GEOTECHNICAL DEFINITIONS
Backfill :
 Soil or rock material placed behind retaining walls, rockeries, and foundations to return the site to finish grade.
Base Rock :
 A layer of clean, free draining gravel or crushed rock placed and compacted beneath pavements, foundations, rockeries, or floor slabs.
Capillary Break :
A layer of free-draining granular material placed beneath floor slabs to break the upward movement of liquid water produced by capillary action in the underlying soil (as opposed to a vapor barrier to prevent the migration of water vapor).
Clays :
 Fine-grained mineral soils with particles less than .005 mm in size that can be made plastic by the adjustment of water content; natural or otherwise. These soils also exhibit considerable strength when air dried.
Colluvium :
A soil deposit derived from down slope movement of material from other soil formations. These deposits are most often found on the walls of ravines or on steep hillsides
Contour :
Lines of equal elevation on topographic map showing variations in land surface elevation.
Contour Interval :
The vertical spacing between contour lines. The larger the horizontal space between contour lines shown on a contour map, the more gentle the change in elevation.
Culvert :
 An enclosed/solid drain crossing under a road or an embankment.
Downcutting :
 The erosive action by flowing water that removes surface material and cuts into the ground surface. This term is usually associated with stream action in ravines.
Engineered Fill :
 Fill which is wetted or dried to near its Optimum Moisture Content, placed in lifts of 12 inches or less, compacted to a minimum Percent Compaction specified by a Geotechnical Engineer, all under observation and testing by the Geotechnical Engineer to verify compaction.
Erosion :
 Wearing away of soil or rock by wind, water, ice, or gravity.
Fill or Manmade Fill :
 All artificially placed deposits of soil or rock.
Fine-grained Soils :
Mineral soils that include clays and those silts exhibiting clay-like behavior
Footing Drain :
 A drainage system at the outside of footings used to collect water moving through the adjacent soil or rock and carry it to a controlled discharge point. Typically, a footing drain will consist of a perforated drain pipe and free-draining granular material laid at a uniform gradient to a positive discharge point. Surface or roof drains should never be connected to footing drains.
Free-draining Granular Material :
Clean, free-draining gravel or crushed rock generally containing no more than 5 percent fine-grained Soil (particles passing No. 200 sieve) based on the fraction passing the 3/4-inch sieve. Or material with sand equivalent of at least 30
Geotechnical Engineer :
A Professional Engineer currently registered in his State of operastion, qualified by experience and education in the practice of geotechnical engineering, and designated by the owner as the Geotechnical Engineer of record for the project.
Granular Soils :
 Mineral soils that include sands and gravels and those silts exhibiting sand-like behavior.
Impervious Surfaces :
 Surfaces resistant to infiltration by or absorption of moisture. Generally, they are man-made paved or hardened surfaces such as roofs, streets, sidewalks, and parking lots
Mass Movement :
Any sizeable natural displacement of a hillside; slump; landslide.
Mat Foundation :
A mat or raft foundation is a combined footing that covers the entire area beneath a structure and supports all the walls and columns.
Moisture-sensitive Soil :
 Soil which is easily made unsuitable for fill or backfill by the addition of small amounts of moisture. Fine-grained soils are typically moisture sensitive.
Optimum Moisture Content :
The moisture or water content of a soil, expressed as a percent by dry weight of the soil, at which it is most easily compacted. The optimum moisture content depends on the soil type and percent compaction desired.
On-site Fill Material :
Soil obtained at the project site during excavation (following clearing and stripping) which is then used for fill. Typically, only the portion of the excavated material which is free of organic contaminants, perishable material, and rocks or lumps greater than 6 inches in maximum dimension is considered suitable for use as on-site fill material. Organic Soils and Peat : Soils composed of a high percentage of decaying and decomposed plant matter mixed with varying percentages of mineral soil material.
Overexcavation :
 Excavation beyond the depth that is required to achieve the minimum subgrade elevation. Typically, the material over excavated is replaced with fill suitable to support the above pavement section, foundations, or floor systems.
Overstory :
Vegetation above 10 feet in height.
Pavement Section :
 A sequence of materials placed and compacted to support vehicle traffic and parking loads. Typically, the pavement section consists of asphalt concrete or cement concrete, base rock, subbase, and a properly prepared soil subgrade.
Percent Compaction :
The required in-place dry density of a soil or rock material, expressed as a percentage of the maximum dry density of the same material as determined in the laboratory by an ASTM Test Method. The specific test method should be clearly defined.
Permanent Slope :
 A slope at the geometry proposed after final grading of a site for long-term use.
