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Geophysical and geotechnical exploration
Short answer
Geophysical exploration measures physical properties (seismic velocity, resistivity) indirectly from the surface; it is fast, cheap, covers large areas but needs borehole calibration. Geotechnical exploration directly samples and tests ground (boreholes, SPT) to obtain engineering properties, reliable but point-wise and costly.
Describe geophysical and geotechnical exploration (differentiate between them).
Geophysical exploration
It is the study of the sub-surface by measuring physical properties of the ground (velocity, resistivity, density, magnetism) from the surface, without excavation. It is an indirect method.
Methods:
- Seismic refraction/reflection: wave velocity gives layer depth and rock quality.
- Electrical resistivity: detects bed rock, groundwater, clay and cavities.
- Gravity and magnetic methods: large structures and faults.
- Ground penetrating radar and electromagnetic methods for shallow features.
Advantages: quick, cheap, covers large area, non-destructive. Limits: results are interpretation-based and need calibration.
Geotechnical exploration
It is the direct investigation of the ground by boring, test pits, trenches, sampling, and in-situ and laboratory tests, to obtain the engineering properties needed for design (bearing capacity, strength, compressibility, permeability).
Methods: boreholes with SPT, undisturbed sampling, core drilling with RQD, plate load test, vane shear, Lugeon test and laboratory tests.
Difference
| Point | Geophysical | Geotechnical |
|---|---|---|
| Nature | Indirect | Direct |
| Measures | Physical properties | Engineering properties |
| Cost and speed | Cheap, fast | Costly, slow |
| Area covered | Large | Point-wise |
| Accuracy | Interpretive, less precise | Reliable and precise |
| Use | Preliminary stage, interpolation | Detailed stage, design |
The two are used together: geophysics fills the gaps between boreholes, and borehole data calibrate the geophysics.
✓ Answer checked by Claude Opus 5.5 (high effort)
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