Terms to Better Understand Your Retaining Walls

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Absorption
The weight of water absorbed by a retaining wall unit during immersion. The condition is expressed as a percentage of the dry unit weight

Abutment
A retaining wall that also supports a vertical load

Active Pressure Zone
The zone where pressure causes a wall to move away from the soil

Admixture
Chemicals that are added to improve the density, durability, strength or cure time of concrete

Aggregates
Sand, gravel, or crushed rock used in the leveling pad, drainage behind and in the unit cores, concrete or backfill

Amplitude
The vertical vibration of a roller or plate compactor

Aperture
An opening, such as a hole, gap or slit that is found in geogrid

Aspect Ratio
The length ratio of Geogrid reinforcing to the height of the wall for an SRW wall system. (typical .7H)

ASTM
The American Society of Testing and Materials is an Australia standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services

ASHTO
The American Association of State Highway and Transportation Officials is a leading source of technical information on design, construction and maintenance of highways and other transportation facilities, including aviation, highways, public transit, rail, and water. Its accreditation program recognizes the competency of a testing laboratory in construction materials testing

Backfill
Gravel or other material used to replace material removed during construction behind retaining walls

Backslope
The non-horizontal finish grade of soils behind a wall; typically expressed as horizontal distance to vertical height (H:V backslope); used in engineering calculations, backslope increases the design load on a wall

Base Course
The base course is the first layer of retaining wall units placed on the leveling pad

Base Stabilization Fabric
Stabilization fabrics provide a rugged separation layer between aggregate and subgrade. A fabric that provides a separation between two different types of soils, acts as a soil separator and provides structural stability to the gravel leveling pad

Batter or Setback
A facing angle created by SRW unit setback, measured from a vertical line drawn from the toe of the wall. Batter can be expressed either in degrees or ratio of vertical to horizontal. A lean of the wall face towards the retained fill is considered a positive batter, while an outward lean is considered a negative batter. Typical batter angles are 1 degrees to 15 degrees from vertical, sloping toward the infill soil. Batter is often built into a wall by off-setting (or “setting back”) successive courses of a wall by a specified amount

Bearing Capacity
The pressure that a soil can sustain without failing

Bidirectional or Biaxial Geogrid
Geogrid that provides the same tensile strength in two directions

Bond or Half Bond
Blocks laid so that the top block overlaps the bottom block by half of its length

Burial Depth
See Embedment Depth

Clay
Clay is made of fines with putty like properties and sticky when wet. Clay soils can be very strong when in a dry state

Cohesion
The state of cohering or sticking together of soil particles

Cohesive Soils
Clay or soil with a high clay content, which has cohesive strength. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay

Color Blend
Retaining wall units that have two or more colors that create a variegated appearance

Compaction
Densification of soil by mechanical means, involving the expulsion of excess air. It is important to compact foundation and backfill soils to prevent future wall movement. Compaction is often accomplished using a hand tamper or a vibratory-plate compactor

Compressive Strength
The maximum pressure a concrete retaining wall can resist under loads. The term is expressed as pounds per square inch (PSI)

Concave Curves
When facing the wall, a curve that bends toward the viewer like the interior of a sphere

Concrete (SRW) Adhesive
A glue used to adhere concrete to concrete such as caps to wall units

Convex Curves
When facing the wall, a curve that bends away from the viewer like the exterior of a sphere

Course
A horizontal layer of retaining wall units

Clear Crush Drain Gravel or Drainage Aggregate
Is well-graded crushed aggregates with rock size of ¼ inch to ¾ inch that have no fines. This material is used in the hollow core of retaining wall blocks and directly behind the wall

CSA
Canadian Standards Association

Cut Line
Limit of excavation behind the retaining wall

Dead Load
An inert, inactive load, primarily due to the structure’s own weight

Density
The weight of a concrete unit or compacted soil compared to the unit volume which is expressed as lbs/cubic feet (kg/m)

