Energy Efficiency of Tunnel Boring Machines.

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M ACHINES

Vitaliy Grishenko

February 2014

TRITA-LWR Degree Project

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c

Vitaliy Grishenko 2014

Degree Project at the Master’s Level

Master Programme: Water System Technology

Department of Land and Water Resources Engineering Royal Institute of Technology (KTH)

SE-100 44 STOCKHOLM, Sweden

Reference to this publication should be written as: Grishenko, V. (2014) "Energy Efficiency of Tunnel Boring Machines" TRITA-LWR Degree Project, LWR-EX-2014:03

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SUMMARY INSWEDISH

Herrenknecht AB är en tysk världsledande producent av tunnelborrmaskiner. Företaget tillverkar en rad olika tunnelborrmaskiner lämpade att användas i alla geologiska miljöer och leder även tun- nelprojekt över hela världen. Herrenknecht AB visar upp en stark medvetenhet och omsorg för de miljöfrågor som rör deras produkter, däribland energiframställning och de stödjer forskning kring energieffektivitet som eftersträvar intelligent design av en "grön" tunnelborrmaskin.

Syftet med denna studie är att framställa en "status quo"-rapport rörande energieffektivisering av tre typer av tunnelborrmaskiner utvecklade av Herrenknecht AB (Hardrock TBM, EPB TBM och Mix- shield TBM). Målen med studien är följande:

• Uppskatta kvaliteten på de tillgängliga dataloggarna, nödvändiga för energieffektivitetsstudien;

• Uppskatta energibesparingspotential med fokus på de huvudsakliga energikonsumenterna, två huvudsakliga besparingsalternativ behandlas:

– Energieffektivitet genom design;

– Effektiv energianvändning vid drift;

• Identifiera korrelation mellan energikonsumtion och förändringar i geologiska egenskaper för de projekt där detaljerad geoteknisk information är tillgänglig.

Inom ramen för denna studie analyseras totalt 39 projekt, baserade på lagrade energikonsumtionslog- gar, specifikationer av maskiner och installerad utrustning såväl som geotekniska rapporter samt då det är applicerbart geologiska profiler från tidigare tunnelbyggen. Rapporten innehåller också res- ultatet av tidigare behandlad data (genomfört av Benedikt Broda, tidigare trainee vid Herrenknecht AB). Metodologin baseras huvudsakligen på användandet av beräknings-, plottnings- och statistiska funktioner i Microsoft Excel och MATLAB.

Denna studie bekräftar att det finns datakvalitetsproblem och poängterar behovet av datakvalitetskon- troll. De övriga resultaten av analysen identifierade specifika skillnader mellan energikonsumtion hos de tre analyserade tunnelborrmaskinerna. Användningsanalysen betonar behovet av optimering av utformandet av tunnelborrmaskinens energimatningsenheter och huvudkonsumenter. Studien av den geologiska påverkan på energikonsumtionen visade inte något generellt signifikant samband mellan energikonsumtionen för samma maskiner när de borrar genom sektioner i liknande geologiska miljöer. Orsakerna till dessa observationer diskuteras i detalj.

Sammanfattningsvis visar resultaten från denna studie att det finns en viss energibesparingspotential, vilken kan nås genom att till exempel bättre anpassa maskinernas utformning till lokala geologiska miljöer och genom minskning av energikonsumtion då arbetet ligger nere. En strategi för en imple- mentering av energieffektivisering som indikerar fortsatt nödvändig forskning föreslås och diskuteras.

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SUMMARY INENGLISH

Herrenknecht AG is a German world-leading manufacturer of Tunnel Boring Machines. The company produces a wide range of Tunnel Boring Machines, suitable for operation in all geological environments and is leading tunnel construction projects worldwide. Herrenknecht AG demonstrates a strong awareness and concern regarding the environmental issues associated among others with energy production and supports research on the Energy Efficiency (EE) of their products, aimed at the development of intelligent design for a green Tunnel Boring Machine.

The aim of this project is to produce a ’status quo’ report on EE of three types of Tunnel Boring Machines developed by Herrenknecht AG (Hardrock, EPB and Mixshield TBM). The goals of the research are as follows:

• To assess the quality of the available data logs, necessary for the EE study;

• To assess energy saving potential with focus on the main energy consumers, covering two main saving options:

– EE by design;

– Effective energy use at operation.

• To find correlations between energy consumption and changes in geological properties for the projects where detailed geotechnical information is available.

In the framework of this research 39 projects in total are analysed, based on the filed energy consumption logs, specifications of the machines and the installed equipment as well as on the geotechnical reports and when applicable geological profiles from previous tunnel construction projects. The paper also includes results of already processed data (conducted by Benedikt Broda, former trainee at Herrenknecht AG). The methodology is mainly based on utilisation of calculation tools, plotting and statistical functionalities of Excel and Matlab.

The findings of this study confirm the existence of data quality issue and highlight the necessity of data quality control. The further outcomes of the analysis allowed identification of specific distinctions between energy consumption of the three investigated TBM types. Moreover the utilisation analysis stresses the necessity for optimisation of the layout of TBMs energy supply units and main consumers.

The study of geological influence on energy consumption generally did not demonstrate significant conformity between the energy consumption of the same machines boring through sections with similar geological environments. The reasons for these observations are discussed in detail.

To sum up, the results of this survey suggest that there is a certain energy saving potential, which is achievable by e.g. better adjustment of the machines’ layout to the particular local geological environments and through reduction of energy consumption during idle periods. An EE implementation strategy, indicating further research needs, is suggested and discussed.

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ACKNOWLEDGEMENTS

First of all I would like to thank Andreas Kassel, my supervisor at Herrenknecht AG, for providing me with all the necessary information and advice especially during the familiarisation phase as well as for his help on the refining of the report. I would also like to thank Prof. Bo Olofsson for his advice and recommendations throughout the project. I am also indebted to Benedikt Broda, former trainee at Herrenknecht AG, who developed and documented the methodology I used for the substantial part of the research. Special thanks also go out to Andre Heim, Martine Siefert, Florentine Stiefel and other representatives of Herrenknecht AG, who supported me on various issues along my stay in Schwanau. Moreover I would like to thank Erasmus Mundus TARGET project and its employees for enabling my studies at KTH. Last but not least I would like to thank my family, especially my mother, Valentina Grishenko, who’s invaluable support enabled me to be, where I am now, my wife, Ekaterina Golubina, for her love and support and my grandfather, Ivan Kabanov, for being a great example in my life.

