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Design and Planning of Instrumentation Works
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1
Design and Planning of Instrumentation Works
AECOM Singapore
LIM Chi-Sharn
Associate / Principal Engineer (Geotechnical)
09 May 2013
Outline
09 May 2013 Page 2
• Introduction and Objectives
•Design of Instrumentation and Monitoring Systems – Bored tunnelling
– Mined tunnelling
– Deep excavation
•Planning of Instrumentation and Monitoring Systems – Risk Management
– Information Management
– Contingency Planning
– Ensuring Reliability (System Assurance)
•Challenges
2
Tunnelling and Excavation causes Ground Movements & Other Changes which are kept Within Acceptable Limits in order to Ensure Safety & Protect Adjacent Structures
09 May 2013 Page 3
What is Instrumentation & Monitoring?
a Surveillance System
Instrumentation is
Monitoring is
at Site
09 May 2013 4
3
Objectives
To Verify Design Assumptions by
Comparing Monitored responses against Predicted Values
To Ensure Safety by Limiting Magnitudes & Restricting Trends of Responses
To Minimize Damage of surrounding Structures & Buried Cables, Pipes etc.
09 May 2013 Page 5
Construction Works as an Engineered System
09 May 2013 Page 6
QUALITY
ability to satisfy requirements
Serviceability
use for purpose and for conditions
Safety
acceptability of risks
Compatibility
acceptability of impacts
Durability
freedom from unanticipated
degradation
• Equipment – reliable
• Processes – clearly defined
• People – clear roles and responsibilities
(Bea, 1994, 2002)
4
Benefits of Instrumentation & Monitoring (from Dunnicliff, 1993)
• Defines initial site conditions such as groundwater, background conditions (temperature, noise, vibration, tides)
• Proof testing (test piles)
• Safety and Risk Management
• Observational approach to design and design verification that is based on data
• Construction control
• Legal protection
• Enhances public relations
09 May 2013 Page 7
What are Monitored?
• Ground Movement – Settlement (& at Depths), Heave (& at Base)
– Lateral Displacement (& along Depths)
• Ground Water – Water Table / Pore Water Pressure
• Structural Forces – Strut/Ground-Anchor Supports, Tunnel Lining
• Structural Deformations – Tilt & Crack Widths of Buildings/Structures
– Utilities; Cables & Pipes
– Profile & Shape of Tunnels
• Vibration and Noise 09 May 2013 Page 8
5
09 May 2013 Page 9
TYPICAL INSTRUMENTATION
Ground Settlement Markers
09 May 2013 Page 10
6
Settlement Plates
09 May 2013 Page 11
Settlement at Depth
(Magnetic Extensometer)
09 May 2013 Page 12
7
Settlement at Depth
(Hydraulic Hook)
09 May 2013 Page 13
Settlement at Depth
(Hook Sensor)
09 May 2013 Page 14
8
Deep Leveling Datum
09 May 2013 Page 15
Water Stand Pipe
09 May 2013 Page 16
9
Water Stand Pipe & Piezometer
09 May 2013 Page 17
09 May 2013 Page 18
10
Vibrating Wire Piezometer
09 May 2013 Page 19
Piezometer
09 May 2013 Page 20
11
09 May 2013 Page 21
Push-in Type Piezometer
Building Settlement Markers
For Concrete Surface
For Asphalt Surface
09 May 2013 Page 22
12
Building Settlement Markers
09 May 2013 Page 23
Tilt Meter
09 May 2013 Page 24
13
EL Beam Sensor
09 May 2013 Page 25
EL Beam Sensor As In-Place Inclinometer & for Settlement Profile
09 May 2013 Page 26
14
Convergence Monitoring
09 May 2013 Page 27
Convergence Monitoring
09 May 2013 Page 28
15
Tape Extensometer
09 May 2013 Page 29
Crack Meter
09 May 2013 Page 30
16
09 May 2013 Page 31
09 May 2013 Page 32
17
09 May 2013 Page 33
Strut Load Measurement
09 May 2013 Page 34
18
09 May 2013 Page 35
09 May 2013 Page 36
19
09 May 2013 Page 37
Brillouin optical time domain reflectometry (BOTDR)
Diagram courtesy of ntt.co.jp/news
Distributed strain sensor – BOTDR Average strain over 1m every 20cm Range ~5-10km Resolution 30με (0.003%) Low cost sensors - optical fibre 5 - 25 minutes per measurement Can link or switch between fibres 09 May 2013 Page 38
20
DESIGN
09 May 2013 Page 39
Design Aspects
• Purpose of instrument – What is to be monitored?
• Location of instrument – Where is it to be installed?
