Ground investigation design/considerations for soft/hard ground tunnels

1. Ground Investigation for
Tunnelling Projects
Keith Kong

2. Ground Investigation for
Tunnelling Projects
Topics to be discussed
• Objective
• During Project Planning and
Feasibility Study Stages
• During Design Stage
• During Construction
• Strategy and Techniques of GI

3. Objectives of GI Planning
(a) Suitability To assess the general suitability of the site
(b) Design To enable an adequate and economic design.
(c) Construction
(i) To plan the best method of construction;
(ii) To foresee and provide against difficulties
and delays that may arise during
construction; and
(iii) To explore sources of indigenous
materials for use in construction.
(d) Effect of Change
To determine the changes that may arise in the
ground and environmental conditions.

4. Ground Condition Risks
for
Tunnelling Projects

5. Water Ingress
Water ingress
~2 to 4 liter/sec

6. Ground Collapse
Collapse area 100m by 130m
Settlement up to 15m

7. Soil / Rock Interface

8. Possible Ground Conditions Encountered
Dyke structure

9. Possible Ground Conditions Encountered
Wedge Failure

10. Obstruction
Timber Piles

11. Ground Investigation
Planning

12. GI Planning
Fookes’ (1997) study indicated:
• ~50% of the anticipated geological model
from desk study.
• ~65% of the geology should be know if a
walkover survey is added to the desk
study.
• 95% if comprehensive GI works to be
done.

13. What is comprehensive
GI Planning?

14. US National Committee on Tunnelling
Technology (1984) suggested:
• 1.5 linear metre of borehole per route
metre tunnel alignment, and
• 3% of cost of tunnelling civil works for
ground investigation.

15. GI Planning During Project Planning and
Feasibility Study Stages
Key Issue
• to provide sufficient data for the evaluation
of alternative tunnel routes & portals &
shafts locations
• to assess the technical feasibility and
economic viability of the project
• initial cost and construction programme
estimates

16. GI Planning During Project Planning and
Feasibility Study Stages
Methodology:
• Carry out desk study (including site
reconnaissance by walkover surveys &
mapping, collecting background GI
information, and aerial photograph
interpretation).
• where practicable, very limited ground
investigation works should be carried out.

17. Aerial Photograph Interpretation
Photo-geological Lineament

18. GI Planning During Detail Design Stage
Objective:
• Finalising the tunnel alignment;
• Establishing the potential tunnel influence zone
for identification of sensitive ground and facilities
• Improving the cost and construction programme
estimates
• Preparation of Geotechnical Baseline Report for
construction reference (to allow equitable risk
sharing for difficult and unexpected ground
conditions between the contractor and the
employer)

19. GI Planning During Construction Stage
Objective:
• Provide information to determine possible
variations and potential impacts on cost and
construction programme as early as possible.
• Provide data to assess the impacts caused by
the tunnelling, ground supports and risk
mitigation works designed and implemented by
the Contractor, and to review the long-term
performance of the tunnel.

20. GI Works in Construction Stage
Techniques:
• Conventional GI Practices
• Continuous probe drilling ahead
• Geophysical survey to tunnel face and
sidewall (e.g. Seismic Reflective Image)

21. Probe Drilling for TBM Tunnelling

22. Probe Drilling for TBM Tunnelling
Probe Hole Window

23. Geophysical survey ahead of tunnel face using
seismic reflective image

24. Geophysical survey ahead of tunnel face using
seismic reflective image

25. Strategy and Techniques of
Ground Investigation

26. Strategy and Techniques of GI for
Tunnel Projects
Tunnel Projects involved in:
• Soft Ground
• Hard Rock
• Karst Deposits
• Contaminated Land
Including Marine / River
Crossing Tunnels

27. GI for Soft Ground Tunnel Project

28. Appropriate GI Methods – Laboratory Testing
(Soft Ground Tunnels)

29. Soil Particles Size Vs TBM Selection
(compress air tunnelling

30. Compress Air TBM (BESSAC)

31. GI Guideline for Hard Rock Tunnel Projects

32. Appropriate GI Methods – (Hard Rock Tunnels)

33. Appropriate GI Methods – (Hard Rock Tunnels)
Typical Tests Required to Interpret Design Parameters
In Situ Tests:
 SPT, Water absorption test, Packer
test, Lugeon tests, Impression
packer/BH televiewer
 Geophysical surveys (seismic,
resistivity, micro-gravity, magnetic,
radioactive (e.g gamma density))
 In situ modulus (High Pressure
Dilatometer or Goodman Jack)
 In situ stress tests (Hydrofracture,
Pressuremeters) & High pressure
dilatometer
Laboratory Tests:
 Index tests, Triaxial shear strength
and Oedometer for overburden
 Point load, UCS, Young's Modulus,
Poisson's Ration, Rock shear tests on
joints and Saw cuts for rock
TBM related test:
Thin section petrography, Punch test,
Rock abrasively test, Brazilian test,
Machine Excavation Performance test,
NUTU Drillability test

