Survey Solution on the construction sites North Downs
Tunnel and Medway Crossing Bridge
- HighSpeed-railway from London to the Eurotunnel -
Institut für Geodäsie und Photogrammetrie, Technische Universität Braunschweig
Gaußstraße 22, D-38106 Braunschweig, email@example.com
Beton- und Monierbau GmbH
Wilhelm-Bläser-Straße 8, D-59174 Kamen, firstname.lastname@example.org
Abstract. This paper explains that the application of modern measurement technology
becomes more and more important in tunnelling and bridge construction. New sensors
increase the accuracy and reduce conventional staff intensive measuring concepts. The
interaction of planning, basis measurement and the building concurrent measurements is
currently decisive for smooth operation during these engineering projects.
Key words: Tunnel construction, Control system, Base network, Quality Management
After ten years of detailed planning work Great Britain has started a unique railway
project. In the future the Channel Tunnel Rail Link (CTRL) will connect the destination
railway station St. Pancras in London with the Eurotunnel (Fig. 1).
Figure 1: Route of the Channel Tunnel Rail Link from London to the euro tunnel
The new 109 kilometre long railway line may cost approx.
7.2 bill € up to finishing in 2007. Then the CTRL
duplicates the maximum transportation capacities between
Great Britain and the mainland and halves the time for
travelling from London to the tunnel entrance at
Folkestone. In less than 2½ hours, the metropolises
Brussels and Paris will be reachable from the City of
London with the new high speed train Eurostar (Fig. 2).
Figure 2: Eurostar
2 Tunnel and bridge construction sites
The large construction sites,
contract 350/410 contained
tunnelling and bridge via the
Medway River (Fig. 3). In the
neighbourhood of Rochester in
the earldom Kent was built up
the technically most extensive
and therefore most expensive
fragment of the first route
section. In this contract, a 3.2
km long tunnel crossing the
North Downs Hills was built
synchronous with the 1.3 km
long prestressed bridge via the
Medway River (Fig. 4). In
1998 an international joint
venture, consisting of the
companies Miller (Great
Britain), Dumez (France) and
Beton- und Monierbau
(Austria) were awarded the
contract for carrying out of the
construction . In spring
1999, after extensive
foundation construction work
began the tunnel driving (Fig.
5) and the first work for the
production of the large bridge.
The North Downs Tunnel with
a length of 3196 m was
according to the principles of
the New Austrian Tunnelling
Method (NATM). The NATM
was characterized by spraying
concrete, reinforcement, lattice
girders and anchors.
Figure 3: Longitudinal section North Downs Tunnel
Figure 4: Construction and pillar foundation Medway Crossing Bridge
For excavating, in part very hard cretaceouses, two heavy tunnel roadheader machines
were used. The sectional view with approx. 13 m of width and 10m of height with up to
165 square metre was cut up in individual steps (crown/bench/invert) both from the
southeast (country portal) and from northwest direction (London portal) as well.
The 1340 m long Medway
Crossing Bridge was built up
like a prestressed reinforced
concrete construction. The
bridge rests on 25 pillars and
will go parallel to the Motorway
M2 (Fig. 4). The building was
set up in the incremental
launching system by the two
sides at the same time and
consists of 2 pre-land bridges
and a free porch of 152 m.
Figure 5: Construction North Downs Tunnel (Country Portal)
3 Quality Management
In the course of international co-operation just at large-scale projects like in the tunnel-
or bridge-construction the advantages of the quality management are particularly very
dominant in the project control. By norms (e.g. combined in the DIN EN ISO 9000 -
family) the facts documentation, design steering, contracts etc. are regulated among
other things. Enterprises which merge into a team and are certified according to an
above norm can cooperate without an extensive additional co-ordination. Therefore the
project gets transparent, i.e. uniformly interpreting for every editor on a construction
site uniformly interpreting cash. New possibilities arise according to the security checks
depending on large construction sites.
At first due to the high requirements on the quality assurance in the areas, geodetic and
geotechnical measurements by customers and construction supervision an extensive
description of the scheduled measurement- and adjustment method was required. This
happened by obligatory method instructions, the so-called "method statements".
