GRAVEL LOSS ON UNSEALED ROAD AND

MATERIAL QUALITY

Vasu (Vasantsingh) Pardeshi

Scenic Rim Regional Council

John Byrnes

GenEng Solutions

Dr. Sanjay Nimbalkar

University of Technology Sydney

Abstract: Gravel loss on unsealed roads is financially a major setback for all road agencies. It is also

environmentally unsustainable to continue forever with continual gravel loss. Unsealed road

management issues are difficult to forecast behavior, significant data collection needs, and

vulnerability in the level of service & maintenance practices. The quality of gravel material is one of

the greatest influencing factors. All over the world and in particular researchers from Australia and

New Zealand have developed gravel loss models to estimate gravel loss. Those studies have

developed gravel loss models and deterioration models and maintenance strategies. Some of the

studies have used different approaches such as System Dynamic Modelling Approach which can be

grouped under the Asset management approach. Scenic Rim Regional Council (SRRC) has

commenced a long-term gravel loss project considering flood repair work of unsealed road network

after the reconstruction work of gravel network due to Ex-Tropical Cyclone Debbie. This project aims

to refine the gravel loss model based on proposed minor changes to material specification for use

at SRRC. The gravel material as per modified ARRB specifications is used on the unsealed road

network at SRRC. Gravel loss monitoring stations are established over the entire region to assess

the gravel loss and the implication of using better quality gravel. This paper discusses the gravel loss

monitoring approaches, data analyses, and improved material specification for gravel. It is found

that the modified gravel used on unsealed roads performs better than conventionally used gravel.

Keywords: Gravel Loss, Unsealed Road, Gravel Road, Material Quality

1. Introduction 'Australian road infrastructure (federal, state, and local) which is estimated to be around $230 billion, excluding bridges, as noted by Roads Australia (2015). The annual maintenance and rehabilitation expenditure on Australia's roads are around $14 billion (Martin & Choummanivong 2018). Australia has in total about 900,000 kilometres of roads, of which 575,000 kilometres, or 65 percent, are unsealed according to the ARRB's Unsealed Road's Best Practice Guide 2 (May 2020). The majority of these unsealed roads are the responsibility of the respective local council, which is an onerous task considering many rural and regional councils cover huge areas and have only a small population to try to meet the costs to maintain. Queensland has 51,482 km of unsealed road length comprising62 % of the road network (Australian Rural Road Group, 2010). Gravel roads are the economic backbone of Australia supporting mining, farming, and forestry. These roads usually fall short of the traffic numbers required for upgrading to sealed roads, but their importance cannot be underestimated. As stated in the first paragraph Australia's unsealed road network incorporates approximately 60% of the entire road network and approximately 20% to 30% of the overall road maintenance investment. It is an important part of the public road infrastructure investment. Communities in rural and regional Australia rely on the quality of their local roads to move their products and people safely and efficiently. Major complaints across many councils about gravel roads are related to dust, potholes, and either slippery road after wet weather or loose stones after a long period of dry weather. An often-forgotten advantage of gravel roads, compared to lightly sealed roads, is its forgiveness to external forces. For example, a vehicle with a ten-ton load would damage a lightly sealed road to require re-sealing or even reconstruction. The damage on a gravel road would be much easier and less expensive to correct. For about 575,000 km length of unsealed roads in Australia, the approximate maintenance cost per year is A$ 1 Billion. Scenic Rim Regional Council's annual maintenance budget on the unsealed road is about A$ 2 Million per year (SRRC, 2018). Major issues associated with gravel roads are gravel loss, shape loss, and rideability. Those three major issues are a result of deterioration factors: insufficient drainage capacity, dust, corrugations, potholes, ruts, loose gravel, frost damage. Deterioration is defined as the gradual worsening of conditions that is governed by the behavior of the material (surfacing and roadbed) and the capacity of the drainage system under the combined actions of traffic and the environment. Traffic-dependent factors comprise mainly traffic volume, the composition of traffic, and vehicle speed. Maintenance costs increase as traffic volume increases. Traffic flow influences the scope of maintenance work: the larger the traffic flow, the greater the wear and removal of material. A single heavy vehicle can cause as much as 60 times the wear of a light vehicle simply due to the increased tyre contact area with the road, combined with the higher tyre pressures and tyre rigidity. The geometric factors mainly include road width, alignment, and profile of the road. A wider road normally requires greater use of resources in the form of applied material, while traffic on a narrower road must keep to a smaller area, which results in more track-bound traffic. Physical factors comprise the petrographic composition of the gravel wearing course, particle shape, particle size distribution, frost susceptibility of the road structure, and type of landscape. The quality of the stone material used in the wearing course affects the extent to which the aggregate is crushed by traffic. Maximum stone size plays a big part in surface wear. A large stone size (37.5mm) is required where there is a high volume of heavy vehicles. However, a smaller stone size (19mm or 26mm) results in less surface wear, less damage to vehicles, and less potholing.