• Review levels – What are the safe limits?
• Frequency and duration – When and how often is it to be monitored?
• Contingencies – What should be done when the limits are exceeded, and who should do it?
09 May 2013 Page 40
21
Design Verification – Tunnelling
• Verification of parameters – Water table
– Volume loss
– Ground relaxation
• Comparing predictions with outcomes – Ground movements
– Groundwater changes
– Convergence / radial displacement
• Monitoring at areas of risk – To manage residual design risk, construction risk
09 May 2013 Page 41
Trough Measurements Help to Identify Types of Ground Movement
09 May 2013 42
22
Settlements at Surface Vs at Depth
09 May 2013 43
Monitoring Arrays (Tunnelling)
09 May 2013 Page 44
23
Monitoring Arrays (Tunnelling)
09 May 2013 Page 45
Monitoring Arrays (Tunnelling)
09 May 2013 Page 46
24
Monitoring Arrays (Tunnelling)
09 May 2013 Page 47
Monitoring Arrays (Tunnelling)
09 May 2013 Page 48
25
Interpreted Monitoring Data
09 May 2013 Page 49
• For Both Tunnels, – Min 1 for each drive
– Min. 1 at each soil type encountered
• For 1st tunnel, – Min one at every 100m if clear space <
– Min one at every 25m if clear space < 3m
Convergence Monitoring (Bored Tunnel)
09 May 2013 Page 50
26
• Every 2m from breakout
• 7m from breakout
• Every 20m thereafter 2
m
4m
6m
7m
20
m 0
m
Convergence Monitoring (Cross Passages using SCL)
09 May 2013 Page 51
• Currently Not Monitored at Close Interval
• To Determine Correct Face Pressure with Reference to Ground Water Pressure for Both Slurry and EPBM
• To limit Ground settlement
• To avoid Ground heave, slurry spouts and foam spews
• To validate the design of tunnel segment
Monitoring Ground Water Level
09 May 2013 52
27
Examples
09 May 2013 Page 53
Examples
09 May 2013 Page 54
28
Examples
09 May 2013 Page 55
Examples
09 May 2013 Page 56
29
Role in Risk Management – Managing residual design risk and construction risk
• Tunnelling
09 May 2013 Page 57
Before tunnelling
under buildings (esp. with mixed ground)
Start of tunnelling
Cavities are Not Always Fully Grouted
09 May 2013 58
Leca, E. & Domieux, L. (1990)
30
59 09 May 2013
Drawback – Risk of Slurry Path
Subsurface Monitoring – Rod extensometers @ Close Intervals?
Monitoring for unplanned stoppages
09 May 2013 Page 60
31
09 May 2013 Page 61
Design Verification – Excavation
• Verification of parameters – Water table
– Soil properties
• Comparing predictions with outcomes – Ground movements
– Groundwater changes
– Retaining wall deflections
– Strut forces
• Monitoring at areas of design risk – To manage residual design risk
09 May 2013 Page 62
32
Monitoring Arrays - Excavations
09 May 2013 Page 63
Monitoring Arrays - Excavations
09 May 2013 Page 64
33
Examples
09 May 2013 Page 65
Examples
09 May 2013 Page 66
34
Examples
09 May 2013 Page 67
Examples
09 May 2013 Page 68
35
Examples
09 May 2013 Page 69
Interpreted Monitoring Data
• Possible causes – Observed soil profile different from design – no F2 at the East Wall
– Marine clay Cu and Eu lower than adopted at design
09 May 2013 Page 70
Back-Analysis of Unpredicted Sway of a Cut-And-Cover Deep Excavation in
Singapore Marine Clay (Lim et. al. 2011. Proc of ICAGE)
36
Role in Risk Management – Managing residual design risk and construction risk
• Excavations
09 May 2013 Page 71
2D (ok) 3D (??)
