Flexible Pavement Design IRC:37-2018 · mechanistic-empirical design · layered elastic analysis

IRC 37 example check

130.9 msa · 90 % reliability · total pavement 630 mm · subgrade 61.1 MPa · IRC:37-2018

All checks OK Edit design

1. Design basis and input data

Bituminous pavement designed to IRC:37-2018 (Guidelines for the Design of Flexible Pavements, fourth revision) by the mechanistic-empirical method: the pavement is analysed as a linear elastic, fully bonded layered system under the standard axle (dual wheels of 20 kN at 0.56 MPa, 310 mm c/c; 0.80 MPa for the cement treated base) and the computed critical strains are compared with the allowable strains of the performance models for subgrade rutting (Eq. 3.1/3.2), bottom-up fatigue cracking of the bituminous layer (Eq. 3.3/3.4) and fatigue of the CTB (Eq. 3.5 - 3.7). The layered elastic analysis performed by IITPAVE is carried out by this program (Burmister multilayer solution); its results agree with the IITPAVE values of Annexes II and III within about 1 %.

Project-
Client-
Location / chainage-
Road categoryNational Highway
CarriagewayDual carriageway - two lanes each way
CompositionBituminous + aggregate interlayer + CTB + CTSB
Design period20 years
Bituminous binder (DBM)BC and DBM with VG40 bitumen; average annual pavement temperature 35 deg C
PAVEMENT COMPOSITION AND CRITICAL LOCATIONS Bituminous layers (surface + DBM), 100 mm E = 3,000 MPa, nu = 0.35 (VG40) 100 Aggregate interlayer (crack relief), 100 mm E = 450 MPa, nu = 0.35 100 Cement treated base (CTB), 180 mm E = 5,000 MPa, nu = 0.25 180 Cement treated sub-base (CTSB), 250 mm E = 600 MPa, nu = 0.25 250 Subgrade E = 61 MPa, nu = 0.35 20 kN 20 kN 310 p = 0.56 MPa, a = 106.6 mm et et CTB ev Thicknesses to scale vertically; subgrade semi-infinite. Red dots: critical strain locations (Table 3.1).
Fig. 1 Pavement composition, standard load and critical locations
TYPICAL CROSS SECTION (SCHEMATIC) 3.50 m 3.50 m shoulder shoulder Dual carriageway - two lanes each way - layer thicknesses exaggerated; total pavement 630 mm.
Fig. 2 Typical cross section (schematic)

2. Design traffic

Cumulative standard axles (Cl. 4.6)OK
ReferenceDescriptionCalculationResult
Cl. 4.5Lateral distribution factor DDual carriageway - two lanes each way 0.75
Eq. 4.6Traffic in the year of completion A = P (1 + r)^x5,000 x 50 % (directional) x (1 + 0.06)^0 2,500 CVPD
Cl. 4.4 / Table 4.2Vehicle damage factor Faxle load survey 5.2
Eq. 4.5N = 365 [(1 + r)^n - 1] / r x A x D x F365 x 36.786 x 2,500 x 0.75 x 5.2 130,910,723 = 130.91 msa
Cl. 3.7Reliability of the performance modelsimportant road 90 %
CUMULATIVE DESIGN TRAFFIC 0 5 10 15 20 0 25 50 75 100 125 Years after opening Cumulative standard axles (msa) N = 130.9 msa
Fig. 3 Growth of cumulative standard axles over the design period

3. Subgrade - effective resilient modulus

Resilient modulus of the subgrade (Cl. 6.3, 6.4)OK
ReferenceDescriptionCalculationResult
Eq. 6.1 / 6.2Resilient modulus of the 500 mm subgrade17.6 x 7^0.64 61.1 MPa
Eq. 6.2Effective CBR reported 7.0 %

4. Layer properties for analysis

Layers analysed (Table 11.1); bituminous layers as one layer with the DBM modulus
LayerThickness (mm)E (MPa)Poisson's ratioBasis
Bituminous layers (surface + DBM)1003,0000.35Table 9.2 (BC and DBM with VG40 bitumen at 35 deg C)
Aggregate interlayer (crack relief)1004500.35Cl. 8.3 / Table 11.1
Cement treated base (CTB)1805,0000.25Cl. 8.2 / Table 11.1
Cement treated sub-base (CTSB)2506000.25Cl. 7.3.2 / Table 11.1
Subgradesemi-infinite610.35Cl. 6
Bituminous mix parametersOK
ReferenceDescriptionCalculationResult
Cl. 9.2Volume of air voids / effective bitumen of the bottom DBMmix design Va = 3 %, Vbe = 11.5 %
Eq. 3.3Mix adjustment C = 10^(4.84 (Vbe / (Va + Vbe) - 0.69))10^(4.84 x (11.5 / 14.5 - 0.69)) 3.155

