Deterioration Unsealed Roads
Unsealed Roads Classification
• Gravel
• Earth (or Sand) *
* Engineered roads
2
Unsealed Roads
3
Unsealed Roads Deterioration
4
Models of Distress
• Roughness
• Material Loss
HDM-4
• Rutting
• Looseness
• Impassability
5
Unsealed Road Work Classification
Preservation
Development
• Routine
• Improvements
Off carriageway
 Grading
 Spot regravelling

Widening
 Realignment

• Construction
• Periodic

Upgrading
 New sections

Regravelling
• Special
Emergencies
 Winter maintenance

6
Unsealed Roads Models
• Roughness:
 Progression
 Effect
of mechanical compaction
 Effect
of grading
 Average
 Steady
annual roughness
state roughness
• Material Loss
7
Roughness Without Compaction
30
25
200 veh/day
100 veh/day
50 veh/day
10 veh/day
IRI (m/km)
20
15
10
5
0
0
1
2
3
Surface Age (years)
8
4
5
Grading
9
Long term average roughness
35
No grading
30
Average IRI (m/km)
25
Grading 2 per year
20
Grading 4 per year
15
10
Grading 12 per year
5
0
0
20
40
60
80
100
AADT
11
120
140
160
180
200
Roughness: Effect of Grading
Frequency and Traffic
Effect of Grading Frequency and Traffic on Roughness
Flat and Level Terrain / Sub-humid Environment
21
19
Grading
Frequency
24 Months
18 Months
12 Months
9 Months
6 Months
3 Months
1 Months
Roughness (IRI)
17
15
13
11
9
7
5
3
0
25 50 75 100 125 150 175 200 225 250 275 300
Average Daily Traffic (ADT)
12
Roughness: Effect of Terrain Type
and Traffic
Effect on Terrain Type and Traffic on Roughness
Gradings Every 6 Months / Sub-humid Environment
21
19
Roughness (IRI)
17
Terrain
Type
Mountainous
Hilly & Rolling
Flat & Level
15
13
11
9
7
5
3
0
25 50 75 100 125 150 175 200 225 250 275 300
Average Daily Traffic (ADT)
13
Roughness: Effect of Environment
Type and Traffic
Effect of Environment and Traffic on Roughness
Gradings Every 6 Months / Flat and Level Terrain
21
19
Roughness (IRI)
17
Environment
Type
15
Arid
Semi-arid
Sub-humid
Humid
13
11
9
7
5
3
0
25 50 75 100 125 150 175 200 225 250 275 300
Average Daily Traffic (ADT)
14
Roughness: Effect of Material
Properties
Traffic
(ADT)
25
25
25
25
25
25
25
Frequency
of Gradings
(months)
1
3
6
9
12
18
24
Lateritic Gravel
Semi-arid Environment
Flat &
Rolling &
Level
Hilly
Mountainous
Terrain
Terrain
Terrain
4.0
4.2
4.4
6.0
6.5
7.1
8.3
9.1
10.0
9.7
10.7
11.8
10.8
11.8
13.1
12.3
13.4
14.9
13.2
14.5
16.1
15
Earth Road
Semi-arid Environment
Flat &
Rolling &
Level
Hilly
Mountainous
Terrain
Terrain
Terrain
2.8
3.0
3.3
5.0
5.6
6.3
7.4
8.2
9.3
8.8
9.8
11.1
9.8
10.9
12.3
11.2
12.4
14.0
12.1
13.4
15.1
Material loss
Effect of Rainfall and Traffic
16
Material loss
Effect of Rainfall and Terrain
17
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

•
18
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
19