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D&B versus TBM: Review of the parameters for a right choice of the excavation method

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The right choice of the excavation method is essential in hard rock underground projects. The Drill and Blast (D&B) and Hard Rock Tunnel Boring Method (TBM) are widely and successfully used. Selecting the most appropriate excavation method is not simple as it is depending of several parameters and particular conditions. The purpose of this paper is to make a review of the parameters involved in the selection of proper excavation method. The applicability and level of convenience of each excavation method in function of every parameter defined will be briefly discussed. A final resume of the excavation method comparison is presented and proposed to be general guidelines at the early stages in hard rock tunnelling.
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Rock Engineering and Rock Mechanics: Structures in and on
Rock Masses – Alejano, Perucho, Olalla & Jiménez (Eds)
© 2014 Taylor & Francis Group, London, 978-1-138-00149-7
D&B versus TBM: Review of the parameters for a right choice
of the excavation method
F.J. Macias & A. Bruland
Department of Civil and Transport Engineering, Norwegian University
of Science and Technology (NTNU),Trondheim, Norway
ABSTRACT: The right choice of the excavation method is essential in hard rock underground projects. The
Drill and Blast (D&B) and Hard Rock Tunnel Boring Method (TBM) are widely and successfully used. Selecting
the most appropriate excavation method is not simple as it is depending of several parameters and particular
conditions. The purpose of this paper is to make a review of the parameters involved in the selection of proper
excavation method. The applicability and level of convenience of each excavation method in function of every
parameter defined will be briefly discussed. A final resume of the excavation method comparison is presented
and proposed to be general guidelines at the early stages in hard rock tunnelling.
1 INTRODUCTION
Underground construction industry has been experi-
encing a strong development with enormous techno-
logical improvement. In hard rock projects, drill and
blast excavation method (D&B) and tunnel boring
machine method (TBM) are widely used with success.
In hard rock tunnelling the selection of the exca-
vation method is not a simple issue. It may result in
catastrophic situations as experience has shown.
The choice is more complex than a simple eco-
nomic issue and rarely clear from the early stages of
the projects. It is necessary to have an entire overview
of the parameters involved in the excavation method
choice.
Many parameters are involved with different role
in every project case; project characteristics and pur-
pose, environmental aspects or even social issues are
involved. Every project is unique and a comprehensive
and detailed study should be carried out.
The excavation methods are not mutually exclusive.
Hybrid solutions should be considered taking advan-
tage of them whenever circumstances allow (Barton,
2013).
In the present paper, through a wide literature
review, the main parameters involved in the selec-
tion of the excavation method are briefly discussed.
The extension of the discussion is limited due to the
space available on the paper. A further research is
considered.
The existing literature related to the excavation
method choice in hard rock tunnelling is normally
based on particular cases studied and many “sub-
jective” statements are done. The discussion has
been divided into groups according to the parameters
involved in the excavation method choice.
A final summary in table forms is achieved. It has
been attempted to quantify the parameters based on
literature when possible.
The summary of the comparison is proposed to be
general guidelines in the selection of the excavation
method for tunnels in rock at the early stages.
2 PARAMETERS FOR THE EXCAVATION
METHOD CHOICE
2.1 Introduction
The parameters involved on the excavation method
choice are grouped according to the main topics. A
briefly discussion is carried out following.
2.2 Project design considerations
The geometry of the excavation in the TBM method
is limited to a circular shape while the drill and
blast method allows almost “any” excavation geome-
try.With “any” excavation is meant within reasonable
contour tunnel.
The cross section area is defined from the early
stages of design and it can hardly be changed.
This great versatility of the shapes suppose an
advantage of the drill and blast method in projects with
a variety in the cross section shapes whileTBM method
is more appropriate for projects with constant shapes
(Ehrbar, 2008).
823
With both methods the cross section area available
to excavate are similar, e.g. TBM method can be used
from 2–3 meters diameter and up to approx. 15 m
according to Hansen (2008). Nowadays, tunnel boring
method can even be used in smaller excavation areas
using micro tunnelling. In hard rock conditions it may
be successful from 900 mm. (Nicholas, 2006).
TBMs are more competitive for tunnels with small
cross sections (Nord et al., 1988, 2006; Gütter et al.,
2011). There are limitations in the both methods for
very small diameters (Nord. et al., 1988).
Regarding to the general layout, e.g. curve radius,
slope…, the TBM method has more limitations
(Holen, 1998; Stewart et al., 2006). However, the D&B
method has almost no limitations (Holen, 1998; Jodl,
2011; Stewart et al., 2006).
The length of the tunnel is a key parameter from
the technical and economical point of view. TheTBM
method is more competitive for long tunnels while
D&B method is for short tunnels (Nord, 1988; Holen,
1998; Ehrbar, 2008; Jodl, 2011).
It would be risky to define lengths since every
project has its particular characteristics. It is largely
accepted in the literature that in 3 km length there is a
tipping point.
In a large number of projects the excavation of
niches, branch tunnels, cavern and/or extended cross
sections excavation are required. Since normally drill
and blast is the technique applied, it creates interfer-
ences in the boring operation resulting in machine
downtimes (Holen, 1998). Extra cost in drilling equip-
ment and workers with special drill and blast skills has
to be considered.
