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Tunneling and site investigation process

Short answer

Tunnelling is excavating an underground passage without removing overburden. Investigation stages are desk study, reconnaissance, detailed. Roads: mapping, boreholes at high cuts; bridges: mapping, boreholes at piers with core drilling 3 m into rock, scour study; dams: core drilling with Lugeon, adits, mapping, in-situ deformation tests.

What is tunneling? Describe the process of geological site investigation for roads, bridges and dams.

Tunnelling is the excavation of an underground passage through rock or soil, without removing the overlying ground, by drilling and blasting, mechanised excavators or tunnel boring machines, followed by support and lining. It is used for roads, railways, hydropower waterways, water supply and metro.

Geological site investigation process

Common stages for all structures: (1) desk study, (2) reconnaissance, (3) preliminary investigation, (4) detailed investigation, (5) reporting.

Roads

  • Study maps, air photos; mark landslides, steep and weak slopes.
  • Map geology along alternatives: rock type, joints, bedding dip relative to the cut, weathering, springs.
  • Test pits and trenches, boreholes at high cuts, bridges, and fills; geophysics at doubtful places.
  • Stereographic analysis of slope failure, materials survey.

Bridges

  • Map both banks and river channel; study flood and scour.
  • Boreholes at piers and abutments, core drilling in rock; SPT in soil; geophysics across the river.
  • Lab tests for bearing capacity and tests of aggregate.

Dams

  • Regional geology, structure, seismicity, and reservoir watertightness.
  • Mapping of the dam axis, abutments, and borrow areas.
  • Core drilling with Lugeon tests; adits and trenches; geophysics.
  • In-situ tests for strength and deformation of foundation rock; grouting design; materials investigation.

Outputs: engineering geological maps, sections, logs and recommendations for design.

✓ Answer checked by Claude Opus 5.5 (high effort)

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