Deterioration Unsealed Roads

2

• Gravel

• Earth (or Sand) *

Unsealed Roads Classification

* Engineered roads

3

Unsealed Roads

4

Unsealed Roads Deterioration

5

• Roughness

• Material Loss

• Rutting

• Looseness

• Impassability

Models of Distress

HDM-4

6

Preservation• Routine

Off carriageway Grading Spot regravelling

• Periodic Regravelling

• Special Emergencies Winter maintenance

Development• Improvements

Widening Realignment

• Construction Upgrading New sections

Unsealed Road Work Classification

7

• Roughness:

Progression

Effect of mechanical compaction

Effect of grading

Average annual roughness

Steady state roughness

• Material Loss

Unsealed Roads Models

8

Roughness Without Compaction

0

5

10

15

20

25

30

0 1 2 3 4 5

Surface Age (years)

IRI

(m/k

m)

200 veh/day 100 veh/day 50 veh/day

10 veh/day

9

Grading

11

Long term average roughness

0

5

10

15

20

25

30

35

0 20 40 60 80 100 120 140 160 180 200

AADT

Ave

rag

e IR

I (m

/km

)

No grading

Grading 2 per year

Grading 4 per year

Grading 12 per year

12

Roughness: Effect of Grading Frequency and Traffic

Effect of Grading Frequency and Traffic on RoughnessFlat and Level Terrain / Sub-humid Environment

3

5

7

9

11

13

15

17

19

21

0 25 50 75 100 125 150 175 200 225 250 275 300

Average Daily Traffic (ADT)

Rou

ghne

ss (

IRI)

24 Months

18 Months

12 Months

9 Months

6 Months

3 Months

1 Months

GradingFrequency

13

Roughness: Effect of Terrain Type and Traffic

Effect on Terrain Type and Traffic on RoughnessGradings Every 6 Months / Sub-humid Environment

3

5

7

9

11

13

15

17

19

21

0 25 50 75 100 125 150 175 200 225 250 275 300

Average Daily Traffic (ADT)

Rou

ghne

ss (

IRI)

Mountainous

Hilly & Rolling

Flat & Level

TerrainType

14

Roughness: Effect of Environment Type and Traffic

Effect of Environment and Traffic on RoughnessGradings Every 6 Months / Flat and Level Terrain

3

5

7

9

11

13

15

17

19

21

0 25 50 75 100 125 150 175 200 225 250 275 300

Average Daily Traffic (ADT)

Rou

ghne

ss (

IRI)

Arid

Semi-arid

Sub-humid

Humid

EnvironmentType

15

Roughness: Effect of Material Properties

Lateritic Gravel Earth RoadSemi-arid Environment Semi-arid Environment

Frequency Flat & Rolling & Flat & Rolling &Traffic of Gradings Level Hilly Mountainous Level Hilly Mountainous(ADT) (months) Terrain Terrain Terrain Terrain Terrain Terrain

25 1 4.0 4.2 4.4 2.8 3.0 3.325 3 6.0 6.5 7.1 5.0 5.6 6.325 6 8.3 9.1 10.0 7.4 8.2 9.325 9 9.7 10.7 11.8 8.8 9.8 11.125 12 10.8 11.8 13.1 9.8 10.9 12.325 18 12.3 13.4 14.9 11.2 12.4 14.025 24 13.2 14.5 16.1 12.1 13.4 15.1

16

Material lossEffect of Rainfall and Traffic

17

Material loss Effect of Rainfall and Terrain

18

Road Roughness of Unsealed Roads

• Roughness equations valid for engineered unsealed roads with good maintenance (good drainage). Therefore:

Higher rainfall yields lower roughness Higher percent of trucks yields lower roughness Earth roads (finer soils) have lower roughness than

gravel roads, making difficult to evaluate regravelling works

• In practice, the condition of an unsealed road can be different from what is being predicted by the HDM models, specially related to the passability on the wet season

19

Road Roughness of Unsealed Roads

• HDM equations for deterioration of unsealed roads are valid for engineered roads with proper drainage

• There is a need to understand the HDM relationships and calibrate the equations if proper drainage is not available