- Absorbed Water
- Water, held mechanically within the pore structure of a soil or rock mass.
- Adsorbed Water
- Water, attracted to the surfaces of soil or rock particles by physicochemical forces, resulting in a film coating the surfaces.
- Aeolian Soils
- Soil material, transported by the wind and deposited in sedimentary formations such as loess or dunes.
- Air-Void Ratio
- A ratio of the volume of air space in soil or rock to the total volume of voids in the material.
- Allowable Bearing Pressure
- The maximum load that a bearing surface will tolerate without movement or deformation outside of specified parameters.
- Alluvial Soils
- Soil materials that have been transported in suspension by moving water and deposited by sedimentation.
- Angle of Internal Friction
- A measure of the ability of rock or soil to resist shear force. The angle between the normal force and the resultant force attained when failure occurs due to shearing stress.
- Angle of Repose
- The angle of the maximum slope that a soil assumes through natural deposition processes.
- Angular Particles
- Aggregate or rock particles with well-defined edges formed at the intersection of planar faces.
- AOS
- is a measure of the largest opening (pore size) in a geotextile, expressed as an equivalent U.S. Standard Sieve size or in millimeters. It indicates the diameter of the largest particle that would pass through the geotextile. Also see Apparent Opening Size.
- Apparent Opening Size (AOS)
- A measure of the largest opening (pore size) in a geotextile, expressed as an equivalent U.S. Standard Sieve size or in millimeters. It indicates the diameter of the largest particle that would pass through the geotextile. Also see AOS.
- Aquifer
- A saturated and permeable geologic formation containing a significant amount of groundwater.
- Ash Content
- The percentage by dry weight of material remaining after an organic soil or peat is incinerated in a laboratory muffle furnace.
- Atterberg Limits
- A series of material properties, determined by laboratory tests, of cohesive soils affected by moisture content. Originally proposed by Albert Atterberg and further defined by Arthur Casagrande, current usage usually refers to the liquid limit, plastic limit, and shrinkage limit.
- Basal Reinforcement
- The inclusion of high-strength tensile materials (like geogrids or geotextiles) at the base of embankments or heavily loaded areas to improve soil strength, reduce settlement, and prevent the failure of foundation bearing areas.
- Base Course
- A layer of aggregate material of specified gradation placed and compacted on a soil subgrade to a required depth to support a pavement. The base course supports the pavement, distributes load, and promotes drainage.
- Bedrock
- A continuous formation of rock underlying overburden soils.
- Bentonite
- A clay containing a high percentage of the mineral montmorillonite that can absorb several times its dry mass in water, exhibiting significant swelling. Often used in drilling fluids to flush out cuttings from boreholes.
- Boulder
- A large fragment of rock with a particle size of 12in (305mm) or more, often rounded by weathering or abrasion.
- Boulder Clay
- Soil materials transported by glacial drift that have not been subjected to the sorting action of water and contain a wide range of particle sizes from boulders to clay.
- Bulk Density
- The unit mass of a bulk solid divided by its total volume.
- California Bearing Ratio (CBR)
- A value defining the bearing strength of pavement subgrades, subbase, and base coarse materials as tested in laboratory compacted specimens, or by in-situ field measurements. Strengths are calculated from penetration resistance using procedures described in ASTM D1883 and D4429.
- Capillary Action
- The movement of water against gravity through narrow spaces in a soil or rock matrix due to capillary forces.
- Classification
- The organization, grouping, and description of soil or rock types based on particle size and distribution, composition, origin, and other characteristics. Composition.
- Clay
- A soil or portion of a soil that is fine-grained and exhibits plasticity in the presence of moisture. Particle size is less than 0.002mm to 0.005mm.
- Cobble
- A rock fragment, smaller than a boulder, with particle size between 3in and 12in (75mm to 305mm). Often rounded or sub-rounded through the actions of weathering and abrasion.
- Coefficient of Uniformity
- The ratio D60/D10. The two points on the cumulative particle size distribution curve of a material where 60% of the material is finer and 10% of the material is finer.
- Cohesionless Soil
- A granular soil that does not exhibit cohesiveness at any water content. The Atterberg plasticity index is equal to or less than zero. Also see Nonplastic Soil.
