Manufacture of Precast Tunnel Lining

INDIVIDUAL ASSIGNMENT C

CONCRETE PROCESSES

Image (Thoms & Gertsmann, 2008)

Production of Precast Concrete Tunnel Lining

KN Volmink

Word Count

Main text 2787 Tables (3 x 150) 450 Figures (3 x 150) 450

Total 3687

INDIVIDUAL ASSIGNMENT C CONCRETE PROCESSES Production of Precast Concrete Tunnel Lining

Individual Assignment C

An undersea vehicle tunnel 7 km long, with a circular cross-section of finished internal diameter 5.8m, is to be machine-bored and lined with pre-cast reinforced concrete segments. The segments are 300mm thick, each of the ring segments is 1.5m wide (measured along the longitudinal axis of the tunnel) and there are six segments per ring of approximately equal size. These will be produced by the tunnelling contractor over a period of 18 months. The concrete strength is specified as C60/75 with an intended working life of 100 years. a. Compare and contrast the use of self-compacting concrete with concrete of slump class S2 for the production of segments, and state your preference. b. For your preferred concrete, produce method statements for: i. the production, handling, placing and compaction of the concrete ii. demoulding, inspection, curing, handling and storage of the segments.


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TABLE OF CONTENTS

Page

1. INTRODUCTION ........................................................................................... 1

1.1 Tunnel Lining Production ......................................................................................... 1

1.2 Installation ............................................................................................................... 1

2. CONCRETE FOR PRECAST TUNNEL LINING SEGMENTS ...................... 2

2.1 Introduction ............................................................................................................. 2

2.2 Project Requirements .............................................................................................. 2

2.2.1 Concrete Specification ............................................................................... 2

2.2.2 Production Quantities ................................................................................ 2

2.3 Productivity .............................................................................................................. 2

2.3.1 Concrete Production and Transportation ................................................... 2

2.3.2 Concrete Placement .................................................................................. 3

2.4 Manufacturing Cost ................................................................................................. 3

2.4.1 Material Cost ............................................................................................. 3

2.4.2 Labour Cost ............................................................................................... 3

2.5 Quality ..................................................................................................................... 4

2.5.1 Quality Control ........................................................................................... 4

2.5.2 Concrete Quality ........................................................................................ 4

2.6 Working Environment .............................................................................................. 4

2.7 Conclusion .............................................................................................................. 5

3. METHOD STATEMENT: PRODUCTION, HANDLING, PLACING AND COMPACTION OF SCC................................................................................ 6

3.1 Production ............................................................................................................... 6

3.2 Handling .................................................................................................................. 6

3.3 Placing .................................................................................................................... 6

3.4 Compaction ............................................................................................................. 7

4. METHOD STATEMENT: DEMOULDING, INSPECTION, CURING, HANDLING AND STORAGE OF SEGMENTS ............................................. 8

4.1 Demoulding ............................................................................................................. 8

4.2 Inspection ................................................................................................................ 8

4.3 Curing ..................................................................................................................... 8

4.4 Handling .................................................................................................................. 8

4.5 Storage ................................................................................................................... 9

5. REFERENCES ............................................................................................ 10


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LIST OF FIGURES

Figure 1-1 Mechanised installation of precast concrete tunnel lining segments (Thoms & Gertsmann, 2008) ........................................................................................................... 1

Figure 2-1 Mechanised placing of SCC (EFNARC, 2005) ..................................................... 3

Figure 4-1 Trial ring assembly ............................................................................................... 9

LIST OF TABLES

Table 2-1 Quality control test methods for SCC (EFNARC, 2005) ......................................... 4

Table 2-2 Working environment benefits of SCC (Walraven, 2002) ....................................... 5

Table 3-1 Relative comparison of placement techniques and energy delivered (Daczko & Vachon, 2006) ................................................................................................................ 7


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1. INTRODUCTION

1.1 Tunnel Lining Production

Tunnel lining systems prior to the 1940’s were characterised by bolting steel plates

through flanges and it was only in the 1970’s that precast concrete tunnel lining

systems emerged. (McBean, 1988) Today the use of precast concrete segments is

one the most preferred tunnelling lining methods employed.

Precast concrete tunnel lining owes, to a large extent, its popularity as a

construction method to the high production rates that can be achieved. During the

construction of the Channel Tunnel rail link between Britain and France a total of

about 740,000 precast segments were produced to line more than 53km of the

tunnel. Two precast factories were setup each producing up to 1000 precast

concrete segments per day to keep up with the 11 tunnel boring machines (Wallis,

1989)

1.2 Installation

Besides the production benefits of precast concrete tunnel lining the installation and

relative ease of installation also plays a major role in it being one of the most

preferred systems of tunnel lining. Figure 1-1 details the mechanised installation

process of a precast concrete tunnel lining system highlighting the relative ease of

installation (Thoms & Gertsmann, 2008).

