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STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING

FELSBAU 23 (2005) NO. 6 27

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Pipe-Jacking versus

Conventional TunnellingConfrontation of both methods at the CableTunnel System Graz Main Railway Station

By Helmut Steiner, Gerald Edlmair and Ralf Vergeiner

Rohrvorpressung oder NT-Vortrieb Gegenberstellung der beiden Vortriebsmethodenam Beispiel des Leitungskollektorensystems GrazHauptbahnhof

Der steigende Bedarf an Kabelwegen im Bereich des Gra-zer Hauptbahnhofs machte es erforderlich, unter den be-

stehenden Gleisanlagen einen kontinuierlich aufgefahre-nen Lngskollektor (Rohrvorpressung DN 3 180 mit offe-nen Haubenschild, Lnge 877 m) und einen rechtwinkeligdavon abzweigenden, zyklisch vorgetriebenen Querkollek-tor (Lnge 85 m) zu errichten. Diese Vortriebe wurden beiberdeckungen von 3 bis 14 m in den wrm-glazialen Te-rassenschottern des Grazer Felds ausgefhrt.

Da die beiden Vortriebsmethoden unter gleichen bezie-hungsweise hnlichen Untergrund- und nahezu identi-schen Querschnittsverhltnissen (etwa 12 bis 13 m2 Aus-

bruchquerschnitt) zur Anwendung kamen, war es ab-

schlieend mglich, vergleichende Betrachtungen hin-sichtlich technischer und wirtschaftlicher Gesichtspunktedurchzufhren.

Spezielles Augenmerk wird auf den Vergleich zwischenden vorab gettigten Prognosen und den vor Ort angetrof-fenen Verhltnissen und den dabei gemachten Erfahrun-gen gelegt. Die Aspekte Vortriebsleistung und Bauzeit-vergleich, Oberflchensetzungen und die Auswirkungen

auf den Bahnbetrieb, Vortriebskosten, allgemeine Sicher-heitsbetrachtungen werden nher betrachtet und Ver-gleiche zwischen den beiden unterschiedlichen Vortriebs-methoden gezogen.

The increasing infrastructure requirements of Graz main

railway station required a longitudinal Main Cable Tunnel

with 877 m in length and driven with pipe jacking by in-stalling precasted concrete pipes and utilizing an open

hooded shield (3.18 m internal diameter) for excavation.

The Cross Cable Tunnel (85 m length) was driven by con-

ventional excavation utilizing NATM support and a final

shotcrete lining. The headings of the two tunnels had to be

driven through quaternary sediments above the ground

water table with an overburden varying from 3 to 14 m.

As both excavation methods were carried out with simi-

lar cross sections (approximately 12 to 13m2 excavation

section) and under similar ground conditions, a reliable

comparison of both methods is possible. The paper includes

technical and economical aspects, with the main focus on

the comparison between prognosis and encountered condi-

tions. Additionally following aspects like rates of advance

and construction time, surface settlements and their effect

on the railway operation, construction costs as well as gen-

eral safety aspects are worked out and compared between

the two different tunnelling methods.

The upgrading of the existing railway proper-ties of Graz Main Railway Station and there-fore the increasing infrastructure requirements

necessitate new data and power links. Addition-

ally, the existing southbound railway line Sd-

bahn, the regional railway to Kflach and the

new Koralmbahn Graz Klagenfurt will also

be integrated to the existing and new facilities.The main cables are 15 kV traction power and

110 kV high voltage supply cables and multitudi-

nous links for the railway control systems like

data and telephone cables. Due to the dense ar-

rangement of the existing facilities on the surface,

such as railway tracks, buildings, platforms, a

shallow placement of the cables was impossible.

Therefore an underground solution with two

different orientated tunnels was designed, which

was later on constructed during unrestricted

railway operation at the Graz central station.

These structures consist of the 877 m longitudi-

nal Main Cable Tunnel, the 85 m Cross CableTunnel, three access shafts, several cable ducts

to existing facilities and an underground connec-

tion between the cross tunnel and the basement

of the station building (Figures 1, 2, 11 and 12).

Description of bothtunnelling methods

During preparation of the final design a conven-

tional tunnelling method and a shield tunnelling

method were considered. The costs for both

methods were estimated to be similar. Hence it

was decided to prepare tender documents forboth methods (4). The tenderer could either se-

lect one of the two methods or bid for both meth-

ods. Additionally the tender documents also con-

tained specifications for alternative offers.