Pile Foundation :
 Piles are structural members of small cross-sectional area compared to their length, and are usually installed by vibrating, driving, or drilling in the case of augercast piles. Pile foundations are used where loads must be transferred to more suitable material at a greater depth.
Plasticity :
 The ability to deform rapidly without cracking, crumbling, or changing in volume when a force is applied. There will be very little rebound to the original shape when the force is removed.
Reinforced Soil :
 Soil or rock fill or backfill which includes reinforcement consisting of metal or synthetic materials in bars, strips, or sheets. Typically, reinforced soil requires select fill material. Rockery : A rockery is not a retaining wall or structure. The primary function of a rockery is to protect the slope face by preventing soil erosion and sloughing.
Rockeries should be considered maintenance items that will require periodic inspection and repair. They should be located so that they can be reached by a contractor when repairs become necessary.
Select Fill Material :
Imported or on-site soil consisting of clean, free-draining granular material
Silts :
 Fine-grained mineral soil shaving particles ranging in size from .005 mm to .05 mm. This material may or may not exhibit plastic behavior.
Slide :
The movement of a mass of loosened rocks or earth down a hillside or slope.
Slab-on-grade :
 A slab-on-grade floor is a typically a reinforced concrete slab that is supported by the ground.
Slope :
An inclined ground surface the inclination of which is expressed as a ratio of horizontal distance to vertical distance.
Slope Failure :
The downward and/or outward movement of slope-forming materials (natural rock, soils, artificial fills, or combinations of these materials) constituting the group of slope movements wherein shear failure occurs along a specific surface or combination of surfaces
Slope Steepness or Inclination :
Percent slope is related to the generalized inclination of the land by the following formula: slope (in percent) = vertical rise x 100 % horizontal distance Another method of measuring the inclination of the land surface is by measuring the angle of the surface above a horizontal plane. The following chart shows the equivalents between these two methods of measurement for several slopes.
Slope in Percent
Angle in Degrees
  8.7   5.0
  15.0   8.5
  30.0   16.7
  40.0   21.8
  50.0   26.6
  100.0   45.0
Slump :
 The collapse or sinking of a hillside.
Soils :
 Unaggregated or uncemented deposits of mineral and/or organic particles or fragments derived from the breakdown of massive rocks or decay of living matter. Spread Footing Foundation : A footing is an enlargement of the base of a column or wall for the purpose of transmitting the load to the subsoil at a pressure suited to the properties of the soil. A footing that supports a single column is known as a spread footing.
Standard of Practice :
Performing engineering services in a manner consistent with that level of care and skill ordinarily exercised by members of the engineering profession currently practicing under similar conditions in the same geographic region.
Structural Fill :
Fill material placed and compacted in areas that underlie structures or pavements. Typically, structural fill consists of select fill material compacted to a relatively high Percent Compaction.
Subbase :
 A layer of select fill material placed and compacted beneath base rock to provide better support for pavements, foundations, rockeries, or floor slabs than that provided by the native soil subgrade.
Substrate :
 A part or substance that lies beneath and supports another.
Subgrade :
The soil on which conventional spread footings, a pavement section, or a floor slab support system is placed. Typically it consists of either undisturbed on-site soil exposed by excavation or engineered fill placed after overexcavation.
Surficial :
Of the surface or top level; not at depth. Temporary Slope : A slope that exists for a relatively short period of time, typically during construction, such as a backcut made during a slope repair or utility/footing installation.
Till :
 Glacial deposits consisting of a heterogeneous mixture of sand, silt, and clay forming a matrix in which granules to large boulders are firmly embedded. May contain lenses and layers of sand and gravel. The upper few feet may be loose, sandy, and stoney with fewer silt or clay-sized particles than at greater depth.
Toe of Slope :
 The lowermost portion, bottom, or base of a slope
Top of Slope :
 The uppermost portion, top, or crest of a slope.
Topography :
Surface features including relief and rivers, lakes, etc. and man-made features such as roads, bridges, canals, etc.
Uncontrolled Fill :
Fill which has been placed under unknown conditions or without any controls.
Vapor Barrier :
A barrier preventing the vertical or lateral migration of water vapor (as opposed to a capillary break or wall drain to prevent the migration of liquid water) beneath floor systems or behind retaining walls. Typically, it consists of an impermeable membrane of reinforced plastic or equivalent material.
Wall Drain :
 A drainage system behind retaining walls and rockeries used to collect water moving through the retained soil or rock and carry it to a controlled discharge point. Typically, a wall drain will consist of free-draining granular material or a free-draining synthetic material and a perforated drain pipe.
 
 

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