34. Special Techniques of
GI Methods

35. Ground Investigation on Remote Site
Air mobilisation
Use of scaffolding and platform

36. Inclined Boreholes

37. Inclined Borehole Orientation Measurement
Eastman-Whipstock single-shot or multi-shot
photographic survey tool

38. Special Techniques of GI Methods
Directional Borehole Drilling

39. Directional Borehole Drilling
3D-magnetometers
and accelerometers to define
magnetic and gravity tool
face, azimuth and inclination
of the borehole

40. GI for Marine/River Crossing Tunnel

41. Vibrocoring
Sediment cores are
usually visually
described and
photographed before
being sampled for
grain size and
chemical analysis.
Length1–3m

42. Drilling Works Over Water
Use of
Geophysics
Methods -
Identification of
Geological and
Seabed
Conditions and
Features
Marine Drilling

43. GI Works in
Karst Deposits

44. Karst Deposits

45. GI Works in Karst Deposits
Deep Tunnel
DH
at least 1D
20m continuous fresh
rock recovered
DH
Drillhole spacing should
be 5m to 25m or closer
Cut & Cover Tunnel
Diaphragm wall
Founding level
problem

46. GI Guidelines in Karst Deposits
Typical Properties to be Determined

47. Weathering Classification for Karst Deposits

48. Appropriate GI Methods
in
Contaminated Land

49. Appropriate GI Methods – Tunnelling in
Contaminated Land
Three matrices may need to be sampled:
• Soil
• Water
• Gas

50. Relevant Standards
• AS 4482.1–2005 : Guide to the investigation
and sampling of sites with potentially
contaminated soil, Part 1: Non-volatile and
semi-volatile compounds.
• AS 4482.2–1999 : Guide to the investigation
and sampling of sites with potentially
contaminated soil, Part 2: Volatile
substances.
• BS 10175: 2001 : Investigation of
Contaminated Sites – Code of Practice.

51. Type of Investigations
Indirect
• Geophysical
• Cone Penetration Test
• Gas Bar Probe Surveys
• Radioactive Surveys
Direct
• Drillholes and Trial Pits
• Samplings & Insitu Testing
• Monitoring Installations

52. Geophysical Surveys
(Contrasts of soil physio-chemical properties)
• Apparent Conductivity Anomalies -
differing soil types
• True Resistivity/Conductivity Surveys –
plumes
• Magnetic Field Intensity -
concentrations of heavy metals

53. Cone Penetration Test (1)
Laser Induced Flourescence
Cone (LIF)
• Standard CPT cone with a
laser light source to detect
the range of contaminants
• Laser energy [or Ultra-Violet
Optical Screening Tool
(UVOST)] results in the
compounds flourescing
which is then collected by a
fibre optic cable and
returned to a detector in the
CPT truck

54. Cone Penetration Test (2)
Membrane Interface Probe
(MIP)
• Heated membrane allows
organic hydrocarbons in the
gas phase to cross into a
sampling chamber where
they are driven by an inert
Netgeonge gas flow into a
detector
Detects:
BTEX/ PAH/ CH4/ PCB’s

55. Avoid Cross Contamination
• Plant/ equipments servicing before mobilising
to site
• Do not use GI drill rigs unless modified
– use of vegetable based greases and oils
• Steam Clean equipment and sterilise
– before investigation & between drillholes
– between sampling depths
– sampling and sub-sampling equipment
• Dry drilling as far as possible

56. Decontamination Measures
Sample Storage
Steam cleaning all equipment Cleaning and rising
Laboratory Containers & Cooler Boxes

57. Sampling
• Containers: jars, bags, glass bottles, gresham tubes
• Preservatives where necessary to fix degradable
compounds
• Cleanliness: avoid cross contamination by standardised
cleaning procedures
• Storage samples appropriately on site - in the dark at
4 °C
• Follow a strict “Chain-of-Custody” (i.e. a form contained
sample info) from site to the laboratory

58. Appropriate GI Methods – Tunnelling in
Contaminated Land

59. Site Supervision for
GI Works

60. Site Supervision
To obtain the greatest benefit from a
ground investigation, it is essential that
there is adequate direction and
supervision of the works by competent
personnel who have appropriate
knowledge and experience and the
authority to decide on variations to
the ground investigation when required.

61. Thank you!