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SOIL INSPECTION

 

According to the regulations outlined in BS EN 1997-1 (Eurocode 7), BS 5930, and BS EN 1997-2, soil inspection must include an assessment of soil bearing capacity and shear strength, settlement analysis, and groundwater considerations.

The detailed soil investigation will include the following components. Depending on the specific site conditions and the guidance of a geotechnical engineer, not all components may be applicable:

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1. Soil Type and Classification

  • Determines whether the soil is coarse-grained (sand, gravel) or fine-grained (silt, clay).

2. Soil Bearing Capacity

  • Allowable Bearing Capacity: The maximum pressure that can be applied to the soil without causing unacceptable settlement or failure.

  • Ultimate Bearing Capacity: The maximum pressure the soil can withstand before shear failure occurs.

3. Soil Shear Strength Parameters

  • Cohesion (c): The internal bonding strength of the soil particles, particularly important in clayey soils.

  • Angle of Internal Friction (φ): The measure of the soil's resistance to sliding along internal surfaces. This is crucial for designing against shear failure.

4. Soil Compressibility and Settlement

  • Compressibility: Determines how much the soil will compress under load, affecting how much the foundation will settle over time.

  • Consolidation Parameters: For fine-grained soils, especially clays, understanding how the soil consolidates over time under load is crucial.

  • Immediate Settlement and Long-Term Settlement: Calculating both the immediate settlement upon loading and any long-term settlement due to consolidation or creep.

5. Groundwater Conditions

  • Depth of Water Table: The location of the water table can significantly influence the effective stress in the soil and, consequently, the bearing capacity.

  • Permeability: Determines how water moves through the soil, which affects drainage and the potential for hydrostatic pressure on the foundation.

6. Soil Density and Compaction

  • In-Situ Density: Helps in understanding the existing compaction and void ratio of the soil.

  • Relative Density (for granular soils): Indicates the density of the soil in relation to its maximum and minimum possible densities.

7. Soil Modulus and Elasticity

  • Modulus of Subgrade Reaction (k): Essential for slab-on-grade foundations, as it relates to the stiffness of the soil.

  • Young’s Modulus (E): Indicates the elastic properties of the soil, particularly important for calculating elastic settlement.

8. Soil Stratification and Profile

  • Soil Layers: Understanding the different soil layers (strata) beneath the foundation, as properties can vary significantly with depth.

  • Soil Exploration Logs: Borehole logs or test pits that detail the soil layers, their properties, and depths.

9. Soil Test Data

  • Standard Penetration Test (SPT): Provides an indication of soil density and strength.

  • Cone Penetration Test (CPT): Provides continuous profiles of soil resistance, which can be correlated with soil properties.

  • Laboratory Tests: These include tests for Atterberg limits, unconfined compressive strength, triaxial shear tests, etc., to determine specific soil properties.

10. Seismic Considerations

  • Seismic Site Classification: Based on shear wave velocity, standard penetration resistance, or other parameters, critical for seismic design.

  • Liquefaction Potential: Assessing whether the soil might lose strength and stiffness due to earthquake shaking.

11. Environmental and Chemical Properties

  • Soil Corrosivity: Important if the foundation will include steel elements.

  • Soil Aggressivity: In relation to concrete, to assess the risk of sulfate attack or other chemical reactions.

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