- Cohesive Soil
- A soil with considerable strength when air-dried and unconfined, and significant cohesion when moist.
- Colloidal Particles
- Very small soil particles that react strongly to moisture content and influence the shrinkage and swelling of the soil mass.
- Compaction
- The densification of a soil by natural or mechanical forces.
- Compaction Curve
- A curve showing how the dry density of soil is affected by moisture content (moisture/density relationship) when molded under a controlled compactive force. Also see Proctor Curve and Moisture Density Curve.
- Compaction Hammer
- A sliding drop hammer of specified mass and diameter, used to compact soils into molds for the moisture/density relationship and other laboratory soils tests. Also see Proctor Hammer.
- Compaction Mold
- A cylindrical mold of known volume, into which soil is compacted in a specified manner for the moisture/density relationship and other laboratory soils tests. Also see Proctor Mold.
- Compaction Test
- A laboratory test to determine the moisture/density relationship of soils using a standard compactive effort, as described in ASTM D698, D1557, and other standard test methods. Also see Moisture Density Test. A field test to determine the in-situ dry density of compacted soils, usually expressed as a percentage in comparison to a laboratory compaction test.
- Composite Sieving
- A particle size determination for large samples where the coarse sieve sizes are measured first, then a smaller sub-specimen of the remaining material is extracted to measure the finer particle sizes. The results of sieve tests for the coarse and fine fractions are mathematically combined to determine the gradation of the whole sample.
- Compressibility
- The propensity of a soil material to decrease in volume when subjected to loading.
- Consistency
- The degree to which a soil resists changing its original shape when subjected to outside mechanical forces.
- Consolidated Drained Triaxial Compression Test
- A triaxial test in which the saturated soil specimen is first consolidated by the effective confining pressure. The specimen is sheared to failure under controlled axial strain. Loading (shearing) is slow, allowing dissipation of shear-induced pore pressure, drainage, and consolidation. Low-permeability samples require extensive time periods to drain and adjust. ASTM test method D7181. Also see Triaxial Shear Test.
- Consolidated Undrained Triaxial Compression Test
- A triaxial test in which the saturated soil specimen is first consolidated by the effective confining pressure. The specimen is sheared to failure by axial loading. The specimen is assumed to be saturated and not allowed to drain during testing. Shear-induced pore water pressures can be measured during the process. ASTM D4767. Also see Triaxial Shear Test.
- Consolidation
- The progressive reduction in volume of a soil mass resulting from an increase in compressive force.
- Consolidation Test
- A laboratory soil test where a laterally confined specimen in a ring is subjected to a compressive axial load between porous plates of a load frame or oedometer, as deformation is recorded.
- Constant Head
- A condition in the permeability testing of soils where the hydraulic gradient is kept constant throughout the test.
- Controlled-Strain Test
- Any laboratory soil test where the load applied is controlled by the rate of displacement (deformation) of the specimen.
- Controlled-Stress Test
- Any laboratory soil test where the axial loading of a specimen is applied at a controlled rate specified in the test method.
- Core
- A cylindrical sample drilled from a larger mass of rock, hardened concrete, or grout for testing for strength or other properties.
- Cumulative Percent Retained
- In sieving, the ratio of the mass of the cumulative material retained on a given sieve compared to the mass of the specimen is expressed as a percentage.
- Cumulative Sieving
- A sieving method where the mass of material retained on an individual sieve is added to the accumulated masses of material retained on the coarser sieves of a given stack or set of sieves.
- D10
- The diameter of a soil particle at which 10% by weight of the particles of a particular sample are finer. Synonymous with the effective size or effective grain size.
- D60
- The diameter of a soil particle at which 60 % by weight (dry) of the particles of a particular sample are finer.
- Deformation
- A change in the shape or size of a solid body while total volume remains constant.
- Density
- Mass per unit volume of material. It may be further defined by adjectives such as 'total', 'moist', 'wet', or 'bulk'.
- Designated Separating Sieve
- A sieve selected when performing composite sieving as a boundary between the coarse and fine fractions of a material.
- Differential Settlement
- Consolidation or subsidence that occurs in unequal amounts or rates at various points in a structure.