4 Geodetic measurement concept
4.1 Base network
More than in other applications high precision engineering constructions need a stable
base network with highest accuracy. It is essentially all about the construction of an
unstressed special net at the basis measurement in the tunnel construction for the
assignment of the planned tunnel axis to the locality. These special networks are needed
increasingly as a starting point for the control measurements to be carried out during
the time construction and the geotechnical measurements. A base network for the
generally consists of two
portal networks. These are
21 connected to each other
and attached to primary
points in one big measuring
1 21 campaign. Such a concept
was introduced by  for
the setting out of high-
speed railways. The portal
networks should be at
disposal during the
complete working phase
and furthermore for
London Portal 21 marking and supervision
tasks. Only pillar points
became possible for the
question about a durable
marking. The higher costs
compared to other marking
themselves, however, by
the high stability and by the
inevitable for establishing
37 horizontal and vertical
control points for
37 advantage of a pillar
network is the possibility
that this network can also
serve as a basis for
for longer time and at a
40 sufficient stability .
Figure 6: Base network for the North Downs Tunnel
Starting from the points of the superordinate co-ordinate system Rail Link Engineering
Network (Fig. 6) at first a high exact, unstressed base network had to be laid out as a
starting point for the establishment of horizontal and vertical control points for
tunnelling. For this, in each case six solid concrete pillars were placed on the edge of
the pre-cuts (Fig. 7).
Figure 7: Portal network at Country Portal
Thereupon a GPS based measuring campaign was required for the geodetic integration
of these so-called portal networks into the superordinate co-ordinate system (Fig. 9).
The base network had a expansion of approx. 9 km and were observed by using eight
identical points of the Rail Link Engineering
Network as well as the 12 portal pillars. The
equipment contained six GPS receivers, one GPS
station remained permanent in business during
the complete measuring campaign (Fig. 8).
Supplementary terrestrial measurements in the
portal areas as well as portal connecting precise
levelling were carried out. The obtained
placement accuracy of the pillar points was
better than 4 mm. Figure 8: GPS campaign 1999
Figure 9: Parameter transformation from GPS to the superordinate system
The special bridge network was carried out by conventional measurements using TC
2002 total stations. Seven given survey marks, four marks moving (tide), two proper
benchmarks and 15 pillars were occupied. The network adjustment supplied an
accuracy, less than 5 mm.
4.2 Accompanying measurements and main controls
Being part of the making accompanying measurements are the geodetic underground
measurements, included are the daily routine free stationed measurements for the
positioning and inspection of the gearing lasers. Furthermore, measurements for the
stabilization and continuation of the underground reference network.
At the demand of independent main control measurements by customers and
contractors, however consciously other instruments and software products were used.
Due to the good agreement of several independent control measurements the
contractors renounced the use of gyroscope measurements. The simulation calculation
of the error of breakthrough (Fig. 10) resulted in the prognosticated theoretical standard
deviation with max. 130 mm.
Figure 10: Simulated error of breakthrough, North Downs Tunnel
From the geodetic point of view the error of breakthrough can be defined as the
predicted theoretical standard deviation of the breakthrough. This is derived from the
relative error ellipses of the respectively last traverse station of both advance directions.
Models describe complex facts with mathematical methods. Due to the fact that the
reality can be represented only simplified by the models, the a priori measuring
precisions are mostly set too pessimistically.
The deviations at breakthrough on 8th June 2000 were only 19 mm in horizontal
direction and 15 mm in the height.
The Medway Crossing survey program involved the following survey works:
! Daily: rotation of the two big hammerheads
! Weekly: all measurements in touch with the launching works
o Measurements before launching
# Set out center line on top of the piers by free stationed using
# Setting out of 2 benchmarks for compression measurements at
# Setting out temporary bearings and skidding beams
o Measurements during launching (Fig. 11)
# Deck position monitoring at 2 reference prisms at the first
# Incline measurements on the top of the piers
# Compression and settlement at the temporary bearings
# Visual control of skidding beams and bearings
# Settlement monitoring at pier base by load of the first concrete
o Measurements during jacking
# Geodetic monitoring deck, piers, pile cabs, temp. bearings
# Immediately message in case of out of tolerance 3 mm
# Stop at once by all observers in case of peculiarities
# Course correction by hydraulic jacks
! Monthly: Tower cranes, Bailey bridge
! Quarterly: Control of the base network
Figure 11: Targets and inclinometers for measurements during launching
5 Excavation control systems
The current standard by the New
Austrian Tunnelling Method
(NATM) is the use of total stations
equipped with a motor and
increasingly total stations with
Automatic Target Recognition
In the background of greatest
possible profile precision during the
outbreak, conventional gearing
lasers and automatic motor laser
systems for the indication of the
outbreak line were installed. Both
Figure 12: Laser in use for the excavation control
systems were available for the
position defining processes, the
profile section and the built up of the lattice girders, at the same time. At the production
of the invert outbreak and at the precise contribution of the sub-concrete control
systems based on rotation lasers came for use.