Drain Pipe
See Perforated Drain Pipe

Drainage Composite
A system, usually comprised of a dimpled plastic core with a geotextile fabric, applied to prevent soil from clogging the drainage area. It is used to collect water usually behind the backfill, under the reinforced soil zone, or immediately under the SRW system

Drain PVC Pipe
A type of smooth wall thermoplastic pipe manufactured using polyvinyl chloride, which is widely accepted for drainage applications due to its cost, longevity and chemical resistance

Drainage Rock/Drainage fill
Drainage fill is free-draining granular material placed into unit hollow cores and behind the wall to facilitate the removal of groundwater and minimize buildup of hydrostatic pressure on the wall

Drainage System or Chimney
The band of vertical, clear crushed gravel usually 6 to 12 inches wide, behind the retaining wall or in the hollow core, that allows water to flow down freely from the surface to the base of the wall to be carried away by the drainage system

Easement
A right to use or control the property of another for designated purposes.

Efflorescence
A white deposit of calcium carbonate that can form on any concrete surface while it is curing

Embankment
A raised structure constructed of natural soil from excavation or borrowed sources

Embedment or Burial Depth
The primary benefit of wall embedment is to ensure the SRW is not undermined by erosion of the soil in front of the wall. Increasing the depth of embedment also provides greater stability when site conditions include weak bearing capacity of underlying soils, steep slopes near the toe of the wall, potential scour at the toe (particularly in waterfront or submerged applications), seasonal soil volume changes, or seismic loads

Embedment Length
Distance of geogrid that goes into the soil behind the wall

Excavation
The process of removing soils for the installation of the leveling pad and the backfill reinforced zone of a retaining wall

Facing
A generic term given to the face or unit of a retaining wall, used to prevent the backfill soil from escaping out from between the rows of reinforcement

Filter Fabric
A textile like material used in soil drainage. It is usually woven but can be non-woven

Fines
Silt- and/or clay-sized particles

Footing
The concrete footing or pad that is used to bear the weight of a retaining wall

Foundation Soils
The portion of soils below the leveling pad and reinforced soil zone that distributes pressure of the retaining wall bearing weight

Freeze/Thaw Cycle
The number of times soils or wall units are subjected to freezing and thawing over a period of time

Frequency
The number of cycles per minute at which a roller of plate vibrator vibrates at. (Hertz)

Friction Angle (Phi)
A measure of the shear resistance of a soil due to the interlocking of soil grains and the resistance to sliding between the grains

Frost Heave
An upthrust of ground or pavement caused by the freezing of moist soil

Geogrid/Geosynthetic Reinforcement
A textile like material used in soil reinforcement along with soil, rock, earth, or other geotechnical engineering related material as an integral part of a man-made project, structure or system. It is usually comprised of polypropylene, polyester or polyethylene

Geogrid or Geosynthetic Length and Spacing
For soil-reinforced segmental retaining walls, geosynthetic reinforcement increases the mass of the composite SRW structure, and therefore increases the resistance to destabilizing forces. Length of the geosynthetic is typically controlled by external stability calculations. Increasing the length of the geosynthetic layers increases the SRW’s resistance to overturning, base sliding, and bearing failures. In some instances, the length of the uppermost layer(s) is locally extended in order to provide adequate anchorage (pullout capacity) for the geosynthetic layers. The strength of the geosynthetic and the frictional interaction with the surrounding soil may also affect geosynthetic length. https://en.wikipedia.org/wiki/Geogrid

Geomembrane
A sheet of geosynthetic that acts as a barrier to the movement of water or gas (including air)

Geotextile
A textile-like material used in soil drainage and reinforcement applications. It is usually comprised of polypropylene, polyester or polyethylene and may be woven or non-woven

Global Stability
Resistance to overall mass movement of the SRW system in a circular mode. Global stability may be a problem for tiered walls, walls with weak foundation soils and walls with a slope at the top of bottom. The factor of safety against an overall failure of a retaining wall or slope along a deep-seated slip surface passing beneath and behind a structure