From the authors opinion it should be considered
that in the TBM method, the initial part of the tunnel
is normally performed by D&B technique.
2.3 Final purpose considerations
The excavation geometry and the final quality required
are considerations to consider for the final use of the
underground project.
In water tunnels, the head loss due to wall fric-
tion between unlined TBM tunnels and drill and
blast is substantial. Cross section reductions between
33% (Hansen, 2008) and 40% (Holen, 1998) can
be achieved. In road tunnels, the circular excavation
profile is not optimal.
Since in the D&B method “any” shape is possible,
it is more adapted to any final purpose of the project
(Ehrbar, 2008).
The final operation facilities of the tunnels, as water
and frost protection, can be simplified and optimized,
since systems can be mounted on an even and exact
profile using the TBM method (Hansen, 2008).
2.4 Start-up time
The start-up time in the TBM project is much longer
than in the D&B method. This is due to longer delivery
time equipment, time consumption in assembling and
start-up (Lislerud, 1988).
For a new TBM, the delivery time is 6–12 months
(Holen, 1998) or 10–12 months (Stewart et al., 2006;
Hansen, 2008). For a new drill-jumbo 5–6 months
(Stewart et al., 2006).
The erection time of a TBM and backup, small and
medium hard rock TBMs, takes usually 3–6 weeks
depending local conditions and machinery available
(Holen, 1998). Erection times are highly variable
worldwide and should be considered with caution.
It is also important to consider that TBM method
needs a more comprehensive study in the design phase
with widely geological pre-investigation.
2.5 Health, safety and working
environment
There are almost no worldwide historical data supports
in the literature to say that one method is safer than
the other (Holen, 1998, Tarkoy, 1995), but it is widely
accepted that less numbers of accidents occur with the
TBM method.
By used of the tunnel boring excavation method
serious accident risk from storing or handling explo-
sives are avoided (Hansen, 2008, Holen, 1998) and
the safety is higher in the face and work area (Tarkoy,
1991). In practically all types of TBM the rock support
is installed from protected areas.
2.6 Advance rate
The advance rate has a high impact in the total
construction time and excavation cost.
In normal conditions, it is accepted for many
researchers that the advance rate in the TBM method is
much higher than with drill and Blast method (Kaiser,
1994, Tarkoy, 1995, Holen, 1998, Stewart et al., 2006,
Nord, 2006, Hansen, 2008, Ehrbar, 2008).
The excavation rate, in normal conditions, with
TBM method is estimated 4–6 times faster than with
D&B method (Tarkoy, 1995), 1.5–5 (Holen, 1998) or
nearly to 1–3 times according to Stewart et al. (2006).
The author’s opinion is that would be risky to define a
ratio due to conditions variability worldwide.
However with the D&B method it is easier to
advance in crushed zones due to the high versatility
of the method (Lislerud, 1988).
The influence of rock in TBM excavation makes
the advance rate estimation much more difficult and
uncertain (Nord et al., 2006).
2.7 Flexibility
Flexibility in an excavation method is related to the
ability of adapting it to changes in the layout profile
and in the rock mass conditions.
The TBM method is less or even not flexible than the
D&B method. Changes of the TBM diameter is almost
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limited depending on the machine design, and align-
ment during the construction stage (Hansen, 2008;
Stewart et al., 2006).
The Drill and Blast method advance easier in
crushed zones (Lislerud, 1988). This easier advance
involves a low safety and ground stability risk.
D&B method is the best excavation method for
underground projects with highly variable rock con-
ditions or variable shapes (Ehrbar, 2008).
2.8 Risk
Tunnelling, included D&B and TBM method, is
exposed to greater risks especially because the ground
to excavate and its behavior knowledge is limited
(Thomas et al., 2007).
TBM method has higher advance risk (Stewart et al.,
2006). The TBM risk takes particular significance in
the case of long and deep hard rock tunnels (Barton,
2000).
TBM method requires a more complete and detailed
geological investigation, mapping and testing during
the planning stage. More time and cost in the design
phase is necessary to evaluate the project viability
(Hansen, 2008; Bruland, 2010).
Highly variable rock conditions favor the choice of
the blasting method (Ehrbar, 2008).
2.9 Ground stability
Circular excavation is the most favorable shape from
the point of view of ground stability; therefore the
TBM method has more rock stability under normal
conditions (Hansen, 2008).
In case of water inflow under high pressure, D&B
method is more suitable (Ehrbar, 2008), due to the high
flexibility in the application of auxiliary constructions
methods and rock support applications.
In case of high rock stress conditions the TBM
method may result in important delays.
However, the excavation with TBM method causes
less damage in the rock mass around the excava-
tion. The rock support required, compared with D&B
method, is significantly reduced in the same geologi-
cal conditions (Tarkoy, 1991, Holen, 1998, Nord,2006,
Hansen, 2008).
D&B method alloy a great variability and excava-
tion sequences depending the rock conditions (Ehrbar,
2008) while in the TBM method is fixed.