- Direct Shear Test
- A laboratory test in which soil or rock under a vertical confining (normal) load in a two-part shear box is horizontally sheared to failure by moving one half of the box relative to the other. ASTM D3080. Also See Shear Test.
- Durability
- An assessment of whether rock will remain stable after excavation, wetting-drying, freeze-thaw, or long-term exposure.
- Elastic Limit
- The point at which a material under stress will no longer return to its original form after an applied force is removed.
- Expansive Soils
- Fine-grained clay soils, often containing minerals like montmorillonite or bentonite, which undergo significant volume changes between dry and wet conditions. Such soils exert tremendous pressure when expanding and lose contact with structural elements when shrinking. These cycles cause serious damage to roads and structures.
- Falling Head
- A condition in the permeability testing of soils where the hydraulic gradient is allowed to fall during the test.
- Filtration Compatibility
- The equilibrium state achieved between a base soil and a geosynthetic filter (usually a nonwoven geotextile) that allows water to pass freely while preventing the migration of fine soil particles.
- Fineness Modulus (FM)
- An empirical factor obtained by summing the percentages of an aggregate sample retained on a specified sieve and dividing by 100. Sieve sizes of 150μm (No. 100), 300μm (No. 50), 600-μm (No. 30), 1.18mm (No. 16), 2.36mm (No. 8), and 4.75mm (No. 4) are used for fine aggregates. 9.5mm (3⁄8in.), 19.0mm (3⁄4in), and 37.5mm (1 1⁄2in) sieves are used for FM of coarse aggregates.
- Fines
- That fraction of a soil or aggregate sample that will pass through a given standard sieve opening, typically a No. 200 (75μm) or No. 325 (45µm).
- Flow Curve
- A best-fit straight-line curve drawn through points on a chart plotting blow counts vs moisture contents to determine the Atterberg liquid limit of soils in ASTM test method D4318.
- Foundation Soil
- The upper part of a soil mass that bears the load of a structure.
- Fractional Sieving
- A sieving method where the masses of material retained on each sieve are recorded separately.
- Friable
- Dry, consolidated soil or rock that is easily crumbled or disaggregated under minimal pressure.
- Frost Action
- The freezing and thawing cycles of moisture in soils or aggregates producing mechanical actions that displace the materials and may damage structures they support.
- Geocells
- Three-dimensional, expandable, honeycomb-like structures fabricated from high-density polyethylene (HDPE) or other polymer material. Designed to lock soils or aggregates in place to stabilize and reinforce embankments and engineered soil fills. Also known as cellular confinement systems (CCS).
- Geocomposite
- A geosynthetic product formed by combining two or more distinct types of geosynthetics—such as geotextiles, geogrids, geonets, or geomembranes—into a single integrated system. Geocomposites perform multiple functions simultaneously, most commonly combining high-capacity drainage with filtration, separation, or reinforcement to enhance the technical properties of soil.
- Geogrid
- A synthetic polymer grid-like material used in civil engineering to reinforce soil, stabilize ground surfaces, and control erosion.
- Geonets
- Three-dimensional, interconnected polymeric (plastic) ribs that intersect at various angles to form a net-like mat. Designed to drain and stabilize soil and aggregate fills.
- Geosynthetic Reinforced Soil – Integrated Bridge System (GRS-IBS)
- A bridge construction method using closely spaced layers of geosynthetic reinforcement (geotextile fabric) and compacted granular fill to create a strong composite abutment foundation. Also see GRS-IBS.
- Geosynthetic Reinforced Soil (GRS)
- A geotechnical engineering technique combining compacted soil layers alternating with geosynthetic reinforcement (geogrids or geotextiles) to stabilize and strengthen engineered soil fills. Also see GRS.
- Geosynthetics
- Synthetic, polymeric (plastic) materials such as geotextiles, geogrids, geocells, and geomembranes used in civil engineering to improve the performance of soil, rock, or other geotechnical materials.
- Geotechnical Risk
- Uncertainty in subsurface soil or groundwater conditions poses risks for foundation, embankment, pavement performance, and construction scheduling.
- Geotextile
- A permeable synthetic or natural fabric used in geotechnical engineering to improve soil performance by separating, filtering, reinforcing, protecting, or draining soil layers.
