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STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6 27
PIPE
JACKING
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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PIPE
JACKING
STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
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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STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6 29
PIPE
JACKING
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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PIPE
JACKING
STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6
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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STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6 31
PIPE
JACKING
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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PIPE
JACKING
STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6
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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STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6 33
PIPE
JACKING
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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PIPE
JACKING
STEINER, EDLMAIR AND VERGEINER: PIPE-JACKING VERSUS CONVENTIONAL TUNNELLING
FELSBAU 23 (2005) NO. 6
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