Geotechnical Engineering · Engineering Glossary
Soil compaction is the process of mechanically increasing the density of soil by reducing void space, improving its load-bearing capacity, reducing settlement potential, and increasing resistance to erosion. Compaction is specified as a percentage of maximum dry density determined by a Proctor test and is verified by a compaction testing agency during construction.
The geotechnical engineer specifies the required compaction level for fills and subgrades — typically 90–95% of the modified Proctor maximum dry density for structural fills under pavements and foundations. The contractor uses rollers, vibratory plates, or rammers to achieve the specified density, and a testing agency performs nuclear density gauge or sand cone tests to verify compliance. Over-compaction can be a problem in native soils adjacent to foundations; under-compaction leads to settlement and pavement failure. Compaction testing is particularly important in earthwork for large grading projects, parking lots, and structural fill under slabs-on-grade. Apex Grid coordinates with the geotechnical engineer and testing agency on all civil and grading projects.
Apex Grid Engineering maintains this glossary as a resource for architects, contractors, developers, and property owners who encounter unfamiliar engineering terminology on their projects.
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