The role of site investigation in Tunneling

1. Minimizing Cost and Time Delay during Tunneling Construction
Caused by Unexpected Ground Conditions and Obstacles:
The Role of Site Investigation
Angelo Indelicato, BA, MA, BSc, MSc (candidate), FGS
Senior Engineering Geologist – Dragages HK ltd.
angelo_indelicato@hotmail.com

2. Site Investigation is commonly seen as a
nuisance within construction companies.
Budget are always limited as well as the
amount of resources available.
Despite all, the site investigation has a
crucial role in identifying adverse geology
which can potentially jeopardize the
tunnel project.
Table of content:
1. Definition of Site investigation
2. Definition of Adverse Geology
3. Type of GI used
4. Tunnel Accident Caused by
unexpected ground condition
5. Conclusions

3. Site investigation is the process by
which geological, geotechnical and
other relevant information which might
affect the construction or performance
of a civil engineering or building project
is acquired (Clayton C.R.I. et al. 1982).

4. Conditions considered to be potentially catastrophic during tunnels
excavation such as:
 Saturated, debris-filled cavern in limestone;
 Wide fault zones with clayey and sandy gouge under high water
pressure;
 Rock bursting during excavation;
 Noxious gases under high pressure which have the potential to burst
or seep into tunnel excavation

5. Desk Studies
Air Photo
Interpretation (API)
Walkover Survey
Subsurface
Exploration

6. Aim: to acquire as much information on the ground where the project will be located.
This part of the site investigation might be very important in establish any adverse
geology which might affect the Tunnel. It is quite useful in land project but not in marine
environment. It involves the collection and study of geological maps and references.

7. Information that cannot be retrieved in any
way except from Air, this will include for
example:
 Archaeological site;
 Past land use and contamination;
 Site History;
 Site accessibility.
 Ground instability (i.e. landslides)

8. Purpose: add extra information about the geology of the site and to identify
any possible construction issue.
As per the desk study this type of site investigation is more effective in land
projects.

9. Insitu Examination
Direct
Indirect
• Trial Pit/trenches
• Slope Stripping
• Rock face mapping
• Augering
• Boring
• Drilling
• Probing
• Geophysics

10. Rotary Drilling:
• Vertical drills down to 400m
• Horizontal drill up to 1300m
(HK)

11. The fault zones, in most cases, becomes weaker and influence the
hydrogeological regime affecting the tunnel excavation.
Brittle Fault Fault Gouge
(Fletcher C.J.N. 2010)

12. Advantages
 Full suite of sampling &
testing
 Relative quick
 Can drill all materials
Disadvantages
• Required horizontal working
platforms
• Access difficult in steep terrain
• Mobilization costs are sometimes
higher than drilling

13. The cone penetration or cone
penetrometer test (CPT)
identifies the following
geotechnical parameters:
 the resistance to penetration
of the cone (qc);
 friction sleeve (fs);
 pore pressure (u).

14. Friction ratio (%)
ConeResistanceqt/qa(Mpa)

15. Areas of low qc within the sand
fill.
Possible explanation: CPT
carried out at early stage of
reclamation work so sand did
not have time to settle.
Drop in qc value and
increase of u. Possible
explanation: presence of
disturbed deposit within the
fill (Mud waves).
Low qc and Rf, high
water pressure. Marine
Deposit
Qc around 1.5MPa,
Rf=2% with high pore
water pressure. Alluvium
Clay
Very high qc value
(15MPa), low friction
ratio and low pore
water pressure.
Alluvium Sand
Fill
Marine
Deposit
Alluvium

16. Why are them so important?
1. Identify qc boundaries in relation to the Tunnel alignment
2. To identify any adverse geology (i.e. Faults)

17. Purpose: Identification of fault lines through CPT
qc boundary
Mains: Identification of clusters with an
anomalous drop in depth

18. 1. Fast and continuous profile (from site experience in 2 hours roughly
penetrate approximately 35m);
2. Repeatable and reliable data;
3. Economic and productive (way cheaper than rotary drill boreholes
and capable to cover more locations within a working day);
4. Strong theoretical basis for interpretation.
Disadvantages
1. Requires skilled operators;
2. No soil sample during CPT;
3. Penetration can be restricted in gravel, cement and in general any
hard and dense material, predrill will be necessary with a loss of
information.

19. Aim: locate some form of subsurface anomaly. The anomalies can be
zone of contact between two types of rocks, a fault, underground
services or a cavities.

