A–Z glossary

239 civil engineering terms in plain words.

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

A

Abutment: End support of a bridge or arch that holds back the approach fill and carries the span.
Activated sludge: Biological wastewater treatment in which aerated microbes break down organic matter and are settled and recycled.
Admixture: A chemical added in small doses to change fresh or hardened concrete, such as a plasticiser or retarder.
Aggregate: Sand, gravel or crushed stone that forms most of the volume of concrete and road layers.
Air entrainment: Deliberately adding tiny air bubbles to concrete to resist freeze-thaw damage.
Allowable bearing pressure: The pressure a foundation may apply, limited by both shear safety and settlement.
Anchorage: The device or bar length that transfers force from a tendon or bar into concrete.
Apron: Paved area at an airport where aircraft park, load and refuel.
Aquifer: A water-bearing layer of soil or rock that can yield useful quantities of groundwater.
Arch: A curved member that carries load mainly in compression to its supports.
Atterberg limits: Water contents marking changes in the behaviour of fine soil: liquid, plastic and shrinkage limits.

B

Backsight: In levelling, the first staff reading taken after setting up the instrument, on a point of known level.
Backwashing: Reversing flow through a filter to clean its media.
Ballast: Crushed stone under and around railway sleepers that spreads load and drains water.
Bar bending schedule: A table listing every reinforcing bar's shape, size, length and number.
Barrage: A low river structure with gates that raises water level for diversion into canals.
Base course: Pavement layer below the surface layers that spreads load to the sub-base.
Base isolation: Separating a building from ground shaking using flexible bearings.
Beam: A member that carries load mainly by bending.
Bearing (bridge): A device that transfers load from deck to substructure while allowing controlled movement.
Bearing capacity: The pressure at which soil under a foundation fails in shear.
Bench mark: A fixed point of known reduced level used as a reference for levelling.
Bending moment: The internal turning effect at a section of a member.
Berm: A horizontal step in a slope or embankment.
Bill of quantities: A list of work items with their measured quantities, used for pricing and payment.
BIM: Building Information Modelling: shared digital models carrying geometry and data.
Bitumen: A black, sticky binder from petroleum refining used in asphalt roads.
BOD: Biochemical oxygen demand: oxygen used by microbes to break down organic matter, usually over 5 days at 20 °C.
Bored pile: A pile formed by drilling a hole and filling it with reinforcement and concrete.
Box girder: A hollow closed-section girder that is stiff in bending and twisting.
Breakwater: A structure that shelters a harbour from waves.
Buckling: Sudden sideways failure of a slender compression member.
Bulking of sand: Increase in volume of damp sand compared with dry sand.
Buttress dam: A dam with a sloping face supported by a series of buttresses.

C

Caisson: A hollow box or cylinder sunk into place to form a foundation or breakwater.
Camber: The slight cross slope of a road surface that sheds rainwater.
Cantilever: A member fixed at one end and free at the other.
Capacity (traffic): The maximum flow a road or lane can carry under prevailing conditions.
Cash flow: The timing of money paid out and received over a project.
CBR: California Bearing Ratio: a penetration test that rates subgrade and granular material strength.
Centroid: The geometric centre of an area.
Change point: In levelling, a point with both a foresight and a backsight.
Characteristic strength: The strength below which only a small specified fraction of test results is expected to fall.
Chlorination: Disinfecting water by adding chlorine.
Clash detection: Automatic finding of conflicts between elements in combined BIM models.
Coagulation: Adding chemicals so fine particles in water clump together and settle.
Cofferdam: A temporary enclosure that keeps water out of a work area.
Cohesion: The part of soil shear strength that does not depend on normal stress.
Column: A vertical member carrying mainly compression.
Compaction: Pressing soil or concrete to remove air and increase density.
Composite construction: Steel and concrete connected to act together.
Consolidation: Slow settlement of saturated clay as water is squeezed out under load.
Contingency: An allowance in a budget or schedule for uncertain events.
Contour: A line joining points of equal elevation on a map.
Corbel: A short cantilever bracket projecting from a column or wall.
Cost performance index: Earned value divided by actual cost.
Cover (concrete): The thickness of concrete between a bar and the nearest surface.
CPM: Critical path method for scheduling.
Creep: Slow growth of strain under a sustained load.
Critical path: The longest chain of dependent activities, which sets the project duration.
Cross-drainage work: A structure where a canal crosses a stream, such as an aqueduct or syphon.
Culvert: A small structure carrying water under a road or railway.
Curing: Keeping concrete moist and warm enough for cement to hydrate.
Cut-and-cover: Building a tunnel in an open trench and backfilling over it.

D

Dead load: The weight of the structure itself and permanent fixtures.
Deflection: Movement of a structural member under load.
Delta: In irrigation, the total depth of water a crop needs over its base period.
Design-build: A delivery model in which one party designs and builds.
Development length: The bar length needed to transfer its force into concrete by bond.
Dewatering: Lowering groundwater to allow dry excavation.
Differential settlement: Unequal settlement between parts of a structure.
Disinfection: Killing pathogens in water, usually with chlorine or UV.
Dowel bar: A smooth bar across a concrete pavement joint that transfers load while allowing movement.
Dredging: Removing sediment from the bed of a waterway.
Drip irrigation: Delivering water slowly to the root zone through emitters.
Ductility: Ability to deform well beyond yield without losing strength.
Duty: In irrigation, the area a unit discharge can irrigate over a base period.