- Glacial Till
- Soil material transported by the movement of glaciers and deposited upon their retreat. Normally consisting of a wide range of particle sizes and often consolidated.
- Gradation
- The proportions by weight of soil or aggregate particles in specific size ranges, usually measured by sieving. Also see Particle-Size Distribution and Soil Texture.
- Grain-Size Analysis
- The determination of particle size and distribution in a soil or aggregate sample. Also see Particle-Size Analysis.
- Gravel
- Fragments of rock, often rounded by weathering or abrasion, with particle size between 3in (76.2mm) and No.4 (4.75mm) sieve sizes.
- Ground Improvement
- An umbrella term describing soil stabilization, densification, drainage, modification, and reinforcement.
- GRS
- A geotechnical engineering technique combining compacted soil layers alternating with geosynthetic reinforcement (geogrids or geotextiles) to stabilize and strengthen engineered soil fills. Also see Geosynthetic Reinforced Soil.
- GRS-IBS
- A bridge construction method using closely spaced layers of geosynthetic reinforcement (geotextile fabric) and compacted granular fill to create a strong composite abutment foundation. Also see Geosynthetic Reinforced Soil – Integrated Bridge System.
- Hardness
- The resistance of a material to indentation or scratching. The Mohs hardness scale uses reference minerals of known hardness to scratch the surface of test specimens.
- Hardpan
- A hardened layer of impervious cohesive soil that impedes drainage and root growth.
- Homogenous
- A property of a material that has the same characteristics throughout its mass.
- Horizon (Soil)
- A layer in the soil profile, distinguished by texture, color, structure, and chemical content. "A" horizon—the uppermost layer from which soluble inorganic colloids have been leached. Usually contains a high percentage of organic material. "B" horizon—A layer where material leached from the overlying "A" horizon has accumulated. "C" horizon—The parent material from which the overlying soil profiles have developed.
- Humus
- A dark brown or black material consisting of partly decomposed leaf, vegetable, animal, and other organic matter, accumulating on top of the soil horizons.
- Hydraulic Conductivity
- The rate of the flow of water through soil materials under a controlled hydraulic gradient. Also see Permeability.
- Hydraulic Conductivity
- The capacity of a soil or rock mass to allow the movement of water or air through its matrix. Also see Permeability.
- Hydrometer Analysis
- A laboratory test to determine particle size distribution in fine-grained soils. A soil sample is mixed into a water solution, and a buoyant hydrometer is used to measure solids in suspension during the sedimentation process. ASTM test method D7928.
- Hygroscopic Water Content
- Moisture remaining contained within a rock or soil mass after air-drying.
- In-Situ Monitoring of Geosynthetics
- The field-based real-time or periodic monitoring of the performance, deformation, and stress-strain behavior of geosynthetic materials (geogrids, geotextiles, geocells) and the surrounding soil.
- Instrumentation
- Digital sensors and dataloggers installed in the field to monitor movement, pressure, temperatures, or moisture conditions on elements of a project. Such devices can be used to monitor and collect data for slopes, excavations, retaining systems, and movement-prone rock masses.
- Intact Sample
- A soil or rock sample with properties close enough to conditions of the in-situ formation to allow meaningful laboratory tests. This term is now preferred instead of "Undisturbed Sample."
- Kaolin
- A type of clay containing a high percentage of kaolinite mineral. Kaolin is not subject to significant changes in volume with changes in moisture content.
- Karst
- A landscape topography caused by the dissolution of underlying soluble limestone, leaving caves, fissures, underground streams, and sinkholes.
- Lacustrine Soils
- Soil materials that have settled out of still waters, such as lakes. The formations consist of fine, uniformly graded soils deposited over a wide, flat area.
- Leaching
- The loss of soluble minerals and colloids caused by water percolating downward through the interstices of a soil or rock mass.
- LiDAR (Light Detection and Ranging)
- Maps terrain, slopes, and structures, and creates real-time digital models to detect changes in location or elevation. LiDAR images from aerial drones can monitor slope stability, quarry faces, rockfall potential, and terrain movement.