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ABBREVIATIONS

CAI Cerchar Abrasiveness Index

EC Energy Conservation

EDA Exploratory Data Analysis

EE Energy Efficiency

EIA Environmental Impact Assessment

EPB Earth Pressure Balance (Tunnel Boring Machine)

GHG Green House Gas

HK Herrenknechtt AG

KTH Kungliga Tekniska Hogskolan (Royal Institute of Technology, Sweden) MDB Main Distribution Board

N/A Not Available

RMQ Rock Mass Quality (index)

SME Small and Medium (medium sized) Enterprises TBM Tunnel Boring Machine

UCS Uniaxial Compressive Strength UTS Uniaxial Tensile Strength

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SYMBOLS

Symbol Name Unit

P active power [kW]

τ torque [kNm], [MNm]

ω rotational speed [rpm]

Q flow rate [m³/hour]

P pipeline pressure [bar]

EF pump specific efficiency factor [-]

U_mean mean utilisation [%]

Umax maximum utilisation [%]

Vring ring volume [m³]

E_m energy consumption per excavation volume [kWh/m³] Pm active power per excavation volume [kWh/m³]

k − value hydraulic conductivity [m/s]

Cu not drained cohesion [kN/m³]

U CS uniaxial compressive strength [MPa]

RM R rock mass rating [-]

CAI Cerchar abrasiveness index [-]

RQD rock quality designation [%]

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Herrenknecht AG is a German world-leading Tunnel Boring Machines manufacturer showing strong awareness and concern regarding environmental issues. The company supports research on the Energy Efficiency (EE) of their products, aimed at the development of intelligent design for a green Tunnel Boring Machine. The aim of this project is to produce a ’status quo’ report on EE of three types of Tunnel Boring Machines (Hardrock, EPB and Mixshield TBM). In the framework of this research 39 projects are analysed using calculation tools, plotting and statistical functionalities of Excel and Matlab. The findings of this study inter alia confirm the existence of data quality issue and highlight the necessity of data quality control, allow identification of specific distinctions between energy consumption of the three investigated TBM types, and stress the necessity for optimisation of the layout of TBMs energy supply units and main consumers. Moreover the results of the survey suggest that there is a certain energy saving potential, which is achievable by e.g. an adequate selection of the machine type prior to start of a given project and better adjustment of the machines’ layout to the particular local geological environments. An EE implementation strategy, indicating further research needs, is suggested and discussed.

Keywords: Energy Efficiency; Gripper TBM; Single Shield TBM; Double Shield TBM; Double Shield TBM; Earth Pressure Balance TBM; Mixshield TBM; Herrenknecht AG

1

INTRODUCTION

The acknowledged scarcity of natural resources resulted in general trend towards the green production and environmental friendliness of the products and services. This trend is strongly supported by various legal documents on international, regional and national levels.

In European Union a number of documents and policies were developed in order to promote and support green products and services.

EUROPE 2020: A strategy for smart, sustainable and inclusive growth, EE Plan 2011 and EE Directive 2012/27/EU are some of the examples of such papers dedicated to improve the EE throughout the European Union.

Herrenknecht AG is one of the world leading Tunnel Boring Machines production companies, located in Germany. The company produces a wide range of Tunnel Boring Machines, suitable for operation in all geological environments and is leading tunnel construction projects worldwide. Herrenknecht AG demonstrates a strong awareness and concern regarding the environmental issues and among others supports research on the EE of their products, aimed at the development of intelligent design for a green Tunnel Boring Machine.

1.1 Background

Around 5000 years ago the humankind started to work on construction of tunnels for vari-

ous purposes. The tunnels were, for example, built in order to protect the goods and people, to secure secret underground passes and to enable mining or improvement of transportation routes (Maidlet al., 2012).

The rapid development of tunnelling technology started during the industrialisation age in the beginning of the 19th century, when the railway network was extensively built. Drilling and blasting method was mainly used in the hard rock environments and the development of tunnelling was strongly influenced by the development of drilling equipment for drilling holes for the explosives. At the same time there were attempts to excavate the rock completely by machine (Maidlet al., 2008).

The first mechanised full face TBM was paten- ted in 1876 by John Dickinson Brunton and George Brunton (Maidlet al., 2012). The construction scheme of this machine and a short description are demonstrated in the figure 1.

’The shield had a hemispherical rotating cutting head built up of single plates. The cut material was intended to fall into mucking buckets mounted radially on the cutting head. The buckets threw the excavated material onto a conveyor belt, which transported it backwards out of the shield. The cutting head itself was turned by six hydraulic cylinders, which worked against a ratchet ring fixed to the cutting head’ (Maidlet al., 2012).

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Figure 1: First mechanised full face TBM developed by J.D. Brunton and G. Brunton, pat- ented in 1876. Source: Maidlet al. (2012).

In the first half of the 20th century, tunnelling machines were effectively used for driving gal- leries in potash mines. As a result a number of machines were developed, showing a strong development trend between machine generations with increased quality and boring capacity (e.g.

advance rates) of the modern machines of that time. The breakthrough to the development of the today’s TBMs did not occur until the 1950s, when the first open gripper TBM with disc cutters as its only tools was developed (Maidlet al., 2008).

With a small delay the tunnel boring machines technology has started its development in Europe, with such German manufacturers as Demag and Wirth, which began building TBMs of North American type in the 1960s. The machines were mostly intended for hard rock.

Only the developments of 1970s and 1980s allowed for driving tunnels through brittle rock and the enlargement of tunnel sections. At this stage the consideration of the stand-up time of the soil/rock becomes particularly important.

This has also led to the necessity in support systems, causing their gradual development from steel installations, anchors and mesh-reinforced shortcrete to segmental lining (Maidl et al., 2008).

The various underground constructions nowadays are widely used. The types of application include placement of underground traffic constructions, connections for energy production sites, storage laboratories (e.g.

for highly radioactive materials) and security rooms, walk-in passages as well as utilisations (e.g. electric supply, communications, water supply and sewage removal). The necessity in underground constructions is especially high in densely populated areas, where the space on surface is limited (Maidlet al., 2012).

As a result of the high demand in effective tunnelling the tunnel boring technology has developed further over the period of the last dec- ades, which is evidenced by both the high level of development of the conventional boring machines and by the appearance of a wide range of new TBMs featured with improved equipment allowing for tunnelling in problematic geological environments. According to Maidl et al. (2008) the shielded TBMs have in mean- while reached a state of perfection in Switzer- land, which is indicated by the high advance rates even in changeable geological conditions.