The meteorological factors include precipitation, temperature, humidity, and the length of the period when the road is free from snow and ice. Insufficient rain necessitates measures to prevent dusting, while excessive rain makes the road generally sensitive to the action of traffic. Heavy rain may erode the surface, wash away fine aggregate particles, weaken the subgrade and, as a consequence, cause rutting and promote the development of potholes. Water flowing along steep slopes and for long distances creates erosion channels in the pavement surface. Heat accelerates the drying of the surface gravel, which contributes to the creation of dust. The drying and eventual loss of fine dust particles hasten the breaking up of the whole surface. Cold temperatures also play a role. In areas with frost-sensitive soil and a good supply of water, subfreezing temperatures can cause frost heave and the lifting of stones in the road structure. Frost heave creates bumps and, after thawing, unstable spots Alzubaidi et al (2002). Most of the studies conclude it is difficult to predict deterioration models very accurately for unsealed roads due to several variables involved. Even though some of the models have predicted gravel loss there is a need to develop a gravel loss model suitable for local conditions. Current data collection efforts and procedures for unsealed roads are of questionable value due to the tendency has been to apply sealed road asset management techniques to unsealed roads as asset management science has developed. Decision frameworks for unsealed roads are normally a combination of practical and theoretical approaches. Managing unsealed roads often involves operational issues, because unsealed roads change rapidly and when defects appear, they must be addressed within a short response time. For that reason, the most routine and cyclic maintenance are planned and scheduled according to routine inspections and experience from road operators. However, longer-term maintenance activities, such as re-gravelling and surfacing of unsealed roads, need a more sophisticated process that includes predictive models. A major consideration during these analyses involves the economic appraisal of different maintenance options and timings of intervention. Typical Unsealed Road Management Issues are: • Difficulty to Forecast Behaviour • Significant Data Collection Needs • Variability in Level of Service and Maintenance Practices

Based on the available literature and research below listed are the identified gaps and there is scope for further development: • The requirement to develop better material specification by considering local conditions • Develop Martin model further for localised condition • Include effects of proper maintenance, effects of blading after the use of better-specified material • Establish a better correlation between gravel loss and rough meter based on modified gravel

specification This paper describes modifications to material specifications and the process established to measure gravel loss in the field. It compares the Gravel Loss between the proposed modified gravel specification and established material specification. The aim is to maximise material performance based on its characteristics.

2. Modification to Gravel Material Specification: Scenic Rim Council experience

2.1. Scenic Rim Regional Council

Scenic Rim covers 4,254 square kilometres and is home to approximately 40,000 people. The region is framed by mountain ranges including the Main Range, Mistake Range, McPherson Range, and Teviot Range. It also encompasses valleys including Christmas Creek, Fassifern, Warrill; the Albert

River, Logan River, Coomera River, and the Bremer River Valleys and three dams, Lake Maroon, Lake Moogerah, and Wyaralong Dam. Scenic Rim Regional Council maintains an extensive road network of sealed and unsealed roads. Council provides a road network of 1,816km, which consists of 955km of sealed roads, 861km of unsealed roads, and a small number of unpaved roads. Scenic Rim Regional Council has 47 % unsealed road network and 53 % of the unsealed road network. On 30 and 31st, March 2017 Cyclone Debbie and the cold front meeting over the Scenic Rim Regional Council (SRRC) produced the rainfall which ranged from 350mm in the West of the Scenic Rim region to 800mm in the East in 24 hours. The annual average rainfall for Scenic Rim was 892mm (Cryna weather station). The 24-hour flood event was approximately equal to the annual rainfall. The previous maximum recorded daily rainfall was 419mm in January 1974. The Mount Tambourine weather station highest daily record was 563mm in 1974 while the average annual rainfall is 1567mm. The ETC Debbie event was by far the most significant in a 24-hr period on record. Roads and drainage are not designed to withstand this level of rainfall in such a short period. The eastern part of the Southern Downs Regional Council and the Western and Central part of the Scenic Rim Regional Council (SRRC) bore the brunt of the combined Ex-Tropical Cyclone Debbie and the cold front colliding. Although these areas received less overall rain than the eastern part of SRRC, the intensity was extremely high. This resulted in high rainfall in short periods. In turn, the groundwater velocities were very high causing severe scour damage to most gravel surfaces. The short duration of the high-intensity flows resulted in a short period of high-level flooding, and dissipation was relatively fast. Sealed roads suffered very little damage, while gravel roads and bridges received major damage.

