GI For Tunnel Projects


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Ground investigation design/considerations for soft/hard ground tunnels

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GI For Tunnel Projects

  1. 1. Ground Investigation for Tunnelling Projects Keith Kong
  2. 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. 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. 4. Ground Condition Risks for Tunnelling Projects
  5. 5. Water Ingress Water ingress ~2 to 4 liter/sec
  6. 6. Ground Collapse Collapse area 100m by 130m Settlement up to 15m
  7. 7. Soil / Rock Interface
  8. 8. Possible Ground Conditions Encountered Dyke structure
  9. 9. Possible Ground Conditions Encountered Wedge Failure
  10. 10. Obstruction Timber Piles
  11. 11. Ground Investigation Planning
  12. 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. 13. What is comprehensive GI Planning?
  14. 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. 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. 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. 17. Aerial Photograph Interpretation Photo-geological Lineament
  18. 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. 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. 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. 21. Probe Drilling for TBM Tunnelling
  22. 22. Probe Drilling for TBM Tunnelling Probe Hole Window
  23. 23. Geophysical survey ahead of tunnel face using seismic reflective image
  24. 24. Geophysical survey ahead of tunnel face using seismic reflective image
  25. 25. Strategy and Techniques of Ground Investigation
  26. 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. 27. GI for Soft Ground Tunnel Project
  28. 28. Appropriate GI Methods – Laboratory Testing (Soft Ground Tunnels)
  29. 29. Soil Particles Size Vs TBM Selection (compress air tunnelling
  30. 30. Compress Air TBM (BESSAC)
  31. 31. GI Guideline for Hard Rock Tunnel Projects
  32. 32. Appropriate GI Methods – (Hard Rock Tunnels)
  33. 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. 34. Special Techniques of GI Methods
  35. 35. Ground Investigation on Remote Site Air mobilisation Use of scaffolding and platform
  36. 36. Inclined Boreholes
  37. 37. Inclined Borehole Orientation Measurement Eastman-Whipstock single-shot or multi-shot photographic survey tool
  38. 38. Special Techniques of GI Methods Directional Borehole Drilling
  39. 39. Directional Borehole Drilling 3D-magnetometers and accelerometers to define magnetic and gravity tool face, azimuth and inclination of the borehole
  40. 40. GI for Marine/River Crossing Tunnel
  41. 41. Vibrocoring Sediment cores are usually visually described and photographed before being sampled for grain size and chemical analysis. Length1–3m
  42. 42. Drilling Works Over Water Use of Geophysics Methods - Identification of Geological and Seabed Conditions and Features Marine Drilling
  43. 43. GI Works in Karst Deposits
  44. 44. Karst Deposits
  45. 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. 46. GI Guidelines in Karst Deposits Typical Properties to be Determined
  47. 47. Weathering Classification for Karst Deposits
  48. 48. Appropriate GI Methods in Contaminated Land
  49. 49. Appropriate GI Methods – Tunnelling in Contaminated Land Three matrices may need to be sampled: • Soil • Water • Gas
  50. 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. 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. 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. 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. 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. 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. 56. Decontamination Measures Sample Storage Steam cleaning all equipment Cleaning and rising Laboratory Containers & Cooler Boxes
  57. 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. 58. Appropriate GI Methods – Tunnelling in Contaminated Land
  59. 59. Site Supervision for GI Works
  60. 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. 61. Thank you!