Presented in Malaysian Geotechnical Conference 16 March 2004 and a month later on 20 April 2004, there was the Nicoll Highway Collapse ! This system, if it had been used could have provided early warning to the site supervisors. The system was developed in 2001/2002 and had been used in many projects in Singapore.

1. MGC2004
REAL TIME MONITORING
SYSTEMS FOR TUNNEL &
DEEP EXCAVATION PROJECTS
Dr Ng Tiong Guan
GeoEng Consultants
Dr Tan Guan Hong
SysEng (S) Pte Ltd
MALAYSIAN GEOTECHNICAL CONFERENCE 2004
16 – 18 March 2004

2. MGC2004
Outline of Presentation
 Introduction
 Requirement for continuous monitoring
 Automated Tunnel Monitoring System
 Case History 1
 Real-time eMonitoring System
 Case History 2
 Concluding Remarks
 Is there a need?
MGC2004

3. MGC2004
Introduction
 In urban areas, construction and
basement excavation near to existing
structures & services are inevitable.
 Due to higher demand and better
market value, developments near to
existing MRT stations/tunnels are
popular.
 In the construction of new MRT line
and interchange, expansion of existing
facility often need to be carried beside
operating MRT station/tunnel.

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Deep excavation very near to
existing buildings & services

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Deep excavation
near to existing MRT
station.

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Expansion of existing siding tunnel to
accommodate future MRT line.

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 For development
near to existing
MRT structures,
stringent controls
are specified in
CPRP.
 Including allowable
movement &
requirement for
Continuous
Monitoring…

8. CODE OF PRACTICE FOR RAILWAY PROTECTION, LTA

9. MGC2004
Table 12.1 Allowable Limits for Rapid Transit Systems
Structure and Track
Type of MRT
structure
Bored tunnel,
cut-and-cover
tunnel, station
and viaduct
Total movement in
any direction
< 15mm
Differential
movement
in any plane
15mm or 1:1000
whichever is
lesser
Code of Practice for Railway Protection
Clause 12.1.1 Structural and Track Limits
“The design and construction of development or building works
within the railway protection zone shall satisfy the
requirements of Table 12.1…”

10. Required if predicted cumulative movement of rapid transit systems structure due to all
construction activities within the railway protection zone exceeds 5mm

11. MGC2004
Automated Tunnel
Monitoring System

12. MGC2004
Semi-automated system with manual data retrieval and manual alert system
Fully automated system with automatic data retrieval and SMS alert system

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Typical Set-up of Automated Tunnel
Monitoring System
Glass prism as reflectors
Range 20 to 100m
Accuracy +/- 1.0mm + 1ppm

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Smart SMS Alert System

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Case History 1:
2-level basement excavation
within Railway Protection Zone

16. Case History 1
Wall Type B
Wall Type C
Existing
Church
2-level
Basement
Existing
MRT Tunnels
Case History for Automated Tunnel Monitoring System

17. MGC2004
Case History for Automated Tunnel Monitoring System

18. MGC2004Finite Element Modelling

19. Automated Tunnel Monitoring System Deployed
• A total of 27 rings of the south
bound tunnel was monitored.
• Each ring contained 4 prism
targets.
• The spacing of the monitored
rings was typically 5m apart.
• The tunnel was monitored 3
cycles/day.
• The results were sent to
contractor, consultants and
authorities immediately, upon
automatic processing, through
e-mail.

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21. MGC2004

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Case History for Automated Tunnel Monitoring System

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Real Time eMonitoring
System

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Real Time eMonitoring System

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Comparison between GSM & GPRS
System GSM GPRS (General Packet
Radio Service)
Speed 9600 bps 32,000 bps
Connection By demand through
dial-up
Always on
Bandwidth Occupied full
bandwidth even
without data transfer
Occupied bandwidth
only during data
transfer
Cost Depend on
connection time
Depend on amount of
data send

26. MGC2004
Case History 2:
Deep excavation project for
cut-and-cover tunnel

27. MGC2004CCL2 LTA Contract 821 Kim Chuan Depot
Eastern Ramp
Sheet pile wall with 2-3
layers of horizontal strutting
Approx. 800m
Case History for Real Time eMonitoring System

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Case History 2:
Plan & Typical
Section
19m deep
excavation with 5
layers of compound
struts

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Real-time eMonitoring System Deployed
 40 nos or 15% of the total no of struts were
instrumented/monitored.
 10 nos or 25% of the instrumented struts are
monitored by VW load cell.
 Total 100 channels of VW strain measurement.
 Monitoring frequency every 10min.
 The results were sent to central server and eMS
web-site.
 SMS alert to contractor and consultants when
measured strut force exceeding 70% of design
value

30. MGC2004
Case History for Real Time eMonitoring System

31. MGC2004VW Load Cell
Case History for Real Time eMonitoring System

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VW Strain Gauges
Case History for Real Time eMonitoring System

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Solar Powered eMonitoring Data
Logger
Case History for Real Time eMonitoring System

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Average Axial Force in Level 1 Strut 21-A
-100
0
100
200
300
400
500
600
700
800
900
14-Nov
15-Nov
16-Nov
17-Nov
18-Nov
19-Nov
20-Nov
21-Nov
22-Nov
23-Nov
24-Nov
25-Nov
26-Nov
27-Nov
28-Nov
29-Nov
30-Nov
01-Dec
02-Dec
03-Dec
04-Dec
05-Dec
06-Dec
07-Dec
Date
Force(kN)
S21-1-A Trigger Design Allow able
Average Axial Force in Level 1 Strut 21-B
-100
0
100
200
300
400
500
600
700
800
900
14-Nov
15-Nov
16-Nov
17-Nov
18-Nov
19-Nov
20-Nov
21-Nov
22-Nov
23-Nov
24-Nov
25-Nov
26-Nov
27-Nov
28-Nov
29-Nov
30-Nov
01-Dec
02-Dec
03-Dec
04-Dec
05-Dec
06-Dec
07-Dec
Date
Force(kN)
S21-1-B Trigger Design Allow able
Preload
Excavation to
next level
Preload
Excavation to
next level
Case History for Real Time eMonitoring System

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36. MGC2004
SMS Alert

37. MGC2004
CONCLUDING
REMARKS
Is There a Need for
Continuous Monitoring…?

38. Tunnelling Affects Roads

39. MGC2004
Tunnelling Affects Roads

40. Tunnelling Affects Buildings

41. This Can Happen in 24 hours ! Reported in
Front Page of Straits Times
Glassgow Road Sumitomo

42. MGC2004
Failure of Shaft Excavation Causes Road Settlement

43. Excavation Failure Causes Road and Building Subsidence

44. PREVENTION IS
CHEAPER AND
BETTER THAN
CURE
CONCLUSION…

45. MGC2004
THANK YOU
MALAYSIAN GEOTECHNICAL CONFERENCE 2004
16 – 18 March 2004