2.10 Operation and construction crew
For operation and crew, the TBM method is more
advantageous than D&B method.
The tunnel boring operation is a continuous (non-
cyclical) operation, so is a repetitive process; crew
perform repetitive activities with limited competences
and skills which facilities training and learning is con-
tinually reinforced (Tarkoy P.J., 1995), which means
less human factor.
2.11 Costs
Construction time and cost detailed studies must be
made at the earliest project stages and have to be
updated periodically Ehrbar (2008).
In TBM method, capital cost or initial investment
are higher while marginal cost for the excavation
phase are less (Holen H., 1998).This means important
finance and negative cash flows at the beginning of the
project which is a disadvantage for the TBM method.
In addition, the excavation cost for TBM method has
large variability (Holen, 1998),
However, life time costs, operation and mainte-
nance, for TBM excavation may be significantly less
than for a D&B tunnels (Hansen A.M., 2008).
The most extraordinary cost saving that can be done
with TBM excavation is the possibility of eliminating
temporary excavation structures such as access adits
according Tarkoy (1995).
As already mentioned, TBM method reduces the
rock support. The amount of rock support and concrete
lining are more predictable in the TBM method for
normal conditions (Hansen, 2008). This means lower
rock support costs and more predictable rock support
and lining costs.
Anyway, tunnel cost estimation in theTBM method
is much more difficult and uncertain (Nord et al.,
2006).
2.12 Overbreak and tunnel profile quality
Most of the authors agree that tunnel boring exca-
vation produces less geological overbreak compared
to drill and blast (Nord G., 2006; Stewart P. et al.,
2006). The overbreak with TBM method is near elim-
ination (Tarkoy P.J., 1995). With D&B method should
be predicted not less than 10% overbreak.
When the geology is not favorable, the overbreak
is very difficult to control, but always is much lower
with TBM.
2.13 Environmental disturbance
Using the TBM method, less environmental distur-
bances, noisy and vibrations, are caused in the sur-
rounding areas (Holen H., 1998; Hansen A.M., 2008).
TBM method will be easier acceptable from an envi-
ronmental point of view due a lower construction time
and adits with roads and porwerlines may be omitted
(Holen H., 1998).
2.14 Temporally access and implantation layout
TBM method has a higher potential when it is neces-
sary to avoid or have no possibilities to make additional
adits or being able to start a heading from the opposite
end of the tunnel (Hansen, 2008). One example of this
is the AMR project (India) where with only two adits
it will perform more than 40 km of tunnel by TBM
method.
However,TBM method has increased requirements
for mobilization and demanding infrastructure as well
825
as TBM requires more electric power than drill and
blast (Hansen, 2008).
In projects with difficult access, complicated orog-
raphy or urban areas, D&B method is especially
appropriated (Ehrbar, 2008). TBM method is more
suitable for projects with a good accessibility.
2.15 Contractual considerations in the choice of
the excavation method
High risks are involved in underground construction.
Uncertainties in the rock conditions and behavior,
unforeseen conditions, dependency of the excavation
method and the high construction risk are associated
with this type of construction. Therefore is very impor-
tant a specific and differently contracting practices
(Ehrbar H., 2008).
The choice of the excavation method should be
responsibility of the contractor, always based on the
owner’s comprehensive design, except in special cases
with project restrictions (Ehrbar H., 2008).
The level of initial investigation should be adapted
to the excavation method requirements.
The total investment and delivery time for new
machines emphasizes the need for reliable prognoses
of rock conditions (Barton, 2000).
Table 1. Comparison between D&B and TBM method
related to the project design considerations.
D&B Method TBM Method
Geometry “Any” shapeCircular
Almost same range∗∗
3m
2–180 m2
TBM micro tunnelling: 0.9–3 m2
Cross Section Not competitive
Area small Competitive small
General layout Almost Restrictions
no restrictions
Tunnel Length Shorter Longer
Optimal 3 km (5 km–25 km)
Start-up Time Shorter Much longer
5–6 months 6–12 months
(new machine) (new machine)
Niches and Less problematic More problematic
Branch Tunnels
“any shape” excavation means within reasonable contour
tunnel.
∗∗Commonly cross section areas used.
Table 2. Comparison between D&B and TBM method
related to final purpose considerations.
D&B Method TBM Method
Purpose by Any purpose Variably suitable
geometry Road Water
Purpose by Lower Higher
quality
3 CONCLUSIVE REMARKS
A summary in table form of the parameters involved
in the excavation method choice discussed earlier are
shown in the following.
Table 3. Comparison between D&B and TBM method
related to health, safety and working environment.
D&B Method TBM Method
Safety Lower Higher
Storage Terrorism and Avoided
explosives accident risk
Handling Serious accident Avoided
explosives rick
Rock support No protected area Protected area
installation
Working Temporary worse Improved
environment Toxic gases Dust
Principal safety Handling and Cutter changes
risk storage explosives
Loading and
hauling
Table 4. Comparison between D&B and TBM method
related to advance rates.
D&B Method TBM Method
Higher
Lower (1.5–6 times)
Lower std. dev. Higher std. dev.
