Civil Engineering Glossary

Granular materials such as sand, gravel, and crushed stone used as a component of concrete and asphalt. Aggregates constitute the bulk of these mixtures and significantly influence strength, workability, and durability.

The maximum pressure that soil or rock can sustain under a foundation without experiencing shear failure or excessive settlement. It is a critical parameter in foundation design determined through field tests and analytical methods.

The mechanical process of increasing soil density by reducing air voids, typically using rollers, rammers, or vibrators. Proper compaction improves soil strength, reduces permeability, and minimizes future settlement.

The degree to which a structural element is displaced from its original position under load. Deflection must be limited to prevent structural damage, aesthetic concerns, and discomfort to occupants, and is governed by building codes.

Treated or untreated wastewater that is discharged from a treatment plant, sewer, or industrial outfall into the environment. Environmental regulations set limits on effluent quality parameters such as BOD, suspended solids, and contaminant concentrations.

Temporary molds or structures used to contain and shape freshly poured concrete until it gains sufficient strength to support itself. Formwork can be made from timber, steel, aluminum, or plastic and represents a significant portion of concrete construction costs.

A fluid mixture of cement, water, and sometimes sand or admixtures used to fill voids, seal joints, and consolidate soil or rock. In construction, it is commonly used to fill the cores of masonry blocks and anchor bolts into concrete.

The rate of change in hydraulic head per unit distance in the direction of groundwater flow: $i = \frac{\Delta h}{L}$. It drives the movement of water through soil and is a key parameter in Darcy's Law for calculating seepage and groundwater flow.

A material property indicating that the material has identical mechanical and physical properties in all directions. Steel is generally considered isotropic, while wood and layered soils are anisotropic, having different properties along different axes.

A connection point between two or more structural members, or a deliberately formed gap in concrete, masonry, or pavement. Joints may be designed to transfer forces (structural joints) or to accommodate movement from thermal expansion, shrinkage, or settlement.

The wedge-shaped stone or element at the apex of an arch that locks the other pieces in place and bears the compressive forces from both sides. In modern engineering, the term refers to any critical element whose removal would cause structural failure.

An embankment or wall, typically earthen, built along a waterway to prevent flooding of adjacent land. Levees confine river flows within the channel during high water events and are critical components of flood control systems.

A measure of a material's stiffness, defined as the ratio of stress to strain within the elastic (linear) region of the stress-strain curve: $E = \frac{\sigma}{\epsilon}$. Also known as Young's Modulus, it indicates how much a material deforms under a given load.

The imaginary line or plane within a beam cross-section where there is neither tension nor compression during bending. Material above the neutral axis is in compression and material below is in tension (for a simply supported beam with downward loads).

The soil, rock, or other material lying above a specific geological feature, foundation level, or stratum of interest. Overburden pressure increases with depth and affects soil behavior, consolidation, and the design of deep excavations and tunnels.

An instrument used to measure pore water pressure within soil, rock, or concrete structures. Piezometers are installed in boreholes or embedded in dams and embankments to monitor groundwater levels and assess the stability of earthen structures.

A state in which upward seepage pressure in saturated soil equals the downward gravitational force, causing the soil to lose all effective stress and behave like a liquid. Also known as quicksand, it represents a critical failure condition in excavations and dams.

Steel reinforcing bars embedded in concrete to provide tensile strength. Rebar is available in various diameters and grades, and is placed according to engineering calculations to resist bending, shear, and temperature-induced stresses in concrete structures.

The internal stress ($\tau$) that acts parallel to the cross-section of a structural element, caused by forces that tend to slide one portion of the material past another. Calculated as $\tau = \frac{V}{A}$ for average shear stress. Shear stress is critical in the design of beams, bolted connections, and soil stability analysis.

A survey that determines the positions and elevations of natural and man-made features on the surface of the Earth. The resulting topographic map with contour lines is essential for site planning, drainage design, earthwork calculations, and foundation layout.

The maximum stress that a material can withstand before fracture or failure under tension, compression, or shear. In structural design, ultimate strength is used with load and resistance factors to ensure adequate safety margins.

The ratio of the volume of voids to the volume of solids in a soil sample: $e = \frac{V_v}{V_s}$. It is a key parameter in soil mechanics that influences permeability, compressibility, shear strength, and the behavior of soil under loading.

A small opening in a retaining wall, foundation wall, or masonry structure that allows trapped water to drain out, relieving hydrostatic pressure that could otherwise cause structural damage or instability.

The stress level ($\sigma_y$) at which a material begins to deform permanently (plastically). Below $\sigma_y$, the material returns to its original shape when the load is removed. Yield strength is a primary design parameter for steel structures.

A theoretical curve on a compaction diagram representing the maximum dry density achievable at a given water content if all air were expelled from the soil. No compaction effort can achieve densities above this line, making it an upper bound reference in compaction testing.