contained in this presentation are taken “Mechanized ...Process control in mechanized urban...

"Process control in mechanized urban tunnelling“

Zurich, 10 May 2012

All the concepts contained in

this presentation are taken from the book

“Mechanized Tunnelling in Urban Areas”

Edited by Vittorio Guglielmetti, Piergiorgio Grasso, Ashraf Mahtab, Shulin Xu

Balkema - CRC Press – 2007 (Taylor&Francjs Group)

• Tunnelling is a complex process, and tunnelling in urban areas is even

more complex and needs special care for disturbing as little as possible the integrity of the ground surface and the built-up environment above.

• Nowadays we have a powerful method for excavating tunnels in urban environment: the use of Tunnel Boring Machines (TBMs) or “mechanized tunnelling”, due to the low disturb of the daily activities of the cities, assuring at the same time quality, safety, and the project’s target in term of time & cost.

"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012

Tunnelling by using Closed-face Machines (which is a “must” in urban environment) is “factory” like, not the “mining” type. This means a safer work environment for the workers, but also a more industrialized process, which is based on standard operations during working cycle, being thus

possible or even let say “easy” to control.


It should be highlighted that methods of excavation or TBMs endowed with “magic” powers do not exist, thus

any excavation method requires a strict system to control its use, respecting relevant procedures and work instructions. If the correct choice of the machine can be considered as “primary mitigation measure” for the excavation risks, the application of the control system can be seen as a “secondary mitigation measure”. In fact, it shall enable an actual “minimisation” of the construction risks to the point of making them acceptable, or to the so called “residual risk”. Of course, if the residual risk-level is still too high (i.e. non acceptable), additional mitigation measures must be implemented, like for example, ground treatments.

“The correct choice of machine operated without the correct management and operating controls is as bad as choosing the wrong type of machine for the project” BTS/ICE, 2005


All existing guidelines for underground or geo-engineering works require:

• A Solid Design based on site investigations, design calculations and necessary studies

• A Monitoring Plan with definition of threshold values of key parameters to be checked during construction

• Detailed Technical Specifications & Method Statements for construction


In addition to all this, for assuring the necessary performance to the project it is needed:

• An Experienced Contractor

• A Designer Representative on site to follow the implementation of his design

• A Resident Engineer responsible for Construction Supervision


• Clearly, all of the above elements are

necessary! but

• Are they enough?


Collapses can heavily injure third parties and/or cause serious damages to people and private properties.


Even if a solid design is done, checked and approved, and a

consistent monitoring system is implemented for the construction,

accidents could still occur!

WHY ???

"Process control in mechanized urban tunnelling“ Zurich, 10 May 2012

Why do accidents occur ?

• Variability & uncertainty in geological, geotechnical and hydrological conditions;

• Deviation of ground behavior from predicted;

• Lack of excavation process control, due to: • Lack of timely interpretation of

monitoring data; • Lack of (adequate) counter-measures

• Human factors.


Thus, a more consistent approach is required:

1. Make a Robust Design based on probabilistic (and not deterministic) approach;

2. Do a complete Risk Analysis; 3. Design a Monitoring Plan with definition of thresholds; 4. Predefine the necessary counter-measures; 5. Prepare an appropriate mechanism for the activation of

the counter-measures; 6. Collect in real time the monitoring data, and share them

among all people involved, in order to:

7. Take the RIGHT DECISION at the RIGHT TIME


All that leads to implement a rigorous Control System

What is a Control System?

The control theory states that in a control system, the output of a process is fed back through parameters measurement and comparison with reference values. The controller then takes the error (difference) between the reference and the output as indication to change the inputs to the system under control. Very simple, isn’t it?

INPUT +

- Process

Controller

OUTPUT THRESOLDS

YES

NO

REFERENCE


But … ... … when the process is complex like a Tunnel Construction things get harder!!!

Tunnel Design

+

-

Tunnel Construction

Counter-measures

Output Monitoring System

YES

NO

Measures

Design specifications


Main Risk Scenarios

Kovari, 2004

Damage due to ground deformations (settlements)

Collapse to surface Voids


NO

The control system activation gives real-time warnings to the process controllers, even before the threshold values are being exceeded, when their trend is showing a tendency to the limits, thus allowing the prompt adoption of counter measures.

Define critical parameters • Settlement • Load, etc

Define threshold values • Settlement: S1=alert, S2=warning • Load: L1=alert, L2=warning

Apply and/or modify countermeasures • What/If S=S1/S2? • What/If L=L1/L2

1. Measure 2. Analyze/Validate

Compare with threshold values.

are S>S1? L>L1?