20. Purpose: Geophysical survey techniques are based on determining
“changes” in physical properties of the subsurface material.
Means:
 Electrical conductivity (Resistivity);
 Density (Gravimetric);
 Magnetic Susceptibility (Magnetic);
 Velocity of sonic waves (Seismic).
Advantages
1. Relative low cost (for land GI)
2. High speed of the methods
Disadvantages
1. Noise and other
unwanted vibrations
2. Need to be confirmed by
boreholes

21. Aim: Identify any
potential hazard
during tunnel
excavation.
Relevant feature to
be identified:
 Excessive water
infiltration;
 Unstable wedge;
 Faults not
identified
by boreholes.

22. Purpose: identify potential geological or hydrogeological hazards
Means :
 Drilling energy (Instrumented rig)
 Cuttings
 Return water (flow and colour)

23. Case 1: Ping Lin Pilot Tunnel – Taiwan 1996
Project: Ping Lin Pilot Tunnel
Failure: groundwater infiltration reached 750 Lt./s, causing a severe collapse with
a huge volume of debris flow
Cause: unforeseen groundwater
Plan view of the 10th stoppage of pilot tunnel
TBM, Tseng D. et al. 2001

24. Case 2: Seoul Metro Line 5 – Phase 2, Korea
1993
Project: Seoul Metro tunnel
Failure: Tunnel collapse after removing spoil and
an water inflow of up to 300 Lt/min was recorded
Cause: High groundwater pressure
Sinkhole in Yongdungpo, Seoul from Shin
J. et al. 2006

25. Case 3: Laerdal Road Tunnel – Norway 1999
Project: Road Tunnel
Failure: Collapse of rock mass within the tunnel
Causes:
swelling clay in condition of high stress
(Karlsrud K. 2010)

26. The case histories show how the lack of knowledge
of existing geological conditions can be disastrous
for any civil engineering project.
The role of engineering geologists is to reduce the likelihood
of physical or economical failures through the early
identification of adverse geology

27.  Clayton C.R.I., Matthews M.C., Simons N.E. 1982 - Site investigation, Halsted Press
 Fletcher C.J.N. 2010 – Geology of Site Investigation Boreholes from Hong Kong. A Practical Guide for Geologist and
Engineer, AGC
 GEO 1990 – Guide to Site Investigation. Geoguide 2. Geotechnical Control Office, Civil Engineering Services
Department, Hong Kong
 Geotechnical Research Group 2012 - practical Applications of the Cone Penetration Test , Department of Civil
Engineering, The University of British Columbia http://www.geoplanning.it/test/wp-content/uploads/2012/02/Practical-
applications.pdf
 Indelicato A. 2012 – Management & Mitigation of Groundwater within Deep Excavation Shaft – The HATS2A project
experience in 32nd Annual Seminar, Geotechnical Division, Hong Kong Institute of Engineers, pp.111-117.
 Karlsrud Kjell (2010). Technical Note : Experience with tunnel failures in Norwegian tunnels. The Government of the
Hong Kong Civil Engineering and Development Department. (Unpublished).
 Kipko E., Spichak Y., Pozolov Y. 1998 – Water Sealing of Fault Zones at Ping Lin Pilot Tunnel in Taiwan in
Proceedings of International Mine Water Association Symposium, Johannesburg, South Africa, 1998, pp.141-148.
 Lee, I. M. & Cho, G. C. (2008). Underground construction in decomposed residual soils (presentation slides). The 6th
International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground (IS-Shanghai 2008),
Tongji University, Shanghai, April
 Robertson P.K., Cabal K.L. 2010 – Guide to Cone Penetration Testing for Geotechnical Engineering, Gregg Drilling &
Testing, Inc.;
 Robertson P.K. 2010 – Estimating in-situ permeability from CPT & CPTu in 2nd International Symposium on Cone
Penetration Testing, Huntington Beach, CA, USA, May 2010.
 Shin J., Lee I., Lee Y., Shin H. 2006 – Lessons from Serial Tunnel Collapse during Construction of the Seoul Subway
Line 5 in Proceedings of the World Tunnel Congress and 32nd ITA Assembly, Seoul, Korea, April 2006, pp. 22-27.
 Tseng D., Tsai B., Chang L. 2001 – A case study on ground treatment for a rock tunnel with high groundwater
ingression in Taiwan in Tunnelling and Underground Space Technology, Vol.16, Issue 3, pp.175-183.