1 Design and Planning of Instrumentation Works AECOM Singapore LIM Chi-Sharn Associate / Principal Engineer (Geotechnical) [email protected]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
•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
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Tunnelling and Excavation causes Ground Movements & Other Changes which are kept Within Acceptable Limits in order to Ensure Safety & Protect Adjacent Structures
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What is Instrumentation & Monitoring?
a Surveillance System
Instrumentation is
Monitoring is
at Site
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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.
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Construction Works as an Engineered System
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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)
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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
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What are Monitored?
• Ground Movement – Settlement (& at Depths), Heave (& at Base)
– Lateral Displacement (& along Depths)
• Ground Water – Water Table / Pore Water Pressure
• Structural Deformations – Tilt & Crack Widths of Buildings/Structures
– Utilities; Cables & Pipes
– Profile & Shape of Tunnels
• Vibration and Noise 09 May 2013 Page 8
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TYPICAL INSTRUMENTATION
Ground Settlement Markers
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Settlement Plates
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Settlement at Depth
(Magnetic Extensometer)
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Settlement at Depth
(Hydraulic Hook)
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Settlement at Depth
(Hook Sensor)
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Deep Leveling Datum
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Water Stand Pipe
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Water Stand Pipe & Piezometer
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Vibrating Wire Piezometer
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Piezometer
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Push-in Type Piezometer
Building Settlement Markers
For Concrete Surface
For Asphalt Surface
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Building Settlement Markers
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Tilt Meter
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EL Beam Sensor
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EL Beam Sensor As In-Place Inclinometer & for Settlement Profile
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Convergence Monitoring
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Convergence Monitoring
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Tape Extensometer
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Crack Meter
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Strut Load Measurement
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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
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DESIGN
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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?
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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
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Trough Measurements Help to Identify Types of Ground Movement
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Settlements at Surface Vs at Depth
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Monitoring Arrays (Tunnelling)
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Monitoring Arrays (Tunnelling)
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Monitoring Arrays (Tunnelling)
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Monitoring Arrays (Tunnelling)
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Monitoring Arrays (Tunnelling)
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Interpreted Monitoring Data
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• 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)
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• 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)
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• 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
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Examples
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Examples
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Examples
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Examples
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Role in Risk Management – Managing residual design risk and construction risk
• Tunnelling
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Before tunnelling
under buildings (esp. with mixed ground)
Start of tunnelling
Cavities are Not Always Fully Grouted
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Leca, E. & Domieux, L. (1990)
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Drawback – Risk of Slurry Path
Subsurface Monitoring – Rod extensometers @ Close Intervals?
Monitoring for unplanned stoppages
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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
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Monitoring Arrays - Excavations
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Monitoring Arrays - Excavations
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Examples
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Examples
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Examples
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Examples
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Examples
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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
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Back-Analysis of Unpredicted Sway of a Cut-And-Cover Deep Excavation in
Singapore Marine Clay (Lim et. al. 2011. Proc of ICAGE)
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Role in Risk Management – Managing residual design risk and construction risk
• Excavations
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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
