment lesseasy. This seepage was virtuallystopped by means of grout injec-tion. The source of the moisture wasbelieved to be due to capilliaryaction along the inside of the inter-locks from the water bearingaquifer; as the sealing product hadbeen applied on the outside (land-side and waterside) of the locks theground water could only seep outinto the garage.The impermeability of the pilingmay have been further improvedby applying a sealing product insidethe entire sheet piling interlock.

8.2. Drainage during construction

Once the excavation had beenpumped dry, further drainage wasminimal because of the imperme-ability of the sheet piling. Noinfluence on the surroundings hasbeen observed since the excava-tion has been drained.

8.3. Inconvenience on the sur-roundings

As a noise screen was used aroundthe piling hammer during driving,minimal inconvenience was caused

Piling Subcontractor: van SplunderFunderingstechniek b.v., Rotterdamand Visser & Smit Bouw b.v.,Papendrecht

Soil Analysis: GrondmechanicaDelft, Delft

Design Consultant: AronsohnRaadgevende Ingenieurs b.v.,Rotterdam

Contractor:DURA BOUW b.v., Rotterdam

Management: BouwkundigAdviesbureau Derks b.v., Leiden

Architect: de Jong, Hoogveld, de Kat architecten, Utrecht

reinforcing bars welded to steel sheet pilesupporting the in situ casted concrete beams

to the direct surroundings. Theonly exception to this was whilstdriving the short stretch of pilingimmediately adjacent to the exist-ing office block.

8.4. Subsidence of the railwayembankment

The vertical and horizontal move-ments of the railway were meas-ured at regular intervals duringthe various stages of construction.Measurements taken later con-

firmed that no significant subsi-dence was measured during theinstallation of the ground to thefinal level.

8.5. Maintenance

The drainage pipes are positionedbelow the ground water levelwhich will reduce the risk ofblockage due to drying out.Maintenance is limited to periodicpurging of the drainage pipes tofacilitate the flow of water.

sheet piling. The centre interlocksof the paired piles have beentreated with a bituminous sealingproduct.

3rd Phase: Excavation to first ground anchor level

During construction, before thecar park levels were constructed itwas necessary to support the pil-ing by temporary ground anchorsand steel walling on the inside.On the side adjacent to the rail-way, to ensure that track subsi-dence was kept to a minimum, 2rows of temporary groundanchors were used. The positionsof the anchors correspond to theground floor and the first base-ment floor. The third phase of thework involved drainage and exca-vation to the top anchor level andinstallation of the ground anchors. In each row, the anchors lay alter-nately at an angle of 20 degreesand 27 degrees to the horizontal.The top row of anchors had alength of 20 m.

4th Phase: Excavation to lower ground anchor level

The excavation was then takendown to the lower anchor level. Inorder to reduce the possibility ofsubsidence a supporting berm wasleft against the sheet piling adja-cent to the railway until the pileson the central axis had been driv-en. Once the piles on the centralaxis had been driven, the tempo-rary berm was removed and thelower row of ground anchors wasinstalled, these having a length of14 m.

5th Phase: Completion of excavation

The excavation is completed anddrained to the base level.

7.

8.

9.

Phasing of excavation construction

12 13

Evaluation

Parties involved in this project

1st Phase: Pre-Drilling of BentoniteCement filled holes

Holes of 30 cm ø were drilled at1.2 m spacing (driving width ofthe paired piles) and filled with abentonite mix prior to driving thepiles. The pre-drilling was neces-sary to reduce the ground vibra-tions in order to minimise thepotential for subsidence duringpile driving and to improve thequality of the sheet pile installa-tion.

2nd Phase: Pile Driving

The piling was driven using a pil-ing hammer with an impact ener-gy of 120 kN/m per blow. The pil-ing was driven in crimped pairsbetween the pre-drilled holes suchthat each free lock that had notbeen previously treated wasplaced in a bentonite hole. Thecomposition of the bentonitecement mixture was such that itwas considered to be extremelywatertight with respect to the

8.1. Impermeability

The requirements stipulated withregard to permanent drainagewere amply met. However, somemoisture had entered the structurenear the sheet piling interlockswhich made surface treatment lesseasy. This seepage was virtuallystopped by means of grout injec-tion. The source of the moisture wasbelieved to be due to capilliaryaction along the inside of the inter-locks from the water bearingaquifer; as the sealing product hadbeen applied on the outside (land-side and waterside) of the locks theground water could only seep outinto the garage.The impermeability of the pilingmay have been further improvedby applying a sealing product insidethe entire sheet piling interlock.

8.2. Drainage during construction

Once the excavation had beenpumped dry, further drainage wasminimal because of the imperme-ability of the sheet piling. Noinfluence on the surroundings hasbeen observed since the excava-tion has been drained.

8.3. Inconvenience on the sur-roundings

As a noise screen was used aroundthe piling hammer during driving,minimal inconvenience was caused

Piling Subcontractor: van SplunderFunderingstechniek b.v., Rotterdamand Visser & Smit Bouw b.v.,Papendrecht

Soil Analysis: GrondmechanicaDelft, Delft

Design Consultant: AronsohnRaadgevende Ingenieurs b.v.,Rotterdam

Contractor:DURA BOUW b.v., Rotterdam

Management: BouwkundigAdviesbureau Derks b.v., Leiden

Architect: de Jong, Hoogveld, de Kat architecten, Utrecht

reinforcing bars welded to steel sheet pilesupporting the in situ casted concrete beams

to the direct surroundings. Theonly exception to this was whilstdriving the short stretch of pilingimmediately adjacent to the exist-ing office block.

8.4. Subsidence of the railwayembankment

The vertical and horizontal move-ments of the railway were meas-ured at regular intervals duringthe various stages of construction.Measurements taken later con-

firmed that no significant subsi-dence was measured during theinstallation of the ground to thefinal level.

8.5. Maintenance

The drainage pipes are positionedbelow the ground water levelwhich will reduce the risk ofblockage due to drying out.Maintenance is limited to periodicpurging of the drainage pipes tofacilitate the flow of water.

sheet piling. The centre interlocksof the paired piles have beentreated with a bituminous sealingproduct.

3rd Phase: Excavation to first ground anchor level

During construction, before thecar park levels were constructed itwas necessary to support the pil-ing by temporary ground anchorsand steel walling on the inside.On the side adjacent to the rail-way, to ensure that track subsi-dence was kept to a minimum, 2rows of temporary groundanchors were used. The positionsof the anchors correspond to theground floor and the first base-ment floor. The third phase of thework involved drainage and exca-vation to the top anchor level andinstallation of the ground anchors. In each row, the anchors lay alter-nately at an angle of 20 degreesand 27 degrees to the horizontal.The top row of anchors had alength of 20 m.

4th Phase: Excavation to lower ground anchor level

The excavation was then takendown to the lower anchor level. Inorder to reduce the possibility ofsubsidence a supporting berm wasleft against the sheet piling adja-cent to the railway until the pileson the central axis had been driv-en. Once the piles on the centralaxis had been driven, the tempo-rary berm was removed and thelower row of ground anchors wasinstalled, these having a length of14 m.

5th Phase: Completion of excavation

The excavation is completed anddrained to the base level.

10.

1514

Court Münster D picture 1

Congress Centre Amsterdam NL picture 2

House for dentistry Münster D picture 3

Malieveld Den Haag NL picture 4

KLM Amstelveen NL picture 5

City hall Rouen F picture 6

Münsterstrasse Düsseldorf D picture 7

Marketsquare Coesfeld D picture 8