Figure 1 - Scenic Rim and surrounding Council in South East Council, Queensland (Map reproduced from Department of Local Government, Queensland website) Scenic Rim Regional Council has a planned maintenance schedule resulting in a fairly well-maintained gravel road network. Before the cyclone Debbie event SRRC contracted a private company, IMG to rate all the roads in the region. The majority of the gravel roads have been rated at a 3 or better on a 1 to 5 scale, where 1 is excellent. In many instances, the damage is not immediately apparent as there is no evidence of destructive damage (washes, slips, major erosion). The damage is in the loss of surface material across the entire road surface, loss of shape, loss of fines, washes in wheel tracks. The volume of water on the roads in a short period has resulted in surface erosion of almost all of the gravel roads to some extent. By using the information before the flood and the information from data collected the range of restoration treatments proposed were:

• A minimum of a medium grade • A heavy grade with a 50mm or 75mm top-up • A heavy grade with a 100mm top or 100mm resheet • A full 150mm resheet.

Figure 2 - Left photo shows severe scour over the whole surface on Kerry Road which became a creek during the storm. The right photo shows regravelled Kerry Road. Due to a large amount of gravel road involved and many roads were getting resheeted Scenic Rim Regional Council initiated a gravel road related research project. This project aims to enhance the existing gravel material specification, measure gravel loss and calibrate the existing gravel loss models, refine those existing gravel loss models to better suit the SRRC area, based on those refined models develop a gravel road maintenance strategy.

2.2. Background on Gravel Road Material specification The ARRB Gravel Roads manual (Unsealed Roads Manual: Guidelines to Good Practice (3rd edition March 2009) and latest published (2020) 'ARRB Unsealed Roads Guide' and 'ARRB Materials Guide' are an excellent source of information for the construction and maintenance of gravel roads. These guides contain several specifications for gravel to be used on unsealed roads (section 3). Many of these specifications have been developed over many years in different parts of the world and are proven to provide good gravel. The damage caused to gravel roads by Ex-Tropical Cyclone Debbie in the SRRC area amounted to 500,000 tonnes. SRRC decided to rebuild the gravel road network using the ARRB gravel specifications. The specification used is the combined Wearing Course / Base Course material described in section 3.5.2 of ARRB Unsealed Roads Manual (2009). The summary of the specification is shown below. Cocks et al. [2] used Paige - Green grading coefficient and shrinkage product concept to refine limits on mine haul roads in western Australia.

Figure 3: Relationship between shrinkage product, grading coefficient performance of base/wearing course (Figure reproduced Pardeshi et.al 2020) Table: 1: Unsealed Road Gravel Specification

It is important to understand the intent of the specification that is described in the preamble to the ARRB specification. The intent is to create a practical specification not constrained by tight limits such as a narrow range of PI, tight grading curve, etc. It is recommended that the specification be adapted to the available material and the circumstances. The basis of the ARRB specification is that the road needs structure in terms of the grading coefficient and binder in terms of the shrinkage limit. The goal is to find a balance between these two to provide a material that performs in all weather and is easily constructible. The ARRB nomograph provides a means to obtain this balance. The SRRC experience is detailed below and hopefully provides a deeper understanding of the ARRB specification. For ease of reference, we have called the unsealed gravel material 'Type 4.5'.