In this research three main types of TBMs will be investigated:

1. Hardrock TBMs (Gripper TBM, Single Shield TBM and Double Shield TBM);

2. Earth Pressure Balance Shields TBM;

3. Mixshield TBM.

The main principles behind the operation of each of these TBM types and general design features are described in the literature review section under the respective headings. Each of these machine types is suitable for a certain range of geological conditions. In general one can say, that Gripper TBMs are suitable for good rock with high stand-up time and low fracturing, Single and Double Shield TBMs are more suitable for low water content fractured hard rock, whereas EPB and Mixshield TBMs are designed especially for soft rock, soil and highly fractured hardrock especially with high water contents. The difference between the last two is that Mixshield TBMs are more suitable for the geological environments containing large amounts of groundwater.

There are several issues concerning EE of TBMs, which are caused by different application practices. For example according to Kassel (2013) the clients tend to choose the equipment based on their working experience, giving priority to the machines they used before and generally ignoring the desirable adaption of the solution to the particular geological environ-

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ments. This may often negatively influence the advance rates and cause higher total costs of a tunnel construction project. Moreover it dra- matically deteriorates the EE of a project. The energy costs are however minimal when compared with the total costs of the TBM machines and thus represent rather an insignificant share in the overall costs of a project (Kassel, 2013).

As a result the costumers generally neglect energy costs and do not try to implement energy effective boring techniques.

1.2 Aim and limitations

The aim of this project is to produce a ’status quo’ report on the EE of three types of Tunnel Boring Machines developed by Herrenknecht AG (Hardrock TBMs, EPB and Mixshield TBM). The research is based on the filed energy consumption logs, specifications of the machines and the installed equipment as well as on the geotechnical reports and when applicable geological profiles from previous tunnel construction projects. It should include the results of already processed data (conducted by Be- nedikt Broda, former trainee at Herrenknecht AG) and the new data from 2011-2012 to be processed within this master thesis.

The goals of the research are as follows:

1. To assess the quality of the available data logs, necessary for the EE study;

2. To assess energy saving potential with focus on the main energy consumers, covering two main saving options:

(a) EE by design (optimisation of the installed power of the main consumers);

(b) Effective energy use at operation (idle hardware deactivation).

3. To find correlations between energy consumption and changes in geological properties for the projects where detailed geotechnical information is available.

The given research has a number of limitations.

These include e.g. the absence of data of application of different machines in the same or even similar geological environments (a quality, sig- nificantly affecting advance rates), pre-processed

nature of the studied datasets, low share of energy costs in the overall construction project ex- panses and relatively low energy costs in general.

1.3 Scope and methodology

In total 39 previous tunnelling project cases are to be analysed in the framework of this master degree project, including 15 Hardrock TBMs (Gripper TBM, Single Shield TBM, Double Shield TBM), 19 Earth Pressure Balance Shield TBMs, and 5 Mixshield TBMs.

The data on energy consumption, descriptions of the respective geological environments as well as necessary information about the design of the machines under investigation are collected from various representatives of Herrenknecht AG personnel responsible for the respective projects. For the collection and pre- liminary analysis of the data internal software and network tools were used. The data is analysed using calculation tools, plotting and statistical functionalities of Excel and Matlab.

The research project is limited to the analysis of 39 preselected previous tunnel construction cases and includes the results of further 24 projects, analysed by Benedikt Broda. During the selection the availability and the quality of the data is considered giving higher priority to the projects with available energy consumption data and geotechnical information.

2

LITERATURE REVIEW

2.1 Tunnel Boring Machines

There are a wide variety of Tunnel Boring Ma- chine types (Fig. 2). The diversity of TBMs is determined by the variety of geological and geotechnical conditions the machines are operating in. Many of the TBM types can be applied in various geological environments, but most of the introduced developments allow for a better fit to the particular often more difficult conditions. As a result some of the TBMs are more adapted for certain geological environments then the others and there is no univer- sal TBM. For instance, Gripper TBMs are nor- mally used in good hardrock conditions with little fractures and low water content. In this rock type, where the stand-up time of the rock is relatively high, there is no or rather little risk of water inflow or rock falling. Closed system

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Tunneling Machines

...

Tunnel Boring Machines

(TBM)

...

TBMs with full-face excavation

Shield TBMs

Gripper TBMs

TBMs with cutting

wheel shield

TBMs with roof shield and side

steering shoes

TBMs with roof shield Open TBMs

Closed systems

Double shield TBMs

Single shield TBMs

Earth Pressure

Balance support (EPB)

Fluid support application (Mixshield)

Figure 2: Overview of tunnel driving machines according to Maidlet al. (2008) (modified).

tunnel boring machines (such as Mixshield and EPB) on the other hand are best suitable for operation in unstable soil, fractured soft and hard rock containing groundwater.

In case of unforeseen geological conditions change certain risks occur and special engineering solutions need to be applied. The examples of such solutions include freezing of groundwater with liquid nitrogen in order to shortly stop groundwater inflow, installation of additional shield protection in order to secure safe working environment for the TBM crew in fractured rock or installation of additional lining support systems in order to enable secure tunnel construction. Many of such measures need to be implemented in combination with the others.

This might cause substantial cost increase of the tunnel construction project.

The selection of a particular TBM solution is thus always a trade-off between the initial costs of the machine and additional costs, which can occur during the tunnelling. In order to make an informed decision many aspects should be

taken into account. This is probably one of the main reasons for an extensive geophysical investigation of the planned construction site, which has to be conducted prior to the selection of the suitable TBM.

The figure 2 is a modified compilation from DAUB (2010) and DAUB (1997). In this research only full face excavation tunnel boring machines will be taken into account, with a particular focus on Gripper TBM, Single shield TBMs, Double shield TBMs, Earth Pressure Balance Support TBMs and Mixshield TBMs (denoted with bold text in the figure 2).

2.1.1 Hardrock TBMs

This subdivision of Gripper TBM, Single and Double shield TBMs into the Hardrock TBM section is rather subjective. Both closed systems TBMs considered in this research can also be used in hard rock. This will however require a certain level of modification especially on the cutter wheel, which has to sustain higher stresses when applied to hard rock. The facts, descriptions and further thoughts presented in

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Figure 3: Overview of various machine systems of tunnel boring machines with full-face excavation. Source: Maidlet al. (2008).

this subsection of the report are mainly based on the information gained from Maidl et al.

(2008).

