Distinction and division between subgrade and pavement in highway works: term definitions, the dividing plane (bottom of pavement structure = top of subgrade = top of roadbed) and the roadbed/embankment depth numbers, plus classification, pricing, and acceptance split calibers

Topic Positioning

Term definitions, essential distinction, dividing plane (bottom of pavement structure = top of subgrade) of subgrade and pavement in highway works, and their classification, pricing, and acceptance split calibers. For cost compilation, construction-interface division, and acceptance — to judge whether an item of work belongs to subgrade or pavement works.

Core Conclusions

1. Term definitions (verbatim)

• Subgrade (GB/T 50083-2014 Clause 5.2.2): "a strip structure built along the route alignment and to specified technical requirements; it is the foundation of the pavement and bears the traffic loads transmitted through the pavement." Materials are earth and rock (natural or fill), also subject to water, temperature, and freeze-thaw.
• Pavement (GB/T 50083-2014 Clause 5.1.1): "structural courses laid with road-building materials on the highway subgrade for vehicle travel, comprising the surface course (including wearing course), base course, and subbase." It directly bears traffic loads, precipitation, and temperature variation.
• Caliber caution: in codes "pavement" is the collective term for structural courses (surface + base + subbase, plus subbase where provided); in everyday speech it often means only the top wearing course — the two must not be conflated.

2. Dividing plane and layering

• Division: bottom of pavement structure = top of subgrade = top of roadbed. Below the plane (roadbed, embankment/cutting) is subgrade works; above (subbase, base, surface) is pavement works.
• Roadbed (GB/T 50083-2014 Clause 5.2.3): "the part of the subgrade within 0.80 m below the bottom of the pavement, structurally divided into upper roadbed (0-0.30 m) and lower roadbed (0.30-0.80 m)." CJJ 194-2013 Clause 2.1.2 to the same effect: "the part of subgrade within 0.80 m below the bottom of the pavement structure, divided into upper (0-0.30 m) and lower (0.30-0.80 m) roadbed."
• Embankment (GB/T 50083-2014 Clause 5.2.4): "fill subgrade above the original ground. Structurally divided into upper and lower embankment: the upper embankment is the fill within 0.80-1.50 m below the bottom of the pavement; the lower embankment is the fill below the upper embankment."
• Construction-interface basis (DB14/T 1319-2021 Section 301, verbatim): "This section covers laying various subbases, base courses, and surface courses on subgrade completed and accepted by the Supervisor; pavement and median drainage; cultivating soil shoulders, median backfill and curb setting, and related operations for pavement auxiliary facilities." Accepted subgrade is the precondition of pavement work; material standards, general construction requirements, trial sections, quarry operations, mixing-plant hardening and rain shelters, rainy-season work, etc., in that section are not measured separately but included in the relevant items.

3. Engineering composition and classification (GB/T 50841-2013 Clause 4.2.2) A highway generally consists of subgrade works, pavement works, and other works:

• Subgrade works: earth-rock works (cut/fill); subgrade drainage (surface/underground); special subgrade (soft soil, landslides, rockfalls and talus, debris flows, karst, permafrost, loess, expansive soil, saline soil, wind-blown sand, snow damage, icicles, mined-out areas, coastal and reservoir areas); subgrade protection (slope, riverside); subgrade retaining (retaining walls, anti-slide piles).
• Pavement works: base and subbase (two categories); surface courses (asphalt concrete, cement concrete, others); pavement drainage (edge drains, median drainage, internal drainage); pavement auxiliaries (sidewalks, curbs, asphalt edge strips, soil-shoulder hardening).
• Other works: safety facilities (guardrails, fences, signs, markings, glare screens) and environmental protection (greening, noise control).
• Pavements by surface material: asphalt, cement concrete, block, and granular; by function: surface, base, subbase, and subbase-cushion courses (four levels).

4. Pricing and acceptance split calibers

• Estimates/budgets (JTG 3830-2018 Section 2.4): under Part 1 construction-and-installation costs, "Item 2 subgrade works" and "Item 3 pavement works" are listed separately; item numbering expands by part (1 digit), item (2), sub-item (2), section (2), detail (2); subgrade (LJ) and pavement (LM) schedules in Appendix B; where actual projects differ, Parts 1-5 and item numbers/contents stay fixed, missing sub-items added nearby with numbering unchanged; "unified item numbering shall be used in compiling estimates and budgets".
• Unit-works division: within each contract section, subgrade, pavement, and traffic-safety facilities are each a unit work (DB35/T 2094-2022 Section 4.3); a unit work is a part with independent construction conditions, e.g., subgrade, pavement, bridge, culvert, traffic-safety facilities (DB12/T 942-2020 Clause 4.1.2). For urban roads, unit/divisional/item works and inspection lots are fixed before commencement; each independent contract determined by the employer's tender documents is a unit work (CJJ 1-2008 Clause 18.0.1).
• Municipal BOQ codes (GB/T 50857-2024 Appendix B): subgrade treatment 040201, road base 040202, road surface 040203.

Applicable Boundaries

• Terms from GB/T 50083-2014 (fundamental terminology for engineering structural design — highway structures) and CJJ 194-2013 (urban roads): highway and urban-road definitions of "roadbed = within 0.80 m below pavement bottom" agree and may be cross-referenced.
• Industry terminology differs: railway works have "subgrade surface" ("the top of subgrade between the outer edges of the shoulders on both sides", GB/T 50262-2024 Clause 6.1.5), not to be conflated with the highway subgrade/pavement division.
• 0-0.30 m, 0.30-0.80 m (roadbed), 0.80-1.50 m (upper embankment) are definitional numbers; actual course thicknesses, subbase provision, and treatment schemes follow the design.
• Estimate/budget items and codes per current JTG 3830-2018; this card does not replace a project's design and pricing agreements.

Further Reading

• GB/T 50083-2014 Standard for Fundamental Terminologies of Engineering Structural Design, Clauses 5.1.1 (pavement), 5.2.2 (highway subgrade), 5.2.3 (highway roadbed), 5.2.4 (highway embankment)
• GB/T 50841-2013 Standard for Classification of Construction Works, Clause 4.2.2 (civil works — highway classification)
• CJJ 194-2013 Code for Design of Urban Road Subgrade, Clause 2.1.2; CJJ 1-2008 Code for Construction and Quality Acceptance of Urban Road Works, Clause 18.0.1 and Table 18.0.1
• JTG 3830-2018 Measures for Compiling Estimates and Budgets of Highway Project Construction, Section 2.4 (items and coding), Appendix B (LJ/LM schedules)
• DB14/T 1319-2021 Standard BOQ and Measurement Specification for Highway Works, Section 301 (general)
• DB35/T 2094-2022 Technical Specification for Quality Testing at Completion (Handover) Acceptance of Highway Works, Section 4.3; DB12/T 942-2020 Standard for Quality Inspection and Evaluation of Rural Highways, Clause 4.1.2
• GB/T 50857-2024 Standard for Measurement of Municipal Works, Appendix B (040201/040202/040203); GB/T 50262-2024 Standard for Railway Engineering Terminology, Clause 6.1.5