2.3. SRRC Experience on gravel material In the beginning, SRRC worked with a single local quarry. The quarry produced the material giving results within the envelope on the ARRB nomograph. Initially, SRRC decided to allow the full range of the shrinkage product from 100 to 350. The Shrinkage Product was within the desired range, around 180, the grading coefficient was at the midpoint of the allowable range and the CBR averaged

30. A production run was made following the testing, and the test results confirmed that the material conformed. This material was trialled on three roads and performed beyond expectations. It had good constructability and excellent wearing ability. The wearing surface provided a smooth ride, required little maintenance, and created little dust. Tenders were called to create a panel of gravel suppliers using the ARRB specification as is. The next production run from the same quarry tested within specification but much higher on the shrinkage product, reaching 300. Although within specification the material was not easy to use, sticking to machinery and machinery getting bogged. The slightest rain caused a very slippery surface and vehicle bogging. Over the next few weeks, the in-specification material continued to be hit and miss. Many tests were conducted and, although the material was within the ARRB specification, there was no clear indicator of why some material was good and some were bad. To find a solution it was important to understand the nature of the gravel required. The material has two main parts. Firstly, the grading must be such that there is a good structure providing interlocking and support. Secondly, the material fines properties (percentage passing 0.425) must have the ability to bind the structure without being overly plastic. Putting the two parts together, there must be enough structure and the correct blend of fines to create the correct material. Approximately 80 material quality tests were conducted from numerous stockpiles. All the test results were listed, and the material was rated by constructability and service. There was no immediate pattern as to why some materials were good and others were poor. In particular, there was a tendency to produce material that reduced to mud at the slightest wetting. From visual inspections of the material, comments from the supervisors, and the tests it was realised that the muddy material had little structure, although it was within the limits of the ARRB grading coefficient specification. After some analysis, it was revealed that the better performing materials had a good structure defined by the percentage passing 19mm minus the percentage passing 4.75mm. The better materials had values of between 35 and 50 with those with values around 40 performing the best. This "structure" factor is not the same as the Grading Coefficient. However, this still does not fully coincide with the experienced performance. It was then decided to investigate the binder or clay portion. After some analysis, a correlation emerged showing that the PI x the % passing the 0.075 mm was significant. It seemed to represent the amount of plasticity in the material. By dividing this by the structure calculation above a definite correlation was found for wet performance. If this value was below 5 the material was easy to construct and supported the traffic without rutting or tracking and the material did not stick to the car wheels. Between 5 and 10 the material was sticky, more difficult to work with and wheels created tracks. Above 10 the material shows little support and rutting was evident immediately. We called this factor the Wet Performance Indicator (WtPI). WtPI = PI x %0.075 / (%19 -%4.75) Note that the WtPI is an indicator developed by SRRC as an additional indicator for suitability of material with high Shrinkage Product. There is not sufficient evidence to support that it will provide accurate indications for all materials. Using this factor, a clear correlation with performance was apparent. The WtPI made us realise the importance of the ratio of binder and the structure. Now that the test results could be ranked, the analysis of the test parameters could be undertaken. The ARRB specification allows a maximum Shrinkage Product of 350 but mentions that 240 is preferred. The results showed that 240 is the limit and even that is not suitable in continuously damp areas, such as roads under trees on the south side of a hill. The relationship between the binder and structure was examined in greater detail. With low PI material, and the resulting low Linear Shrinkage (normally 50% of the PI) more fines (0.425 and less) are required to create a material that provides an adequate binder. However, if the percentage fines get too high the structure deteriorates and the material is too sandy to work with. From field experience, this starts to happen when the percentage passing 0.425mm approaches 30%. This roughly equates to a PI of 7 (LS of 3.5) to get the minimum 100 shrinkage product. From this, our specification starts the PI at 8.

On the other extreme when the PI is high, the number of fines must be reduced. There is a limit to how few fines are required. If there are not enough fines the binding action does not take place. For the modified ARRB nomograph we use a maximum of 220 for the shrinkage product. The lower limit of workability for 0.425mm is 15%. Below this, the material is too bony. This equates to a shrinkage limit of around 15 or a PI of around 30. Working with a PI of 30 is not easy. The material sticks to the machinery, it tends to lump the fines together, the clay prevents the water from penetrating, etc. From experience on-site, it seems that a PI of around 25 is the limit for workability. This equates to a shrinkage limit of around 12. To remain within specification the maximum fines (0.425mm) is around 18%. As 15% is the minimum for workability, this small range is not possible to work with. It is almost impossible for quarries to produce to this fine tolerance. For this reason, the PI is limited to 20. The SL is around 10 giving a % passing the 0.425 of 22%. This leads to the limits of the 0.425mm being 15% to 22%. We allowed 15% to 25% but will analyse material for suitability if it is outside this range. As the PI is fixed to the material available, the quarry needs to vary the fines and the grading curve to match the PI. Although the other factors like the LL and SL are important, they are less sensitive for this material, provided the PI, percentage fines, and structure (19-4.75) are within the required limits. The fines ratio should be around 0.65 but there is no evidence that departure from this causes much of a problem. Note that the ratio of the fine for type 4.5 is typically higher than most other materials. On the ARRB nomograph, the climate must also be taken into account. In wetter areas, it is advisable to aim lower towards the 100 and in drier areas, it is recommended to aim towards the 220. We found that due to variations of material between quarries and also variations of materials within quarries the specification needs to be adaptable to the specific material.