Gripper TBM

Gripper TBM is a classic example of a TBM machine. The name originates from the clamping units aka grippers. There are several variations of Gripper TBM, including open TBM, roof shield TBM, roof shield and side steering shoes TBM, and cutter head shield TBM (Fig. 3). The Gripper machines are in general applied in hard rock conditions with medium to high stand-up time and have rather less sophisticated design.

Open TBMs have no static protection against falling rock behind the cutter head. This type of TBMs is nowadays used only for construction of tunnels with small diameter. Roof shield TBM contains partial static protection roofs se- curing the safe working conditions for the crew.

It is applied in stable hard rock, where only

minor rock-falls are to be expected. An example of a roof shield Gripper TBM during assembly is demonstrated on the figure 4. The side steering shoes provide additional protection of the front part of the machine during advance and allow steering of the cutter wheel prior to and during the boring process. The cutter head shield TBMs provide protection from the falling rock for the area in the direct proximity of the cutting wheel.

In order to produce the necessary thrust force behind the cutter head, clamping units aka grippers of the machine are used. These are hydraulically pressed against the tunnel walls in radial directions. Although clamping forces exerted through clamping units, especially grippers, may negatively impact the stability of the surrounding rock, various sources (DAUB (2010), Maidl et al. (2008), Olofsson (2012)) insist that TBMs are generally more environ- mentally friendly due to the low impact of cutter head on the surrounding rock, especially when compared to such conventional methods as drilling and blasting.

The application of Gripper TBM is especially economically effective in the rock environments where no or little rock support is necessary. In fractured rock with low stability the installation of steal mesh, anchors and other support constructions should be conducted as close to the cutting wheel as possible. The grouting on the other hand should take place in the gentry area in order to reduce fouling (DAUB, 2010). According to Maidlet al. (2008) the development of rock support installation

Figure 4: Roof shield Gripper TBM ø 3.8 m developed by Herrenknecht AG during the assembly in Schwanau (Germany).

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systems has the highest potential for the improvement of overall increase in advance rates of Gripper TBMs, whereas the further reduction of the boring time would only lead to minor improvement.

Single Shield

The Single shield Tunnel Boring Machines are widely used in hard rock with short stand-up time and in fractured rock. The machine is equipped with a shield covering the entire machine area starting from cutter head (Fig. 3).

The Single shield machines are equipped with a support installation system. The support can be either permanent or temporary and represents a tube made of reinforced concrete. The tube is built from segments, the number of which depends on the machine design, the diameter of the tunnel face and other project specifications.

The lining segments are installed under the protection of the shield.

In contrast to Gripper TBM the thrust forces are exerted onto the existing tunnel support construction. The properties of the last should correspond the geological environments the tunnel is being advanced through in order to prevent segments from cracking and fracturing.

Cutting wheel as well as most other design elements is similar to those of a Gripper TBM.

Double Shield

The Double Shield tunnel boring machines are applied in the conditions similar to those of single shields. Double shield machines however have some important constructional differences. First of all, the Double shield TBMs con- sist, as one can anticipate from the name, of two shields (Fig. 3). The front shield covers the area from cutting wheel to the connecting telescopic jacks. The rear shield also called gripper, or the main shield, contains clamping units. The machine can either use tunnel support in order to push off and create necessary thrust and torque (in soft geological environments) or the clamping units of the gripper shield to radially push to the tunnel walls.

As a result of such design in good rock conditions the machine can move forward transfer- ring the thrust and torque forces either to support lining or via the rear gripper unit. This enables continuous operation and installation

of lining and thus allows increasing advance rates. This design however has its disadvant- ages in some cases, when the rear shield gets blocked due to the fractured rock material en- tering the telescopic jacks. Moreover the ad- vantages of Double shield machines can be limited in certain geological conditions. For example, in stable rock types the construction of tunnel support can be excluded (DAUB, 2010) and thus only gripper unit can be used. Soft rock, on the other hand, only allows operation of tunnel support clamping units and thus gripper unit remains idle.

2.1.2 Closed System TBMs

The closed system Tunnel Boring Machines are designed to sustain difficult geological environments consisting of e.g. soil, unstable or fractured soft or hard rock with very short stand-up time, often containing high amounts of groundwater.

Special equipment systems are used in order to oppose groundwater and earth pressure and prevent tunnel face from uncontrolled falling or groundwater from massive inflow. The closed system TBMs can be classified further based on the type of tunnel face support system utilised.

In this report only two categories will be taken into consideration: Earth Pressure Balance Sup- port TBMs (EPB) and Mixshield TBMs (fluid support application).

The application of closed system TBMs allows reducing negative environmental impact of tunnelling due to their ability to operate in groundwater rich geological conditions, where the reduction of groundwater level is either im- possible or forbidden (DAUB, 2010).

This subsection of the report is written mainly based on the information found in the book (Maidl et al., 2012). When otherwise the sources are indicated after the respective bits of text.

Mixshield Tunnel Boring Machines

The shielded TBMs with fluid support application aka Mixshield TBMs use pressurised fluid as medium in order to provide support to the tunnel face. The main elements of a Mixshield TBM are (Fig. 5):

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Figure 5: Schematic design of Mixshield Tun- nel Boring Machines (Source: Herrenknecht AG).

(1) Cutting wheel or cutter head (main excavation tool);

(2) Excavation chamber (the area of the shield, where the cutting wheel rotates);

(3) Pressure bulkhead (separates the section of the shield under atmospheric pressure from working chamber);

(4) Feed line (supplies bentonite suspension);

(5) Air bubble (injects the bentonite suspension into the excavation chamber);

(6) Submerged wall (separates the excavation chamber from the working chamber);

(7) Reinforced lining segments (secure the stability of the tunnel);

(8) Erectors (install the reinforced lining segments).

During the application of a Mixshield TBM both the existing earth and groundwater pres- sures are compensated (Fig. 6). This type of support systems is mostly utilised in coarse-grained and mixed-grained soil types. The groundwater level should be located at a considerable dis- tance above the tunnel roof.

In order to protect tunnel face working chamber is separated from the tunnel by a bulkhead. The required face support pressure can be very precisely regulated using the installed submerged wall, delivery rate of feed pump and removal rate of the slurry pump. Prior to operation the face support pressure has to be calculated for the entire length of the tunnel (DAUB, 2010).

The soil is excavated by the cutting wheel and hydraulically removed from the tunnel. The

Figure 6: Main principle of the slurry (fluid) support. Source: Maidl et al. (2012).

stones and boulders, which cannot be pumped out, are ground by the stone crusher. The sep- aration of the excavated soil from the support fluid is necessary (DAUB, 2010). It is usually conducted outside from the tunnel as it is de- picted on the figure 7.