Ok process continues

YES

Design and Construction control


Monitoring and instrumentation can be classified with reference to the object to be monitored:

1. Monitoring of underground excavation; 2. Monitoring of surface and utilities; 3. Monitoring of buildings; 4. Environmental monitoring (air, noise and vibrations);

Monitoring of underground excavation

Monitoring of surface and

utillies

Monitoring of buildings

Environmental monitoring


An example of Real-time Management of TBM monitoring data, with the possibility to transmit values from the data logger to everywhere through a WEB connection for sharing the information, but also for a potential “remote control”.


But the purpose of our control system is to prevent accidents not only to explain them “a posteriori”, looking for a possible guilty, too often identified in the “unforeseen & unforeseeable ” behaviour of the ground …


The modern data loggers give us the possibility to control a lot of parameters and are powerful instruments of process control …

… the monitoring data logger on a TBM is very similar to an airplane flight recorder.

http://www.haisentito.it/foto/brasile-aereo/

http://en.wikipedia.org/wiki/File:Caixa-Preta_GOL.jpg

• Let us see now how it can be possible to organize a control system of the two main types of Closed-face Machine available for urban tunnelling:

• The Slurry Shield, and • The EPB Machine


The control of a SLURRY SHIELD


• Pressure at the face: Compressed air pressure and slurry pressure, controlled by TBM automatic system plus slurry level control in the chamber, can be automatic or manual by controlling feeding and extraction pumps;

• Quality of the slurry: Viscosity, Yield value, Density, Cake thickness, through the on-site laboratory

• Quantity and quality of mucked material: through calculations derived from double measurement system (density and flow) on the in- and out- pipelines, and observations at the treatment plant as well;

• Segment mortar grouting: quantity and pressure of injection pumps, through manometers and automatic control system.


The control of Slurry Shield

Slurry Shield parameters under

control

Portland project, South Drive. Excavation parameters at rings 875 to 878.



The bentonite slurry level: why it is so important?



High level

Low level

A significant change of inclination of the graph showing the dry quantity of extracted material, can signify two equally dangerous things: (a) the beginning of a loss of slurry out of the face into the surrounding ground, with consequent loss of extracted material, or (b) the start of a plugging at the suction point due, for instance, to the presence of boulders, or sticky material, or (c) the formation of clogging along the first stretch of the pipeline. Conversely, a sudden increase of slope of the curve, which is less frequent but even more worrying, would signify a sudden unexpected “inflow” of solid material in the chamber, i.e. the possible beginning of face instability with the danger of collapse, or at least the beginning of an over-excavation.

Quantity of “dry extracted material” of a Slurry Shield v/s the excavation stroke



EPB TBM control: the Key Parameters

Excavation chamber always full of materials

Longitudinal grouting Control of Face-support Pressure

Balances & measure the extracted material quantity

Secondary Face Support System (SFSS)


The control screen of an EPB Machine, with all the key-parameters under the control of the TBM Operator

The Key parameters to be controlled are: • Pressure in the excavation chamber and along the screw conveyor. • Extracted quantity of material (in volume and/or in weight). • Apparent density of the material into the chamber • Volume and pressure of grouting in the annular void behind the lining. • Torque, stroke, rotating speed of the cutterhead, and TBM advancement speed.


The control of EPBM

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

19:0

9:06

19:2

5:46

19:4

2:26

19:5

9:06

20:1

5:46

20:3

2:26

20:4

9:06

21:0

5:46

21:2

2:26

Bulk

head

pre

ssur

es (b

ar)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

29.1

1.20

01

Bulk

head

pre

ssur

es (b

ar)

Face Support Pressure monitoring


The control of EPBM

TAV NODO DI BOLOGNA TBM PARI - Peso netto estratto

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

1395

1415

1435

1455

1475

1495

1515

1535

1555

1575

1595

1615

1635

1655

1675

1695

1715

1735

1755

1775

1795

1815

1835

1855

1875

1895

1915

1935

1955

1975

1995

2015

2035

2055

2075

2095

2115

2135

2155

2175

2195

2215

2235

2255

2275

2295

2315

2335

2355

2375

2395

2415

2435

2455

2475

2495

2515

2535

2555

2575

2595

2615

2635

2655

2675

2695

N. spinta

peso

al n

etto

dei

liqu

idi (

ton)

