This section specifies the commonly used terminology and symbol definitions in field testing of highway subgrade and pavement. It is applicable to highway engineering inspection, quality control, and scientific research and analysis. The content is based on domestic highway engineering standards and is supplemented with internationally recognized engineering terminology systems (such as ASTM, AASHTO, and EN standards) to ensure unified understanding of industry terminology and facilitate technical communication.

1 Terms

1.1 Subgrade width

The total width of the carriageway and shoulders, measured in meters (m). Where a median, acceleration/deceleration lanes, climbing lanes, or emergency stopping lanes are provided, their widths shall also be included.

1.2 Pavement width

The total width of the pavement, including the carriageway, edge strips, acceleration/deceleration lanes, climbing lanes, hard shoulders, and emergency stopping lanes, measured in meters (m).

1.3 Subgrade cross slope

The ratio of the elevation difference between the centerline of the road channel and two edge points on the subgrade cross-section to the horizontal distance, expressed as a percentage.

1.4 Pavement cross slope

The slope of the straight portions on both sides of the road crown or central median in the pavement cross-section, expressed as a percentage.

1.5 Deviation of pavement center-line

The distance between the actual centerline of the pavement and the designed centerline, measured in millimeters (mm).

1.6 Degree of compaction

The ratio of the density of compacted road construction materials to the standard density, expressed as a percentage.

1.7 Roughness

The vertical deviation of the pavement surface relative to an ideal plane, typically expressed by maximum gap, International Roughness Index (IRI), or accumulated bump value, measured in mm or m/km.

1.8 Deflection

The total vertical deformation (total deflection) or elastic rebound deformation (rebound deflection) of the subgrade or pavement under a specified load, measured in units of 0.01 mm.

1.9 Texture depth

The average depth of surface voids on the pavement surface, also known as macrotexture depth. It is commonly expressed as tD, SMtD, or MPD, measured in mm.

1.10 British Pendulum Number (BPN)

An index of pavement skid resistance measured using a pendulum friction tester. It represents 100 times the friction coefficient and is dimensionless.

1.11 Sideway Force Coefficient (SFC)

The ratio of the lateral friction force between the tire and the pavement to the vertical load when the test wheel runs at a certain slip angle. It is dimensionless.

1.12 Water permeability coefficient

The volume of water infiltrating into a specified pavement area per unit time, measured in mL/min.

1.13 Faulted joint slabs

The abrupt change in elevation occurring at joints between different structures or adjacent concrete slabs, measured in mm.

1.14 Rut

A longitudinal deformation groove formed on the pavement under repeated vehicle loading. It is typically characterized by the maximum rut depth, measured in mm.

1.15 Field CBR of Soil Subgrade

An index characterizing the bearing capacity of highway subgrade, specifically the ratio of the test load pressure applied at a specified penetration depth to the standard load pressure under field conditions, expressed as a percentage.

1.16 Resilient Modulus

The ratio of stress generated in the subgrade, pavement, and road construction materials under load to their corresponding rebound strain, expressed in MPa.

1.17 Distress Ratio

The ratio of the sum of the equivalent damaged areas of various pavement damages to the surveyed pavement area, expressed as a percentage.

1.18 Broken Slab Ratio

The ratio of the total number of cement concrete pavement slabs completely broken into two or more pieces to the total number of pavement slabs in the surveyed section, expressed as a percentage.

1.19 Pavement Cracking Ratio

The ratio of the equivalent area of pavement cracks to the total area of the inspected section, expressed as a percentage.

1.20 Disengagement

A type of discontinuous void that appears between pavement structural layers, usually expressed as the size of the void, measured in mm.

2. Symbols

BPN — British Pendulum Number;

CBR — California Bearing Ratio;

Cw — Water permeability coefficient;

D — Pavement faulting;

E0 — Subgrade resilient modulus;

E1 — Pavement material resilient modulus;

IRI — International Roughness Index;

K — Degree of compaction;

Ru — Pavement rut depth;

SFC — Sideway Force Coefficient;

tD (SMtD, MtD, MPD) — Texture depth;

VBI — Vehicle Bump Index;

ΔCL — Deviation of pavement centerline;

Δm — Roughness (maximum gap);

μ — Poisson’s ratio of pavement material.