Foundations and Geotechnical Inspection

According to NP EN 1997-1 Section 3 and NP EN 1997-2, a ground investigation campaign must be carried out to determine soil conditions. The scope of investigation depends on the Geotechnical Category (GC1, GC2, GC3). For GC2 and GC3, boreholes, CPT or trial pits are required. Soil parameters must be determined according to NP EN 1997-2.

1. Check that a ground investigation report covering the site exists

2. Confirm that the location and depth of boreholes/CPTs are adequate for the structure

3. Confirm that the soil parameters used in the design match the investigation results

4. Check that the groundwater level has been determined and monitored

5. Check for contamination or problematic soils (peat, expansive clays, fill)

- Insufficient investigation depth — weak layers not detected below foundation level

- Groundwater level higher than assumed in the design

- Fill or contaminated soils not detected

- Soil parameters not representative — insufficient number of test points

According to NP EN 1997-1 Section 6, shallow foundations must be verified for bearing resistance (ULS) and settlement (SLS). The formation level must be inspected to confirm that the soil matches the design assumptions. Blinding concrete must be placed promptly to protect the exposed soil. Dimensions and levels must comply with design tolerances.

1. Inspect the formation level — the soil must match the geotechnical report (visual inspection + hand tests)

2. Check the foundation dimensions (length, width, depth) against the structural drawings

3. Confirm that the formation level is at the correct depth below ground level

4. Confirm that blinding concrete is placed before the reinforcement

5. Check for the absence of water ingress or softening of the soil at formation level

- Formation soil softer than expected — insufficient bearing capacity

- Excavation left open too long — soil softened by weather or groundwater

- Foundation dimensions or levels not matching the design

- Over-excavation backfilled with unsuitable material

According to NP EN 1997-1 Section 7, pile design must be verified by static load tests, dynamic tests or calculation from ground test results. Execution of bored piles according to EN 1536, displacement piles according to EN 12699. Pile integrity testing according to EN ISO 22476 (series). Pile position tolerance typically +/-75 mm (EN 1536).

1. Check pile installation records — depth, driving resistance or concrete volume

2. Confirm pile positions against the layout plan — tolerance +/-75 mm according to EN 1536

3. Review integrity test results (sonic echo, cross-hole or equivalent)

4. Check static or dynamic load test results against the design capacity

5. Inspect pile heads after trimming — undamaged, at the correct level for the pile cap

- Piles not reaching the design depth or bearing stratum

- Shaft defects (necking, inclusions) in bored piles

- Excessive positional deviation of piles requiring pile cap redesign

- Insufficient load test results for capacity verification

According to NP EN 1997-1 Section 9, retaining structures must be verified for overall stability, bearing capacity, sliding and overturning. Earth pressures must be calculated according to NP EN 1997-1 Annex C. Drainage behind retaining walls is essential to prevent hydrostatic pressure build-up. Wall movements must be monitored during and after construction.

1. Check that wall dimensions and reinforcement match the design

2. Confirm the drainage system behind the wall — filter geotextile, drainage layer, weepholes or drain pipes

3. Confirm that the backfill material is suitable and compacted in layers (<=300 mm)

4. Check the verticality and alignment of the wall within tolerances

5. Check for signs of excessive movement, cracking or tilting

- Blocked or missing drainage — hydrostatic pressure causes wall failure

- Unsuitable backfill material (clay instead of granular material)

- Backfill compaction too close to the wall causing lateral overload

- Surcharge loads not considered in the design