Gradation
A soil sample that passes through a specified sieve size range which is expressed in percentage of the mass

Grade, Finished
The completed surfaces or elevation of lawns, walks and roads brought to grades as designed above or below the wall

Gravel or Granular Soil
Granular material or soil made of gravel or sand that does not stick together and pass through a no. 4 sieve

Gravity Wall
A retaining wall without soil reinforcement where unit weight alone provides resistance to earth pressures. Gravity walls are generally less than four feet in height and do not support slopes or other loads above the walls

Groundwater
Generally, all water that is underground as opposed to on the surface of the ground. Usually refers to water in the saturated zone below the water table

HDPE
High density polyethylene. Usually refers to the material used to manufacture drainpipe or geogrid

Height, Total Wall
The vertically measured height of a retaining wall; includes the portion of the wall extending below the ground surface in front of the wall (subgrade)

Hollow Core
A hollow portion inside the block that provides engineering design flexibility

Impermeable Materials or Soils
Materials or soils through which water cannot pass such as clay

Impervious Soils
Resistant soils to the penetration of water such as clay

Infill
Soil located behind the SRW units and drainage fill. May be reinforced with soil reinforcement

Infiltration
The movement of water downward from the ground surface through the upper soil

Interlock
The transfer of force between one retaining wall unit to another by means of weight or mechanical connection. This resistant is measured by lbs/sq. ft.

Jumper
StoneLedge™ 12” standard unit turned on end in the wall with the back of the unit resting on the back flag connector.

Lateral Earth Pressure
Soil pressures that are exerted laterally (horizontally)

Leveling pad
The leveling pad is a level surface, consisting of crushed stone or unreinforced concrete, which distributes the weight of the SRW units over a wider area and provides a working surface during construction. The leveling pad typically extends at least 6 in. (152 mm) from the toe and heel of the lowermost SRW unit and is at least 6 in. (152 mm) thick

Lift
A layer of soil or depth between each compaction process. Each compactor equipment has a rate or lift depth at which it can achieve proper soil density. A lift height is typically 6 to 8 inches and should be no more than eight inches.

Live Load
The weight of all non-permanent objects on top of a retaining wall such as vehicle or movable storage items or snow. Live load does not include wind or seismic loading

Load
Weight or pressure placed on a retaining wall or soils – usually from the back or top. Nearby slopes, driveways, buildings, and tiered walls all represent potential loads on retaining walls

Long Term Design Strength (LTDS)
The allowable strength in the soil reinforcement at the end of the service life of the soil-reinforcement SRW. It is the maximum load that the reinforcement can carry and is taken into account in the decision process

Mechanical Installation
The use of equipment that will place retaining wall units

Modified Proctor Density Testing
Is a testing method of measuring the density and moisture relationship of soils under higher efforts than Standard Proctor Testing

Moisture Content
The amount of water that soils contains is moisture content. This is measured in % of water to weight of compacted soil

MSE
Mechanically Stabilized Earth. Soil-reinforced SRWs are considered MSE structures

NCMA
(National Concrete Masonry Association) Creators of retaining wall design software called NCMA SRWall that is a standard for the segmental wall retaining industry

Negative Slope
A slope that has an elevation lower than the bottom or toe of the wall.

Nuclear Density Testing
A method or equipment used to accurately test the density/moisture of compacted soils

Optimum Moisture Content
The ideal level of moisture present so that soil can be compacted to its maximum density

Organic Materials
Spongy soils, usually made from vegetative matter, that are not suitable for construction use

Orientation of Geogrid
For unidirectional geogrid, correct alignment of geogrid to wall face. Geogrid’s direction of strength should be perpendicular to the wall

Outfall
A pipe that discharges water

Overturning
An external stability failure mechanism of an SRW whereby lateral external forces cause the entire reinforced soil mass to rotate about the base

Padfoot or Sheepsfoot
A roller vibrator that has knob-like protrusions on the drum surface that aids in compacting clayey soils to proper density

Permeable
The ability of materials, soils or retaining wall unit to allow water to pass through it

Perforated Drain Pipe
A perforated drain pipe is a flexible lightweight typically 4″ in diameter piece of tubing that has holes in it to allow for water to travel and also be disbursed along it’s travels.