Cross sectionThe cross section was designed to meet the re-

quirements of a clearance profile of 1 m width

and 2.1 m height, twelve cable trays on the walls

and three cable ducts in the invert for 15 and 110

kV power cables (Figure 3).

Excavation methodsThe excavation equipment had to be suitable for

the geological situation with quaternary sandy

gravel, silty gravel, silt and sand lenses, occa-

sionally stones/blocks up to several dm diameter

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FELSBAU 23 (2005) NO. 6

Fig. 2 Top view detailof the Main and the

Cross Cable Tunnel.

Bild 2 Luftbilddetaildes Lngs- undQuerkollektors.

Fig. 1 Top view

of the Cable TunnelSystem Graz MainRailway Station.

Bild 1 Luftbild desLeitungskollektoren-Systems am GrazerHauptbahnhof.

Fig. 3 Cross sec-

tions for conventionaltunnelling and in case

of shield excavation.

Bild 3 Regelquer-schnitte fr zyklischen

und kontinuierlichenVortrieb.

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FELSBAU 23 (2005) NO. 6 29

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Fig. 4 Schematicallylongitudinal and cross

section for conven-

tional tunnelling.

Bild 4 SchematischerLngs- und Quer-

schnitt den zyklischenVortrieb betreffend.

Fig. 5 Supportingworks at conventionaldrive.

Bild 5 Sicherungs-

arbeiten beim zykli-schen Vortrieb.

Fig. 6 Schematicallylongitudinal sectionthrough the openhooded shield.

Bild 6 Schema-tischer Lngenschnittdurch das offeneHaubenschild.

so called Murnockerl and maybe local are-

as with conglomerates (6). Also further anthro-

pogenic material in areas with low overburden

and the possibility of relics from the 2nd world

war had to be considered. As the ground water

table is below the tunnel, only seepage water

was expected.

For conventional excavation a intersection

of the cross section in the upper top heading

section and the combined bench/invert section

was foreseen. The maximum distance between

tunnel face and invert closure was defined to

be less than 4 m (Figures 4 and 5). The surface

settlements were estimated to be less than

10 mm.

The shield construction applied was an open

hooded shield (1). The accessibility of the tunnel

face was a precondition for the method in order

to remove anthropogenic material upon re-

quirement. The basic design parameters of the

shield are 72 inclined cutting edge, a longitudi-

nal cutting head, three forepoling blades in the

roof section, three breasting plates to support

the upper face section and a horizontal intersec-

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Fig. 8 Shield drive performance per day and net shield drive performance per hour.

Bild 8 Schildvortriebsleistungen pro Tag und netto Schildvortriebsleistungen proStunde.

tion of the face called table (Figures 6 and 7).

The expected surface settlement in case of

shield excavation was between 20 and 30 mm.

Tunnel liningFor conventional tunnelling a single shell shot-

crete lining, thickness 0.25 m, lattice girders and

two layers of wire mesh were designed. As there

were no special requirements concerning even-ness and water tightness of the cable tunnel, no

final lining was necessary.

In case of shield excavation a segmental lin-

ing, thickness 0.25 m, was defined in the tender

documents. Within the alternative tender the

segmental lining was replaced by precasted con-

crete pipes with 3.68 m outer diameter, 3.2 m

length, 0.25 m thickness and 21.8 t weight (2, 3).

ForepolingThe forepoling for conventional tunnelling was

designed by the use of steel sheets (t = 5 mm,L = 2 to 2.5 m, b = 0.22 m, up to 30 pcs) or fore-

poling piles (d = 26 mm, L = 2.3 to 3.5 m, 25 to

40 pcs). The decision weather to use sheets or

piles was made on site, depending on the soil

density (see Figures 4 and 5).

The shield was equipped with three blades in

the roof section which were set with hydraulic

jacks with a maximum stroke of 0.6 m (see Fig-

ure 6).

Face stabilityThe face stability for conventional tunnelling

was ensured by intersection of the cross sectionin the upper top heading section and the com-

bined bench/invert section, a supporting core

and further face support by shotcrete and wire

mesh (see Figures 4 and 5).

In case of shield excavation the inclined tun-

nel face (between 40 and 72), the horizontal

intersection (table) to create an upper support

body of ground material and the three breasting

plates for face support in case of a longer exca-

vation stop, guaranteed the face stability (see

Figures 6 and 7).

