Are there simple and practical ways to improve the way maintenance is completed on unsealed roads, so that I maximise the money that I have available?
The only major controllable aspects that an organisation has in maximising the life of its unsealed road gravel pavement are in the below two techniques.
- Regular Grading of the road surface using correct techniques to ensure the removal of road defects and compaction of a uniform layer of retrieved material at optimum moisture content, to ensure maximum stability and long life.
- Re-gravelling of the Road with better quality gravel materials , to specification, will ensure the decrease of gravel loss over time and also reduce the frequency of grading required.
How Different Grading Techniques Affect The Roughness Of Road
The rate of deterioration is directly related to aspects of grading like;
- T he amount and technique of adding moisture in the grading process.
- Effective removal of road defects, by adequate cut depths.
- Compaction equipment used.
As you can see in the graph;
-
The minor grade has not totally removed the defect and the material from the cut process is placed back over the defect with some moisture and rolling. After a short period the material over the defects will disappear and the defect will be exposed again.
-
The major grade has totally removed the defects and the material from the cut process has been placed back in a uniform layer with the right amounts of moisture and rolling.
Even though the minor grade type will cost less, the effectiveness of this grade type in reducing the roughness over time is poor compared to say a major grade type. (Possibly 5 weeks compared to 4 months)
Also, if you look at the cost effectiveness on both techniques, you will find that a major grade can be more cost effective in the long term.
The reason for this is a major grade ensures that all the defects on the road have been removed and the material that is retrieved in the cut process is placed back down on the road with adequate amounts of moisture and compaction to ensure maximum stability. (In this case with a grader, water truck and roller.)
How Gravel Quality Affects The Roughness Of Road
The other major controllable aspect that can be used to control the deterioration rate of an unsealed road is in the correct selection of the gravel quality used for the resheeting process
Material quality affects two things:
- The deterioration of the road after grading.
- The amount of gravel loss over time.
Common defects on unsealed roads have a direct relationship to the material quality .
It is therefore suggested that the organisation maintaining unsealed roads complete soil testing of their gravel materials before it is used on their unsealed roads network.
Over the last four years I have been using a gravel material chart that lets you know in simple terms how a gravel material will perform on an unsealed road. I have found this chart very useful in predetermining the suitability of gravel's for unsealed roads.
By soil testing the gravel materials, you can manage the quality. By managing the quality you will be able to save money in the long term. (Gravel quality of the gravel directly affects the rate of deterioration of a road in two ways; the rate of gravel loss and time grading is required)
Suggested Gravel Soil Tests and Assessment
By completing linear shrinkage and grading soil tests then you will be able to use the below chart that will measure the performance of those materials. (This chart is used in the latest ARRB Unsealed Road Manual, which is commonly used for councils.)
Source: “Neural networks for performance prediction on unsealed roads” by Lea, Paige-Green and Jones. RTR 1999.
The horizontal axis, for this chart, is calculated by:
-
Grading Coefficient = {(% Passing 26.5mm - % Passing 2.0mm)x(% Passing 4.75mm)/100}
The vertical axis, for the above chart, is calculated by:
-
Shrinkage Product = (Linear Shrinkage x % passing 0.425mm Sieve)
Operational techniques are one of the major aspects where council can save money. If you would like to discuss this aspect further or organise a training day with operators and supervisors please contact me by email