Figure 4: SRRC gravel results plotted on 'shrinkage product, grading coefficient performance of base/wearing course' graph (Figure reproduced Pardeshi et.al 2020) The blue dots in Figure 4 substantiate, the gravel used for reconstructing unsealed roads within the SRRC area was conforming material. Total 696 test results are plotted in this graph and the majority are within 'Good' area E of this graph.

2.4. SRRC Modified Gravel Specification It is important to understand that the specification should be broad and allow quarries some flexibility when manufacturing the material. Where the material is out of specification it should first be analysed for suitability before rejecting it.

Figure 5: Modified 'shrinkage product, grading coefficient performance of base/wearing course' graph suitable for SRRC (Figure reproduced Pardeshi et.al 2020) Scenic Rim Regional Council has modified gravel material specification through field experience.

Table 2 provides Grading coefficient and Shrinkage product limits. Table 3 provides Characteristic

limits for modified gravel specification. Table 4 details gradings for 37.5mm, 26mm and 19mm

maximum size stones. The Grading Coefficient and Shrinkage Product limits are mandatory. Table

2,3,4 assist in production and selection of Type 4.5 gravel.

Table: 2: Grading coefficient and Shrinkage product limits at SRRC

SRRC Limits SRRC Ideal

Grading Coefficient 16 to 34 16 to 34 Shrinkage Product 100 to 250 150 to 220

Maximum Aggregate Size

There are three sizes: 19mm; 26mm and 37.5mm. They are used as follows:

19mm Sealed road gravel shoulders, very low volume roads, long narrow cul-de-sacs

26mm General use road gravel for use on most roads.

37.5mm for use with high volume heavy vehicle traffic only.

Scenic Rim has developed additional information to assist in the improved selection of gravel.

Table: 3: Modified Unsealed Road Gravel Specification limits at SRRC: Characteristic limits

Characteristic Limit 37.5mm Limit 26mm Limit 19mm

PI Range 8% to 24% Range 8% to 20% Range 8% to 24%

Linear Shrinkage Range ~4 to ~13 Range ~4 to ~10 Range ~4 to ~13

% passing 0.075 Range 6% to 17% Range 6% to 15% Range 6% to 21%

% passing 19 - % passing 4.75

Minimum 35% Minimum 40% Minimum 45%

% passing 4.75mm Maximum 50% Maximum 40% Maximum 40%

% passing 0.425 12% to 30% 12% to 25% 12% to 35%

Fines Ration < 0.7 < 0.7 < 0.7

Table: 4: Modified Unsealed Road Gravel Specification limits at SRRC: Gradings

37.5mm 26mm 19mm

Sieve Size Minimum Maximum Minimum Maximum Minimum Maximum 37.5 100 26 94 97 100 19 82 90 85 97 100 9.5 50 80 50 80 85 95 6.7 40 70 40 70 65 80 4.75 35 50 25 40 30 40 2.00 20 40 15 35 25 40

0.425 12 30 12 25 12 35 0.075 6 17 6 15 6 21

A further test is to use the Scenic Rim Regional Council developed Soaked Performance Indicator. This indicator gives a fair estimation of the performance of the gravel in wet weather. SPI = (PI x % passing 0.075) / (% passing 19 - % passing 4.75) The acceptable value of this is 5 and below. Values between 5 and 10 have shown to result in sticky and slippery surfaces. Values over 10 have shown to result in deep tracking and rutting. Values over 15 have shown to result in structural failure.