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

3050

3080

3110

3140

3170

3200

3230

3260

3290

3320

3350

3380

3410

3440

3470

3500

3530

3560

3590

3620

3650

3680

3710

3740

3770

3800

3830

3860

3890

3920

3950

3980

4010

4040

4070

4100

4130

4160

4190

4220

4250

4280

4310

4340

4370

4400

4430

4460

4490

4520

4550

4580

4610

4640

4670

4700

4730

4760

4790

4820

4850

4880

4910

4940

4970

5000

pk (m)

peso netto peso teorico (range g=2,0-2,1 t/m3) all + all -

Quantity of Extracted Muck: Weight and Volume


The control of EPBM

0,0

0,5

1,0

1,5

2,0

2,5

15:2

8:00

16:0

1:20

16:3

4:40

17:0

8:00

17:4

1:20

18:1

4:40

18:4

8:00

19:2

1:20

19:5

4:40

20:2

8:00

21:0

1:20

21:3

4:40

22:0

8:00

22:4

1:20

23:1

4:40

23:4

8:00

00:2

1:11

00:5

4:31

01:2

7:51

02:0

1:11

02:3

4:31

03:0

7:51

03:4

1:11

04:1

4:31

04:4

7:51

05:2

1:11

05:5

4:31

06:2

7:51

07:0

1:11

07:3

4:31

08:0

7:51

08:4

1:11

09:1

4:31

Time

Ben

ton

ite to

tal v

olu

me

(m3 )

0,0

0,5

1,0

1,5

2,0

2,5

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

18.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

19.0

9.20

01

Date

P7

bulk

hea

d pr

essu

re (b

ar)

P7 bulkhead pressure bentonite total volume

An example of the Secondary Face Support System

SFSS application, for

controlling the face support pressure during the TBM

stoppages. The intervention of injection pump is

here automatically controlled.

Red line : Face support pressure; Black line: bentonite quantity injected

"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012 The control of EPBM

The face-support pressure during standstill

A manual application of the Secondary Face-Support System - SFSS


The control of EPBM

The face-support pressure during standstill

AVERAGE APPARENT DENSITY INSIDE THE CHAMBER

(= Difference between pressure of sensors n.7 and 1,6 divided for 2m)

0

5

10

15

20

25

30

336

340

344

348

352

356

360

364

368

372

376

380

384

388

392

396

400

404

408

412

416

420

424

428

432

436

440

444

448

452

456

460

464

468

472

476

480

484

488

492

496

500

504

508

512

516

520

52

4

528

532

Mounted ring number

Av

era

ge

ap

pa

ren

t d

en

sit

y (k

N/m

3 )

0

5

10

15

20

25

30

Ave

rag

e a

pp

are

nt

den

sit

y (

kN

/m3 )

during standstill during advance Lower limit

The “apparent density” provides an indication of the consistency of the material in the excavation chamber, as well as its capacity to supply adequate face support pressure. It also gives an effective indication of the filling rate of the plenum

γapp = ∆P / ∆h

Remember: This is not a real “physical parameter”, it is only a good “marker” of what happens into the excavation chamber.


The control of EPBM

The Apparent Density Control

tail sealing system liner segment

grout stopper

cutter wear 20-25mm

tail skin longitudinal grouting

Squeezing clearance

tail-sealing system

Closing excavation profile

Grouting behind the lining


The control of grouting system is the same for Slurry Shield and EPBM

TAV NODO DI BOLOGNA TBM DISPARI - Volumi e pressioni di malta

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

2357

2377

2397

2417

2437

2457

2477

2497

2517

2537

2557

2577

2597

2617

2637

2657

2677

2697

2717

2737

2757

2777

2797

2817

2837

2857

2877

2897

2917

2937

2957

2977

2997

3017

3037

3057

3077

3097

3117

3137

3157

3177

3197

3217

3237

3257

3277

3297

3317

3337

3357

3377

3397

3417

3437

3457

3477

3497

3517

3537

3557

3577

3597

3617

3637

3657

3677

3697

3717

3737

3757

3777

3797

3817

3837

3857

3877

3897

3917

3937

3957

3977

3997

4017

4037

4057

4077

N. spinta

volu

mi m

alta

(m3)

0

1

2

3

4

5

6

7

8

9

10

pres

sion

i mal

ta (b

ar)

malta malta teor. press malta

pk 4

+500

Affiancamento Pozzo

pk 7

+095

Tail Void Grouting: Volume and Pressures

Blue line: grouting volume Green line: grouting pressure


The control of grouting system

The main sources of settlements are: Face volume loss Radial volume loss around the shield Radial volume loss around the lining

If we are able to control the key-parameters of the excavation

process, we can also control the surface settlements.


The results: the control of surface settlements

Development of settlement with distance from TBM1 face

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5-60 -40 -20 0 20 40 60 80 100 120

distance from TBM face to monitoring section (m)

sett

lem

en

t (m

)

before stoppage

after stoppage

Phase 1

Phase 2

An example: The “Nodo di Bologna High Speed Railway” project in Italy


The results: the control of surface settlements

Without a rigorous control system

After the control system application

Lessons learned:

1. No construction project is risk free: Risk can be managed, minimized, shared, transferred, or simply accepted, but it cannot be ignored. (Sir Michael Latham, 1994).

2. Be wise a priori: Nowadays the “unexpected” is no

longer acceptable from a strict “risk management” point of view.

By Vittorio Guglielmetti

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