- Liquefaction
- A decrease in the shear resistance of a soil that temporarily transforms it into a fluid mass. The process is triggered by sudden shock and a resultant increase in pore water pressure.
- Liquid Limit
- The water content of a cohesive soil in percent, at the point where it transitions from a semi-liquid to a plastic state. One of the Atterberg limit indexes.
- Liquidity Index
- A value for cohesive soils calculated by subtracting the plastic limit of the specimen from its natural water content and dividing that number by the plasticity index. If this index is less than 0, the sample will be dry/crumbly. If near 0, it will have plastic tendencies, and if greater than 1, it will exhibit liquid flow.
- Loam
- A soil made up of sand, silt, and clay, with nutrients and organic matter that support the growth of plants.
- Loess
- An unconsolidated and unstratified aeolian (wind) deposit of mostly silty or loamy soil.
- Long-Term Design Load
- The tensile load allowable on a geosynthetic material at the end of its service life, often 75 to 120 years buried in the ground.
- Long-term Design Strength
- The allowable strength of a geosynthetic material remaining at the end of its service life, often 75 to 120 years, while buried in the ground.
- Marginal Materials
- Soils that may perform poorly for load-bearing applications on construction projects. Such soils may have a high organic content, a high fines content, or simply do not meet project specifications for the desired application.
- Marl
- A calcareous clay soil with a high calcium carbonate (CaCO3) content.
- Mechanically Stabilized Earth (MSE)
- A technique that strengthens soil by incorporating artificial tensile reinforcement such as steel strips, geogrids, or geotextiles within compacted granular backfill. Also see MSE.
- Mohr Circle
- Used in geotechnical engineering as a graphical representation of the normal and shear stresses of soils.
- Mohr Envelope
- A series of Mohr circles representing the stress conditions at failure of a soil or other material sample under load.
- Moisture-Density Curve
- A curve showing how the dry density of soil is affected by moisture content (moisture/density relationship) when molded under a controlled compactive force. Also see Proctor Curve and Compaction Curve.
- Moisture-Density Test
- A laboratory test to determine the moisture/density relationship of soils using a standard compactive effort, as described in ASTM D698, D1557, and other standard test methods. A field test to determine the in-situ dry density of compacted soils, usually expressed as a percentage in comparison to a laboratory compaction test. Also see Compaction Test.
- Montmorillonite
- A group of clay minerals that exhibit a high degree of volume change when subjected to wetting or drying. Also see Expansive Soils.
- MSE
- A technique that strengthens soil by incorporating artificial tensile reinforcement such as steel strips, geogrids, or geotextiles within compacted granular backfill. Also see Mechanically Stabilized Earth.
- Nonplastic Soil
- A granular soil that does not exhibit cohesiveness at any water content. The Atterberg plasticity index is equal to or less than zero. Also see Cohesionless Soil.
- Optimum Moisture Content
- The water content ideal for a soil to be compacted to its maximum dry unit weight with a given compactive effort.
- Organic Soil
- Soils with a high organic content. Organic soils are typically weak and compressible, making them unsuitable for load-bearing or other structural applications.
- Overburden
- Excavatable soil materials overlying bedrock formations or a specific point below the surface.
- Particle-Size Analysis
- The determination of particle size and distribution in a soil or aggregate sample. Also see Grain-Size analysis.
- Particle-Size Distribution
- The proportions by weight of soil or aggregate particles in specific size ranges, usually measured by sieving. Also see Gradation.
- Pavement Reinforcement and Stabilization with Geosynthetics
- The use of geosynthetics, geogrids, and geotextiles between the soil subgrade and aggregate base to prevent contamination of the base, restrict lateral aggregate movement, and strengthen weak soil. Reduces the required thickness of construction materials and improves long-term load-bearing capability.
- Penetrometer
- A device equipped with a piston or needle that measures the force required to penetrate the surface of a soil mass to a specific depth. Results are most often correlated to the shear strength of the material or related to an indication of strength at a given moisture content.
- Percent Compaction
- A ratio of dry density (unit weight) of in-situ soil vs the laboratory maximum dry density obtained from the moisture/density relationship (Proctor) test, expressed as a percentage.
