Soil Exploration & Boring Methods: Techniques and Applications

Soil Exploration and Boring Methods

Soil exploration and boring methods are crucial when constructing a solid foundation whether for a  high-rise building, a bridge, or even a house, it is important to know what is under the ground. But what have you ever thought of the process of engineers and geotechnical experts learning about the secrets of the subsurface? The solution is found in the soil exploration. A critical process which makes us discover the secret features of the soil and rock under our feet. In this blog post, we shall have a more detailed look at the world of the soil exploration, its techniques and methods and its significance in providing stability and safety of our structures.

Shallow Soil Exploration

Significance of Soil Exploration.

In geotechnical engineering, soil exploration plays an important role of learning about the condition of the underground. It assists in determining the properties of soil such as shear strength, compaction, and moisture content that are safe in foundation designing. Among the risks detected in the process include instability, expansive clays or groundwater problems and mitigation strategies are adopted. Soil exploration also maximizes design eliminating over or under engineering.

Soil Exploration Planning.

The process of soil exploration to be used in a structure is normally conducted in four steps:

1. Gathering the Data on the Structure:  

It involves the collection of such information as the kind of structure under construction, its use, the local building code provisions, and the loads the columns and load carrying walls will support. In the case of bridges, it is important to know the span length and the loads that will be expected to be applied on the piers and abutments.

2. Investigation of Existing Subsoil Data: 

It is always in good taste to review the available information on the condition of the subsoil of the site before commencing the exploration process. This could include:

•  Geologic survey maps Soil survey maps of the U.S. Department of Agriculture.

•   Soil manuals of state highway departments.

•  Past soil reports of other projects in the area.

Soil Property Testing

3. On Site Inspection: 

Site visit is a very critical factor in getting to know the area. Vegetation may also on occasion indicate the kind of soil it covers. Accessibility of site, drainage patterns and open cuts close to the site can provide information on the soil layers. In addition, settlement may be indicated by the cracks in the nearby buildings owing to soft soils or expansive soils.

Site Inspection and sample collection

4. Detailed Testing: 

This step entails drilling of test borings on the different locations on the site and gathering of soil samples at different levels. These are sampled visually and even in the lab to understand the soil better. The depth and the number of borings is based on the needs of a certain project.

 

Boring Methods: 

It is the practice of cutting or digging holes to gather soil or rock samples to investigate the site and design foundations.

There exist numerous methods that are boring, yet we will examine the most popular methods that are applied in everyday life:

    1.       Auger Boring

  2.       Rotary Drilling

  3.       Percussion Drilling

  4.       Wash Boring

  5.       Displacement Boring

  6.       Continuous Flight Auger (CFA)

    We will look at most common boring techniques their applications and limitations.

 Auger Boring:

      It is a process that involves the use of a helical screw (auger) to excavate the ground and cut the soil or rock. It is a low-cost method of shallow drilling in the light to medium soils. As the auger is drilling, it keeps removing the cut material.

Shallow Soil Exploration

     Applications:

         ·       Auger boring drilling is applied when drilling soft to medium soils such as sand or clay.

         ·       This method is used in shallow foundations like playing residential buildings and others.

      Limitation of Auger Boring:

        ·       Limited depth (typically less than 30 meters).

        ·       Not effective in hard soils or rock layers.

        ·       Soil samples may be disturbed, particularly sandy soils.

        ·       Less effective in waterlogged or saturated soils

  

Rotary Drilling: 

Under this technique, the soil or rock is broken through with the help of a rotating drill bit. The bit is typically connected to a long drill pipe and a drilling fluid (mud or water) is circulated through the pipe to cool down the bit as well as to remove debris. It is suitable in hard rock drilling and drilling far down. 

Deep Rock Drilling

     Applications:

        ·      This is deep drilling of water wells especially in places where there is a hard rock formation.

        ·      Applied in oil and gas industry in drilling.

        ·      Commonly employed in geotechnical research in large scale construction such as highways.           

      Limitation of Rotary Drilling:

        ·       High price because of specialized equipment and staff.

        ·       Needs constant flow of fluid, which poses a problem with garbage disposal.

        ·       May will work poorly in loose or granular soil causing collapse of boreholes.

 

 Percussion Drilling: 

      This technique involves a hammering action where a heavy drill bit is repeatedly lifted and dropped to break through hard soil or rock. It's particularly useful for hard, consolidated layers and is often used in combination with rotary drilling to reach deeper depths.

Hard Soil Penetration

       Applications:

      ·      Drilling through hard, consolidated layers of rock or dense soil.

      ·      Frequently used in mining exploration and for creating deep wells.

       Limitation of Percussion Drilling:

     ·      Slow and labor-intensive, especially in soft soils.

     ·      Limited depth compared to rotary drilling.

     ·      Can disturb soil samples, making it harder to obtain undisturbed samples.

     ·      Inefficient in cohesive soils like clay.

Wash Boring:  

It is a technique of drilling that is applied in the exploration of the shallow soils, usually soft or unconsolidated soils. It is a process that entails the removal of soil particles using water or mud slurry as the drill bit moves forward. The method is appropriate in obtaining disturbed soil samples, which is frequently employed when conducting environmental research and geotechnical tests. Wash boring can be used to a depth of 30 meters but not in hard, compacted and rocky soils. It also has a weakness of offering uninterrupted samples.

Shallow Soil Sampling

    Applications:

•  Determining shallow soil exploration in soft or unconsolidated soils.

•  Applied in environmental research and site pollution.

•  Usually used in geotechnical tests of small scale (e.g. residential buildings, roads).

•  Offers expedited site evaluations on sites that have unconsolidated or waterlogged soils.

    Limitations of Wash Boring:

•     Maximum depth (usually not more than 30 meters)

•     Alters soil samples rendering them unsuitable in case of undisturbed sample collection. 

•     Not suitable to deep penetration or complicated profile.