IRC 37:2018 HIGHWAY STANDARDS

Flexible Pavement Design (IRC 37:2018)

Compute cumulative traffic repetitions in Million Standard Axles (MSA), subgrade resilient modulus ($M_R$), and layer thickness recommendations for BC, DBM, WMM, and GSB.

1. Traffic Volume & Growth Parameters

Initial Traffic A (CVPD)Commercial Vehicles / Day

Design Period n (Years)

Annual Growth Rate r (%)

Vehicle Damage Factor (VDF)

Road Carriageway Configuration

2. Subgrade Strength (CBR %)

Subgrade 4-day Soaked CBR (%)Minimum 8% CBR recommended for high traffic expressways per IRC 37 Cl. 4.2.

Design Traffic Repetitions

-- MSA

Subgrade Resilient Modulus MR = -- MPa

Bituminous Concrete (BC):-- mm

Dense Bituminous Macadam (DBM):-- mm

Granular Base (WMM):250 mm

Granular Sub-Base (GSB):200 mm

Total Structural Crust Thickness:-- mm

Pavement Layer Cross-Section

IRC 37 Catalog

IRC 37:2018 Flexible Pavement Design Theory

1. Cumulative ESAL (MSA)

Standard axle traffic calculation over design life $n$ with compound growth rate $r$:

N = [365 * ((1+r)^n - 1) * A * D * F] / r

2. Resilient Modulus (MR)

• For CBR ≤ 5%: M_R = 10 × CBR (MPa).

• For CBR > 5%: M_R = 17.6 × (CBR)^0.64 (MPa).

3. Mechanistic Fatigue Check

Pavements are checked against horizontal tensile strain at bottom of DBM (fatigue cracking) and vertical compressive strain on subgrade top (rutting).