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Investigation details for bridge foundation

Short answer

Obtain subsoil profile at each pier and abutment from boreholes, engineering properties (strength, SPT N, rock RQD), groundwater level and chemistry, river data (flood level, scour depth), pile/well capacity parameters, seismic/liquefaction potential, and construction aspects. Bore depth ≥1.5× foundation width below foundation level, at least 3 m into rock.

For a site investigation for the design of a bridge foundation, what kind of detailed information do you set out to obtain?

For a bridge foundation the investigation must give the information needed for the pier, abutment and approach design. It seeks:

  1. Subsoil profile at every pier and abutment: boreholes at each foundation location, with soil type, thickness, density/consistency, and depth to rock or hard stratum.
  2. Engineering properties: unit weight, cc, ϕ\phi, SPT NN, compressibility and bearing capacity (and rock RQD, strength, core recovery for rock).
  3. Groundwater data: level, fluctuation, artesian pressure and chemical content (sulphates, chlorides) for durability.
  4. River data: high flood level, low water level, discharge and velocity, bed material and the scour depth (decides foundation level); type of bank, river training and possible shifting.
  5. Deep foundation parameters: pile or well capacity, skin friction, end bearing, negative skin friction, and presence of boulders and obstructions that could stop the sinking of wells/piles.
  6. Seismic and geology: faults, liquefiable sand layers, seismic zone, slope stability of abutments and approach embankments.
  7. Construction aspects: cofferdam or caisson needs, dewatering, access, availability of local materials, and effects on adjacent structures. The depth of boring is at least 1.5 times the width of the foundation below the foundation level (and 3 m or more into rock).

✓ Answer checked by Claude Sonnet 5.5

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