5. Structural analysis - linear elastic layered system

Standard axle: one set of dual wheels, 20 kN each, 310 mm c/c, uniform contact stress 0.56 MPa (contact radius 106.6 mm); fully bonded interfaces (Table 3.1). Responses at the bottom of the bituminous layer, the bottom of the CTB and the top of the subgrade, under the centre of one wheel (x = 0) and midway between the wheels (x = 155 mm). Strains in microstrain, tension positive; x along the line joining the wheels.

Computed responses at the critical locations
Locationx (mm)exeyezVertical stress (MPa)
Bottom of bituminous layer, z = 100 mm089.7127.5-172.6-0.2678
Bottom of bituminous layer, z = 100 mm155-79.0108.5-54.1-0.1840
Bottom of CTB, z = 380 mm (0.80 MPa)029.341.3-29.7sx 0.199 / sy 0.247
Bottom of CTB, z = 380 mm (0.80 MPa)15533.044.3-32.7sx 0.222 / sy 0.266
Top of subgrade, z = 630 mm052.862.7-159.1-0.0095
Top of subgrade, z = 630 mm15558.765.3-168.6-0.0100
VERTICAL STRESS WITH DEPTH (DUAL WHEELS, 0.56 MPa) 0 0.1 0.2 0.3 0.4 0.5 0.6 1,000 800 600 400 200 0 Vertical compressive stress (MPa) Depth (mm) Bituminous layers / below Aggregate interlayer / below Cement treated base / below Cement treated sub-base / below under a wheel (r = 0) between the wheels (155 mm)
Fig. 4 Vertical compressive stress with depth
STRAINS ACROSS THE DUAL WHEELS -200 0 200 400 0 50 100 150 Distance from the centre of one wheel (mm); second wheel at 310 Strain (microstrain) wheel wheel Tensile strain, bottom of bituminous Vertical strain, top of subgrade
Fig. 5 Critical strains across the dual wheel set

6. Performance checks

Performance criteria (Cl. 3.6)OK
ReferenceDescriptionCalculationResult
Eq. 3.2Allowable subgrade strain (N = design traffic)(1.4100e-8 / 130,910,723)^(1/4.5337) 300.6 microstrain
AnalysisComputed vertical strain, top of subgrademax. of x = 0 and 155 mm 168.6 microstrain OK
Eq. 3.2Rutting life NR1.4100e-8 (1 / 1.686e-04)^4.5337 1,802.90 msa OK
Eq. 3.4Allowable tensile strain, bottom of bituminous layer(0.5161 x 3.155 x 1e-4 x 3,000^-0.854 / 130,910,723)^(1/3.89) 150.0 microstrain
AnalysisComputed tensile strain, bottom of bituminous layermax. of x = 0 and 155 mm 127.5 microstrain OK
Eq. 3.4Fatigue life Nf0.5161 x 3.155 x 1e-4 (1 / 1.275e-04)^3.89 (1 / 3,000)^0.854 246.26 msa OK
Eq. 3.5CTB life N = RF [(113000 / E^0.804 + 191) / et]^12, RF = 11 x [(113000 / 5,000^0.804 + 191) / 44.3]^12 14,400.79 msa OK
Summary of checks
CheckReferenceComputedLimitResult
Subgrade rutting - vertical strain on subgradeEq. 3.1/3.2168.561 microstrain300.598 microstrainOK
Bituminous fatigue - tensile strain at bottomEq. 3.3/3.4127.535 microstrain150.029 microstrainOK
CTB fatigue - life from tensile strain (0.80 MPa)Eq. 3.5130.911 msa14,400.792 msaOK
CTB under construction traffic (7-day strength)Eq. 3.6, II.40.698 MPa0.795 MPaOK
CTB cumulative fatigue damage (axle spectrum)Eq. 3.6/3.70.7881.000OK
Minimum layer thicknessesCl. 7 - 90 issue(s)0OK

7. Cumulative fatigue damage of the cement treated base

Tensile stress at the bottom of the CTB for every axle load class at 0.80 MPa contact stress; tandem axles as two and tridem axles as three single axles (Cl. 3.6.3.2); modulus of rupture 1.4 MPa; log10 Nf = (0.972 - SR) / 0.0825.