E

Earned value: The budgeted cost of the work actually completed.
Earth pressure: Lateral pressure exerted by soil on a wall.
Effective length: Length of an equivalent pin-ended column with the same buckling load.
Effective stress: Total stress minus pore water pressure; it controls soil strength.
Efflorescence: White salt deposits on masonry surfaces.
EIA: Environmental Impact Assessment.
Embankment: A raised bank of compacted fill.
Energy dissipator: A structure below a spillway that destroys the energy of falling water.
EPC: Engineering, procurement and construction contract.
Equilibrium: State in which forces and moments on a body balance.
Escalation: Increase in prices over time allowed for in an estimate.
Expansion joint: A gap that lets a structure move with temperature.
Extension of time: Contractual extra time granted for delays the contractor is not responsible for.

F

Factor of safety: Ratio of capacity to demand.
Falsework: Temporary structure supporting formwork and fresh concrete.
Fatigue: Failure under many repeated loads below the static strength.
FIDIC: International federation of consulting engineers and its standard contract forms.
Filter (geotechnical): A graded layer that lets water pass but holds soil particles back.
Fineness modulus: An index of the coarseness of an aggregate from sieve analysis.
Flakiness index: Share by mass of aggregate particles thinner than a set fraction of their size.
Flexible pavement: A pavement of bituminous and granular layers.
Float: Time an activity can slip without delaying the project.
Flow net: A grid of flow lines and equipotentials used to analyse seepage.
Fly ash: Fine ash from coal power stations used in cement and concrete.
Footing: A spread foundation under a column or wall.
Foresight: In levelling, a staff reading on a point whose level is wanted, the last before moving.
Formation: The prepared surface on which a road or rail structure is built.
Formwork: Temporary moulds that shape concrete until it hardens.
Freeboard: Height between maximum water level and the top of a dam or channel bank.
Friction pile: A pile that carries load mainly by friction along its shaft.
Froude number: Ratio of flow inertia to gravity; above 1 flow is supercritical.

G

Gantt chart: A bar chart showing activities against time.
Gauge (railway): Distance between the inner faces of the rails.
Geotextile: A permeable fabric used to separate, filter or reinforce soil.
GGBS: Ground granulated blast-furnace slag, used as a cement replacement.
Girder: A main beam, usually large, carrying other members.
GNSS: Global navigation satellite systems used for positioning.
Grade separation: Separating crossing traffic streams at different levels.
Gradient: Slope expressed as a ratio or percentage.
Gravity dam: A dam that resists water pressure by its own weight.
Grout: A fluid mix of cement and water, sometimes with sand, used to fill voids.
Gully trap: A trap outside a building collecting waste water from kitchens and baths.

H

Head (hydraulic): Energy of water per unit weight, expressed as a height.
Honeycombing: Voids in hardened concrete from poor compaction.
Hydraulic jump: Sudden rise in water level where fast shallow flow becomes slow deep flow.
Hydraulic radius: Flow area divided by wetted perimeter.
Hydrograph: A graph of river flow against time.

I

Imposed load: Load from occupancy, furniture and movable items.
Infiltration: Entry of rainwater into the soil.
Influence line: A graph of a response at one point as a unit load moves along a structure.
Intake: A structure that draws water from a source.
Interchange: A grade-separated junction with ramps.
Invert: The lowest inside level of a pipe or channel.
Isolated footing: A footing under a single column.

J

Joint (rock): A natural fracture in rock without visible movement.

L

Lap splice: Overlapping two bars to transfer force between them.
Levelling: Measuring height differences between points.
Lime: Calcium oxide or hydroxide used in mortar and soil stabilisation.
Limit state: A condition beyond which a structure no longer meets a design requirement.
Lining (canal): An impervious layer on a canal bed that cuts seepage.
Lintel: A beam over a door or window opening.
Liquefaction: Loss of strength of loose saturated sand during shaking.
Live load: Common name for imposed load.
Load path: The route by which loads travel through a structure to the ground.
Longitudinal section: A profile along the centre line of a road, railway or pipe.

M

Manning's n: Roughness coefficient in the Manning equation.
Mass-haul diagram: A plot of cumulative earthwork volume along a route.
Modulus of elasticity: Ratio of stress to strain in the elastic range.
Moment distribution: An iterative method for analysing indeterminate beams and frames.
Moment of inertia: Second moment of area; measures a section's bending stiffness.

N

NATM: New Austrian Tunnelling Method.
Neutral axis: The line in a bent section where strain is zero.
Non-destructive testing: Testing without damaging the structure, such as rebound hammer or ultrasonic tests.

O

Overhead tank: An elevated water tank providing pressure by gravity.