Additional measures aheadof excavation works

Experience shows that within the well graded

soil, sometimes lenses of non-cohesive rounded

gravel occur. Though these gravels were not en-

countered within the site investigation pro-

gramme, their existence had to be expected. Uni-

form sized layers could have a non-cohesive

flowing behaviour and might jeopardize the sta-

bility of the tunnel face.

As a precautionary measure grouting ahead

of the tunnel face was carried out. Within the

design of the conventional excavation method,

grouting was foreseen by means of 6 m grouting

lances. The lances are set every second round

and grouted with low pressure to improve the

abutment area of the forepoling.

Fig. 7 View through the open shield to the excavation face.

Bild 7 Blick durch das offene Schild in Richtung Ortsbrust.

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Fig. 9 Detail of theexcavation face with

partly solidified soilby grouting material Mixed Face Condi-

tions.

Bild 9 Detail derOrtsbrust mit teilweise

durch Injektionsgutverfestigtem Boden.

For shield excavation the underground grout-

ing by use of lances out of the shield was estimat-

ed to be not economical because it would slow

down the advance rate in a significant degree.

Hence it was decided to carry out grouting meas-

ures from the surface. Expected problems were

the spoiling of railway ballast substructure with

grout and the interference of the grouting works

with the railway operation.

Estimated advance ratesThe advance rates for conventional tunnelling

were estimated to be between 2.5 and 3.5 m per

day. For shield excavation the rates were esti-

mated to be about 8 m/d. Due to the lower ad-

vance rates for conventional tunnelling two

drives would be necessary to meet the time

schedule.

Additional safety measures

World War II relicsGraz Central Station and the nearby factories

were subject to heavy bombing in the years 1944

to 1945 (5). Experience shows an percentage of

about 10 to 15 % of the bombs were duds. Sever-

al areas and points were traced by the depart-

ment of civil defence in Graz where duds were

thought to be. As these areas covered nearly the

whole project area, it was decided to carry out a

systematic exploration by means of a magnetic

field probe. With this method three possible

points were traced and later on explored by

means of test pits. One of the pits contained a

500 kg dud, which was deactivated by an expertfrom the ministry of the interior.

Monitoring

The monitoring for conventional tunnelling con-

sisted of deformation measurements of shotcrete

lining and of ground and track settlements. The

monitoring for shield excavation consisted only

of surface measurements of ground and track

settlements. In both cases the inclination of rail-

way catenary masts in critical excavation phases

are monitored around the clock.

Conditions and excavationvelocity at the longitudinalMain Cable Tunnel

According to the Austrian Flexible Model of

Construction Time the average mechanical tun-

nel drive had been offered by the contractor with

a daily rate of 9.5 m. This rate already included

the launching of the tunnelling machine, all cal-

culated interruptions due to the working proc-

ess, geological problems, predicted downtimes,

reinstalling of the machinery and the refilling of

the ring space. The real net tunnelling advance

was calculated by the contractor with approxi-

mately 17 m/d.

The daily excavation works were carried out

on a 24 hour basis, three shifts eight hours each.

The first days were embossed by a very slow ad-

vance because equipment like the conveyor belthad to be installed simultaneously. But after a

few days, on the 1st of October 2004 the excava-

tion velocity reached the overall peak with

23 m/d due to favourable geological conditions

and short mucking times (Figure 8).

From chainage 230 m on increasing jacking

pressures up to a level of over 500 bar and prob-

ably also the bended lining at the area of the

Middle Shaft led to much lower advance rates

than before. Around the 18th of November 2004

the shield advance reached again peak values up

to 22 m/d although the mucking distance was

fairly long (approximately 650 m). It seemed thatat this part of the drive the excavation crew got

used to the driving conditions, which could be

interpreted as learning curve. The late rising of

the learning curve is probably the result of unex-

pected unfavourable face conditions and that the

jacking pressures were on their limit. Finally on

6th of December 2004 the shield reached suc-

cessfully the target shaft north.

It was intended to create a more or less homo-

geneous injection umbrella along the whole tun-

nel roof by drilling injection pipes in a certain

grid with following grouting. During excavation

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Fig. 11 Longitudinal section of the Main Cable Tunnel including geology and vertical settlements.