Single axles - CFD 0.089
Load class (kN)Axle load (kN)Single axle reps niStress (MPa)SRFatigue life Nfni / Nf
185 - 19519070,0000.6040.4313.571e+060.0196
175 - 18518090,0000.5750.4106.415e+060.0140
165 - 17517092,0000.5450.3891.158e+070.0079
155 - 165160300,0000.5150.3682.102e+070.0143
145 - 155150280,0000.4850.3463.833e+070.0073
135 - 145140650,0000.4540.3257.027e+070.0092
125 - 135130600,0000.4240.3031.295e+080.0046
115 - 1251201,340,0000.3930.2812.399e+080.0056
105 - 1151101,300,0000.3620.2584.469e+080.0029
95 - 1051001,500,0000.3300.2368.369e+080.0018
85 - 95901,350,0000.2980.2131.576e+090.0009
75 - 85803,700,0000.2660.1902.984e+090.0012
Tandem axles - CFD 0.548
Load class (kN)Axle load (kN)Single axle reps niStress (MPa)SRFatigue life Nfni / Nf
390 - 410400400,0000.6330.4521.998e+060.2002
370 - 390380460,0000.6040.4313.571e+060.1288
350 - 370360480,0000.5750.4106.415e+060.0748
330 - 350340470,0000.5450.3891.158e+070.0406
310 - 330320450,0000.5150.3682.102e+070.0214
290 - 310300950,0000.4850.3463.833e+070.0248
270 - 290280900,0000.4540.3257.027e+070.0128
250 - 2702602,870,0000.4240.3031.295e+080.0222
230 - 2502402,500,0000.3930.2812.399e+080.0104
210 - 2302202,370,0000.3620.2584.469e+080.0053
190 - 2102002,000,0000.3300.2368.369e+080.0024
170 - 1901801,600,0000.2980.2131.576e+090.0010
150 - 1901706,400,0000.2830.2022.167e+090.0030
Tridem axles - CFD 0.151
Load class (kN)Axle load (kN)Single axle reps niStress (MPa)SRFatigue life Nfni / Nf
585 - 615600105,0000.6330.4521.998e+060.0526
555 - 585570120,0000.6040.4313.571e+060.0336
525 - 555540120,0000.5750.4106.415e+060.0187
495 - 525510135,0000.5450.3891.158e+070.0117
465 - 495480129,0000.5150.3682.102e+070.0061
435 - 465450330,0000.4850.3463.833e+070.0086
405 - 435420300,0000.4540.3257.027e+070.0043
375 - 405390990,0000.4240.3031.295e+080.0076
345 - 375360900,0000.3930.2812.399e+080.0038
315 - 345330825,0000.3620.2584.469e+080.0018
285 - 315300780,0000.3300.2368.369e+080.0009
255 - 285270540,0000.2980.2131.576e+090.0003
240 - 2702552,160,0000.2830.2022.167e+090.0010
Total CTB cumulative fatigue damage = 0.089 + 0.548 + 0.151 = 0.788 <= 1.0
SINGLE - CFD 0.09 75 100 125 150 175 0 0.005 0.01 0.015 0.02 Axle load (kN) Damage ni / Nfi TANDEM - CFD 0.55 200 250 300 350 400 0 0.05 0.1 0.15 0.2 Axle load (kN) Damage ni / Nfi TRIDEM - CFD 0.15 300 400 500 600 0 0.02 0.04 0.06 Axle load (kN) Damage ni / Nfi
Fig. 6 CTB fatigue damage by axle load class

8. Construction traffic

Sub-base / CTB under construction traffic (Cl. 7.2.2, Annex II)OK
ReferenceDescriptionCalculationResult
Annex II.2VDF of a dumper (rear tandem as two single axles)2 x (120 / 80)^4 + (80 / 65)^4 12.42
Cl. 7.2.2 (v)Construction traffic (min. 10,000 SA)max(200 x 12.42, 10000) 10,000 SA
Eq. 3.2Allowable subgrade strain 2433 microstrain
Eq. 3.6Allowable stress, 140 reps of 120 kN, 7-day MR 1 MPa1 (0.972 - 0.0825 log 140) 0.795 MPa
Annex II.4Tensile stress at bottom of CTB (CTB + sub-base + subgrade, 0.80 MPa) 0.698 MPa OK

9. Bituminous layer thickness trials

Other layers as given; total bituminous thickness varied. Least thickness satisfying all life checks: 100 mm.

