Unsealed Road Grading Techniques

Hall, Nick (2022) Unsealed Road Grading Techniques. [USQ Project]

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Australia has approximately 900 000 kms of road network length widely spread throughout the country, with approximately 575 000 km (63%) being made up of unsealed roads. These unsealed roads play a pivotal role in the transportation network with approximately 80% of all roads being the responsibility of Local Governments throughout Australia. These unsealed roads are often the only route for primary industry transportation purposes within rural communities and provide critical access to and around rural communities (Australian Road Research Board 2020).

The Australian Roads Research Board (2020) identified that since 1990/91 the annual road freight has more than doubled causing substantially more impact on the road network. The annual funding on construction, maintenance and operating of all Australian public roads is over $30 Billion, with only 6% of this spent on 63% of the road network, being the unsealed roads (Australian Road Research Board 2020, p. 4). This limited spending across the unsealed road network is causing major challenges.

An important element to obtaining the longest life of the gravel layer on an unsealed road is periodic maintenance grading. The grading of an unsealed road is considered the single most important function in maintaining an unsealed road network. Therefore, this project will aim to determine the most cost-effective grading technique to perform on unsealed roads by trialling and assessing the various techniques to a case study unsealed road within the Charters Towers Regional Council (CTRC) area.

The stages involved in the execution of the project include: 1. Undertake a literature review of unsealed road deterioration factors, grading techniques and maintenance strategies. 2. Identify and select a gravel road to be segmented into four sections for grading techniques – Light Grade Lot, Medium Grade Lot, Heavy Grade Lot, and a Control Lot. 3. Conduct appropriate gravel testing for each road segment for soil classification and work quality completed. 4. Conduct and document grading techniques and costs required for each segment. 5. Condition survey each segment at the completion of treatment and then periodically after, to obtain a deterioration rate. 6. Analyse deterioration rate and determine maintenance frequency and performance costs of each technique. 7. Identify and recommend the most cost-effective grading technique to be performed on unsealed roads.

An intervention for grading is identified as the International Roughness Index score of 8. A roughometer is used throughout the project to measure the IRI and obtain datapoints against each Lot. The intervention of IRI 8 was not met during the project therefore, the regression model was only used to extrapolate 12 months of forecasting. With these results, the heavy grade is the lowest IRI at 12 months and therefore, this IRI is used as an “intervention IRI” to compare and cost analyse each technique. The IRI intervention level is now 4.57. Using the intervention timeframe, costed day rates and kilometres of road graded per day, a Performance Cost for each grading technique is determined as follows: Light Grading Performance Costs $4.64/km/Day; Medium Grading Performance Costs $8.10/km/Day; Heavy Grading Performance Costs $12.26/km/Day.

It is concluded that Light Formation Grading unsealed roads is the most economical grading technique to use when maintaining unsealed roads. The Medium Formation grading will cost 75% more than the Light Formation Grade and Heavy Formation Grading will cost 164% more than the Light Formation Grade. There is scope to refine this conclusion through continuing to monitor the test road until intervention of IRI 8 is met along with completing a repeating cycle where the grading technique is completed on a road that is starting at an IRI of 8. Substantial cost savings can be made by Local Governments selecting Light Grading over the other two commonly used methods.

This project can provide the industry three set grading technique procedures with data and insight into the three grading techniques cost and deterioration performance. This project can now provide ideas for future projects in determining how other roads deteriorate with different variables to this project.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors: Thorpe, David
Qualification: Bachelor of Engineering (Civil)
Date Deposited: 20 Jun 2023 04:07
Last Modified: 20 Jun 2023 04:07
Uncontrolled Keywords: unsealed roads; maintenance grading; gravel
URI: https://sear.unisq.edu.au/id/eprint/51900

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