"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.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
• Clearly, all of the above elements are
necessary! but
• Are they enough?
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
Collapses can heavily injure third parties and/or cause serious damages to people and private properties.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
Main Risk Scenarios
Kovari, 2004
Damage due to ground deformations (settlements)
Collapse to surface Voids
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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”.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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 …
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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.
• 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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
The control of a SLURRY SHIELD
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
• 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.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
The control of Slurry Shield
Slurry Shield parameters under
control
Portland project, South Drive. Excavation parameters at rings 875 to 878.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
The control of Slurry Shield
The bentonite slurry level: why it is so important?
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
The control of Slurry Shield
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
The control of Slurry Shield
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)
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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.
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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
"Process control in mechanized urban tunnelling“ Vittorio Guglielmetti - Zurich, 10 May 2012
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