STRAINS vs BITUMINOUS LAYER THICKNESS 100 200 300 0 50 100 150 200 Total bituminous layer thickness (mm) Strain (microstrain) allowable et 150 allowable ev 301 design 100 mm Tensile strain, bottom of bituminous Vertical strain, top of subgrade
Fig. 7 Critical strains against bituminous layer thickness
PAVEMENT LIFE vs BITUMINOUS LAYER THICKNESS 100 200 300 100 1,000 10,000 100,000 Total bituminous layer thickness (mm) Allowable traffic (msa) design traffic 130.9 msa design 100 mm Fatigue life (bituminous) Rutting life (subgrade) CTB fatigue life (Eq. 3.5)
Fig. 8 Allowable traffic against bituminous layer thickness
Trial thicknesses
Bituminous (mm)etevFatigue lifeRutting lifeCTB lifeResult
40132.2205.1214.02 msa740.17 msa781.65 msaNOT OK
45141.3201.6165.12 msa800.86 msa970.69 msaNOT OK
50146.6198.2143.34 msa865.01 msa1,214.91 msaNOT OK
55149.0194.9134.36 msa933.06 msa1,531.00 msaNOT OK
60149.5191.7132.60 msa1,005.47 msa1,940.56 msaNOT OK
65148.7188.6135.61 msa1,082.72 msa2,471.57 msaNOT OK
70146.9185.6142.23 msa1,165.30 msa3,160.19 msaNOT OK
75144.4182.6151.95 msa1,253.71 msa4,053.11 msaNOT OK
80141.5179.7164.57 msa1,348.48 msa5,210.51 msaNOT OK
85138.2176.9180.11 msa1,450.18 msa6,709.82 msaNOT OK
90134.8174.0198.73 msa1,559.40 msa8,650.46 msaNOT OK
95131.2171.3220.67 msa1,676.75 msa11,159.82 msaNOT OK
100127.5168.6246.26 msa1,802.90 msa14,400.79 msaOK
110120.2163.3310.10 msa2,084.42 msa23,965.69 msaOK
120113.0158.1394.30 msa2,410.05 msa39,781.45 msaOK
130106.1153.1504.05 msa2,786.67 msa65,759.59 msaOK
14099.5148.3645.72 msa3,222.06 msa108,125.03 msaOK
15093.4143.6827.05 msa3,724.98 msa176,697.59 msaOK
16087.7139.11,057.25 msa4,305.32 msa286,833.53 msaOK
17082.4134.81,347.22 msa4,974.21 msa462,341.05 msaOK
18077.8130.51,681.51 msa5,744.19 msa739,820.98 msaOK
19074.2126.52,024.38 msa6,629.33 msa1,175,075.16 msaOK
20070.7122.62,438.16 msa7,645.42 msa1,852,490.71 msaOK
21067.4118.82,935.99 msa8,810.11 msa2,898,674.29 msaOK
22064.3115.23,533.20 msa10,143.14 msa4,502,109.69 msaOK
23061.3111.74,247.62 msa11,666.52 msa6,941,290.36 msaOK
24058.5108.35,099.87 msa13,404.77 msa10,624,692.23 msaOK
25055.9105.06,113.75 msa15,385.12 msa16,147,175.89 msaOK
26053.3101.97,316.61 msa17,637.81 msa24,369,035.83 msaOK
27051.098.98,739.78 msa20,196.35 msa36,526,069.18 msaOK
28048.796.010,419.04 msa23,097.79 msa54,381,869.42 msaOK
29046.693.312,395.15 msa26,383.08 msa80,437,256.95 msaOK
30044.690.614,714.33 msa30,097.35 msa118,216,578.82 msaOK
31042.788.017,428.91 msa34,290.34 msa172,656,848.00 msaOK
32040.985.620,597.96 msa39,016.72 msa250,633,724.67 msaOK
33039.283.224,287.94 msa44,336.55 msa361,668,633.18 msaOK
34037.680.928,573.46 msa50,315.67 msa518,874,432.25 msaOK
35036.178.733,538.02 msa57,026.24 msa740,213,717.23 msaOK