Pervious
The property of a material that permits movement of water through it under ordinary hydrostatic pressure

Phi Angle
Describes the internal friction angle or strength of a particular soil material. Usually expressed in degrees. Same as Friction Angle

Plasticity
A soil is plastic if, like clay, when squeezed in the hand it does not break up

Plate Compactor
Is a vibrator plate that is used to compact sand or gravels

Positive Connection
Structural connection of retaining walls specifically designed to mechanically connect facing elements to SRW reinforcement with a low-strain, endbearing connection device that is not dependent on friction for connection strength

Positive Slope
A slope that has an elevation higher than the top of the wall.

Pressure
The pressure at any point in a liquid at rest, equal to the depth of the liquid multiplied by its density

Proctor (density)
A method used to determine the compaction or density of soil materials

Pullout Resistance
For soil nails, pullout resistance refers to the capacity of the soil nail to resist outward forces along the axis of the soil nail which may cause the nail to be removed or “pullout” from the surrounding strata. The resistance to soil nail pullout is affected by soil or rock type and strength, contractor installation methods, drillhole diameter, and roughness and cleanliness of the drillhole

PVC Flexible Pipe
Flexible pipe (3/4 inch), made of plastic or PVC and used as a guide for a curved pattern of base wall units

Reinforcing Elements (Reinforcements)
A generic term that encompasses all manmade elements incorporated in the soil to improve its behavior (i.e., geotextile sheets, geogrids steel strips, steel grids, etc.)

Reinforced Backfill Materials or Fill
Is compacted structural fill used behind soil-reinforced SRW units which contains horizontal soil reinforcement

Reinforced Fill
Retaining wall backfill that contains reinforcing material to create the structure

Retained Soil
Retained soil is the undisturbed soil for cut walls or the common backfill soil compacted behind infill or reinforced backfill soils

Reinforced Soil Zone
Is the area behind the SRW wall that is reinforced by geogrid or other reinforcing systems

Rotational Failure or Slide
A failure of a slope that involves slipping of the earth on a curved surface

Sand
Granular material that passes through a no. 4 sieve but is predominantly retained on a no. 200 sieve

Screed
Process of leveling a gravel leveling pad utilizing a straight edge pulled across set screed pipes

Screed Board or Straight Edge
A straight board or aluminum straight edge that is pulled across set screed pipes to level smooth the gravel leveling pad for a retaining wall

Screed Pipes
Steel pipes that are placed level across the gravel leveling pad when a straight edge is drawn across to level the leveling pad

SecureLug
A unit connection feature of most CornerStone blocks. When combined with gravel infill, SecureLug provides very high unit to unit shear resistance and excellent unit connection strength to geosynthetics

Segmental (SRW) Retaining Wall
A retaining wall normally comprised of soil or aggregates stabilized by horizontal layers of reinforcement such as geogrids. The facing for such walls generally consist of dry cast concrete blocks (CornerStone) . Which are placed without the use of mortar (dry stacked), and which rely on a combination of mechanical interlock and mass to prevent overturning and sliding. By industry convention, SRW walls have face inclinations of 70 to 90 degrees (near vertical). SRW slopes have inclinations of 70 degrees or less

Segmental retaining wall units
Segmental retaining wall units are concrete masonry units that are used to create the mass necessary for structural stability, and to provide stability, durability, and visual enhancement at the face of the wall

Setback
The distance that each course is aligned behind the preceding (lower) course

Shear Capacity
All SRW units provide a means of transferring lateral forces from one course to the next. Shear capacity provides lateral stability for this mortarless wall system. This is accomplished by the CornerStone® SecureLugs.