Figure 1-1 Mechanised installation of precast concrete tunnel lining segments (Thoms & Gertsmann, 2008)


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2. CONCRETE FOR PRECAST TUNNEL LINING SEGMENTS

2.1 Introduction

To achieve the production rate that makes precast concrete tunnel lining such an

efficient method of construction all the components to the manufacturing and

installation process must be optimised.

One critical component of the manufacturing process is the type of concrete used.

The productivity, manufacturing costs, quality, and working environment are all

affected by the type of concrete used. Successful precast tunnel lining

manufacturing is therefore dependant on the type of concrete used.

Self-compacting concrete (SCC) and conventional concrete (CV) are two different

families of concrete presenting different advantages and disadvantages to the

manufacturing process. These concretes are critically compared to determine which

is best suited for the demands of precast tunnel lining manufacturing.

2.2 Project Requirements

2.2.1 Concrete Specification

A C60/75 strength and S2 consistence concrete with a 100 year service life is

required for the precast concrete tunnel lining of 7km undersea road tunnel. This

specification, according to BS EN 206-1:2000, translates to a concrete with

characteristic cube strength of 40 MPa and slump of 50mm to 90mm.

The specified consistence is for concrete compacted by conventional means and is

measured with the slump test. This therefore precludes the use of SCC unless

presented as an alternative to the specification. This alternative would have to

specify a slump flow class according to BS EN 206-9:2010 for the SCC.

Walraven (2003) recomends a slump flow class of SF2 for floor and slabs which

most closely resembles a tunnel lining segment in geometry.This consistence class

is therefore be recommended for the SCC.

2.2.2 Production Quantities

Based on the 7km tunnel length and the 1.5m ring width (along the longitudinal axis

of the tunnel) approximately 28 000 precast concrete segments will be required.

These segments are to be produced over a period of 18 months which results in a

production rate of approximately 76 segments per working day (based on a 5 day

week and including construction holidays). To achieve this production rate the

production time of each segment has to be minimized.

2.3 Productivity

2.3.1 Concrete Production and Transportation

The mixing time for SCC is longer than that of CV as more time is required for the

efficient dispersion of the finer constituent materials to ensure mix homogeneity and

stability. (Gaimster & Dixon, 2003) This would increase production time should

there not be sufficient concrete production capacity.


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2.3.2 Concrete Placement

Agitation during the placement of the concrete to achieve compaction is not

necessary with self-compacting concrete. Therefore the placement process is often

mechanised as shown in Figure 2-1. This is a major advantage SCC has over CV

with regards to productivity as SCC can be placed faster and with fewer workmen

than conventional concrete.

2.4 Manufacturing Cost

2.4.1 Material Cost

The only evident difference in material costs between SCC and CV is due to

cementitious binder and admixture content. The higher paste content and the fresh

concrete requirements for cohesion and segregation resistance, typically results in

SCC having a higher cementitious binder content than CV. Also admixtures

(superplasticizers) are essential in SCC to reduce water content and maintain

fluidity (Beushausen, 2009) As a result the material costs of SCC is greater than

that of CV.

2.4.2 Labour Cost

Despite the higher material costs of SCC the labour costs of manufacturing with

SCC is lower than that of CV. In addition to the greater productivity the self-

compacting property of SCC means fewer workmen are required to place the

concrete. Therefore the labour cost for placing SCC is lower than CV.

Figure 2-1 Mechanised placing of SCC (EFNARC, 2005)


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2.5 Quality

2.5.1 Quality Control

More rigorous quality control of materials used in SCC is required than for CV due

to the fact that minor changes in material properties may have a significant

influence on workability. (Beushausen, 2009)

EFNARC (2005) outlines the various test methods, given in Table 2-1, for the filling

ability and stability of SCC defined by four key characteristics i.e. flowability,

viscosity, passing ability and segregation. The process from production to

placement may be more time-consuming for SCC than for CV. This is as a result of

the the testing reuired to ensure the compliance of the SCC, by the manufacturer,

before the concrete is dispatched and in the field where the concrete is used.

CHARACTERISTIC TEST METHOD(S)

Flowability Slump-flow Test

Viscosity (assessed by rate of flow) T500 Slump-flow test or V-funnel test

Passing Ability L-box test

Segregation Segregation resistance (sieve) test

2.5.2 Concrete Quality

Despite the more arduous testing, improved homogeneity is achieved with SCC.