P

Passenger car unit: An equivalence factor converting vehicles to cars.
Pavement: The layered structure of a road, runway or yard.
Penstock: A pressure pipe carrying water to turbines.
Permeability: How easily water flows through soil or rock.
PERT: Program Evaluation and Review Technique.
Pier: An intermediate support of a bridge.
Pile: A long slender foundation member carrying load deep into the ground.
Pile cap: A block joining the heads of a pile group.
Planned value: Budgeted cost of work scheduled up to a date.
Plinth: The part of a building between ground and floor level.
Plumbing stack: A vertical drainage pipe collecting waste from floors.
Poisson's ratio: Ratio of lateral to axial strain.
Pore water pressure: Pressure of water in the voids of soil.
Portal frame: A rigid frame of columns and rafters, common in sheds.
Post-tensioning: Stressing tendons after concrete hardens.
Pozzolana: A material that reacts with lime to form cementing compounds.
Pre-tensioning: Stressing strands before concrete is cast around them.
Precast: Concrete cast away from its final position and then installed.
Prestress loss: Reduction in prestress force over time.
Prime coat: Low-viscosity bitumen sprayed on a granular base before asphalt.
Prismoidal formula: An earthwork volume formula exact for prismoids.
Punching shear: Shear failure of a slab around a concentrated load or column.

Q

Quantity surveying: Measuring and valuing construction work.

R

Radius of gyration: √(I/A), a measure of a section's resistance to buckling.
Raft foundation: A single slab foundation under a whole building.
Rapid sand filter: A filter at high rate cleaned by backwashing.
Rate analysis: Breaking a unit of work into resources to price it.
Rebound hammer: A device estimating concrete surface hardness.
Reduced level: Height of a point above a datum.
Reinforcement: Steel bars or mesh embedded in concrete.
Resource levelling: Rescheduling activities within float to smooth resource demand.
Retaining wall: A wall that holds back soil.
Rigid pavement: A pavement with a concrete slab.
Rip-rap: Loose large stones protecting a slope from erosion.
Risk register: A record of project risks, ratings, owners and responses.
Rock bolt: A steel bar anchored in rock to support an excavation.
RQD: Rock quality designation, the share of core in sound pieces of at least 100 mm.
Runoff: Rainfall that flows over land to streams.
Rutting: Permanent depressions in wheel paths of a flexible pavement.

S

Sanitary landfill: An engineered site for disposing of waste with liners and cover.
Schedule performance index: Earned value divided by planned value.
Section modulus: I divided by the distance to the extreme fibre.
Sedimentation: Settling of suspended particles under gravity.
Segregation: Separation of coarse aggregate from mortar in fresh concrete.
Seismic zone: A region grouped by expected earthquake intensity.
Septic tank: A watertight tank that settles and partly digests household sewage.
Service reservoir: A tank balancing supply and demand in a distribution network.
Settlement: Downward movement of a foundation.
Shear force: The internal force at a section acting across it.
Shear wall: A wall designed to resist lateral forces.
Shotcrete: Sprayed concrete.
Sight distance: The length of road visible to a driver.
Sleeper: A beam under rails that holds gauge and spreads load.
Slenderness ratio: Effective length divided by radius of gyration.
Slump: Drop of fresh concrete in the slump test, a measure of workability.
Soft storey: A storey much less stiff than those above it.
Spillway: A structure that passes flood water safely past a dam.
Standard penetration test: A field test counting blows to drive a sampler 300 mm.
Stilling basin: A basin that contains a hydraulic jump below a spillway.
Stirrup: A bar loop resisting shear in a beam.
Strain: Change in length divided by original length.
Stress: Force per unit area.
Subgrade: The natural or fill soil at the bottom of a pavement.
Superelevation: Banking of a road on a curve.
Surge tank: A tank that absorbs pressure surges in a water conductor system.

T

Tack coat: A light bitumen coat bonding two asphalt layers.
Tendon: A prestressing steel element.
Tie bar: A deformed bar across a longitudinal pavement joint holding slabs together.
Time of concentration: Travel time of runoff from the farthest point to the outlet.
Total station: An instrument measuring angles and distances electronically.
Trap: A water-filled bend preventing sewer gas from entering a building.
Traverse: A series of connected survey lines with measured angles and lengths.
Truss: A framework of members joined in triangles.
Tunnel boring machine: A machine that excavates a tunnel by a rotating cutterhead.
Turbidity: Cloudiness of water from suspended particles.

U

Unit hydrograph: Runoff hydrograph from one unit of effective rain over a set duration.
Uplift: Upward water pressure under a dam or structure.

V

Variation: A change to the work instructed under a contract.
Vent pipe: A pipe that admits air to drainage and protects trap seals.
Void ratio: Volume of voids divided by volume of solids.

W

Water hammer: A pressure surge when flow in a pipe stops suddenly.
Water-cement ratio: Mass of water divided by mass of cement in a mix.
Waterlogging: Rise of the water table into the root zone.
Weir: A barrier over which water flows, used to raise level or measure flow.
Well foundation: A large caisson sunk to carry a bridge pier in a riverbed.
Work breakdown structure: Hierarchical breakdown of project scope into work packages.
Workability: Ease of placing and compacting fresh concrete.

Y

Yield strength: Stress at which steel begins to deform plastically.