(24 %)(45 %)∗∗
Better prediction Uncertain prediction
Advance rate Low potential High potential
Rock mass Lower Much higher
influence
,∗∗, Case stories (Stewart et al. (2006).
Table 5. Comparison between D&B and TBM method
related to flexibility.
D&B Method TBM Method
Profile Highly Not flexibility
Layout, rock support... High Very low
Advance in crushed Easier Very difficult
zones
Profile variability High Fairly limited
in construction
Table 6. Comparison between D&B and TBM method
related to risk.
D&B Method TBM Method
Geological risk Lower Higher
Rock mass conditions Any Optimal midrange
826
Table 7. Comparison between D&B and TBM method
related to ground stability.
D&B Method TBM Method
Ground stability Lower Higher
Water inflow Higher Lower 50–75%
induced reduction
Water pressure Lower Higher
influence
Rock stress Lower delay risk Higher delay risk
conditions
Rock support Increased Reduced 30–90%
required Less predictable More predictable
Excavation variations Great variability No variability
Auxiliary support Much easier More difficult
Faster Slower
Table 8. Comparison between D&B and TBM method
related to operation and construction crew.
D&B Method TBM Method
Operation Cyclical Continuous
(repetitive)
Manpower Almost same manpower
per volume excavated
Exc./support Interfere Not interfere
operation
Equipment Inappropriate Appropriate
for mucking non continuous continuous
Construction All skills required Less skills required
crew More difficult Easier training
training
Table 9. Comparison between D&B and TBM method
related to construction costs.
D&B Method TBM Method
Design cost Lower Higher
Initial investment Lower Higher
Adits impact: High Limited
investment and cost
Marginal rate More increased Less increased
Construction costs Not vary Highly variable
very much
Life time cost Higher Significantly
lower
Table 10. Comparison between D&B and TBM method
related to overbreak and tunnel profile.
D&B Method TBM Method
Overbreak Higher 15–25 cm. Much lower
<10 cm.
Tunnel profile Difficult Nearly total
quality
Filling concrete High extra cost Limited extra cost
Concrete lining Less predictable More predictable
Table 11. Comparison between D&B and TBM method
related to the environmental disturbance.
D&B Method TBM Method
Noise and vibrations Higher Significantly
lower
Environmental impact More difficult Easier
acceptable acceptable
Blasting fumes Continuously Not
Avoid Contamination Not possible Reduction
potential
Table 12. Comparison between D&B and TBM method
related to the adits and implantation layout.
D&B Method TBM Method
Temporally access Necessary Omitting or
reducing
Portal space Little Ample
Electrical power Lower Higher
Difficult access Especially Not appropriate or
appropriate not allowed
4 CONCLUSIONS
There is not too much research about the selection of
the excavation method, D&B versus TBM, based on
field data. Many “subjective” statements are done.
Most of the authors agree that the main advan-
tages of the D&B method are high flexibility of the
method, almost no restrictions in the general layout,
great adaptability to unexpected situations or lower
start-up and initial investments.
In the TBM method case, most of the authors agree
in the most suitability for longer tunnels, has high
potential in advance rate, high potential reducing of
the rock support and overbreak with a concrete lin-
ing more predictable, the possibility of omitting and
reducing temporally access or less skills and easier
training of the crew. As well as most of them have a
wide acceptance that the disadvantages of the TBM
method are a high geological risk, high cost design
and initial investments or long start-ups.
The choice is more complex than a simple economic
issue and rarely the selection is clear from the early
stages of the projects. Depending on the particular cir-
cumstances of a project, the parameters that in a case
are not even considered may be decisive in the choice
for others.
Hybrid solutions, considering the excavation meth-
ods advantages, D&B & TBM, should be considered
whenever circumstances allow.
A further work it will consist in the application of
the risk matrix method considering all the parame-
ters described in the present paper. Application of the
matrix can be utilised in the decision of the excavation
method in future tunnelling projects.
827
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... The choice of the more suitable excavation method for every project case is more complex than a simple economic issue. Every project is unique and many parameters with different role are involved in the decision being necessary to carry out a comprehensive and detailed study (Macias et al., 2014a). ...
... Other parameters such as higher geological risk or limited flexibility compared to D&B method, among others, might also be relevant on the excavation method selection. As mentioned in Macias et al, (2014a), all the parameters involved in the choice of the excavation method should be considered and carefully analyzed. ...
... Rock boreability can be defined as the resistance (in terms of ease or difficulty) encountered by a TBM when it penetrates in a rock mass composed of intact rock properties and rock mass parameters (Macias et al. 2014a). ...