- Percent Fines
- The mass of soil or aggregate material finer than a given sieve, usually the No. 200 (75μm) sieve, expressed as a percentage.
- Percent Passing
- The ratio of the portion of material by mass in a sieve analysis sample that passes through the openings of a given sieve, compared to the total mass of the sample, expressed as a percent.
- Percent Retained
- The ratio of the portion of material by mass in a sieve analysis sample retained on a given sieve, compared to the total mass of the sample, expressed as a percent.
- Percent Saturation
- The ratio of the volume of water in a soil or rock mass compared to the total volume of voids in the mass, expressed as a percentage.
- Percolation
- The movement of water through a soil or rock matrix by gravity.
- Performance-Based Geotechnical Design
- Geotechnical design based on the required outcome, performance, and function, rather than prescriptive specifications that dictate procedures, methods, and materials.
- Permeability
- The rate of the flow of water through soil materials under a controlled hydraulic gradient. Also see Hydraulic Conductivity.
- Permeability
- The capacity of a soil or rock mass to allow the movement of water or air through its matrix. Also see Hydraulic Conductivity.
- Permeameter
- A closed cell or chamber designed to contain a test specimen when measuring hydraulic conductivity.
- Permittivity
- The volumetric flow rate of water per unit area, per unit hydraulic head, measured perpendicular to the plane of the geosynthetic. It describes how easily water can pass through the geotextile.
- Ph
- A quantitative index to characterize the acidity or alkalinity of liquids or solid materials in suspension.
- Piping
- The progressive erosion of small passages through soil formations by percolating water.
- Plastic Limit
- The water content of a cohesive soil in percent, at the point where it transitions from a plastic to a semi-solid state. One of the Atterberg limit indexes.
- Plastic Soil
- A soil that exhibits plasticity over a range of water contents and will retain its shape after drying.
- Plasticity Index
- The difference between the liquid limit and plastic limit measurements of a cohesive soil.
- Pore Water Pressure
- The pressure of water held within the spaces (pores) of a soil or rock mass between the solid particles.
- Porosity
- The ratio of the volume of voids in a unit volume of a soil or rock mass compared to the total volume of the mass.
- Proctor Curve
- A curve showing how the dry density of soil is affected by moisture content (moisture/density relationship) when molded under a controlled compactive force. Also see Compaction Curve.
- Proctor Hammer
- A sliding drop hammer of specified mass and diameter used to compact soils into molds for the moisture/density relationship and other laboratory soils tests. Also see Compaction Hammer.
- Proctor Mold
- A cylindrical mold of known volume, into which soil is compacted in a specified manner for the moisture/density relationship and other laboratory soils tests. Also see Compaction Mold.
- Proctor Penetration Curve
- A curve developed using a Proctor penetrometer that compares penetration resistance vs water content of molded soil at different points in the moisture/density relationship (Proctor) test.
- Quick Condition (Quicksand)
- A condition of a soil formation where upward groundwater pressure is sufficient to reduce the bearing capacity through the disruption of intergranular contact.
- Reconstituted Soil
- Soil material manipulated in the laboratory to change its gradation or moisture using a specified procedure to meet the requirements of a standard test method.
- Relative Density
- A relationship comparing the loosest and densest states of a cohesionless soil, expressed as a percentage.
- Remolded Soil
- Soil material destructured (crumbled or kneaded) in the laboratory and reformed with the same moisture and density into a shape usable for a specified test method.
- Residual Soil
- Soil formed in place as a result of weathering of the underlying parent material.
- Resilience
- The degree to which soils, slopes, embankments, and foundations resist changing climate conditions, flooding and storm events, earthquakes, and other environmental events.
- Riprap Stone
- Large rock material up to 2 tons (1814kg) in mass, placed on slopes or banks to prevent erosion by rainfall, water current, or waves.
- Rock
- A large formation of naturally deposited solid mineral matter, or fragments derived from such a deposit.
- Rock Mass Characterization
- An integrated assessment of the structural, geological, and geotechnical properties of a rock formation to evaluate its suitability for a design application.
- Rock Mechanics
- A science that studies the mechanical behavior of rock in theoretical and practical applications.
- Rockfall Hazard
- A consideration for hazard mitigation or slope management in geotechnical designs that include slopes or exposed rock faces.