Bild 11 Schnitt durch den Lngskollektor Darstellung der Geologie und der Setzungen.

it was visible that wide areas around the roof

were not injected because of the compactness of

the ground. But also loose gravel layers were

encountered uninjected possibly due to a too

wide drilling grid (Figure 9). Unexpected chang-

ing of the ground compactness led to a reduction

of the drive velocity as well as the above average

maintenance times. Also the bentonite slurry

used as a lubricant film around the jacking pipes

could not built up properly due to permeable

gravel layers in the quaternary sediments. The

effects of this behaviour were high jacking pres-

sures due to the high friction between the con-crete pipes and the surrounding soil.

Maintenance and downtimes calculated by

the contractor have been exceeded significantly

(7).

Fig. 10 Theoreticalcomparison of con-struction time between

shield and conven-tional excavation atthe Main Cable Tunnel.

Bild 10 TheoretischerBauzeitvergleich

zwischen zyklischemund kontinuierlichemVortrieb beim Lngs-kollektor.

Conditions and excavationvelocity at the mined CrossCable Tunnel

The mined tunnel part of this project could be

finished without any problems, except for steel

lagging problems at one short part of the tunnel

due to big stones in the tunnel perimeter. After

changing steel lagging to forepoling piles no fur-ther problems were encountered.

Because of the very small tunnel profile and

the very short learning time for the tunnel crew

the average driving performance was approxi-

mately 3 m/d.

Comparison of theexcavation velocities

A theoretical comparison of the overall construc-

tion time based on the actual advance rates

shows, that two conventional drives (north andsouth) for the longitudinal Main Cable Tunnel,

would have shown the same construction time as

a shield drive (approximately 180 d). Manufac-

turing time as for the shield was not needed in

the case of conventional tunnelling which had

positive effects on construction time (Figure 10).

Settlements

Settlements encountered at thelongitudinal Main Cable Tunnel

From the beginning of excavation it had to be

learned that the geological conditions changedsuddenly in an unpredictable way. The geotech-

nical safety management plan has foreseen that

the normal settlement values would not exceed

10 mm. The 1st level alert criterion was reached

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FELSBAU 23 (2005) NO. 6 33

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Fig. 12 Longitudinal

section of the CrossCable Tunnel including geology andvertical settlements.

Bild 12 Schnitt durch

den Querkollektor Darstellung derGeologie und der

Setzungen.

by exceeding 10 mm surface settlements at the

driving area and 20 mm 10 m behind the face.

The 2nd level alert criterion has been triggered by

reaching 50 mm and the 3rd criterion by exceed-

ing 50 mm and posing effects to the safety of peo-

ple or structures.

Sudden inrushes of mostly loose gravel always

triggered the 3rd level alert criterion. Fortunately

these occurrences did not effect the surface im-

mediately. Volume losses in front of the excava-

tion face spread slowly within one to two days to

the surface, depending on the overburden. Sothere was always enough time to inform the

management of Graz Main Station. The average

settlements had been measured with 40 to

60 mm at the area of overburden between 3.5

and 7.5 m (Figure 11). Afterwards the volume

losses had to be filled up with cement grout from

the surface to prevent further settlements and

the tracks had to be readjusted by a ballast

tamping machine.

Settlements encounteredat the Cross Cable Tunnel

The same alert level criteria were valid for the

cross passage, excavated by conventional min-

ing technique. By using forepoling items like

steel lagging and forepoling piles volume losses

could be prevented when passing difficult geo-

logical conditions. The maximum settlements at

the surface have been measured with 9 mm,

which did not really effect the railway tracks

(Figure 12). The excavation of the cross passage

could be finished without interruption of the

train sequence above.

Comparison of settlementsAt comparable tunnel sections by shield driving

and by conventional tunnelling with similar

overburden and geology one can clearly see adifference on the surface effects between the two

methods. Similar areas are for the Main Cable

Tunnel from tunnel metre 510 to the end of the

drive (tunnel metre 877) and for the cross pas-

sage from the beginning to the end. Both zones

have been excavated with overburdens from 3.5

to approximately 7.5 m.

Primary settlements

Whereas the excavation of the cross passage

could be finished without interruption of the reg-

ular train operation, settlements above the

shield drive led to continued interruption of train

service on tracks above. The maximum vertical

surface displacements have been measured with

only 9 mm at the cross passage area. The peak

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value of settlements at the shield driving area

was more than 200 mm, the average between 40

and 60 mm.

Secondary consolidation

Whereas the secondary consolidation stopped

immediately after ring closure at the mined tun-

nel part, the consolidation above the shield drive

kept on for weeks. The bulking of the surround-ing soil caused by volume loss during shield drive

led to excessive secondary consolidation. Three

month after penetrating shaft north end of

shield drive the average was measured with

8 mm at the area mentioned above.