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The drill and blast method (D&B) and tunnel boring method (TBM) are widely used with success as tunnelling methods in a wide range of rock mass quality. A 'faulted rock mass' is difficult ground conditions for tunnelling in general, and for TBMs in particular, and comprises from extremely fractured rock mass to completely sheared weak rock. Some of the main geotechnical problems and instability situations associated to faulted rock as well as the most common stabilization methods, which apply for D&B and TBM tunnelling, are briefly discussed in the paper. It is not intended to be a thorough description, but rather a general overview and state of the art. The D&B method can adjust more easily to situations caused by faulted rock, solving the majority of instabilities caused by faulted rock. Technically speaking, the TBM method can tackle most of the cases of stability problems caused by faulted rock. However, important considerations need to be taken from initial study stages. Anyway, D&B and TBM methods are complementary methods and the most appropriate method should be selected by considering the complete ground conditions for both methods. They have the same purpose, and the use of "hybrid" solutions must be considered according to the particular characteristics of the project.
... The matter has been discussed in the literature where Nord and Stille (1988), Holen (1998), Kaiser and McCreath (1994), Tarkoy (1995), Barton (2000Barton ( , 2013, Nord (2006), Stewart et al. (2006), Suorineni et al. (2008), Zare and Bruland (2013) and Macias and Bruland (2014), have compared the methods and studied the influencing parameters. Nord and Stille (1988) reviewed the factors that determine the choice of D&B or TBM and highlighted them by examples from two case histories where both methods had been applied. ...
... Hybrid solution means using TBM on the ground better investigated and characterized or lower-cover section of the project and D&B for the ground with limited information and less explored or high-cover part due to inherent risks involved, i.e. ground squeezing and adoptability of D&B in such conditions. Macias and Bruland (2014) reviewed the parameters for selection of the excavation method. They made an attempted to collect and summarise the parameters impacting the tunnelling operation into twelve groups, e.g. ...
Article
Drill and Blast (D&B) and Tunnel Boring Machine (TBM) are the two dominating excavation methods in hard rock tunnelling. Selection of the cost effective excavation method for a tunnel is a function of tunnel cross section area, rock conditions, tunnel length, availability of skilled labour and proper equipment, and project schedule. Over the past few decades, major technological development and technical advances have been achieved in both methods. Yet, in many tunnelling projects, choosing the excavation method is still a challenge and requires considering pros and cons of each method and estimating construction time, costs, as well as post construction and operation & maintenance, and related risk in the planning phase. In this study, the productivity and efficiency of the D&B and TBM options for excavating certain size tunnels have been examined. The analysis is based on recent NTNU prediction models for advance rate and unit excavation cost for given ground conditions and tunnel geometry. For excavation of large size tunnels in very hard rock, the D&B method seems to be the cost effective choice irrespective to tunnel geometry. This is compared to smaller long tunnels with good boreability were the TBM has higher advance rate. The tunnel size and rock conditions have higher impact on the TBM performance and costs than for D&B. This refers to lower risk of using D&B where the use of this method is otherwise justified.
... Lastly, the total construction time includes the site preparation time, portal excavation, and unforeseen rock conditions. Regarding this, Macias and Bruland [37] concluded that it would take 5-6 months for a tunnel start-up when using a new machine. Daller [2] mentioned that 3-4 months are needed for mobilisation, site installation and portal excavation. ...
Article
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This paper analyses the construction time and advance rate of a 3 km long drill and blast tunnel under various geological conditions using an upgraded NTNU drill and blast prediction model. The analysis was carried out for the five types of Korean tunnel supports according to the rock mass quality (from Type 1, meaning a very good rock mass quality; to Type 5, meaning a very poor rock mass quality). Four kinds of rock properties, as well as the rock mass quality, for each tunnel support type were applied to simulate different geological conditions based on previous studies and the NTNU model. The construction time was classified into five categories: basic, standard, gross, tunnel and total, according to the operation characteristics to more effectively analyse the time. In addition, to consider the actual geological conditions in tunnelling, the construction times for the three mixed geological cases were analysed. It was found that total construction time of a tunnel covering all the operations and site preparations with a very poor rock mass quality was more than twice that of a tunnel with a very good rock mass quality for the same tunnel length. It is thought that this study can be a useful approach to estimating the construction time and advance rate in the planning or design stage of a drill and blast tunnel.
... It is known that hard rock excavation by means of tunnel boring machines (TBM) brings many benefits in terms of productivity and safety, but at the same time the tunnel geometry is limited to a circular shape [1], so the method is more appropriate for projects with constant shapes [2]; moreover, it is not recommended for tunnels shorter than 1 km, as the installation times would be of the same order of magnitude as the excavation times [3,4]. ...
Article
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The study takes into account different classes of tunnel boring machines (TBM), with the aim of identifying correlation models which are meant to estimate, at a preliminary design phase, the construction time of a tunnel and to evaluate the mechanical and operational parameters of the TBMs, starting from the knowledge of the tunnel length and the excavation diameter. To achieve this goal, first of all a database was created, thanks to the collection of the most meaningful technical parameters from a large number of tunnels; afterwards, it was statistically analyzed through Microsoft Excel. In a first phase, forecasting models were identified for the three types of machines investigated, separately for compact rocks (open TBM) and fractured rocks (single and double shield TBM). Then, the mechanical parameters collected through the database were analyzed, with the aim of obtaining models that take into account, in addition to the type of TBM, the geological aspect and the type of rock characterizing the rock mass. Finally, the validation of the study was proposed in a real case, represented by the Moncenisio base tunnel, a work included in the new Turin–Lyon connection line. The estimated values were compared with the real ones, in order to verify the accuracy of the experimental models identified.