- Sand
- Particles of soil and rock of a size between the No. 4 [4.75-mm] sieve and the No. 200 [75-μm] U.S. standard sieve.
- Sand Equivalent
- A test that puts a sample of fine aggregate in a water suspension to measure the amount of silt or clay contamination present. ASTM test method D2419).
- Saturated Soils
- A moisture condition in soils in which all voids in the soil are completely filled with water.
- Saturated Surface-Dry Condition (SSD)
- For aggregates and coarse-grained soils, a state in which the particles are saturated, but there is no visible water on their surface.
- Sensitivity Ratio
- A comparison of the strength of an intact specimen of cohesive soil to the strength of the same specimen after remolding.
- Shaking Test
- A qualitative test to estimate the presence of silt or very fine sand. A pat of wet soil with a paste-like consistency is shaken in the palm of an open hand, and the surface is observed for a glossy or livery appearance. The pat is then squeezed and observed for rapid apparent drying and cracking.
- Shear Strength
- In soil mechanics, the maximum shear stress that a soil mass can sustain. Shear strength of soil results from friction, interlocking particles, and cementation.
- Shear Test
- A soil mechanics test method to measure the resistance of a fine-grained soil to horizontal shear forces applied in a direction perpendicular to its normal orientation. ASTM D3080. Also see Direct Shear Test.
- Shrinkage Index
- In Atterberg limits of soils, the numerical difference between the plastic limit value and shrinkage limit value.
- Shrinkage Limit
- In Atterberg limits of soils, the maximum water content is the point at which a reduction in water content does not cause a decrease in soil volume.
- Sieve Analysis
- A determination of the proportions of particles of soil or aggregate classified within size ranges by separation on testing sieves with different size openings.
- Silt
- Non-plastic soil or rock material finer than 75µm (No. 200 Sieve) that exhibits little or no strength when air-dried. Particle size is generally coarser than 0.002mm.
- Site Variability
- Soil conditions may change significantly across short distances. Assumptions that soil layers are uniform over a wide area entail risks and may result in design and construction problems.
- Slake Durability
- ASTM Standard Test Method D4644 determines the degradation or stability of rock following repeated wetting and drying cycles. Samples are tumbled in water-immersed mesh drums, and the loss of mass is calculated.
- Slaking
- Rapid deterioration of rock or indurated soil masses when immersed in water.
- Slickensides
- Soil or rock with striated and polished surfaces resulting from movement along a bedding plane or fault.
- Soil
- Accumulations of sediments or other solid particles produced by the weathering and physical or chemical disintegration of rock formations.
- Soil
- Sediments or other formations of weathered rock particles produced by the physical and chemical disintegration of rocks.
- Soil Cement
- The result of a process where lime or hydraulic cements are mixed into in-place soils and compacted for the purpose of stabilization. The treatment is used on soils that are wet or otherwise marginally suitable for use as engineered fills.
- Soil Mechanics
- Application of the laws and principles of mechanics and hydraulics to define the properties of soils as an engineering material.
- Soil Profile
- An actual or schematic vertical section, showing and identifying the soil types and layers ordered in the sequence of deposition.
- Soil Stabilization
- The chemical or mechanical treatment of an existing or engineered soil mass to improve its engineering properties. An alternative treatment for low-strength soil subgrades.
- Soil Texture
- The proportions by weight of soil or aggregate particles in specific size ranges, usually measured by sieving. Also see Particle-Size Distribution and Gradation.
- Soil-Geosynthetic Interaction
- The mechanical and physical bond that develops between synthetic materials, such as geogrids or geotextiles, and soil particles.
- Specific Gravity of Soil
- The ratio of the mass of a unit volume of soil solids to the mass of the same volume of gas-free distilled water at 20°C.
- Specimen
- A portion taken from or prepared from a sample for the purpose of conducting a laboratory test.
- Subbase
- A layer of a pavement system placed over the soil subgrade and below the asphalt or concrete pavement, designed to strengthen and stabilize the system.
- Subgrade
- An in-situ or engineered soil surface, prepared and graded to support a structure or pavement system.
