Soil Exploration Methods in Geotechnical Engineering

Soil exploration stands as a critical phase in comprehending the unique characteristics and properties of soil at a specific construction site. From the initial site reconnaissance to the compilation of the final report, the soil exploration process encompasses various steps that we've previously discussed in the article What is Soil Exploration?

In this blog post, our focus is on the major methods employed for the analysis of soil during construction soil exploration.

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Understanding the Three Key Steps

1. Soil Drilling

Soil drilling involves using specialized equipment to create boreholes or holes in the ground. This process enables engineers and scientists to inspect the soil profile, gather soil samples, and conduct a range of tests. These tests play a crucial role in evaluating the suitability of the soil for construction.

2. Soil Sampling

In construction, soil sampling entails extracting representative soil specimens from specific depths. These samples are then analyzed for physical and chemical properties, providing valuable insights for foundation design and construction methodologies.

3. Soil Testing

Soil testing is the final step and involves the thorough analysis of collected soil samples. Properties such as density, moisture content, shear strength, and permeability are examined to assess the soil's suitability for construction. The results of these tests inform critical engineering decisions.

These steps may be executed individually or collectively, depending on the complexity of the construction project.

Classification of Soil Exploration Methods

Soil exploration methods can be broadly classified into three categories:

1. Direct Methods

Direct methods entail physically accessing the soil to directly observe, sample, or test it. Examples include Trial Test Pits or Trenches and Cone Penetration Tests (CPT), where drilling, sampling, and testing occur simultaneously.

2. Semi-Direct Methods

Also known as boring methods, semi-direct methods involve step-by-step processes of 

1. Boring
2. Sampling
3. Soil Testing

Various methods like auger boring, rotary drilling, and wash boring are employed, with sampling using different types of samplers such as Thin-Walled Tube Sampler or Shelby Tube Sampler. The choice of the sampler and whether the samples collected are disturbed or undisturbed depends on the type of boring method and the soil strata.

Read More on:  Boring Methods

Read More On:  Soil Sampling Methods

Soil tests after boring and sampling are either done at the site or at the laboratory. Here is a quick overview of some key soil tests, indicating whether they are conducted as field tests or laboratory tests and the results they aim to determine:

Tests Conducted	Field Tests	Laboratory Tests	Result Tested
Visual Inspection	✓		Soil Composition
Sieve Analysis	✓	✓	Particle Size Distribution
Atterberg Limits	✓	✓	Liquid Limit, Plastic Limit, Plasticity Index
Moisture Content	✓	✓	Moisture Content
Proctor Compaction	✓	✓	Maximum Dry Density, Optimum Moisture Content
Triaxial Shear	✓	✓	Shear Strength, Stress-Strain Characteristics
Permeability	✓	✓	Permeability
Consolidation	✓	✓	Compression, Settlement
California Bearing Ratio (CBR)	✓	✓	Resistance to Penetration
Direct Shear	✓	✓	Shear Strength
Unconfined Compression	✓	✓	Compressive Strength
Specific Gravity	✓	✓	Soil Particle Density
Standard Penetration Test (SPT)	✓		N-value (Soil Resistance)
Cone Penetration Testing (CPT)	✓		Cone Resistance, Friction Ratio
Dynamic Cone Penetration (DPT)	✓		Penetration Resistance
Vane Shear Test	✓	✓	Undrained Shear Strength
Plate Load Test	✓	✓	Bearing Capacity

3. Indirect Methods

Indirect methods assess soil conditions without direct physical access. These methods rely on measurements, observations, or data collected from the surface or surroundings. Examples include Remote Sensing, Inclinometers, Piezometers, Geophysical Methods, and Geological Engineering Mapping.

Conclusion

Soil exploration methods are diverse, catering to the unique needs and challenges of each construction project. Whether directly drilling into the ground, employing semi-direct methods like boring, or relying on indirect methods for surface assessments, the choice of exploration method is a crucial determinant of a project's success. Understanding the soil at a site is fundamental to ensuring the stability and safety of structures, making soil exploration an indispensable aspect of the construction process.

Read More: What is Soil Liquefaction?