On the role of the Engineering Geologist in the Construction Phase of Challenging Tunnel Projects

Abstract

Independently, if hardrock or soil conditions, conventional or mechanized tunnelling -
the role of the engineering geologist as an „interpreter“ of the naturally formed subsurface conditions
is undergoing significant changes in the course of the planning and realization process of any tunnel
project. Even with the most detailed and most competent site investigation risks for adverse subsurface
conditions will still remain. The remaining uncertainties regarding ground behaviour and the
interaction of ground and structure and the implied risks for the technical and contractual aspects of
underground construction do indeed require further involvement of engineering geological expertise
in the course of project realization. The presented paper is intended to analyse the roles and tasks for
engineering geologists involved in a tunnelling project either as a representative of the builder / client,
the authorities or the contractor.

Full text

Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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1 INTRODUCTION
1.1 Ground Risks in Tunnel Construction
In tunnel construction, insufficiently recognized
or inadequately considered ground conditions
can lead to considerable construction time
prolongation, cost increases or even damage such
as collapses or damage to existing infrastructure.
According to an analysis of international
reinsurance companies, tunnel construction is
regarded as the only sector in the construction
industry, where possible damage can exceed the
costs of the construction project itself several
times (Lombardi, 2004; Wannick, 2007).
Challenging tunnel projects have therefore
always placed great demands on the ability of the
engineering geologist and geotechnical engineer
to properly explore, describe and predict the
geological circumstances and interactions
between the ground and the tunnelling method.
1.2 Project phases
From the view of the engineering geologist, the
following project phases may be distinguished
during the realization of a tunnel construction
project:
• the preliminary site investigation phase(s), in
which the geologist is usually responsible for
the planning of the investigation measures and
the identification of relevant project risks,
• the tender preparation phase for the main
construction works,
• the project execution phase in which the
geologist(s) may have different roles
depending on their individual task and
affiliation,
• as well as a post-project phase, where
experiences gained during the execution are
either processed for documentary background
or within the framework of ongoing litigation
procedures.
On the role of the Engineering Geologist
in the Construction Phase of Challenging Tunnel Projects
Ralf J. Plinninger
Dr. Plinninger Geotechnik, Bernried, Germany.
Peter Sommer & Gerhard Poscher
geo zt gmbh – consulting geologists, Hall in Tirol, Austria.
ABSTRACT: Independently, if hardrock or soil conditions, conventional or mechanized tunnelling -
the role of the engineering geologist as an „interpreter“ of the naturally formed subsurface conditions
is undergoing significant changes in the course of the planning and realization process of any tunnel
project. Even with the most detailed and most competent site investigation risks for adverse subsurface
conditions will still remain. The remaining uncertainties regarding ground behaviour and the
interaction of ground and structure and the implied risks for the technical and contractual aspects of
underground construction do indeed require further involvement of engineering geological expertise
in the course of project realization. The proposed paper is intended to analyse the roles and tasks for
engineering geologists involved in a tunnelling project either as a representative of the builder / client,
the authorities or the contractor.

Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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1.3 Roles within the project
The role of the geologist is defined by his
position within the project group and the project
phase (Poscher, 2004). Usually it refers to one of
the following positions and functions:
• Geologist, representing the client (transport
authority, energy supplier, etc.);
• Geologist representing the contractor, taking
over tasks within the scope of the construction
company´s chances and risk management,
either during the tendering phase and / or in
the execution phase of the project;
• Geologist, representing public authorities (for
example in the area of Health, Safety or
Environmental Protection).
In the following paragraphs the involvement
and usual core tasks of the engineering geologist
during the construction phase of larger tunnel
projects will be discussed.
2 DOCUMENTATION – THE “VIEW
BACK”
2.1 Objectives
A comprehensible and objective documentation
of the encountered geological and geotechnical
conditions during excavation is a basic element
for answering any ground-related question. Such
documentation on the one hand serves as a tool
for controlling the tunnelling works, i.e. adapting
excavation sequence and support to the actual
ground conditions (® Section 3.2) and on the
other hand serves as evidence for objective
discussions on contractual topics between client
and contractor.
Unquestionably, the preparation of such
documentation is one of the core tasks of the
involved engineer geologist(s), regardless of
their role and affiliation in the project. However,
for especially challenging or conflict-prone
projects, the implementation of the so-called
"two man rule" has proven as a valuable method
for enhancing objectivity and credibility of the
work. Such procedure includes the joint
inspection of tunnelling works, joint assessment
of relevant rock and rock mass parameters and
mutual acceptance of documents by geologists
acting on behalf of different parties in the project
(Figure 1).
Figure 1. Executing the “two man rule” during geological
documentation: A close cooperation between geologists
of client and contractor contributes to an objective and
reliable geological documentation (Photo: Vigl).
2.2 Documentation for conventionally mined
tunnels
For conventional excavation, mapping of the
excavation face is still the main tool of geological
assessment. The favourable conditions for direct
examination of rock and rock mass properties
and the possibility to directly measure the
orientation of relevant discontinuities contribute
to a generally high level of quality for geological
and geotechnical documentation. Additionally,
usual advance rates of some meters to
dekametres per day provide a sufficient density
of observation. Figure 2 shows an example for
such full-face mapping of the crown section of a
road tunnel.
Figure 2. Example for geological face mapping in the
crown section of a road tunnel including generalized
information on lithological units and discontinuities.

Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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2.3 Documentation for TBM tunnels
Under favourable conditions, for instance during
open gripper TBM operation, partial mapping of
the face might be supplemented by
documentation of even larger scale outcrops in
the perimeter of the tunnel.
Under unfavourable conditions, for instance
operation of a double shield TBM with precast
segmental lining and largely closed cutterhead
design, limited access to the rock mass, the
impossibility to take proper readings with a
magnetic compass and the usually high advance
rates achieved might significantly limit the
possibilities for proper direct documentation at
appropriate intervals. Under such circumstances,
it might even be useful to distinguish between a
"mapping" of the actually visible areas at the face
and a larger-scale "interpretation" of the
geological conditions in order to equally meet
both mentioned requirements of the
documentation, excavation control and filing of
evidence (Figure 3).
However, a continuous acquisition of relevant
machinery data and subsequent data back-
analysis might be used as a tool to overcome
some of these problems and to derive a
sufficiently detailed and sufficiently dense
interpretation of the encountered conditions. As
recently presented by Radoncic et al., 2014, daily
comparison of geological documentation,
observed rock mass behaviour and analysed
machinery data can provide interpretations on
relevant rock mass-TBM-interactions like:
• steerability of TBM,
• stability of rock mass at the face,
• blockiness in the cutter head area,
• general degree of fracturing of the rock mass,
• overall intact rock strength,
• or the state of the annular gap.
For the application of such methods (Figure
4), a close interdisciplinary cooperation of
geologists, geotechnical engineers, civil
engineers and surveyors is mandatory in order to
provide more or less real-time interpretation and
to allow adjustment of excavation and additional
measures to the actual geological and
geotechnical prognosis.
Figure 3. Example for TBM Face Mapping (middle
figure) and TBM Face Interpretation (lower figure) under
the limited possibilities of a more or less closed Æ 10 m
TBM cutterhead (upper figure).

Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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Figure 4. Example for the comparison of geological data
and various machinery data sets for an alpine TBM tunnel
(from: Radoncic et al, 2014, Figure 6, page 574).
2.4 Visualization and Data Management
In order to provide data for computer-assisted
communication and analysis, database-supported
documentation software is increasingly used,
especially in large projects. In addition to the
mere distribution of rock units at the face,
additional data on the orientation of relevant
discontinuities, rock properties, rock mass
parameters and displacement measurements can
also be filed in such database systems.
Based on these raw data sets, such programs
allow computer-assisted visualization of the
conditions encountered (Figure 5) as well as easy
evaluations of the recorded parameters (for
instance comparisons between predicted vs.
encountered conditions).
Figure 5. Example for the three-dimensional visualization
of several face mappings in a conventional drill and blast
excavation by use of GIS-based software.
3 PROGNOSIS – THE “VIEW AHEAD”
3.1 Objectives
Ground exploration in front of the current
tunnelling station represents a highly relevant
and highly dynamic task, which is strongly
influenced by the further improvement and
development of technical possibilities. However,
the procedures outlined in the sections below are
only a selection of relevant methods. Usual
practice includes a combination of several
different methods, often applied according to a
predefined stage concept.
3.2 Improvement of the Geological Model
In the course of tunnel excavation, there are
generally far better possibilities for observing
rock and rock mass and for assessment of the
interactions between excavation and ground than
during any preliminary site investigation.
Therefore, the findings of the geological-
geotechnical documentation as described above
will usually allow further improvement and
detailing of the existing geological-geotechnical
model. The complementation of the geological
model and the combination of geological and
geotechnical observations is therefore an
essential component of any risk management in
tunnelling (Schubert, 2001).
3.3 Core Drilling ahead of the face
The execution of horizontal or flat inclined core
drilling methods for ground investigation ahead
of the face definitely represents the highest
quality possible to obtain information on the

Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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lithology, the structure and the rock
characteristics of the ground ahead. Especially
for TBM application, conventional core drilling
with single or double coring tubes is practically
ruled out as a result of the required handling time
for rods and missing borehole support during
those roundtrips, so wireline systems are
frequently used there (Kogler & Krenn, 2014).
However, even for these systems the usually high
efforts for machinery setup, related downtimes
and costs do in fact conflict with the frequent
application of this high-level investigation
method (Figure 6).
Figure 6. Subhorizontal Core Drilling ahead of the TBM
advance from the upper deck of a Æ 10 m doubleshield
TBM using an Atlas Copco DIAMEC U6 Drill Rig.
3.4 Hammer drilling ahead of the face
Due to their usually good availability, relatively
low cost and high drilling performance, rotary-
percussive drilling methods (also referred to as
“hammer drillings”) without extraction of cores
can more easily be integrated into the working
cycle of both, conventional and TBM excavation.
Although only small drill cuttings can be used for
direct geological observation, a large number of
other relevant information on rock and rock mass
composition can be determined indirectly, with
corresponding recording of drilling data. This
allows relatively accurate predictions on the
occurrence of larger cataclastic fault zones, loose
soil, or zones with increased ground water
inflow.
Figures 7 and 8 show examples for the
evaluation and visualization of such drill data. In
the referring case, the data is derived from
standard blasthole drilling, with the data being
recorded using Atlas Copco´s MWD (“Measure
While Drilling”) system and being evaluated
with the referring "Underground Manager"
software.
Figure 7. Example for the interpretation of rotary percus-
sive blasthole drilling for a conventional tunnel drivage
using the Atlas-Copco MWD and Underground Manager.
Figure 8. Example for the interpretation of rotary percus-
sive blasthole drilling using Atlas-Copco´s MWD and
Underground Manager software.
3.5 Application of borehole video inspection
Dropping prices for miniaturized video systems
with cable lengths of ≤ 100 m have in the past
few years allowed an increasing use of optical
inspection systems for boreholes with a
minimum diameter of approx. Æ 40 mm. If
interpreted by a skilled geologist, such optical
inspection opens up a large number of
additionally relevant geological information, in
particular if used in combination with rotary
percussive drillings, where no core is available.

Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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Figures 9 and 10 give a lucid example for the
images and interpretation.
Figure 9. Example for video image in a folded quartz
phyllite series in a Æ 75 mm drillhole used for ground
investigation ahead of a TBM.
Figure 10. Example for the interpretation and
documentation of a borehole video inspection using
project-specific classifications of geological observation.
3.6 Application of geophysical methods
In addition to direct investigation methods, as
described in the sections above, indirect
geophysical methods, e.g. seismic, geoelectric or
georadar methods can also be used from the
undergoing advance. A number of case studies
recently published (Brückl et al., 2008; Kaus &
Boening, 2008; Radinger et al., 2014) do on the
one hand summarize on a useful application of
these methods within the referring projects, but
on the other hand also give hints towards the still
existing uncertainties in the interpretation of
these data (see Figure 11).
Figure 11. Comparison of different stages in the evolution
of the geological model, from top to bottom: Prediction
from preliminary site investigation) – Geophysical
Forecast (Tunnel Seismic While Drilling) – Percussive
Drilling – Encountered Geology (from: Radinger et al.,
2014, Fig. 7, page 574).
4 INTERDISCIPLINARY COOPERATION
ON SITE
As shown in the previous sections of this paper,
state-of-the art documentation and prognosis
includes a vast number of different data sets
gained from various sources. In order to
understand the interactions between ground and
tunnel and to provide optimum solutions, the
engineering geologist on site has to be
implemented into a competent team of
neighbouring expertise. Usually, the main
interactions exist with the following disciplines:
• Civil engineers (planning, realization),
• Geotechnical engineers,
• Surveyors,
• Geophysicists,
• Hydrogeologists and engineering geologists
with other affiliation.
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Proceedings of the World Tunnel Congress 2017 – Surface challenges – Underground solutions. Bergen, Norway.
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an idea of the required interdisciplinary
cooperation:
• Documentation of drill cuttings during rotary
percussive drilling ahead of the face
(® Driller, Civil Engineer),
• Evaluating and geological interpretation of
drilling data for hammer drilling (for instance
MWD) (® Civil Engineer),
• Geological interpretation of TBM operational
parameters (® Civil Engineer, Geotechnical
Engineer),
• Geological interpretation of deformation
monitoring (® Surveyor, Geotechnical
Engineer),
• Geological interpretation of geophysical
investigations (® Geophysicist),
• Actualization of ground water model
(® Hydrogeologist),
• Adjusting support and excavation sequence to
the actual geological and geotechnical
prognosis (® Civil Engineers),
• Judging technically on contractual impacts of
encountered ground conditions (® Civil
Engineers).
5 CONCLUSION
In challenging tunnel projects, the geological
model is inevitably undergoing a process of
increasing detailing and sharpening with an
increasing density and quality of observations
from the preliminary site investigation phase to
the actual excavation. This process also applies
to the understanding of the interactions between
tunnel advance and ground conditions.
While the involvement of the engineering
geologist in the preliminary site investigation
phase is hardly ever doubted, an intensive and
competent on-site support of the construction
works by engineering geologists is from the
authors point of view still not common standard.
However, actual experience shows, that the on-
site employment of engineering geologists as
part of an interdisciplinary team of skilled
experts can significantly contribute to the
reduction of remaining residual risks within the
project. This not only applies to an increased
health and safety aspect by adjusting support and
excavation sequence to an actualised prognosis
of the conditions ahead, but also contributes to
objective discussion of contractual impacts
between client and contractor.
State-of-the-art methods like detailed
geological documentation, hammer drillings
ahead of the face, borehole video inspections or
back-analysis of TBM machinery data are only
some of the core issues, where the engineering
geologist is able to provide specialist knowledge
for the project team.
Vice versa, the authors are convinced, that
neglecting the engineering geologist's expertise
in the project phase does indeed despise the
remaining residual ground risks and will
definitely reduce the possibilities to sharpen the
geological model and to fully understand the
complex interactions between tunnel excavation
and rock mass.
REFERENCES
Brückl, E., Chwatal, W., Mertl, S., Radinger, A. (2008):
Exploration Ahead of a Tunnel Face by TSWD – Tunnel
Seismic While Drilling. Geomechanics and Tunnelling,
1, 5, p. 442–449.
Kaus, A. & Boening, W. (2008): BEAM – Geoelectrical
Ahead Monitoring of TBM-Drives. Geomechanics and
Tunnelling, 1, 5, p. 460–465.
Kogler, K. & Krenn, H. (2014): Drilling processes to
explore the rock mass and groundwater conditions in
correlation with TBM-tunnelling. Geomechanics &
Tunnelling, 7, 5: p. 528-539 (Wiley).
Lombardi, G. (2004): Kosten im Tunnelbau – Vom
Voranschlag zum Endpreis, Vortrag an der
Generalversammlung der FGU in Zürich vom 14.Mai
2004, FGU Fachgruppe für Untertagbau, U.Ref.:
102.1-R-157 / 7.47 A
Poscher, G. (2004): Die Rolle des Geologen bei der
Vertragsabwicklung, in: Leitner, W. & Wais, A. (eds.,
2004): Aktuelle Fragen der Vertragsgestaltung im Tief-
und Tunnelbau, Proceedings of the International
Consulting and Construction Workshop, ICC 5,
Innsbruck/Austria.
Radinger, A., Fasching, F. Pack, G., Kreutzer, I. & Kostial,
D. (2014): Consistent exploration by probe drilling and
TSWD through the example of the Koralm Tunnel.
Geomechanics & Tunnelling, 7, 5: p. 540-550 (Wiley).
Radoncic, N., Hein, M., Moritz, B. (2014): · Determination
of the system behaviour based on data analysis of a
hard rock shield TBM. Geomechanics & Tunnelling, 7,
5: p. 565-576 (Wiley).
Schubert, W. (2001): Optimierungsmöglichkeiten beim
Tunnelbau durch geologisch-geotechnische Begleitung
/ Überwachung und laufende Besserung des
Baugrundmodells. 24. NDK Short Course „Geology in
Tunnelling“, Technische Universität Graz & 3G
Gruppe Geotechnik Graz ZT GmbH, Graz/Austria.
Wannick, P. (2007): „Tunnel Code of Practice“ als
Grundlage für die Versicherung von Tunnelprojekten,
Tunnel, 8, p. 23-28 (Bauverlag BV GmbH)