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Phase with supplementary core drilling

Short answer

Supplementary core drilling is performed during the detailed (final design) phase, after site selection. Closely spaced additional boreholes define foundation conditions, weak zones, RQD, depth of weathering, and permeability, filling gaps between earlier exploration points for final design and treatment.

In which phase of a civil engineering project is sub-surface site investigation carried out with supplementary core drilling?

Sub-surface investigation with supplementary core drilling is carried out in the detailed (final design) phase, after site selection.

  • In the reconnaissance and preliminary phases, only a few exploratory holes are used.
  • In the detailed phase, additional (supplementary) core-drill holes are placed at closely spaced positions, to define foundation conditions, weak zones, rock quality (RQD), depth of weathering and permeability, and to fill the gaps between earlier holes and geophysical profiles.
  • The results are used in the final design and for foundation treatment (grouting, excavation depth).

✓ Answer checked by Claude Opus 5.5 (high effort)

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