Subgrade

Layers in the construction of a mortarless pavement: A.) Subgrade B.) Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand

Section through railway track and foundation showing the sub-grade

In transport engineering, subgrade is the native material underneath a constructed road,^[1] pavement or railway track (US: railroad track). It is also called formation level.

The term can also refer to imported material that has been used to build an embankment.

Construction[edit]

Subgrades are commonly compacted before the construction of a road, pavement or railway track

^ http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance highwaysmaintenence.com

Investigation and
instrumentation

Field (in situ)

Types	Clay Silt Sand Gravel Peat Loam Loess
Properties	Hydraulic conductivity Water content Void ratio Bulk density Thixotropy Reynolds' dilatancy Angle of repose Friction angle Cohesion Porosity Permeability Specific storage Shear strength Sensitivity

Structures (Interaction)

Natural features	Topography Vegetation Terrain Topsoil Water table Bedrock Subgrade Subsoil
Earthworks	Shoring structures Retaining walls Gabion Ground freezing Mechanically stabilized earth Pressure grouting Slurry wall Soil nailing Tieback Land development Landfill Excavation Trench Embankment Cut Causeway Terracing Cut-and-cover Cut and fill Fill dirt Grading Land reclamation Track bed Erosion control Earth structure Expanded clay aggregate Crushed stone Geosynthetics Geotextile Geomembrane Geosynthetic clay liner Cellular confinement Infiltration
Foundations	Shallow Deep

Forces	Effective stress Pore water pressure Lateral earth pressure Overburden pressure Preconsolidation pressure
Phenomena/problems	Permafrost Frost heaving Consolidation Compaction Earthquake Response spectrum Seismic hazard Shear wave Landslide analysis Stability analysis Mitigation Classification Sliding criterion Slab stabilisation Bearing capacity