The density and respective viscosity of the fluid medium should be variable, depending on permeability of the geological environment.

Bentonite suspensions are often applied as conditioners for this purpose (DAUB, 2010). The basic idea behind the introduction of the support medium is to build an impermeable membrane between the suspension and the soil. This process strongly depends on the permeability of the soil. In low permeability soils and with ap- propriate amount of bentonite, the suspension under the pressure difference penetrates the soil, building the impermeable membrane (Fig. 8: a).

This is a rapid process that takes approximately 1 to 2 seconds.

In the highly permeable soil conditions (permeability over 5x10⁻³[m/s]) the development of a membrane on the tunnel surface is hampered by the uncontrollable flow of bentonite suspension into the surrounding ground (Fig. 8: b). Adding fine-grained material or other compounds, allowing the improvement of rheological properties of the fluid, can solve this problem.

In stable rock with long stand-up time the fluid support system can be run in the open mode without application of pressure using water as a support medium (DAUB, 2010).

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Figure 7: Hydraulic muck removal during the excavation of the Radau header. Source: Maidlet al.

(2008).

Earth Pressure Balance Shields Tunnel Boring Machines

The Earth Pressure Shield TBMs have structural similarities with Mixshield TBMs.

However there are some substantial differences.

As shown on the figure 9 the main elements of the EPB TBMs are:

(1) Cutting wheel (main excavation tool);

(2) Excavation chamber (the area of the shield, where the cutting wheel rotates);

(3) Pressure bulkhead (separates the section of the shield under atmospheric pressure from excavation chamber);

(4) Thrust cylinders (push the machine further, creating pressure and enabling the excavation);

Figure 8: Membrane build-up and penetration models. Source: Maidlet al. (2012).

(5) Screw conveyor (removing the excavated muck from the excavation chamber);

(6) Erectors (install the reinforced lining segments);

(7) Reinforced lining segments (secure the stability of the tunnel).

In EPBs the excavation chamber (2) is separated from the tunnel by the pressure bulkhead (3).

The mixing units located on both the backside of the cutting wheel and on the bulkhead secure the proper consistency of the excavated muck.

The pressure sensors located on the front side of the bulkhead allow the pressure control. The excavated material is transported from the ex-

Figure 9: Schematic design of an EPB Tunnel Boring Machines. Source: Herrenknecht AG.

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Figure 10: System groups of a Tunnel Boring Machine. Source: Maidl et al. (2008).

cavation chamber by a pressure-tight screw conveyor (5).

The support pressure in the working chamber is controlled by changing the screw conveyor rotation speed or via volume of injected condi- tioning matter (DAUB, 2010). The apt pressure level should be created in the excavated muck, so it gets in equilibrium with the forces exerted on the tunnel face.

The main principle of tunnel face support is rather similar to that realised in the machines with fluid support system. However there are substantial differences in support pressure con- trolling as well as in muck transportation techniques. Moreover for the machines with Earth Pressure Balance the support pressure medium should have higher density and viscosity.

In the EPBs the tunnel face support is provided directly by the excavation material. This on one hand creates some limitations for soil properties in which EPBs can be applied. The ideal soil should have soft to stiff plastic consistency or be easily converted to mass of this kind. The fraction of fine-grained materials (smaller then 0,06 mm) has a substantial influence and should not be smaller then 30%. On the other hand the application area of EPBs can be expended by the use of soil conditioners, such as bentonite, poly- mers or foam. It is important to mention that in coarse-grained and mix-grained soil types as well as in hard rock along with increase of face support pressure there is a disproportional increase in face contact force and torque. This can lead to the substantial increase in energy demand.

Due to the structural similarities between the presented close systems TBMs, in practice there are examples of machines, which can be relatively easily transformed from one type to another, depending on the anticipated geological conditions. These are however not presented among the projects considered in the framework of this research.

2.2 Energy Efficiency of Tunnel Boring Machines

In order to discuss EE of TBMs the basic design elements should be discussed. These include:

cutting wheel, cutting wheel carrier with the cutting wheel drive motors, the machine frame, as well as the clamping and driving equipment.

The control facility and auxiliary equipment are usually connected to this construction on one or more trailers. (Maidlet al., 2008) The main system groups featured in a TBM are presented on the figure 10 and include (Maidl et al., 2008):

- Boring system (denoted with 1);

- Thrust and clamping system (denoted with 2);

- Muck removal system (denoted with 3);

- Support system (denoted with 4).

2.2.1 Boring system

The boring system is the most important part, determining the performance of a TBM. Main elements of the boring system are the cutter housings with disc cutters mounted on a cutter head (also known as cutting wheel). Cutting wheels can be designed in various ways in order to better fit the geological conditions and im-

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Figure 11: Main cutter head construction elements. Source: Maidlet al. (2008).

prove performance rates. Thus the spatial distribution of the disc cutters, reamers and muck removal buckets, as well as size and amount of these elements generally depend on the geological conditions, in which the machine is intended to operate. (Maidlet al., 2008)

Main cutter head construction elements are de- picted on the figure 11. Disk cutters are used to exert pressure on the rock material causing its breaking. Because the disc cutters to various extent exposed to wearing, these are mounted on special housing, which enables more effective replacement of the worn cutters on the cutter head. The excavated muck is then collected through the buckets (Maidlet al., 2008). On the TBMs operating in fractured soft rock and soils further excavation tools such as scrapers, drag picks, flat and round chisels and rippers are mounted onto the cutter head (Maidlet al., 2012).

2.2.2 Thrust and clamping system

Thrust and clamping system also influences the performance of a TBM. The total thrust creating the necessary cutting wheel loadings and counteracting the friction forces from the shield of the machine (which depend on its type) is to be provided, in order to enable sufficient penetration rate during the tunnel advance process. Hydraulic cylinders a TBM is equipped with create the required pressure. The length of

the piston of the thrust cylinder determines the maximum stroke, or the length of one advance step. (Maidlet al., 2008)

The schematic design of a single gripper clamping system developed by Herrenknecht AG is demonstrated on the figure 12. It shows the position of gripper units and propulsion cylinders in relation to the other parts of the TBM.

Clamping system is used in order to exert the total thrust forces axially either directly to the tunnel walls (Gripper TBM, Fig. 12), which requires a very good (stable) rock to be bored through, or to the previously installed tunnel support, built of reinforced segments. The lat- ter must have the capacity to withstand the total thrust forces. The number of the segments generally depends on the diameter of the tunnel.

