NICET CMT Soils key terms

The water contents marking the boundaries between the solid, semisolid, plastic, and liquid states of a fine-grained soil, reported as shrinkage limit, plastic limit, and liquid limit.

The water content at which a remolded fine-grained soil closes a standard 12.7 mm groove under 25 blows of the Casagrande cup, or the equivalent penetration using a fall cone.

The lowest water content at which a soil thread can be rolled to 3.2 mm diameter without crumbling, marking the transition from semisolid to plastic behavior.

The numerical difference between liquid limit and plastic limit, expressing the range of water content over which the soil remains plastic; higher values indicate more clay-like, compressible behavior.

The Unified Soil Classification System groups soils by grain-size distribution, plasticity, and organic content into symbols such as GW, SP, CL, and CH, used widely in specifications and design.

A soil grouping system using groups A-1 through A-7 with a group index, based on gradation, liquid limit, and plasticity index, historically used for highway subgrade evaluation.

A numerical value computed from percent passing the No. 200 sieve, liquid limit, and plasticity index that rates how much a granular or silty-clayey soil is weakened as a subgrade material.

The distribution of particle sizes in a soil, determined by sieve analysis for coarse particles and hydrometer analysis for fines, and plotted as percent finer versus particle size.

A laboratory procedure that shakes a dried soil sample through a stack of standard sieves to determine the mass retained on each sieve and the percent passing each size.

A sedimentation test that measures the density of a soil-water suspension over time to estimate the size distribution of particles finer than the No. 200 sieve, based on Stokes' law.

The ratio of the particle diameter at 60 percent finer to the diameter at 10 percent finer (D60/D10), indicating how widely the grain sizes in a soil are spread.

A shape index computed as D30 squared divided by the product of D60 and D10, used with the coefficient of uniformity to judge whether a gradation curve is well graded.

The fraction of a soil sample finer than the 0.075 mm sieve, used to separate coarse-grained from fine-grained soils and to compute group index and fines content.

A laboratory compaction test using a 2.5 kg rammer dropped 305 mm in three layers in a 944 cm3 mold, producing a lower maximum dry density and higher optimum moisture content than modified effort.

A higher-energy laboratory compaction test using a 4.5 kg rammer dropped 457 mm in five layers, producing a higher maximum dry density and lower optimum moisture content than standard effort.

A plot of dry density versus molding water content from a laboratory compaction test, typically a smooth hump whose peak defines maximum dry density and optimum moisture content.

The peak dry unit weight reached on a compaction curve for a given compaction effort, serving as the reference value against which field density is compared.

The molding water content at which a given compaction effort produces the maximum dry density for a soil; field moisture is usually controlled near this value.

A reference curve on a compaction plot showing the dry density at 100 percent saturation for each water content; no compaction result can plot to the right of it.

Field dry density expressed as a percentage of the laboratory maximum dry density for the same soil and effort, the usual acceptance criterion in compaction specifications.

A field density method in which a hole is excavated, the removed soil weighed, and the hole volume measured by calibrated sand poured from a cone apparatus.

A field device that estimates wet density and water content by counting radiation transmitted or scattered through the soil, requiring regular calibration and safety handling.

The in-place dry unit weight of compacted soil, computed from field wet density and measured water content, and compared to laboratory maximum dry density.

The mass of water in a soil sample expressed as a percentage of the oven-dry mass of solids, determined by drying at 110 plus or minus 5 degrees Celsius.

The fraction of the void volume in a soil occupied by water, expressed as a percentage; it links water content, void ratio, and specific gravity.

The loose or compacted depth of a single placed layer of fill; it must be limited so the specified compaction effort can reach the full depth of the layer.

A field inspection in which a loaded truck or roller passes over a prepared subgrade to reveal soft spots, pumping, or unstable areas before placing the next layer.

Clearing, stripping, grading, and compacting the natural ground or embankment surface to the specified lines, grades, and density before pavement or fill is placed.

A constructed fill of compacted soil or rock that raises the grade for a roadway, railway, or structure, built in controlled layers to meet density and slope requirements.

Soil or granular material placed and compacted against a structure, wall, or pipe after excavation, often under restricted access that demands small equipment and careful lift control.

The inspection process of checking moisture, lift thickness, equipment passes, and field density against specification limits so that each layer achieves the required relative compaction.

The process of testing and accepting an off-site soil or aggregate source for use as fill, including sampling, classification, and compaction testing before material is hauled to the project.

A written scheme defining sample locations, depths, frequencies, sizes, and handling methods so that test results represent the material and satisfy specification requirements.

A portion of material collected so that its properties reflect the larger mass from which it was taken, avoiding segregated, contaminated, or non-typical material.

Reducing a bulk field sample to test-size portions by riffle splitter, quartering, or mechanical divider so each subsample retains the same gradation and properties.

A documented record of who collected, transported, stored, and tested a sample, and when, preserving traceability and defensibility of results for acceptance or dispute resolution.

A formal record of test results that identifies the sample, test method and standard, equipment, date, technician, calculations, and any deviations or limitations affecting interpretation.

The determination of whether measured field or laboratory results meet the contract's stated acceptance criteria, such as minimum relative compaction and moisture range.

Protecting samples from moisture change, contamination, and physical disturbance between collection and testing, typically by sealed containers and prompt transport to the laboratory.