With CV proper compaction of the concrete is dependant on skilled workmanship, of

which there is a great shortage, (the original reason for developing SCC, Okamura

& Ouchi, 1999). The full compaction of SCC is however not workmanship

dependant and therefore lends itself to improved homogeneity. This Improved

homogeneity in turn enhances concrete quality with regards to durability and

surface finish.

2.6 Working Environment

A marked difference in the working environment where SCC is used as compared

to CV is the reduction in noise levels due to the elimination of hand held poker

vibrators to compact the concrete. (Skarendahl & Billberg, 2006)

Table 2-2 (Walraven, 2002) illustrates that with the high production demands of

precast concrete tunnel lining construction and due consideration of occupational

health and safety using SCC is more beneficial.

Table 2-1 Quality control test methods for SCC (EFNARC, 2005)


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Conventional

Concrete

Self-compacting

Concrete

Recommended

Limits

Noise Protection 93 dB < 80 dB Protective measure required if > 80 dB

Vibrations 0.75 to 4 m/s2 0 m/s

2

Protective measure required if > 0.25

m/s2

Quartzite dust Not measured 0.01 mg/m3 Max 0.075 mg/m

3

Dust 3–4 mg/m3 0.2 mg/m

3

Industry goal is 1 mg/m

3

Savings due to elimination of vibration

Energy Consumption: - 10 % Forms cost: - 20 % Maintenance Cost: -

10 % Illness time: - 10 %

2.7 Conclusion

In comparing the various aspects of the manufacturing of precast concrete tunnel

lining using self-compacting concrete (SCC) and conventional concrete (CV), SCC

is clearly the better alternative.

The main advantages of using SCC as opposed to CV are summarised as follows:

� Greater productivity

� Lower construction costs

� Higher quality

� Better working environment

Table 2-2 Working environment benefits of SCC (Walraven, 2002)


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3. METHOD STATEMENT: PRODUCTION, HANDLING, PLACING

AND COMPACTION OF SCC

3.1 Production

The same batching and mixing equipment for the production of conventional

concrete may be used. On site concrete trials are to be done on an approved mix

design to determine the best batching sequence and the optimum mixing time.

Routine quality control testing is to be conducted to ensure that the required

concrete properties are achieved before dispatching to the site. Table 2-1, in the

previous section, details the test to be done and the concrete property that is

measured.

Due to the sensitivity of SCC to moisture variation (Daczko & Vachon, 2006) the

aggregate moisture content shall be carefully controlled and accurately monitored.

Any variation in the moisture content of the aggregate must be compensated for in

the mix proportions.

3.2 Handling

SCC can be transported in the same concrete mixing trucks as conventional

concrete however due to the higher fluidity attention must be given to possible

leakage. If the transportation route is causes shaking of the mixer further

consideration to the possible segregation of the mix is to be given. The concrete

must therefore be further mixed after transportation and before placing.

The distance over which the concrete is transported is to be evaluated to ensure

that the workability of the concrete is retained. The concrete is to be further tested

in the field before placing to ensure the specified flowability of SF2. The slump flow

test must therefore be done on every batch before placing.

3.3 Placing

Concrete shall be placed in such a manner that the discharge direction corresponds

to the direction of flow unless placed vertically. The rate of placing shall be slow

enough to ensure sufficient time for the escape of air bubbles but fast enough to

maintain flowability. The energy imparted to the concrete shall therefore be

considered in choosing the placing equipment/technique (Daczko & Vachon, 2006).

Table 3-1 compares the different placement techniques and the energy delivered to

the concrete.

Placement shall be continuous to prevent the formation of any joints. In the case of

a discontinuity the concrete already in place may require agitation (not through

vibration) to ensure placing against a live concrete surface.

Concrete may be allowed to flow uninterrupted through forms however the flow

length is to be limited to 10m to prevent dynamic segregation or void formation.

(EFNARC, 2005) Time to finishing shall be carefully monitored as thixotropic

thickening can resulting difficulty on finishing.


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Placement

Technique

Discharge

Rate

Discharge

Type

Single

Discharge

Volume

Relative

Energy

Delivered

Truck Discharge

Pump

Conveyor

Buggy

Crane and Bucket

Auger Discharge

Tremie

High

Medium/High

Medium

Medium

High

Medium

High

Continuous

Continuous

Continuous

Discontinuous

Discontinuous

Continuous

Discontinuous

High

Medium

High

Low

Low

Medium

High

High

Medium/High

High

Low

Low/Medium

Medium

High

3.4 Compaction

Vibrating equipment shall not be used to achieve compaction as this may cause

segregation and unwanted movement in the concrete once in place. Compaction

should be achieved through correct placement practices detailed above.