The tunnel advance process can be divided into two main stages with respect to function of the thrust and clamping system. During the first stage (the boring process) the clamping units are pushed against the tunnel walls or the tunnel support, rotating cutter head is pressed against the tunnel face. This stage continues until the limit of the thrust cylinder pistol length limit is reached. During the second stage the clamping units are loosened, moved to the new position and braced against the tunnel walls again. The tunnel support if at all is generally built during this stage as well.

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Figure 12: TBM with single gripper clamping system (Main Beam TBM S-167 by Herrenknecht, ø 9.43). Source: Maidlet al. (2008).

2.2.3 Muck removal system

The removal of the excavated materials is an important task, which has to be fulfilled continu- ously in order to prevent idle times during the tunnel construction. The muck removal starts from the tunnel face and continues up to above the ground level. In Hardrock TBMs material transportation starts with buckets, which col- lect the excavated muck and transport it to the conveyor. In case of Earth Pressure Balance Support TBMs the high-density muck is removed from the excavation chamber by a screw conveyor (Fig. 13). In Mixshield TBMs low- density material is transported by slurry pump.

Thus transportation method used is highly dependant on the properties of the excavated material. (Maidlet al., 2012)

Moreover energy consumption strongly depends on the transportation method in use, e.g.

screw conveyors and slurry pumps belong to the main energy consumers on the respective TBM types.

There are various types of material transport systems through the tunnel, which in general can be divided into two main groups: open transport and piped transport (Maidl et al., 2012).

Open transport is mainly suitable for the transportation of hard rock material, dry material or high-density slurry. The nowadays most com- monly used open transport type is belt con-

veyor. This technology has developed to a high level, allowing for example to even operate in tunnels up to 6 km long and with curves. Other open transport techniques include rail transportation systems (mainly suitable for large diameter tunnels), and muck cars. (Maidl et al., 2008), (Maidlet al., 2012)

Piped transport is generally used on Mixshield TBMs. It is suitable for low-density material transportation, since in this method the muck is pumped out from the excavation chamber to above the ground level, where the slurry goes through a special treatment process. During this process excavated sludge is removed and the conditioner, e.g. water, can be reused. (Maidl et al., 2012)

2.2.4 Support system

The support system of a TBM is used in order to install tunnel lining. The role of the tunnel lining is to secure structural safety, durability and serviceability for the entire period of tun-

Figure 13: Screw with and without central shaft. Source: Maidl et al. (2012).

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Figure 14: Installation of crown arch support with mesh reinforcement and anchor drill.

Source: Maidlet al. (2008).

nel life (Maidl et al., 2012). There are various types of lining, including grouting, installation of anchors, steel arches, steel rings, meshes or a combination of these (Fig. 14), as well as liner plates and segmental lining.

The type of lining required strongly depends on the quality of the rock the tunnel is being advanced through. Here a parameter called stand-up time is of the highest importance. In geological conditions with long stand-up time, generally low fractured and non-weathered hard rock, none or minor lining, such as grouting, needs to be installed. In case of highly fractured hard and soft rock, where rock falling is to be expected the installation of anchors often in combination with meshes and steel arches or steel rings is required. In highly fractured rock with high water content the installation of segmental lining is preferable in order to secure the tunnel and avoid decrease of groundwater level having highly negative environmental impact as well as negative impact on above ground constructions due to subsidence. In soils with or without water content the installation of seg- ment lining is inevitable in order to secure stability of the tunnel and avoid water inflow.

The design and constructional features of a TBM are rather complicated and cannot be covered within this report. Thus by interest original sources, mainly Maidlet al. (2008) and Maidlet al. (2012) should be referred to.

2.2.5 Research trends

Generally one can state that over the period of TBM technology development many stud-

ies were (and still are) focusing on the improvement of TBM performance, especially with respect to the boring process (Bilginet al., 2012).

Other researches implemented in this area include e.g. investigation of correlations between various geotechnical properties of the rock and the applied machinery, in order to predict the performance of a TBM in various geological environments and to secure a better fit between these two (Nishioka et al., 1997), (Zhao et al., 2007), (Balci, 2009), (Hassanpouret al., 2010). A number of computational models were created for this purpose (Acarogluet al., 2008).

At the same time little attention seems to be paid to the EE issues when it comes to TBM equipment. One of the possible reasons is the still relatively low energy expenses especially when compared with the overall costs of the tunnel construction projects, as was men- tioned before. Another reason, which some- how originates from the first, is the difficulty in motivating clients to purchase machines with lower capacities. However the lack of published materials on this subject should not necessary mean that no work is being done in this field.

Taking into consideration the growing global concerns regarding EE one can assume that the TBM producers are conducting some research activities in this area, but their results are not publicly available.

EE with regard to TBMs is a very wide and complex topic, which has to deal with wide range of issues, such as geological and hydro- geological and geotechnical influence, technological influence and influence of driving ap- proach of the TBM crew. Another problematic issue, which is worth mentioning here, is the widespread re-use of sometimes energy inefficient or not particularly suitable in EE sense equipment pieces (e.g. main distribution boards of higher capacity then required, inefficient slurry pumps). And whereas the re-use does make (environmental) sense, this practise sometimes leads to the construction of over- powered TBMs with higher energy consumption then necessary. Taking into consideration the complexity of the topic, tons of high quality data (including energy consumption logs, geotechnical information including high-resolution geology profiles, reliable information on layout of the machines as well as the conditions un-

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der which these operate, e.g. electricity supply characteristics) need to be analysed in order to achieve solid and reliable results.

2.3 Environmental impact and European legal framework

2.3.1 Energy Efficiency and Energy Conser- vation

According to (Croucher, 2011) there is a dis- tinct difference between terms Energy Effi- ciency (EE) and Energy Conservation (EC). EE generally focuses on adjusting directly input re- quirements (electricity) for a given output decision (goods and services) with the aim to reduce the energy demands of electricity intens- ive production or utilisation process. EC on the other hand focuses on reducing the overall output decisions, leading to reduction of the required amount of energy. An example of EC is switching of the light, when it is not needed.

Both of the practices strive to achieve the same goal of rationalised energy consumption and therefore are closely related.

Over 40 years ago with the oil crisis in 1970s the policy-makers in many industrialised coun- tries demonstrated understanding of the necessity in efficient use of energy by giving priority to the subject (Chai & Yeo, 2012).

Nowadays efficient use of energy is a must and a very hot topic, spiced by scarcity of fossil fuels, limitations of natural resources and a variety of environmental issues associated among others with energy production and utilisation.