6 Profile control systems
Cross-section measurements normally are part of the daily routine measurements
according to the NATM tunnelling method. By permanent controls one can react fast at
stated lower or over-profiles and in many cases a greater damage can limited by
Due to an obviously very uneven spraying concrete picture (high and depression areas),
the construction site North Downs Tunnel decided on a full flat photo with a digital
picture measuring system. Two DIBIT-Tunnelscanner were used based on stereo photo-
grammetry recording of the spraying concrete surfaces with CCD cameras (Fig. 13).
In the result the construction
site received a high qualitative
photo documentation and a
full flat profile control of the
existing spraying concrete
surface with an accuracy of
approx. ± 10 mm (Fig. 14).
By detailed screening one
could prove, that the high and
lows did not lie in the
suspected range and therefore
were for the further
construction planning of
Figure 13: Dibit Tunnelscanner in use
Figure 14: Dibit results with lover and over-profile. Red = lower profile > 3cm, Green = over profile
0-9cm and Blue = over prolile > 12cm
7 Geotechnical measurement concept
Normally follow the order, execution and evaluation of geotechnical measurements in
the tunnel construction of a approved planning, the geotechnical measuring concept. In
this the procedure is regulated the inquiry for deformation distortions on predefined
stations as well as the frequencies of measurements, places for the instrumentations etc.
In special cases e.g. at unexpectedly high settlements, however also additional
measures for the recording of the deformation event can be ordered.
At the construction site North Downs Tunnel the underground geotechnical
measurements confined themselves to visual deformation observations and the
installation of tunnel extensometers with different lengths. The originally scheduled
pressure measurements were renounced with regard to the stable geology.
Based on the stable portal pillar networks, the high exact underground reference
networks for the 3D deformation recording into the tunnel excavations developed in the
course of the progressive tunnelling. The deformation measurements were oriented by
calmed points in the back and produced millimetre documentations of the deformation
in the excavation area.
The measurement results from both excavation went out to the responsible person for
the interpretation of all results from geotechnic, geology and spraying concrete strength
check directly after the adjustment.
In a post processing the results of the geotechnical measurements immediately went to
an electronic stability check. In the result one contained a classification of the
measuring cross-cuts in three alarm limits. The layering reached from "quite safe"
about "immediate need for action" to the introduction of the complete evacuation over
effective clay and light signals in the complete construction site area, the so-called
"evacuation alarm". By the hand over of safety identity cards at the tunnel portals the
immediate summary to the number of persons situated in the tunnel was also ensured
for this emergency.
The measurement results altogether showed low deformations at the North Downs
Tunnel in the area of few centimetres and a quickly subsiding of these deformations.
The distance of the measuring cross-cuts was predominantly 25 m, only in the portal
areas the distances of the cross-cuts were reduced.
The settlement observations of the surface with precise levelling completed the
geotechnical measuring program. The results of these measurements, represented in
cross-sections and longitudinal profiles, were an important aid to the judgment of the
went ahead settlements. This fact is not ascertainable by underground deformation
measurements since the zero measurement can be carried out only after the spraying
Further levellings were carried out at some route near buildings. The results of these
levelling measurements showed a good agreement with the underground observations.
The deformation characteristic corresponded of a slow, very balanced settlement with
low extent without conspicuous cracks with maximum values of approx. 40 mm in
 Kahmen, H., et al.: Technical Networks for High-Speed Railway lines. Symposium on
Geodesy for Geotechnical and structural engineering, Eisenstadt/A, 1998, p.
 Schäfer, M., et al.: Messtechnische Konzepte im Tunnelbau von der Planung bis zur
Fertigstellung. Zeitschrift für Vermessungswesen, 2000, Volume 11: p. 381-
 Weithe, G.: Channel Tunnel Rail Link Englands HighSpeed-Bahntrasse von London
zum Eurotunnel, Vermessungstechnische Komplettlösung an der Baustelle
North Downs Tunnel. Ingenieurvermessung -Aktuelle Baustellen-, VDV-
Schriftenreihe, 2001, Volume 18: p. 51-66