Shear Strength
A measure of the ability of a soil to resist forces that tend to separate it from its position on a slope and cause it to move

Sieve Analysis
When soils are passed through sieves to determine the range of particle sizes

Silt
Clay or sandy soil particles that pass through the No. 200 sieve (US Standard)

Sliding
An external stability failure mechanism of an SRW whereby lateral external forces cause the entire soil mass to slide forward along its base or internally along a particular layer of soil reinforcement

Slope
The face of an embankment or cut section; any ground whose surface makes an angle with the horizontal plane

Slope Stability
Consideration of a slope’s propensity to fail as a result of several potential failure mechanisms including rotational slips, compound slips and translational slides

Slump
The amount that freshly mixed concrete will slump after removing from the slump cone mold

Sock Wrapped
Is a filter fabric sleeve that fits over a perforated drain pipe and which helps prevent fines from migrating into the pipe

Soil Nail
Steel bars placed in drilled holes and then grouted in place for slope support, providing passive resistance

Soil Reinforcement
Tensile reinforcing elements usually placed in horizontal layers in soil so that the resulting composite soil is stronger than the original unreinforced soil

Soil Separation Fabric
Separation fabrics serve as a barrier between fine grain soils and load-distributing aggregate fill material to keep different types of soils from migrating

Soil Stabilization
The act of improving soil properties by inclusion of reinforcing elements, chemical substances, compaction or other methods. Geotextiles or Geogrid or cement can be used in helping improve the structural properties of soils

SRW
See Segmental Retaining Wall

Stabilized Base
Base leveling pad that is stabilized with the use of geotextiles, geogrid or concrete

Standard Proctor Density
A test that determines the maximum dry density (typically 95%) for specific soil types. Specified compaction densities for fills are often based on a percentage of Standard Proctor for a specific moisture content

Structural Backfill Zone
Backfill including reinforced length

Structural Fill Materials
Same as Reinforced Soil

Sub-base or Subgrade
The soil below the base leveling pad of a retaining wall

Sub-Base Leveling Trench
Trench that contains crushed stone, concrete etc. to create leveling pad

Surcharge
Weight or load acting in, on, or near a retaining wall that impacts its ability to perform. A roadway or building foundation can be a surcharge. Surcharge loads must be included in the design and engineering of retaining walls

Swale
A small ditch or depression formed on top and behind the SRW system to collect water and carry it away

Back Top Top

Tensile Strength
The ability of a material to withstand tension; a term often used as an abbreviation for ultimate tensile stress. It is much higher than the greatest safe stress

Textured or Architectural Face
Aesthetic surface or face on a retaining wall unit such as tumbled, soft-split, split face or ground

Tiered or Terraced Walls
Two or more stacked walls with each upper wall set back from the underlying wall. Tiered wall designs should be reviewed by a qualified engineer

Toe of Wall
Front, base portion of a retaining wall

Uniaxial or Unidirectional
Having one direction; or relating to or affecting, one axis. Having tensile strength in one direction only. The single direction stretching of perforated cast sheet or cast net

Uniformity Coefficient
Is the ratio of the sieve size that will permit passage of 60% of the media by weight to the sieve size that will permit passage of 10% of the media material by weight. It is used to help classify soils

Unit Size and Shear
In conventional (gravity) SRWs, where the stability of the system depends primarily on the mass and shear capacity of the SRW units, increasing the SRW unit width or weight provides greater stability, larger frictional resistance, and larger resisting moments. In soil-reinforced SRWs, heavier and wider units may permit a greater vertical spacing between layers of geosynthetic

Water-Cement Ratio
Water-Cement Ratio is a key factor in the design and proportioning of concrete mixes. It is the relationship between the weight of water and the weight of cement in the mix. It can be determined by dividing the weight of water in the mix by the weight of cement. Typical values will run between 0.4 and 0.

Weep Pipe
A pipe that connects to behind the retaining wall drainage allowing collected water to drain

Well Graded Gravel (GW)
Are aggregate materials that have a full range of sizes from dust to the largest rock

Retaining Wall Glossary