- Subgrade Characterization
- A detailed study of subgrade soil strength, consistency, and stability to evaluate its ability to sustain anticipated loads, resist degradation, and estimate its lifecycle cost.
- Subsidence
- The downward displacement of the surface of soil or rock formations. Causes may include soil settlement, subsurface voids, aquifer drawdown, or earthquakes.
- Subsoil
- Soil that exists below fill materials, or part of a soil profile occurring below the topsoil or "A" horizon.
- Test Boring
- A hole advanced through soil or rock using augers or drill bits, characterized by periodic or continuous sampling of materials. Soil descriptions from boring logs create a soil profile for foundation design or to identify strata for other purposes.
- Test Pit
- A shallow excavation made to examine and characterize the properties of subsurface soils.
- Topsoil
- The fertile upper "A" zone of the soil profile. High in organic content, darker in color, loose, and unconsolidated.
- Toughness Index
- A ratio comparing the Atterberg plasticity index of a soil to the flow index.
- Transition Zone
- A zone in the geologic column that transitions to a different type of soil, from soil to rock, or from weathered rock to sound rock.
- Transmissivity
- The in-plane hydraulic conductivity measured as the discharge rate per unit width under a specific normal load. The ability of the geosynthetic to transport fluids parallel to its plane.
- Transported Soil
- Soil transported by wind, water, or ice from the place of its origin and deposited in another location.
- Triaxial Shear Test
- A laboratory soil test in which a cylindrical sample is encased in an impervious membrane and subjected to confining fluid pressures while being axially loaded to failure. Also see: Unconsolidated-Undrained Triaxial Compression Test (Quick Test), Consolidated Drained Triaxial Compression Test, Consolidated Undrained Triaxial Compression Test
- Unbound Aggregate Base Performance
- An evaluation of the performance under load of granular base course and subbase materials. These materials, such as sand, crushed stone, or gravel, are not bound together by cement, bitumen, or other binders.
- Unconfined Compressive Strength
- The axial load per unit area required to cause failure in compression of a cylindrical soil or rock specimen.
- Unconfined Compressive Strength
- The load per unit area at which an unconfined soil or rock specimen with no lateral confining pressure fails in simple axial compression.
- Unconsolidated-Undrained Triaxial Test (Quick Test)
- A type of triaxial soil test where the water content of the specimen remains the same throughout the application of confining pressure and axial (shearing) loads. ASTM test method D2850. Also see Triaxial Shear Test.
- Undisturbed Sample
- A soil or rock sample having the same composition and properties as the material in situ. Both the term and the condition are now considered impractical. See Intact Sample
- Uniformly Graded
- A quantitative characterization of a soil when the majority of particle size fractions are nearly the same percentage.
- Unit Weight
- Mass per unit volume of material. It may be further defined by adjectives such as 'total', 'moist', 'wet', or 'bulk'. Also see Density.
- Unsaturated Soils
- A moisture condition in soils in which not all voids in the soil are completely filled with water.
- UV Resistance
- The ability of polymer-based geotextiles or geogrids to maintain their structural integrity, strength, and functionality when exposed in place to sunlight (UV radiation), oxygen, heat, and environmental moisture.
- Vane Shear Test
- A test with several variations that can be performed in-place or on intact samples in the laboratory. A rod with thin, perpendicular radial vanes is pushed into the soil, and the force required to rotate them is measured.
- Void
- In a mass of soil or rock, a space occupied by air or water rather than solid matter.
- Void Ratio
- A ratio comparing the volume of void space to the space occupied by solid matter in a unit volume of soil or rock.
- Water Content
- The ratio of the mass of water contained between the particles and within the pore spaces of soil or rock material, to the mass of solid particles, and expressed as a percentage.
- Weathered Rock
- Rock that has undergone physical changes to its original properties as a result of exposure to wind and rain, freezing and thawing cycles, or chemical action. Often a transitional zone between soil and sound rock, which respond differently to applied loads.
- Weathering
- The wearing down and disintegration of rock caused by the actions of water, frost, wind, heat, and exposure to the atmosphere.
- Zero Air Voids Curve
- Often included on the laboratory compaction (Proctor) curve, the zero air voids curve is the relationship between water content and dry density at 100% saturation.
