Geotechnical engineering is a branch of civil engineering that focuses on the behavior of earth materials, such as soil, rock, and groundwater, and their interaction with structures built on or in them.  Geotechnical engineers use their knowledge of the physical and mechanical properties of soil and rock to design and construct safe and stable structures, such as buildings, roads, bridges, tunnels, dams, and levees.  Every construction design infrastructure that is supported by foundations, above or below ground such as bridges, dams, plants, slopes, structures, tunnels, etc. uses geotechnical engineering.

• See Article  -  Geotechnical Glossary
• Tags: Hydraulic Soil Geotechnical Engineering Civil Glossary

 Geotechnical Engineering Index

• Soil Types (OSHA)
• Soil Types
• Soil Mechanics (OSHA)
• Atterberg Soil Indexes
• Atterberg Soil Limits
• Geotechnical Engineering Standards
• Geotechnical Abbreviations
• Geotechnical Engineering Glossary

The work of a geotechnical engineer typically involves site investigation and analysis, soil and rock testing, foundation design, slope stability analysis, and groundwater assessment.  They use a variety of tools and techniques, such as borehole drilling, geophysical surveys, and laboratory testing, to gather data about the properties of the soil and rock at a construction site.

Geotechnical engineering is an important field because the behavior of earth materials can have a significant impact on the safety and longevity of structures.  By understanding the properties of the soil and rock, geotechnical engineers can design structures that are stable and safe, even in challenging conditions such as earthquake-prone areas or sites with difficult soil conditions.  They also play a key role in environmental engineering, where they study the behavior of soil and groundwater to ensure that contaminants are properly contained and remediated.

Soil Types (OSHA)

• Stable Rock  -  Natural soil material that can be excavated with vertical sides and remain intact whole exposed.  It is usually identified by a rock name such as granite or sandstone.  Determining wheather a deposit is of this type may be difficult unless it is known wheather cracks exist and wheather or not the cracks run into or away from the excavation.
• Type A  -  Cohesive soils with an unconfined compression strength of 1.5 tons per square inch or greater.  Includes clay; sandy clay; silty clay; clay loam; and in some cases, silty clay loam and sandy clay loam.  No soil is Type A if it is fissured; is subject to vibration of any type; has previously been disturbed; is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical or greater, or has seeping water.
• Type B  -  Cohesive soils with an unconfined compression strength greater than 0.5 tons per square inch but less than 1.5 tons per square inch and granular cohesionless soils.  Includes angular gravel; silt; silt loam; sandy loam; and unstable rock; previousely disturbed soils unless otherwise classified as Type C; soils that meet the unconfined compressive strength or cementation requirements of Type A soils but are fissured or subject to vibration; dry unstable rock; and layered systems sloping into the trench at a slope less than four horizontal to one vertical.
• Type C  -  Cohesive soils with an unconfined compression strength of 0.5 tons per square inch or less.  Includes granular soils such as gravel; sand and loam sand; submerged soil; soil fron which water is freely seeping; and submerged rock that is not stable.  Also included in this classification is material in a slope, layered system where the layers dip into the excavation or have a slope of four horizontal to one vertical or greater.
• Multi Type Soil  -  Layered geological strata.  Whlere soils are configured in layers. where a ayered geological structure exists, the soil must be classified on the basis of the soil classification of the weakest soil layer.  Eacs layer may be classified individually if a more stable layer lies below a less stable layer, where a Type C soil rests on top of stable rock.

Soil Types

• Clay  -  Clay soil is composed of tiny particles that are hard and able to become easily compacted.  This compaction makes it difficult to plant or even shovel within the soil.While clay soil can be difficult to work with, it can be beneficial to the growth of certain plants.  It is able to hold onto the roots of plants better and provide a more stable environment than many other types of soil.
• Clay Loam  -  A fine-textured soil that breaks into clods or lumps that are hard when dry.  When the moist soil is pinched between the thumb and finger, it will form a thin ribbon that will break readily, barely sustaining its own weight.
• Loam  -  Soil comprised of almost equal amounts of sand and silt and a little less clay.  Of the three components, sand particles are the largest. Sand does not hold onto moisture, but it provides good aeration.  On the opposite end, clay particles are much smaller and easily compact.  That makes clay a great material for building bricks, but not so great for allowing water, air, and plant roots through.
• Loamy Sand  -  This soil type is normally made up of sand mixed with a majority of silt and clay.  Many people prefer loamy sand soil for their gardening because this type of soil normally allows for good drainage.
• Silty  -  Silty soils have a distinct silky and soft feeling, typically quite fertile, and have the ideal balance of decent nutrient density without terrible drainage.  Silt soils are usually easy to grow most crops in, although amendments for drainage may be needed for optimal crop performance.  Silty soils don’t compact as easily as clay soils and they are softer and lighter, however, they do lack a robust structure in their soil profile that can be improved through the planting of perennial crops whose root presence holds them together.
• Silty Clay  -  Silt has larger particles than clay and is mainly inorganic in nature.  A silty clay soil has a higher percentage of clay than silt.
• Sand  -  This type of soil is easy to cultivate but, since it allows for more drainage than needed, it is important to water it regularly, especially during summer days.  As sandy soils don't allow the water to pool around the roots, they are a good choice for plants that have a tendency to suffer from root decay.
• Sandy Loam  -  Sandy loam soils have a high concentration of sand that gives them a gritty feel.  In gardens and lawns, sandy loam soils are capable of quickly draining excess water but can not hold significant amounts of water or nutrients for your plants.  Plants grown in this type of soil will require more frequent irrigation and fertilization.