The parallelism between energy consumption

1980 1985 1990 1995 2000 2005 2010 2015

1.5 2 2.5 3 3.5x 10⁴

Time [year]

Total CO2 emission [Million Metric Tons]

1980 1985 1990 1995 2000 2005 2010 2015200 250 300 350 400 450 500 550 600

Total primary energy consumption [Quadrillion Btu]

Total primary energy consumption Total CO2 emission from energy consumption

Figure 15: Total CO2 emission from energy consumption vs. total primary energy consumption. Data source: U.S. Energy Inform- ation Administration, 2011.

Nuclear, 12.96%

Hydroelectric, 16.82%

Geothermal, 0.33%

Wind, 1.69%

Solar, Tide and Wave, 0.15%

Biomass and Waste, 1.55%

Total Conven+onal Thermal, 66.62%

Hydroelectric Pumped Storage,

-‐0.11%

Worldwide electricity net genera+on by type (2010)

Figure 16: Worldwide electricity net genera- tion by type as for 2010. Data source: U.S.

Energy Information Administration, 2011.

and carbon emissions denoted by (Linares &

Labandeira, 2010) for the industrialised coun- tries from 1990-2007 is also notable when plotting worldwide data for the period 1980-2011 ac- quired from (U.S. Energy Information Admin- istration, 2011) (Fig. 15).

Current electricity production is among others very dependant on fossil fuels, especially coal and gas. Over 65% of electricity generated globally originates from conventional thermal power plants (Fig. 16 ), requiring fossil fuels in order to generate heat and produce steam, which drives the turbine allowing to generate electricity.

According to (McLean-Conner, 2009) successful implementation of EE provides following benefits:

• Lower energy costs (the less energy is utilised the lower are the energy bills coupled with a better control and understanding of energy usage patterns on the side of the costumer);

• Cost-effective investment (investments in EE have impact on the future costs of energy);

• Fast and significant energy savings (as a result of EE implementation);

• Environmental benefits (reduction of energy consumption decreases the anthropo- logical stress exerted on the natural systems);

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• Faster economic development (e.g. more competitive position of companies investing in EE, creation of new jobs in EE sector).

However despite steady progress in the technical efficiency the global energy consumption continues to increase (Moriarty & Honnery, 2012). This phenomenon could be partially explained by the constant population growth leading to increasing energy demand. Another important reason is relatively low penetration rate of seemingly cost-effective EE technologies, which is described in EE literature as EE gap (Croucher, 2011).

According to (Croucher, 2011) EE gap can be explained by the following reasons:

• Additional investments (implied when re- placing less energy efficient technological solution with a better one);

• Higher discount rates of the customers (when calculating net present value of a given option);

• Lack of information (customers do not have sufficient information about EE features of the products);

• Loss aversion (customers are more satisfied when saving at purchase then when expect- ing gain from reduced energy costs);

• Liquidity constraints (lack of access to credit markets or high interest rates of the banks);

• Principal-agent problem (one group makes the investment decision and another ac- quires benefits).

In order to achieve the benefits of EE the above named barriers need to be dealt with by ap- plying specific means, e.g. investing in development or purchase of more energy efficient technologies, clearly demonstrating the advant- ages of EE products, making necessary information available for the clients preferably in their native language and close interaction with the customers, partners and other stakeholders, act- ively promoting EE solutions.

Moreover organisations advocating EE principles can be contacted and implicated into the

implementation process for the new energy efficient products in order to secure effective co- operation, public relations, promotion and lob- bying among the respective stakeholders, as well as proper labelling of the EE products.

The EE gap, its barriers and limitations as well as principles and practices to overcome these and promote EE solutions are further discussed in McLean-Conner (2009), Linares

& Labandeira (2010), Chai & Yeo (2012) and Croucher (2011).

2.3.2 Legal framework in Europe

Energy is an important commodity for existence and development of any country or re- gion. European Union as one of the most pro- gressive parts of the world is not an exception.

Most of the energy consumed in EU today is being imported from other locations. Rapidly growing prices for energy sources along with increasing emissions of carbon dioxide and other GHGs pushing forward the already progressing climate change have created the conditions in which counteraction is inevitable (Caproset al., 2011).

As a result wide range of legal documents and policies was adopted, including Action Plan for EE (2007-12), Ecodesign for energy-using appliances 2009/125/EC, Promotion of the use of energy from renewable sources 2009/28/EC, Product energy consumption: Information and labelling 2010/30/EU, EUROPE 2020: A strategy for smart, sustainable and inclusive growth (2010), EE Plan 2011 and EE Directive 2012/27/EU to name a few. The full assessment of legal framework for EE in European Union is beyond the scope of this paper. Only EE Plan 2011 as the most relevant document to the field of this study is presented and shortly discussed below. In order to avoid misinterpretation of EE Plan 2011 the further text generally represents copied bits from the original paper.

EE Plan 2011

The EE Plan passed by the European Commis- sion in 2011 is a supplement for the Europe 2020 Strategy and is meant to assist in realisa- tion of the strategy with regard to EE concept, its targets and practices, as described in the strategy.

According to the (Commission, 2011) ’EE measures will be implemented as part of the

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EU’s wider resource efficiency goal encom- passing efficient use of all natural resources and ensuring high standards of environmental protection’.

Buildings and constructions

’The greatest energy saving potential lies in buildings. The plan focuses on instruments to trigger the renovation process in public and private buildings and to improve the energy performance of the components and appliances used in them. It promotes the exemplary role of the public sector, proposing to accelerate the refurbishment rate of public buildings through a binding target and to introduce EE criteria in public spending. It also foresees obligations for utilities to enable their customers to cut their energy consumption’ (Commission, 2011).

Transportation

’Transport has the second largest potential.

This issue is addressed by the White Paper on Transport (2011), seeking to develop a competitive and resource efficient transport system throughout European Union. The White Paper on Transport defines a strategy for improving the efficiency of the transport sector that includes e.g. the introduction of advanced traffic management systems in all modes, infrastructure investment and the creation of a Single European Transport Area to promote multimodal transport’ (Commission, 2011).

Industry

’About 20% of the EU’s primary energy consumption is accounted for by industry. EE in industry will be tackled through EE require- ments for industrial equipment, improved information provision and development of appro- priate incentives for SMEs, measures to introduce energy audits and incentives to introduce energy management systems for large companies’ (Commission, 2011).