The Impact of Geometry on Re-Entrant Corner Behaviour in Deep Excavation Retaining Walls: Two Case Studies from Stage 4 of the Circle Line. (Lim C.S. and Jee Y.Y., 2008, Proc. Of ICDE)
Ensuring Safety and Minimizing Impact – Adjacent Structures
• Comparing predictions with outcomes / safety limits – Ground movements
– Groundwater changes
– Building movements and strains
• Comparing outcomes with legal limits / guidelines – Noise
– Vibration
09 May 2013 Page 72
37
Structure Monitoring
09 May 2013 Page 73
09 May 2013 Page 74
38
Structure Monitoring
09 May 2013 Page 75
Structure Monitoring
09 May 2013 Page 76
39
Effects of tunnelling on pile foundations
Base
Load
Shaft
Friction
Volume Loss
Volume Loss
F
F
B
B
W
W = F + B
Tunnel volume loss
causes base load B to
reduce, pile settles
and shaft friction F
increases
(slide from Mair, 2009)
09 May 2013 Page 77
-50
-40
-30
-20
-10
0
settlm
ents
(mm
)
4
-1
-6
-11
-16
-21
dep
thb
elo
wre
f.le
vel(
m)
-30 -20 -10 0 10
-30 -20 -10 0 10
distance from tunnel (m)
piles tunnel
pile
settlement
surface
settlement
Bored tunnelling below full scale pile trials in the Second Heinenoordtunnel site (Kaalberg et al, 2005)
Zone A
Zone C
Zone B
30o
45o
(slide from Mair, 2009)
09 May 2013 Page 78
• Piles in Zone A settle > ground surface
• Piles in Zone B settle ~ ground surface
• Piles in Zone C settle < ground surface
• Field trials : wooden and concrete piles above two 8.3m OD tunnels
• End-bearing piles, shaft friction very low
• Volume losses
– 1st tunnel : 1~2%
– 2nd tunnel : 0.75%
• 0.5D was considered to be safe distance between pile toe and tunnel
40
Structure Monitoring (Real Time)
09 May 2013 Page 79
09 May 2013 Page 80
Structure Monitoring (Real Time)
41
Design Role of the Qualified Person for Geotechnical Aspects of GBWs
09 May 2013 Page 81
(Building Control Regulations)
09 May 2013 Page 82
PLANNING (For the construction phase)
42
Supervision Role of the Qualified Person for Geotechnical Aspects of GBWs
• Tunnels
09 May 2013 Page 83
(8th Schedule, Part II, Building Control Regulations)
Supervision Role of the Qualified Person for Geotechnical Aspects of GBWs
• Deep excavations
09 May 2013 Page 84
(8th Schedule, Part II, Building Control Regulations)
43
Construction Works as an Engineered System
09 May 2013 Page 85
QUALITY
ability to satisfy requirements
Serviceability
use for purpose and for conditions
Safety
acceptability of risks
Compatibility
acceptability of impacts
Durability
freedom from unanticipated
degradation
• Equipment – reliable
• Processes – clearly defined
• People – clear roles and responsibilities
(Bea, 1994, 2002)
Monitoring Works as an Engineered System
09 May 2013 Page 86
QUALITY
ability to satisfy requirements
Serviceability
use for purpose and for conditions
Safety
acceptability of risks
Compatibility
acceptability of impacts
Durability
freedom from unanticipated
degradation
• Equipment – reliable
• Processes – clearly defined
• People – clear roles and responsibilities
(Bea, 1994, 2002)
44
Role in Risk Management
Safety & Design RISKS are Managed
by
Setting Limits on Each Response
&
Comparing Monitored Responses
Against these Set Limits
09 May 2013 Page 87
Land Transportation Excellence Awards 2011
Best Innovation Partner
4 Key plan with instrumentation locations
2 Trend graphically visible
1 X-axis annotated with dates
5 Table readings against Review Levels
3 Activity against trend
09 May 2013 Page 97
FORM
IS
FUNCTION
Interpreting monitoring data – key information required
45
• Sufficient & Correct Instrumentation
• Proper Installation & Establishment of Initial Readings
• Monitoring Schedule Updated Regularly &
Strictly Adhered To
• Readings Taken by Competent Technicians
• Proper Data Deduction & Verification
• Daily Results into Summary Format
09 May 2013 98
Instrumentation & Monitoring Quality Plan (1 of 2)
Instrumentation & Monitoring Quality Plan (2 of 2)
• Daily Trend Watch
• Daily Check on Results Vs Review Levels
• Weekly Reports with Tables, Trend Plots
• Regular Meetings among Key Personnel
• Full Participation of QP(S) & PE
• Increased Monitoring at High Risk Area
• Increased Monitoring at High Activity Area
• Prompt Replacement of Damaged Instruments
• Calibration of Tools as per Schedule
• Manual checks of automated real-time monitoring
09 May 2013 99
46
Challenges of Instrumentation & Monitoring
– Key responses of ground and structures are monitored
– Correct type of instrumentation is used
– Review Levels are set for each instrumentation
– Monitoring frequency matched with site activities
– Prompt processing of monitored data
– Graphical outputs to visualized trends
– Responses are tracked against Review Levels
– Regular review of monitored readings with key personnel
– Continuous training of personnel involved
Timely Interpretation
Voluminous Data
Monitor and Analyze trend Graphical output
Relate to
construction
activities Tracking
against
Predicted Levels
09 May 2013 Page 100
THANK YOU
09 May 2013