PE Geotechnical key terms

A field test in which a split-spoon sampler is driven into soil by a hammer, and the blow count for the final 12 inches is recorded as an index of density and strength.

A field test that pushes an instrumented cone into the ground at a constant rate and continuously measures tip resistance and sleeve friction to characterize soil layering and strength.

A written record of a subsurface exploration hole showing depths, soil and rock descriptions, sample locations, groundwater observations, and test results used to build a site model.

A thick-walled, split-barrel tube driven into soil to retrieve a disturbed sample while simultaneously providing the blow counts used in the Standard Penetration Test.

A cased borehole with a screened interval installed to measure the depth to groundwater and collect water samples over time at a specific subsurface zone.

A geophysical method that generates seismic waves at the surface and measures arrival times at sensors to estimate the depth and velocity of subsurface layers.

The degree to which a granular soil's in-place void ratio approaches its loosest or densest possible state, expressed as a percentage and used to judge compactness and liquefaction susceptibility.

The water contents marking the boundaries between solid, semisolid, plastic, and liquid states of a fine-grained soil, used to classify and predict its behavior.

The numerical difference between a soil's liquid limit and plastic limit, indicating the range of water content over which the soil behaves plastically.

A laboratory test that loads a saturated soil specimen incrementally in a confined ring and measures settlement over time to determine compressibility and consolidation characteristics.

A soil parameter describing how quickly excess pore water pressure dissipates and consolidation progresses, used with drainage path length to estimate settlement rate over time.

The intergranular stress carried by a soil skeleton, equal to total stress minus pore water pressure; it controls soil strength, compression, and volume change.

The pressure exerted by water within the voids of a soil mass, which reduces effective stress and can change rapidly during loading, unloading, or shearing.

A model stating that shear failure occurs when shear stress on a plane reaches a value defined by cohesion plus normal stress times the tangent of the friction angle.

The maximum resistance of a soil to sliding along internal planes, governed by interparticle friction and cohesion and used to evaluate bearing capacity, slopes, and walls.

A measure of the internal sliding resistance between soil particles, expressed in degrees and used with normal stress to compute the frictional component of shear strength.

The shear strength component of a soil that exists independent of normal stress, arising from interparticle attraction and cementation, especially in clays.

The ability of a soil to transmit water through its connected voids, quantified by hydraulic conductivity and controlling seepage, drainage, and consolidation rates.

Loss of shear strength in saturated loose granular soil when earthquake shaking or other rapid loading raises pore water pressure until effective stress approaches zero.

A laboratory procedure that compacts soil at several water contents to determine the maximum dry unit weight and optimum water content for a given compaction energy.

A clay-rich soil that swells when wetted and shrinks when dried due to changes in adsorbed water, capable of causing significant foundation and pavement distress.

The maximum pressure a foundation soil can support without shear failure or excessive settlement, commonly computed from soil strength and footing geometry.

A foundation such as a spread footing or mat that transfers loads to soil near the ground surface, generally at a depth less than its width.

A foundation element such as a driven pile, drilled shaft, or caisson that carries load to deeper strata through skin friction and end bearing.

The resistance developed along the shaft of a pile or drilled shaft as it moves relative to surrounding soil, contributing to the foundation's axial capacity.

The resistance provided at the base of a deep foundation as it bears against or penetrates a stronger soil or rock layer.

A field test that applies axial or lateral loads to a pile and measures its movement to verify capacity and load-transfer behavior for design or acceptance.

Downward movement of a foundation or ground surface caused by compression of soil under load, including immediate, consolidation, and secondary components.

Unequal settlement across a structure's supports, which can distort and crack structural elements even when total settlement is modest.

Time-dependent settlement of saturated fine-grained soil as excess pore water drains and the soil skeleton compresses under sustained load.

The horizontal pressure that soil exerts on a retaining structure, varying with wall movement, soil strength, drainage, and surcharge conditions.

The minimum lateral pressure on a retaining wall when the wall yields away from the soil enough to mobilize the soil's shear resistance.

The maximum lateral resistance mobilized when a wall is pushed into the soil, with the soil wedge failing as it is compressed and sheared upward.

The lateral pressure exerted by soil on a wall that does not move or yield, corresponding to zero horizontal strain in the soil mass.

A structure built to hold back soil and maintain an elevation change, designed for earth pressure, surcharge, water, and stability against sliding, overturning, and bearing failure.

The evaluation of whether a natural or constructed slope can resist sliding or failure, usually expressed as a factor of safety from limit-equilibrium analysis.

Mechanical densification of soil by removing air voids through rolling, tamping, or vibration, improving strength and reducing settlement and permeability without significantly changing water content.

The ratio of resisting forces or moments to driving forces or moments in a stability analysis, indicating how much margin exists before failure.

Temporary removal or lowering of groundwater by pumping or drains to allow dry, stable excavation and to reduce uplift and seepage pressures.

Polymeric sheets, grids, or strips placed in soil to improve tensile strength, drainage, separation, or filtration in embankments, walls, and pavements.