... It is known that hard rock excavation by means of tunnel boring machines (TBMs) brings many benefits in terms of productivity and safety, but at the same time the tunnel geometry is limited to a circular shape [1], so the method is more appropriate for projects with constant shapes [2]; moreover, it is not recommended for tunnels shorter than 1 km, as the installation times would be of the same order of magnitude as the excavation times [3,4]. ...
Preprint
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The study takes into account different classes of tunnel boring machines (TBMs), with the aim of identifying correlation models which are meant to estimate, at a preliminary design phase, the construction time of a tunnel and to evaluate the mechanical and operational parameters of the TBMs, starting from the knowledge of the tunnel length and/or the excavation diameter. To achieve this goal, first of all a database was created, thanks to the collection of the most meaningful technical parameters from a large number of tunnels; afterward, it was statistically analysed through Microsoft Excel. In a first phase, forecasting models were identified for the three types of machines investigated, separately for compact rocks (open TBM) and fractured rocks (single and double shield TBM). Then, the mechanical parameters collected through the database were analysed, with the aim of obtaining models that take into account, in addition to the type of TBM, the geological aspect, and the type of rock characterising the rock mass. Finally, the validation of the study was proposed in a real case, represented by the Moncenisio base tunnel, a work included in the new Turin–Lyon connection line. The estimated values were compared with the real ones, in order to verify the accuracy of the experimental models identified.
... Since their development in the 1950s, modern TBMs have been successfully used to construct hydropower, sewerage, road, railway, water supply, underground storage, and utility tunnelling projects Zheng et al., 2016). Hard rock TBMs enable faster tunnel construction and a lower risk level than those of conventional tunnelling methods in favourable ground conditions such as homogenous geology, low-tomedium compressive strength (<300 MPa), low in situ stresses, optimal length of the tunnel (>3 km), and dry ground conditions (Macias and Bruland, 2014;Singh and Zoldy, 2012;Zare et al., 2016). However, in difficult ground conditions the consequences of using TBMs are often far more serious, resulting in the loss of tunnel as well as reduced safety, increased cost, and schedule impacts (Barla and Pelizza, 2000;Barton, 2000). ...
Article
Usage of tunnel boring machines has become the most popular underground excavation method to meet recent underground infrastructure development demands because of the high advance rate associated with this approach. However, using a tunnel boring machine for tunnel construction under difficult ground conditions carries the potential risk of causing undesired events. Determining the exact geological ground conditions before commencement of the project is almost impossible, rendering this industry to be fraught with high risk. Bow-tie risk analysis has emerged as a powerful tool for studying the risk management of undesired events in several high-risk industries but is yet to be comprehensively studied in the context of underground rock engineering. This paper presents a novel risk analysis methodology based on a generic bow-tie method for systematic assessment and management of risks associated with tunnel boring machine in difficult ground conditions. The bow-tie method integrates the fault tree and event tree analyses methods that follow a cause-consequence methodological approach centred on the common undesired event. The proposed risk analysis technique serves as a powerful tool that can aid tunnel boring machine professionals in systematically investigating, evaluating, and mitigating the inherited risks associated with tunnel boring machine in difficult ground conditions. For validation, the proposed methodology is applied to the twin tunnel boring machine project conducted in the Himalayas, and the results demonstrate its applicability as an effective risk analysis method.
... The choice is more complex than a simple economic issue and it is rarely clear in the early stages of the projects. It is necessary to have an entire overview of the parameters involved in the excavation method choice (Macias and Bruland, 2014). Many parameters are involved with different roles in every project case; project characteristics and purpose, environmental aspects or even social issues are involved. ...
Conference Paper
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Drillability is an important parameter in order to assess the influence that intact rock properties have on performance prediction and cost evaluations in connection with drill-and-blast tunnelling, TBM tunnelling, excavations by roadheaders and hydraulic impact hammers and also rock quarrying. Especially in hard rock conditions, drillability will be of great importance for selection of excavation method and a successful project execution. Unanticipated situations and/or inappropriate assessments can result in considerable delays and great risk of cost overruns. Reliable predictions are therefore required; prediction of net penetration rate and tool wear, time consumption and excavation costs, including risk and assessing risk linked to variation in rock mass boreability, establishing and managing contract price regulation. Several methodologies are available to assess drillability (i.e. rock strength, rock surface hardness, rock brittleness, rock abrasivity or rock petrography). This paper includes a review of the state-of-the-art and discussion of relevant parameters that involves drillability assessments in hard rock conditions.
