Soil Classification and Geotechnical Analysis

EK65 Drilling Rig

When you begin planning and defining the scope of any construction project, it is essential to understand your site’s specific conditions and the composition and soil classification. Whether you’re drilling or pile driving for a deep foundation having a comprehensive knowledge of your soil conditions is the best way to be prepared and ensure that you have the proper construction equipment for the job.

Soil classification is a broad subject with nuanced aspects that can cause issues down the road if they are not addressed and evaluated during a professional bore sample and analysis.

Low-quality soils and loosely aggregated soils can present issues that high-density or solid rock do not, and having a complete picture of your conditions is the best way to keep a job on schedule.

EK125HH Piling Rig driving timber piles on the beach.

Understanding Basic Soil Classification Types and Qualifications

There are four primary soil types that most pile driving and drilling projects will encounter: sand, silt, clay, and loam. Though it’s often a better practice to drill through harder soils and rock to install piles, a professional analysis can identify soil resistance to driving (SRD). If your study identifies denser clays or rock at shallow depths, it may require a re-evaluation of what pieces of pile driving equipment you need to avoid damaging piles or machinery.


Typically decomposed quartz, limestone, and granite is one of the most common soil types encountered in marine drilling projects and brackish areas. Sand compaction piles can be used to create sturdy foundations on submarine bedrock and prevent liquefaction, improve stability, and reduce settlement.


Primarily found near lakes and rivers, silt is larger than sand and smaller than clay. Silt is fine and smooth and retains water exceptionally well. When compacted, silt can also provide skin friction on piles to maintain structural integrity and reduce the unanticipated movement of driven piles.


Sticky and dense when wet but brittle and smooth when dry, clay is one of the more problematic soil types for pile and drill rig operators to work in. Because of its high level of cohesion, drilling or driving piles in clay can cause remodeling, ground heave, enlarged holes, and strain softening.

  • Remolding disturbs soil and reduces shear strength
  • Ground heave increases water pressure in soil and can cause cracks and fissures surrounding the entry point
  • Enlarged holes are the result of heavy vibrations in the upper part of the pile, and water is collected in the resulting gap and leads to reduced shear strength
  • Strain softening refers to the reorientation of clay soils which drastically reduces shear strength


Loam contains elements of all three previous soil types and blends the best qualities of drainage and moisture retention without being too dense. It can provide excellent shear strength at load-bearing depth.

Soil Classification and Geotechnical Analysis

What are different Soil Classifications?

Geotechnical engineers refer to the Unified Soil Classification System (USCS) to deliver consistent descriptions of soil conditions. This precise classification is based on grain size analysis and Atterberg Limits obtained from bore samples on the proposed site. This system is primarily utilized for larger projects, including civil construction or commercial development.

The Modified Unified System (MUD) involves manually inspecting the soil sample’s textures at depth and observing the color, plasticity, and texture. These can help identify potential design problems or to determine the possible use of the soil in construction.

Different compositions of soil have different characteristics that can have consequential impacts on a pile driving or operating soil drilling rigs. Shear strength measures the amount of load soil can withstand before collapsing against itself. While permeability refers to the ease of water flow through the soil.

Compressibility is a description of how easily a soil’s volume is reduced under load, while consolidation occurs when pockets containing air and water are subjected to consistent pressure. Consolidation differs from compaction and is typically a characteristic of clay or loam.

Compaction refers to unsaturated soil being made more dense by the expulsion of air pockets. Consolidation refers to the expulsion of water from saturated soils.

Soil Classification by OSHA

Occupational Safety and Health Administration classifies soils as Type A, B, and C. Type A soil is the easiest to excavate and offers a compressive strength of at least 1.5 tons per square foot, and should not contain moisture or fissures. It also minimizes vibrations from pile hammers.

Type B soils are not as compressive as Type A and offer compressive strength between .5 and 1.5 tons per square foot.

Type C soil is very unstable, offers compressive strength under .5 tons per square foot, and includes y soil with water flowing through it.

Pile boring equipment can drill to depth and is the best way to ultimately save time and money by identifying the type of soil to where a pile will terminate. It can also prevent a design from being too conservative.

When you have identified your site’s specific soil conditions, you can start to evaluate what equipment is best suited to your job. RPI Equipment has been providing heavy machinery sales and rentals for over fifty years and will work with you to identify the best pile driving rig or drilling equipment to get the job done safely, effectively, and on time.

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