Soil Mechanics (OSHA)

• Tension Cracks  -  This usually form at a horizontal distance of 0.5 to 0.75 times the depth of the trench, measured from the top of the vertical face of the trench.
• Sliding or Sluffing  -  May occure as a result of tension cracks.
• Topping  -  In addition to sliding, tension cracks can cause toppling.  Toppling occurs when the trench's vertical face shears along the tension crack line and topples into the excavation.
• Subsidence or Bulging  -  An unsupported excavation can create an unbalanced stress in the soil, which, in turn, causes subsidence at the surface and bulging of the vertical face of the trench.  If uncorrected, this condition can cause face failure and entrapment of workers in the trench.
• Heaving or Squeezing  -  Bottom heaving or squeezing is caused by the downward pressure created by the weight of adjoining soil.  This pressure causes a bulge in the bottom of the cut, as illustrated in the drawing above. Heaving and squeezing can occur even when shoring or shielding has been properly installed.
• Boiling  -  The evidenced by an upward water flow into the bottom of the cut.  A high water table is one of the causes of boiling. Boiling produces a "quick" condition in the bottom of the cut, and can occure even when shoring or trench boxes are used.
• Soil Weight  -  Unit weight of soils refers to the weight of one unit of a particular soil.  The weight of soil varies with type and moisture content.  One cubic foot of soil can weigh from 110 pounds to 140 pounds or more, and one cubic meter (35.3 cubic feet) of soil can weigh more than 3,000 pounds.

Atterberg Soil Indexes

• Atterberg Indexes  -  Describes the boundaries of the states of soil in terms of limits and compares the test values mathmatically.
  
  • Liquid Index  -  Scaling the natural moisture content of a soil sample to the liquid limit and plastic limit.
  • Plastic Index  -  The range of water content over which the soil remains in the plastic state.
  • Consistancy Index  -  The range of water content to the firmness of the soil.

Atterberg Soil Limits

• Atterberg Limits  -  The basic measure of the critical water contents of a fine-grained soil.  The water contents where the soil behavior changes are liquid limit, plastic limit, and shrinkage limit.
  • Liquid Limit  -  The minimum water content at which soil just begins to flow.
  • Plastic Limit  -  The water content at which the soil changes from semi-solid state to solid state.
  • Shrinkage Limit  -  The maximum water content at which further reduction in the water content will not cause decrease in volume of soil.

Geotechnical Engineering Standards

ASTM Standards

• ASTM C1242 - Standard Guide for Selection, Design, and Unstallation of Dimension Stone Attachment Systems
• ASTM D559 - Standard Test Method for Wetting and Drying Compacted Soil-Cement Mixtures
• ASTM D560 - Standard Test Method for Freezing and Thawing Compacted Soil-Cement Mixtures
• ASTM D806 - Standard Test Method for Cement Content of Hardened Soil-Cement Mixtures
• ASTM D806 - Standard Guide for Selection of Dimension Stone
• ASTM D2434 - Standard Testing Method for Permeability of Granular Soils (Constant Head)
• ASTM D2487 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• ASTM D2488 - Standard Practice for Description and Identification of Soils (Visual-Manual Procedures)
• ASTM D3282 - Standard Practice for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes
• ASTM D3966 - Standard Testing Methods for Deep Foundations Under Lateral Load
• ASTM D4380 - Standard Test Method for Determining Density of Construction Slurries
• ASTM D4435 - Standard Test Method for Rock Bolt Anchor Pull Test
• ASTM D4525 - Standard Test Method for Permeability of Rocks by Flowing Air
• ASTM D4611 - Standard Test Method for Specific Heat of Rock and Soil
• ASTM D4829 - Standard Test Method for Expansion Index of Soils
• ASTM D4945 - Standard Testing Methods for High Strain Dynamic Testing for Deep Foundations
• ASTM D4992 - Standard Practice for Evaluation of Rock to be Used for Erosion Control
• ASTM D5718 - Standard Guide for Documenting a Groundwater Flow Model Application
• ASTM D5882 - Standard Testing Methods for Low Strain Impact Integrity Testing for Deep Foundations
• ASTM D5889 - Standard Practice for Quality Control of Geosynthetic Clay Layers
• ASTM D6092 - Standard Practice for Specifying Standard Sizes on Stone for Erosion Control
• ASTM D6128 - Standard Test Method for Shear Testing of Bulk Solids Using the Jenike Shear Tester
• ASTM D6285 - Standard Guide for Locating Abandoned Wells
• ASTM D6393 - Standard Test Method for Bulk Solids Characterization by Carr Indices
• ASTM D6599 - Standard Practice for Construction of Live Fascines on Slopes
• ASTM D6683 - Standard Test Method for Measuring Bulk Density Values of Powders and Other Bulk Solids as Function of Compressive Stress
• ASTM D6773 - Standard Test Method for Bulk Solids Using Schulze Ring Shear Tester
• ASTM D6825 - Standard Guide for Placement of Riprap Revetments
• ASTM D6940 - Standard Practice for Measuring Sifting Segregation Tendencies of Bulk Solids
• ASTM D6941 - Standard Practice for Determining Sediment Pond Skimmer Flow Rate
• ASTM D7099 - Standard Terminology Related to Frozen Soil and Rock
• ASTM D7407 - Standard Guide for Determinining the Transmission of Gases through Geomembranes
• ASTM D7765 - Standard Practice for Use of Foundry Sand in Structural Fill and Embankments
• ASTM D8326 - Standard Practice for Measuring of the Kinetic Energy of Simulated Rainfall