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Tough decisions for mega-projects: A methodology for decision making on time-relevant measures at the Gotthard Base Tunnel
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About this book This book describes the stage by stage development of a new method for predicting the penetration rate (PR) and the advance rate (AR) for tunnel boring machines based on an expanded version of the Q-value, termed QTBM. Some 145 TBM tunnels totalling about 1000 km in length were an-alysed and some simple formulae are developed from the results to esti-mate PR and AR from the QTBM value, or to back-calculate QTBM from performance data. Logging methods, empirical TBM tunnel support de-sign, and numerical verification of support are also treated in this slim but practical book on TBM tunnelling. Penetration rates as high as 10 m/hr, but occasionally as low as 0.1 m/hr, are a function both of the machine and rock mass interaction, and of the cutter force and rock strength interaction. Actual advance rates that could be as high as 5 m/hr for one day, or as low as 0.005 m/hr (while stuck for several months in a major fault zone) are quantitatively ex-plained. This book is a useful source of reference for consultants, contractors and owners of TBM tunnels, and for those involved with feasibility stud-ies, machine and support design and follow-up of tunnel progress. Among the geotechnical community, the book will be useful for geolo-gists, engineering geologists and rock mechanics engineers, and for all civil engineers who have a professional interest in TBM tunnelling.
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Determining tunnel stability is a key issue during preliminary site investigation. In contrast, problems of excavatability have been largely ignored. While the choice of an economic tunnelling method is admittedly a clear priority in the planning stage, special investigations focussing on rock fragmentation (e.g. drilling or cutting performance, rock mass blastability or tool wear) are rarely carried out. This paper explores possibilities to quantify key parameters for rock mass excavatability in drilling, blasting and cutting by TBMs and roadheaders. RÉSUMÉE: La détermination de la stabilité du tunnel est une question clé lors des études prélimi-naires. En revanche, les problèmes d'excavabilité sont souvent en grande partie ignorés. Tandis que le choix d'une méthode de percement économique est évidemment une priorité claire dans l'étape de planification, des investigations spéciales se concentrant sur la fragmentation de la roche (par exemple le comportement de la roche au forage, à l'excavation ou au dynamitage et l'usure des outil) sont rarement effectuées. Cet article explore les possibilités pour quantifier les paramè-tres clé de la roche lors d'excavation par forage, dynamitage, au tunnelier (TBMs) ou à l'excavatrice. ZUSAMMENFASSUNG: Beim Tunnelbau wir meist die Vorhersage der Stabilität des ausgebro-chenen Hohlraums als Schlüsselfragestellung betrachtet. Im Gegensatz dazu werden Probleme der Gebirgslösung weitgehend ignoriert. Während der Wahl einer wirtschaftlichen Vortriebsmethode während der Planungsphase meist noch eine gewisse Priorität beigemessen wird, werden spezielle Untersuchungen zur Gebirgslösung (Bohr-oder Schneidbarkeit, Sprengbarkeit oder Werkzeug-verbrauch) nur sehr selten durchgeführt. Diese Publikation zeigt Möglichkeiten der Quantifizie-rung von Schlüsselparametern für die Gebirgslösbarkeit auf, also der Bohr-und Sprengbarkeit, der Fräsbarkeit mit Teilschnittmaschinen und der Schneidbarkeit mit TBMs.
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There are many examples of TBM tunnels through mountains, or in mountainous terrain, which have suffered the ultimate fate of abandonment, due to insufficient pre-investigation. Depth-of-drilling limitations are inevitable when depths approach or even exceed 1 or 2 km. Uncertainties about the geology, hydro-geology, rock stresses and rock strengths go hand-in-hand with deep or ultra-deep tunnels. Unfortunately, unexpected conditions tend to have a much bigger impact on TBM projects than on drill-and-blast projects. There are two obvious reasons. Firstly the circular excavation maximizes the tangential stress, making the relation to rock strength a higher source of potential risk. Secondly, the TBM may have been progressing fast enough to make probe-drilling seem to be unnecessary. If the stress-to-strength ratio becomes too high, or if faulted rock with high water pressure is unexpectedly encountered, the “unexpected events” may have a remarkable delaying effect on TBM. A simple equation explains this phenomenon, via the adverse local Q-value that links directly to utilization. One may witness dramatic reductions in utilization, meaning ultra-steep deceleration-of-the-TBM gradients in a log-log plot of advance rate versus time. Some delays can be avoided or reduced with new TBM designs, where belief in the need for probe-drilling and sometimes also pre-injection, have been fully appreciated. Drill-and-blast tunneling, inevitably involving numerous “probe-holes” prior to each advance, should be used instead, if investigations have been too limited. TBM should be used where there is lower cover and where more is known about the rock and structural conditions. The advantages of the superior speed of TBM may then be fully realized. Choosing TBM because a tunnel is very long increases risk due to the law of deceleration with increased length, especially if there is limited pre-investigation because of tunnel depth.
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As one stands inside one of the new hi-tech closed face TBMs one could almost believe that everything is computerised and all risks are completely under control. Sadly the truth is that, not only do surface collapses sometimes occur above TBM tunnels, but also the costs associated with the collapses are increasing rapidly. This has caused a crisis in the insurance industry and prompted the publication of a Code of Practice for Risk Management of Tunnel Works in the UK. Insurers are demanding that contractors adopt the code of practice if they are to be given project insurance. An international version of this code is being prepared. This paper will discuss the risks associated with TBM tunnels and how risk management can be applied to TBM tunnelling. This paper will illustrate how these general procedures can be applied by describing a recent project where TBM tunnels have been driven successfully in a high risk urban area.