Working conditionsfor the tunnel crew

Shield driveThe soils encountered usually during the shield

drive had a constant humidity so that no dustcould develop. The shielded space showed ex-

cellent air conditions for the tunnelling crew

during the whole drive and also the staffs ac-

cess to the shield was mostly dry and clean. Al-

though sudden inrushes of soil into the shield

occurred, the staffs health and safety were

never at risk due to the sufficient distance be-

tween the machine driver and the excavation

face.

Conventional tunnellingDue to small portions to be supported step by

step this could only be managed by applicationof dry shotcrete. During spraying and signific-

ant time after the small tunnel profile was still

full with dust although the tunnel was ventilat-

ed. Especially to the nozzle man the situation

was quite uncomfortable because of very re-

duced visibility during placing the shotcrete.

The stability of the tunnel itself was never in

danger.

Theoretical comparisonof excavation costs

A retrospective comparison show similar costs

of about 5 100 EUR per metre for both methods.

The sum includes tunnelling costs, costs for

shield and mining equipment, cost for site facil-

ities, time related cost, cost for muck transport,

costs for surface grouting and costs for explora-

tion on war legacies.

Summary

According to construction costs and time there is

no significant difference between the two meth-

ods. However a glance at surface settlements

and its effects on railway operation gives the

mined method conventional tunnelling a

clear preference for projects with similar bound-

ary conditions in the future. The constant threatof surface instability above the tunnel drive

caused by potential sudden inrushes of ground

material is unfavourable for a reliable safety

management on site.

The comparison resumes as follows:

Similar costs per metre,

Similar total construction time, considering

preparation time, maintenance time and

downtime,

Absolute advantage for the conventional

method concerning surface settlements. The

surface settlements of the conventional meth-od add up to only 10 to 20 % of the shield

drive,

Absolute advantage for the conventional

method concerning the face stability and the

minimization of interference on the railway

structures,

Absolute advance for the shield method con-

cerning the working conditions for the tunnel

crew,

Advance for the shield method for the later

maintenance and equipment installations in

the cable tunnels due to the perfect even

shaped concrete surface.

References

1. Steiner, H. ; Vigl, A. ; Vergeiner R. ; Hrlein N.: Leitungs-kollektor Graz Hbf. Pressrohrvortrieb DN 3180 mit offe-

nem Haubenschild. Felsbau 23 (2005) Nr.5, S.76-82.2. Hrlein, N. ; Ppperl, R. ; Steiner, H. ; Schneider, K.: DerKabelkollektor Graz Hauptbahnhof. Beton Zement 4/2004,S. 42-45.3. Kolic, D. ; Hrlein, N. ; Schneider, K. ; Steiner H.: Com-

petitiveness of Pipe-Jacking Tunnels. Symposium KeepConcrete Attractive, Budapest 2005.4. Fischer, P. ; Bauer, F.:Zuschlagskriterien zur Beurteilungvon Alternativangeboten am Beispiel des Wienerwald Tun-

nels. Tagungsband sterreichischer Tunneltag 2004,

S. 87-90.5. Brunner, W.: Bomben auf Graz. Die DokumentationWeissmann. Graz: Leykam Verlag, 1989.6. sterreichische Bundesbahnen: Baugeologische Do-

kumentation und Vortriebsbetreuung des Leitungskollek-

tors Graz Hbf. Mag. Erhard Neubauer ZT GmbH, 2005 (in-tern).7. sterreichische Bundesbahnen: Geotechnische Doku-

mentation Leitungskollektors Graz Hbf. iC consulten, 2005(intern).

Authors

Dipl.-Ing. Dr. mont. Helmut Steiner, BB-Infrastruktur BauAG, Geschftsbereich Projekte, Projektleitung Koralm-bahn 1, Griesgasse 11 / 2. Stock, A- 8020 Graz, Austria,E-Mail [email protected]; Dipl.-Ing. Gerald Edlmair,Laabmayr & Partner, Preishartlweg 4, A-5020 Salzburg ,Austria, E-Mail [email protected]; Dipl.-Ing. Ralf Vergeiner,

iC consulenten, Kaiserstrae 45, A-1070 Vienna, Austria,E-Mail [email protected]

www.vge.de

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FB6 05 Steiner