🚜 To prepare ground ⬇️ Lower quality 🛣️ Base layer

subgrade

7.8

The ground layer prepared to support a road or pavement

noun
/ˈsʌbˌɡreɪd/

Specialized

: subrasante

Before paving, the contractor needed to evaluate the quality of the subgrade to prevent future issues.

Examples

The engineers assessed the subgrade to ensure it could adequately support the new road.
His expertise includes rail fasteners, ballast, and subgrades.

Academic text (2001)
Randomly reinforced stabilized soils may be used for construction projects such as subgrades of highways and pavement of roads.

Academic text (2016)
Chauhan et al. argued that randomly distributed fiber, when used as insertion in highway subgrades, can produce high performance in the stabilization of weak roads.

Academic text (2016)
During the construction of the railway, it was essential to properly compact the subgrade before laying the tracks.

Synonyms

roadbed

vssubgrade

Specialized

2 6.7

A layer of material under a road or train track that supports it

is the layer prepared to support roads, railways, and pavements

substratum

vssubgrade

1 8.9

A layer under something that forms its base, like rock under ruins

is limited to the prepared layer that supports transport surfaces

undersoil

vssubgrade

Specialized

6.7

A layer of soil below the topsoil and above the rock under the ground

is the prepared support layer constructed for roads, railways, or pavements

How Stable

base

3.7

subgrade

Specialized

7.8

sandy soil

1 2.5

Surface Forms

subgrade singular

subgrades plural

Morphology

subgrade = grade (semi-transparent) = sub + grade

Form is clearly sub- + grade, but the technical meaning 'the soil layer supporting a pavement' is domain-specific and may not be obvious to general learners.

Etymology

Subgrade combines sub- 'under' and grade 'level' or 'ground', so it names the layer of soil that sits 'under' a road or pavement and supports the surface.