3. Long term gravel loss monitoring in Scenic Rim Regional Council

3.1. GL Station selection Fifty-six gravel monitoring stations are established within the Scenic Rim Regional Council area. There are 23 stations in the East region and 33 stations in the west region. The flood-affected area was divided into 6 different geographical areas (South West A, Northwest, South West B, East A1, East A2, East B, North East). All roads were investigated, and damages were recorded due to the extensive damage because of ex-tropical cyclone Debbie to the road network. A list of damaged road sections based on this database was developed. The unsealed road sections were selected from this damaged road section list. These sections were going to be either graveled or resheeted. The damaged road list had 2397 rows or sections of road. Each row had asset/road name, asset number, start and finish chainage, treatment type, and geographical region. Using the random generation of numbers 56 stations were selected. This initial list had only 4 d and 4 e class roads. After going through another iteration of the asset list 4a,4b, and 4 c class roads were selected. Each station was inspected on-site for the geometry of the road (horizontal, vertical curve, flat, slope), the number of houses on the road, no through road or connector. Traffic volume was a major

consideration before station location was finalised. This was required as the selected road station was generated with start and end chainage. The actual station location was selected by a site visit and then chainage recorded for a particular station.

3.2. Establishment of GL stations in the field The gravel loss monitoring period for established stations is going to be about 4 years. To be able to validate data, the accuracy of measurement is required. The monitoring station was required to establish considering permanent survey control mark. The permanent control mark was established by driving a 1.8 m star picket deep into the ground. Two-star pickets were driven on both sides of the road. The precast concrete surround was placed to make the top surface even with the surrounding ground level. Due to safety reasons, a plastic cap was placed on the concrete surround. Refer attached survey control mark drawing (figure 6) and a photo (figure 7) of this station. The third survey mark is established to the nearby fence or pole about 100 to 150m from those two permanent stations. The reason behind establishing three reference points is being able to check or cross-verify levels relative to each other due to ground movements. Each station is marked with a unique station number inside the concrete surround.

Figure 6: Gravel Loss station drawing detailing GL station to establish in field

Figure 7: Photo of GL station from distance and close up. Right photo of marker: number 10 indicates station number and 'c 9.5' indicates distance to the centre of road from this station (Part Figure reproduced Pardeshi et.al 2020)

3.3. GL Level records There was a need to establish consistency and uniformity across the whole Scenic Rim Region so that during the level measuring, recording, and analysing stage the level records are validated. For each gravel monitoring location, the Left-Hand Side (LHS) station is while going up the chainage. A permanent marker is attached to the star picket inside the concrete surrounding. On this marker, station number and distance to the centre of the road is marked during the first set of level records. The Centre of the road is established during the first set of level records. Every time a string is pulled between two stations and the centre is established or marked by measuring the distance from the LHS station which is on the marker. From the established centre on road, a point is marked every 500mm towards both the road edges. Pulling a string between two stations and marking the road centre from the LHS centre provides certainty that for each set of level record it is the same position of points on the existing road. RL of 10 is always given to the LHS station and levels are measured with a dumpy level on the same set of points for each road. This process will be repeated during each set of level records. Using the recorded levels cross profiles are plotted. Those cross

Looking at GL station from

distance

Looking at GL station Close up

Station marker close up, number 10 is station

number and 'c9.5' is distance from station to

road centre/ (crown) of 9.5m

profile data will be collected and analysed for actual gravel loss and shape loss at each location.

3.4. GL comparison on existing gravel material and proposed modified gravel material

Out of 54 stations, 20 stations with Existing Material (EM) plus Modified Material (MM) were compared with 10 stations of EM to compare gravel loss across a section of road. This was due to the availability of EM and MM only for 20 stations. The remaining 34 were MM. For all stations, ADT varies from 80 to 1000, and rainfall (MMP) varied from 50 to 117 mm. Material property noted as PF is the product of plasticity index and material passing through a 26.5mm sieve. PF of new material varied from 56 to 268. The Modified Material (MM) was as per modified specification and referred to as modified material (Pardeshi et. al.2020). Figure 8 presents the variation in Gravel Loss (GL) in mm over several days (t). On the existing gravel material road sections, the gravel loss was at a higher rate in lesser duration. For a fair comparison, GL at each station is converted for 365 days (one year) by extrapolating the recorded gravel loss over specific measured days. On EM maximum gravel loss was 214.13 mm. The minimum gravel loss was 7.64 mm within 239 days on one location which is an exception. On the new gravel material road section, the GL was at a lower rate than old gravel and for a longer duration. The maximum GL was 44.37mm for 365 days and even a marginal GL of 1 mm was recorded over 230 days. The median value of GL is 48.66mm on EM for one year and 7.93 mm on MM (Pardeshi et. al.2020). The GL rate seemed to be significantly high for old material which was not modified material. There was a lesser need for regarding the roads due to this improved gravel road due to the use of modified gravel material. The field crew confirmed it demonstrated the reduced need for regrading those roads than normally required to grade. Normally those roads need to be graded within one year but due to modified material, those roads are not graded for almost 18 months since the Modified material was used. This demonstrates the benefits of good gravel material. The Modified material based as per figure 8 shows consistent results of reduced GL (Pardeshi et. al.2020).