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This book covers the fundamentals of tunneling machine technology: drilling, tunneling, waste removal and securing. It treats methods of rock classification for the machinery concerned as well as legal issues, using numerous example projects to reflect the state of technology, as well as problematic cases and solutions. The work is structured such that readers are led from the basics via the main functional elements of tunneling machinery to the different types of machine, together with their areas of application and equipment. The result is an overview of current developments. Close cooperation among the authors involved has created a book of equal interest to experienced tunnelers and newcomers. © 2008 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH und Co.KG, Berlin.
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With a length of 32.9 km, the Koralm tunnel is the key structure on the route of the new 130 km Koralm railway between Graz and Klagenfurt (Austria). This paper defines the most important boundary conditions for dividing the sections and for selecting the methods of tunnelling (sequential or continuous). The focus of the article is mainly on section KAT 3, in which both tertiary sediments and crystalline rock sequences, including the Lavanttal fault zone, are excavated by sequential and continuous tunnelling. The considerations for this section also include the decision to excavate the sediments and the Lavanttal fault zone using a shield machine with earth pressure components. The criteria for defining the different operating modes are described. Der Koralmtunnel mit einer Länge von 32,9 km stellt das Schlüsselbauwerk entlang der 130 km langen neuen Koralmbahn zwischen Graz und Klagenfurt dar. Der vorliegende Beitrag legt die wesentlichen Randbedingungen zur Einteilung der Baulose und zur Wahl der jeweiligen Vortriebsmethode (zyklisch oder kontinuierlich) dar. Der Fokus ist dabei hauptsächlich auf das Baulos KAT 3 gerichtet, in dem sowohl tertiäre Sedimente als auch kristalline Gesteinsabfolgen mitsamt der Lavanttaler Störungszone im zyklischen und im kontinuierlichen Vortrieb durchörtert werden. Die Betrachtungen für dieses Baulos umfassen auch die Entscheidungsfindung, die Sedimente und die Lavanttaler Störungszone mittels Schildmaschine mit Erddruckkomponenten aufzufahren. Die Kriterien zur Abgrenzung der unterschiedlichen Betriebsmodi werden dargestellt.
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The Brenner Eisenbahn GmbH (BEG) was appointed in 1995 to design and construct the new railway line in the Lower Inn Valley between the national border near Kufstein and Innsbruck. In the densely populated Inn Valley, large parts of the line with a planned speed of 250 km/h had to be run through tunnels. Near Jenbach, a semi-quantitative process was used as part of a risk analysis for the decision between the variants of a shallow, mined special construction and a deep mechanically driven tunnel. Die Brenner Eisenbahn GmbH (BEG) wurde im Jahr 1995 mit der Planung und Errichtung der Neubaustrecke im Unterinntal zwischen der Staatsgrenze bei Kufstein und Innsbruck beauftragt. Im dicht bebauten Inntal mussten große Teile der mit einer Spitzengeschwindigkeit von 250 km/h geplanten Strecke in Tunnellage errichtet werden. Im Bereich Jenbach wurde ein semi-quantitatives Verfahren im Rahmen der Risikoanalyse zur Variantenentscheidung zwischen einer seicht liegenden, bergmännischen Sonderbauweise und einem tiefliegende Maschinenvortrieb angewandt.
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The selection of the correct method of tunnelling from the contractor's point of view mostly depends on its chance to survive the competition of the marketplace, in addition to a host of technical constraints. The tendering and award conditions also decisively influence whether the technically and economically optimal solution is chosen. There are also other factors like the market situation, availability of suitable tunnelling machinery and personnel resources, which can have a significant effect on the decision process. Die Wahl der aus Sicht des Unternehmers richtigen Vortriebsmethode hängt neben einer Vielzahl technischer Randbedingungen vor allem davon ab, wie dieser damit im Wettbewerb bestehen kann. Dabei beeinflussen die Ausschreibungs- und Vergabebedingungen ganz wesentlich, ob letztlich auch die technisch und wirtschaftlich optimale Lösung zur Ausführung gelangt. Daneben sind es aber auch Faktoren wie Marktsituation, Verfügbarkeit von geeigneten Vortriebsanlagen, Personalressourcen, die im Entscheidungsprozess der Vortriebsmethode eine gravierende Rolle spielen können.
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Since the end of the 1980s, the Westbahn line has been undergoing successive upgrading to a modern high-speed line. The aim is to considerably increase the capacity and the travel speed up to 250 km/h. Regarding the infrastructure, this entails the new construction or upgrading of many sections including a number of tunnels due to the extended route and the topographical conditions. The requirements applicable to railway tunnels have changed significantly since the start of tunnel construction activities for the upgrading of the Westbahn. At the same time mechanised tunnelling technology has made great progress. These two developments have led to the situation that mechanised tunnel boring has become increasingly established in Austria as a viable alternative to NATM as a construction method for rail tunnels. The present article describes the procedure at the responsible company of Austrian Railways, ÖBB-Infrastruktur AG, in connection with these developments and explains the considerations leading to the selection of the tunnelling method.