Types of Geotechnical investigation methods

Geotechnical investigations employ a variety of methods to assess subsurface conditions. Here are the main types of geotechnical investigation methods:

1. Surface Exploration

• Site Reconnaissance:

  • Involves a visual inspection of the site.
  • Identifies surface features like slopes, drainage patterns, and existing structures.

• Geological Mapping:

  • Maps surface geology to understand soil and rock formations.
  • Uses geological maps and satellite imagery.

2. Subsurface Exploration

• Borehole Drilling:

  • Drilling holes into the ground to extract soil and rock samples.
  • Provides information on soil stratigraphy, groundwater levels, and soil properties.
  • Common drilling methods include auger drilling, rotary drilling, and percussion drilling.

• Trial Pits and Trenches:

  • Excavating shallow pits or trenches for visual inspection.
  • Suitable for shallow investigations and sampling.

• Standard Penetration Test (SPT):

  • Conducted within boreholes.
  • Measures soil resistance to penetration by a split-barrel sampler.
  • Provides data on soil density and strength.

• Cone Penetration Test (CPT):

  • Involves pushing a cone-tipped probe into the soil.
  • Measures resistance to penetration, providing continuous profiles of soil properties.
  • Effective in soft soils and for determining soil stratigraphy, density, and strength.

• Pressuremeter Test (PMT):

  • Measures soil deformation in response to pressure applied within a borehole.
  • Provides data on soil elasticity, strength, and compressibility.

• Vane Shear Test:

  • Used to measure the shear strength of soft clays.
  • Involves inserting a vane into the soil and rotating it to measure resistance.

3. Geophysical Methods

• Seismic Refraction and Reflection:

  • Measures the travel time of seismic waves through the soil.
  • Provides information on soil and rock layers, density, and elastic properties.

• Electrical Resistivity:

  • Measures the soil's electrical resistance to infer subsurface properties.
  • Used to detect changes in soil moisture, voids, and soil types.

• Ground-Penetrating Radar (GPR):

  • Uses radar pulses to image the subsurface.
  • Effective for detecting buried objects, changes in material, and voids.

• Electromagnetic Methods:

  • Measures the soil's electromagnetic properties to infer subsurface conditions.
  • Useful for mapping soil types, moisture content, and contaminant plumes.

4. Laboratory Testing

• Soil Sampling:

  • Collecting soil samples during borehole drilling or from trial pits.
  • Samples are analyzed in the laboratory for various properties.

• Grain Size Analysis:

  • Determines the distribution of soil particle sizes.
  • Important for classifying soil types.

• Atterberg Limits:

  • Measures the plasticity characteristics of fine-grained soils.
  • Includes liquid limit, plastic limit, and shrinkage limit tests.

• Shear Strength Tests:

  • Determines soil's shear strength.
  • Includes direct shear tests, triaxial tests, and unconfined compression tests.

• Consolidation Tests:

  • Measures soil compressibility and rate of settlement under load.
  • Important for assessing long-term settlement behavior.

5. In-Situ Testing

• Dynamic Cone Penetration Test (DCPT):

  • Similar to CPT but with dynamic (hammer-driven) insertion.
  • Used for shallow soil investigations and compaction control.

• Plate Load Test:

  • Measures soil bearing capacity and settlement characteristics.
  • Involves loading a plate on the soil surface and measuring deflection.

Each method has specific applications and is chosen based on the project requirements, site conditions, and the type of information needed. Combining several methods often provides the most comprehensive understanding of the subsurface conditions.