AMIE Section B Civil key terms

The maximum pressure a soil or rock mass can carry beneath a foundation without failing in shear or settling excessively. It is usually expressed as a pressure and compared with the applied foundation pressure.

The safe foundation pressure obtained by dividing the ultimate bearing capacity by a factor of safety, or by limiting settlement to a tolerable value. The lower of the two criteria governs design.

A number greater than one by which calculated strength or resistance is divided, or by which loads are multiplied, to provide margin against uncertainty, variability and unforeseen conditions.

The resistance of a soil to sliding along internal planes, governed mainly by friction between particles and any cohesion or cementation. It controls bearing capacity, slope stability and lateral earth pressure.

The component of soil shear strength that is independent of normal stress, arising from inter-particle attraction or cementation. It is often taken as zero for clean sands and as a drained parameter of zero for long-term sand design.

A measure of the frictional resistance between soil particles, expressed in degrees and used with normal stress to compute the frictional part of shear strength. Dense angular soils have higher values than loose rounded ones.

The downward movement of a foundation caused by compression of the supporting ground. It is divided into immediate, consolidation and secondary components, and differential settlement is more damaging than uniform movement.

The time-dependent volume reduction of a saturated soil as water is squeezed out of its voids under sustained loading. It is the dominant settlement mechanism in soft clays and is analysed using pressure-voids ratio curves.

The intergranular stress that governs soil strength and compression, equal to total stress minus pore water pressure. Changes in effective stress, not total stress, control most soil behaviour.

The pressure of water filling the voids of a soil. Above the water table it is usually negative due to capillary action; below it is positive and increases with depth, reducing effective stress.

Loss of soil strength when saturated loose granular material is shaken and pore pressures rise until effective stress approaches zero. The ground then behaves like a fluid, causing settlement, floatation of buried structures and slope failure.

An in-situ test in which a split sampler is driven into the ground by a falling hammer and the blow count for a set penetration is recorded. The blow count is corrected and correlated with soil density and strength.

An in-situ test that pushes a cone into the ground at a constant rate and measures tip resistance and sleeve friction. Results give a near-continuous profile of soil stratigraphy and strength parameters.

The horizontal thrust exerted by retained soil on a wall. It varies from active pressure, when the wall yields outward, through at-rest pressure, to passive pressure, when the wall is pushed into the soil.

A structure built to hold back soil or other material where a change in ground level is required. It must resist overturning, sliding, bearing failure and internal structural forces, with drainage provided behind it.

The assessment of whether a natural or engineered slope can resist sliding along a potential failure surface. It is expressed as a factor of safety against shear failure and is reduced by water and excavation.

A deep foundation element that transfers load to deeper, stronger strata by end bearing, shaft friction or both. Piles are used where shallow footings would settle excessively or where scour or uplift must be resisted.

A design condition concerning safety against collapse or structural failure, such as rupture, buckling or bearing failure, when the structure is loaded to its maximum. It is checked separately from serviceability conditions.

A design condition concerning the structure's fitness for normal use, covering deflection, cracking, vibration and settlement rather than collapse. Exceeding it impairs function or appearance but not safety.

A composite material in which steel bars carry tensile forces within concrete that is strong in compression. The two materials act together because of bond and because their thermal expansion is similar.

The value of a material property below which a stated small proportion of test results is expected to fall, usually taken as the five percent fractile. It forms the basis for partial factors in limit state design.

A multiplier applied to loads or material strengths in limit state design to account for uncertainty and variability. Design values are obtained by applying the factor to the characteristic value.

The thickness of concrete between the outer surface of the embedded steel and the nearest exposed concrete face. It protects reinforcement from corrosion and fire and ensures bond and adequate anchorage.

The ability of a structure or material to maintain acceptable performance over its design life under its exposure conditions. It depends on mix design, cover, detailing and protection against chemical attack and weathering.

The internal force acting across a section of a beam or slab that tends to slide one part past another. Its magnitude at a section equals the sum of transverse loads on one side of that section.

The internal moment at a section of a structural member caused by loads acting at a distance. It produces bending stresses, tensile on one face and compressive on the other, and is plotted as a diagram along the member.

The displacement of a structural member from its unloaded position under load. It is checked at the serviceability limit state because excessive deflection can crack finishes, pond water or cause discomfort.

Sudden lateral instability of a slender member under compressive load, occurring at a load below the material's crushing strength. It depends on member length, end restraint and bending stiffness.

A framework of straight members connected at joints and arranged in triangles so that loads are carried mainly as axial tension or compression. Ideal analysis assumes pin joints and loads applied only at nodes.

The change in total head of groundwater per unit distance along the flow path. It drives seepage through soil and, where it becomes critical, can cause piping or boiling at an excavation base.

The capacity of a soil or rock to transmit water through its connected voids, quantified by a coefficient of permeability. It governs seepage rates, drainage design and the rate of consolidation settlement.

The densification of soil by mechanical means, reducing air voids and increasing density and strength. It is specified by a target dry density and moisture content determined from a laboratory compaction test.

The moisture contents marking the boundaries between the solid, plastic and liquid states of a fine-grained soil. They are used to classify clays and silts and to predict their compressibility and workability.

The mass of water divided by the mass of cement in a concrete mix. It controls strength and durability: lower ratios give stronger, less permeable concrete but reduce workability.

The ease with which fresh concrete can be mixed, placed, compacted and finished without segregation. It is commonly assessed by the slump test and must be balanced against strength requirements.

Erosion of bed material around bridge piers, abutments or embankments by flowing water. It can remove support and cause collapse, so foundations are taken below the estimated depth of scour.

A line on a map joining points of equal elevation above a datum. The spacing of contours indicates ground steepness, and their shape reveals ridges, valleys and drainage patterns for route and site planning.