10. Design summary and recommendations

All checks are satisfied for the pavement composition: Bituminous layers 100 mm + Aggregate interlayer 100 mm + Cement treated base 180 mm + Cement treated sub-base 250 mm.
  • Surface course: SMA (modified bitumen or VG40), GGRB (crumb rubber modified bitumen) or BC with modified bitumen (Table 9.1).
  • Binder / base course: DBM with VG40 bitumen (viscosity >= 3600 Poise at 60 deg C).
  • Bottom DBM: rich bottom mix designed for Va = 3 % and Vbe = 11.5 % (compacted to 4 % or lower in-place air voids for a two-layer DBM, 4.5 % for a single layer).
  • Granular sub-base with drainage and filter layers extended over the full formation width (Cl. 7.2.1).
  • Subgrade: top 500 mm compacted to 97 % of MDD (heavy compaction), effective CBR 7.0 %.

Report generated 31 Oct 2026.

11. Pavement drawing

Pavement composition with the standard load and critical locations, cross section, strain and life charts and design summary on one A3 sheet.

PAVEMENT COMPOSITION AND CRITICAL LOCATIONS Bituminous layers (surface + DBM), 100 mm E = 3,000 MPa, nu = 0.35 (VG40) 100 Aggregate interlayer (crack relief), 100 mm E = 450 MPa, nu = 0.35 100 Cement treated base (CTB), 180 mm E = 5,000 MPa, nu = 0.25 180 Cement treated sub-base (CTSB), 250 mm E = 600 MPa, nu = 0.25 250 Subgrade E = 61 MPa, nu = 0.35 20 kN 20 kN 310 p = 0.56 MPa, a = 106.6 mm et et CTB ev Thicknesses to scale vertically; subgrade semi-infinite. Red dots: critical strain locations (Table 3.1). TYPICAL CROSS SECTION (SCHEMATIC) 3.50 m 3.50 m shoulder shoulder Dual carriageway - two lanes each way - layer thicknesses exaggerated; total pavement 630 mm. STRAINS vs BITUMINOUS THICKNESS 100 200 300 0 50 100 150 200 Total bituminous layer thickness (mm) Strain (microstrain) allowable et 150 allowable ev 301 design 100 mm Tensile strain, bottom of bituminous Vertical strain, top of subgrade LIFE vs BITUMINOUS THICKNESS 100 200 300 100 1,000 10,000 100,000 Total bituminous layer thickness (mm) Allowable traffic (msa) design traffic 130.9 msa design 100 mm Fatigue life (bituminous) Rutting life (subgrade) CTB fatigue life (Eq. 3.5) DESIGN SUMMARY (IRC:37-2018) Design traffic 130.9 msa (90 % reliability) Effective subgrade modulus 61.1 MPa (CBR 7.0 %) Composition Bituminous + aggregate interlayer + CTB + CTSB Layers (mm) Bituminous layers 100 + Aggregate interlayer 100 + Cement treated base Total pavement thickness 630 mm Bituminous layer modulus 3,000 MPa (VG40) Tensile strain bottom of bituminous 127.5 / 150.0 allowable Vertical strain top of subgrade 168.6 / 300.6 allowable Fatigue life / rutting life 246.3 / 1,802.9 msa CTB tensile strain (0.80 MPa) / life 44.3 / 14,400.8 msa CTB cumulative fatigue damage 0.788 Least bituminous thickness (other layers as given) 100 mm Result: ALL CHECKS SATISFIED NOTES 1. All dimensions in mm. 2. Materials and workmanship to MoRTH Specifications (5th rev.). 3. Bottom DBM: rich bottom mix, design air voids as adopted for fatigue. 4. GSB extended full width with drainage and filter layers (Cl. 7.2.1). IRC 37 example check Flexible pavement 630 mm · Designed: - Checked: - Date: 31 Oct 2026 Scale: as shown Sheet 1 of 1