Table 3-1 Relative comparison of placement techniques and energy delivered(Daczko & Vachon, 2006)


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4. METHOD STATEMENT: DEMOULDING, INSPECTION, CURING,

HANDLING AND STORAGE OF SEGMENTS

4.1 Demoulding

Demoulding of the concrete segments can take place once the concrete has

achieved a recommended strength of 15MPa. (Dwi Hariyanto, et al., 2005) The time

to achieve this strength can be reduced by accelerated curing, detailed below.

The segments shall be lifted using vacuum suction equipment once the side

formwork has been removed.

4.2 Inspection

Inspection of the segments shall take place after demoulding prior to application of

any coatings. Any signs of defects shall be identified for and repaired (if repairable)

immediately as per agreed methodology.

The segment shall be thoroughly inspected for the following defects (all of which are

avoidable):

� Cavities

� Honeycombing

� Blow holes

� Fines loss

� Plastic settlement cracking

4.3 Curing

Steam curing will be used to accelerate the strength achievement of the segments

and enable demoulding to take place sooner. The heating rate, curing time and

cooling rate shall be determined through trials and shall be carefully controlled

during construction.

The heat shall be evenly applied to achieve the required temperature and the

essential moisture maintained. Values for steam curing can range between 6 and 8

hours (Wallis, 1989).

After accelerated curing to achieve the striking strength is complete the segments

shall be lifted and further cured by applying an approved curing compound.

4.4 Handling

The segments shall be lifted using suction lifting equipment after striking of the

formwork. Care shall be taken to ensure that segments are lifted at the specified

lifting positions and the regulated lifting equipment and procedures are employed.

Segments shall be clearly marked with the relevant segment information such as

casting date, segment no etc.


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Trial/mock ring assembly shall be done periodically, as shown in Figure 4-1, to

ensure that segments are constructed within dimensional tolerance and bolting

arrangement is correct.

4.5 Storage

Segments shall be stacked in the approved ring arrangement with the inside face

facing upward. The segments shall be supported by timber spacers and tightly

secured together to prevent falling during transporting. Segment shall be stored in

the prepared and allocated storage area.

Figure 4-1 Trial ring assembly


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5. REFERENCES

1. Beushausen, H., 2009. Chapter 20: Self-compacting Concrete. In: G. Owens, ed.

Fulton's Concrete Technology. Midrand: Cement & Concrete Institute, pp. 317-327.

2. Daczko, J. A. & Vachon, M., 2006. Self-Consolidating Concrete (SCC). In: J. F.

Lamond & J. H. Pielert, eds. Significance of Tests and Properties of Concrete and

Concrete-Making Materials - STP 169D. West Conshohocken: ASTM International,

pp. 637-645.

3. Domone, P., 2010. Part 3: Concrete. In: Construction Materials their Nature and

Behaviour 4th edition. London: Spon Press, pp. 83-208.

4. Dwi Hariyanto, A., Cheong, Y. W. & Kwan, H. P., 2005. Quality Control in Precast

Production - A Case Study on Tunnel Segment Manufacture. Dimensi Teknik

Arsitektur, 33(1), pp. 153-164.

5. EFNARC, 2005. The European Guidelines for Self Compacting Concrete. [Online]

Available at: http://www.efnarc.org/publications.html [Accessed 11 02 2013].

6. Gaimster, R. & Dixon, N., 2003. Self-compacting Concrete. In: J. Newman & B. S.

Choo, eds. Advanced Concrete Technology: Processes. London: Butterworth

Heinemann, pp. 9/1-9/23.

7. McBean, R., 1988. Developing a Tunnel-lining System. Concrete, 22(5), pp. 15-17.

8. Okamura, H. & Ouchi, M., 1999. Self-compacting Concrete: Development, Present

Use and Future. Stockholm, RILEM Symposium on Self-compacting Concrete.

9. Skarendahl, A. & Billberg, P., 2006. Casting of self-compacting concrete, Paris:

RILEM Technical Committee 188-CSC.

10. Thoms, I. & Gertsmann, O., 2008. World-class Tunnel Lining. Civil Enigneering, 1

August, pp. 46-48.

11. Wallis, S., 1989. Precast concrete forms the backbone of the Channel Tunnel,

London: The Arberdeen Group.

12. Walraven, J., 2002. Self-compacting Concrete in the Netherlands. Evanston,

Proceedings of the First North American Conference on the Design and Use of Self-

compacting Concrete.

13. Walraven, J., 2003. Structural applications of self compacting concrete. Reykjavik,

Iceland, Proceedings of the 3rd International RILEM symposium on self compacting.

Documents

Manufacture of Precast Tunnel Lining