’Building on the success of ecodesign measures as an effective tool to stimulate innovation in energy efficient European technologies, the Commission is investigating whether and which energy performance (ecodesign) re- quirements would be suitable for standard industrial equipment such as industrial motors, large pumps, compressed air, drying, melting,

casting, distillation and furnaces’ (Commission, 2011).

Moreover ’in order to support technological innovation, the Commission will continue to foster the development, testing and deployment of new energy-efficient technologies’ (Commis- sion, 2011).

’Improvements to the energy performance of devices used by consumers - such as appliances and smart meters - should play a greater role in monitoring or optimising their energy consumption, allowing for possible cost savings. To this end the Commission will ensure that consumer interests are properly taken into account in technical work on labelling, energy saving information, metering and the use of ICT’ (Com- mission, 2011).

3

METHODOLOGY

In this research the total number of 39 tunnelling projects conducted with Herrenknecht AG machinery were analysed. This includes 19 Earth Pressure Balance Support TBMs, 15 hardrock machines (including Gripper TBM, Single Shield TBM and Double Shield TBM) and 5 Mixshield TBMs. Moreover the results of analysis conducted by Benedikt Broda, which included 24 projects: 13 Earth Pressure Support TBMs, 8 Mixshield TBMs and 3 Gripper TBMs, are also included in this research.

A number of various electronic solutions for data and information storage as well as for data analysis have been used. These are more in detail described in the respective sections below.

3.1 Data analysis software

In order to effectively conduct calculations and analysis of the available data software products were used. These mainly include Matlab and Excel.

3.2 Data analysis

The data analysis encompassed various steps from pre-analysis or the data quality assessment as described above to a number of calculations, generalisations, statistical tests as well as graphical visualisations. These data manipulations are described in detail in the respective subsections below.

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3.2.1 Calculation of the active power

Energy flow in a system can be described with the following terms: active power, which is the useful power producing work (heat, motion etc.), reactive power, which does not transfer energy and represents energy losses, and complex power, which is a sum vector of the previous two. The minimisation of losses due to reactive power is out of the scope of this research. The actual useful power vector, known as active power, is considered as an indicator. Active power is used to calculate power utilisation and energy consumption as described in sections 3.4.2. Power utilisation and3.4.3. Energy consumption respectively.

Cutting wheel

The equation used for calculation of the active power is derived from general equation for the calculation of power:

P = τ ∗ ω (1)

where τ is torque and ω is angular velocity of the rotating object.

Since instead of angular velocity expressed in radians per time unit, rotational speed (ω) expressed in rotations per minute is used, the right side of the Eq. 1 is multiplied with 2π. The torque is usually expressed in [M N m]. In order to acquire active power in [kW ] a conversion factor is added as well (Eq. 2).

Pcw= 2π ∗ τ ∗ ω ∗ 1000/60 (2) Screw conveyor

Screw conveyors belong to the main energy consumers on the Earth Pressure Balance Sup- port TBMs. An equation similar to Eq. 2 is used for the calculation of the active power for screw conveyor. The torque is usually expressed in [KN m]. Thus the conversion factor is slightly different (Eq. 3). As a result the unit for active power is also [kW ].

P_sc= 2π ∗ τ ∗ ω

60 (3)

Pumps

Slurry pumps are often main energy consumers on the Mixshield TBMs. The active power of the slurry pumps is calculated using the Eq. 4:

Psp = Q ∗ P EF ∗ 100

3600 (4)

where Q is the flow rate expressed in [m³/hour], P is the pipeline pressure expressed in bar, and EF is the pump specific efficiency factor obtained from pump performance curve (Fig. 17). The last term in the equation is the conversion factor added in order to obtain the result in [kW ].

3.2.2 Power utilisation

Power utilisation analysis is an important part of this research, which was conducted in order to determine the adequacy of the installed power capacities. The power utilisation is as- sessed as mean and maximum utilisation and is calculated for all main consumers of the TBMs of concern.

Mean power utilisation is the relation between the mean active power over the advance process and the installed capacity of the respective consumer (Eq. 5). The mean power is calculated from the current values by integration of active power dataset over the entire project period using integration functionality in Matlab. The result was then divided by time in order to obtain mean values in [kW ]. The stops during the construction were excluded from the analysis.

Umean= Pmean

P_installed (5)

Maximum power utilisation is, on the other hand, the relation between the maximum active power and the installed capacity of the respective consumer (Eq. 6). The maximum value for active power in each dataset was identified with a special Matlab command.

U_max = Pmax

P_installed (6)

The reserve (R) is the percentage of the installed power, which is not in use. The reserve is calculated with following simple equation:

R = 1 − U (7)

The reserve is used in order to prepare meaningful pie charts, demonstrating the mean and maximum utilisation for the main consumers in each individual project.

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Figure 17: Application of pump performance efficiency curve.

3.2.3 Energy consumption

Energy consumption analysis is another important part of the research project. It was conducted in order to compare energy consumption between different TBM types with various diameters.

In order to calculate the energy consumption per unit volume [m³], the volume per ring has to be calculated. The following equation is used for this purpose:

Vring = r²∗ π ∗ Segmentlength (8) In case of Gripper TBMs, where segmental lining is not constructed, a modification of this for- mula is used:

V_ring = r²∗ π ∗ T unnelmeter (9) Energy consumption per excavated volume is the most unified and meaningful result for com- parison of energy consumption between different machine types. Eq. 10 is used to calculate the energy consumption per excavated volume (Em):

E_m = P ∗ t

V ∗ 3600 (10)

where P is the mean active power, t is the mean advance time, and V is the volume of one ring, calculated in the previous step.

Energy consumption per ring is rather subjective value due to the variation in diameters and slight variation in segmental lengths between the projects. Eq. 11 was used in order to calculate the energy consumption per ring (Er).

E_r= P ∗ t

3600 (11)

In addition active power per excavated volume for both MDB and cutting wheel was calculated using Eq. 12 demonstrated below.

P_m= P

V (12)

3.2.4 Exploratory Data Analysis

Statistical data analysis provides means to better understand the data. There are two general ways to accomplish this task: through visualisa- tion and more formal statistical methods. Ex- ploratory Data Analysis implies the visualisa- tion of large and cumbersome data into easily understandable graphical displays. (Reimann et al., 2011)

The tools of EDA were among others implemented within this research, in which various graphical data representations were prepared in order to explore the data itself and the correlations between different datasets. These include e.g. histograms, various distribution function plots, boxplots and their various combinations.

Energy Efficiency of Tunnel Boring Machines.

M ACHINES

Vitaliy Grishenko

Contents

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