Figure 8: Gravel Loss comparison between Existing and Modified Material (Figure reproduced Pardeshi et. al. 2020)

4. Conclusion There is a huge potential for cost savings by reducing gravel loss on unsealed roads. The majority of gravel loss rate is between 6 to 10mm per year. Thew (2009), estimated the cost of $4.6 million per mm gravel loss in New Zealand. Thew estimated this loss to be $33.7 Million per year on unsealed roads in New Zealand. In Australia, this cost is going to be a lot bigger. There are wider environmental impacts by reducing gravel loss on unsealed roads. Many studies conclude difficulty predicting deterioration models very accurately for unsealed roads due to several variables involved and the requirements of time and resources. Even though some of the models have predicted gravel loss there is a need to develop a gravel loss model suitable for local conditions. Based on the available literature and research the identified gaps and scope for further development are: • The requirement to develop better gravel material specification by considering local

conditions • Develop Martin 2013 (ARRB) model further for localised condition

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700

Gra

ve

l L

oss

, G

L(m

m)

Elapsed Duration, t (days)

13

29

32

51

StationsNew gravel added

• Include effects of proper maintenance, effects of blading after the use of better-specified

material • Establish a better correlation between gravel loss and rough meter Gravel Loss results demonstrate gravel loss is reduced due to the use of the revised specification. The soak performance indicator is proposed for revised gravel specification. The revised material is currently being trialled for assessing effectiveness under wet and dry weather conditions.

Acknowledgments

The authors would like to acknowledge

• Chris Gray, General Manager, Infrastructure Services from Scenic Rim Regional Council for

providing support for this research project.

• Dr. Sanjay Nimbalkar from the University of Technology Sydney for the guidance of gravel

loss project

• This research is supported by an Australian Government Research Training Program

Scholarship for Ph.D. student Vasu (Vasantsingh) Pardeshi

References

• Alzubaidi, H., Magnusson, R., 2002, 'Deterioration and Rating of Gravel Roads, Road

Materials and Pavement Design', Vol. 3, no. 3, pp 235-260

• Cocks et al., 2015, The use of Naturally Occurring Materials for Pavements in Western

Australia, Volume 50, no.1, Australian Geomechanics, Australia

• Department of Local Government, Queensland (2018)

<https://www.dlgrma.qld.gov.au/resources/map/local-government-area-

boundaries.pdf>

• Infrasructure Features, January 2021

https://www.createdigital.org.au/upgrading-outback-way-australias-longest-

shortcut/?utm_source=ExactTarget&utm_medium=email&utm_campaign=EDM-

20210128

• Giummarra, G., J., 2009, Unsealed Roads Manual: Guidelines to Good Practice, 3rd

edn, ARRB Group, Melbourne.

• Henning, T., F., P., Flockhart, G., Costello, S., Jones, V., Rodenburg, B., 2013,

Managing Gravel Roads on the Basis of Fundamental Material Properties, prepared for

presentation at the Transportation Research Board 94th Annual Meeting, Washington

D.C. and possible publication in the Journal of the Transportation Research Board

• Jones, D., Paige-Green, P., Sadzik E., 2003, Development of Guidelines for Unsealed

Road Assessment, Transportation Research Record 1819. Paper No. LVR8-1179.

• Juturna Consulting on behalf of the Australian Rural Roads Group, 2010, Going

Nowhere: The rural local road crisis Its national significance and Proposed Reforms,

Australian Rural Roads Group, NSW, Australia.

• Martin, T. and Choummanivong, L., 2016. The benefits of Long-Term Pavement

Performance (LTPP) research to funders. Transportation Research Procedia, 14,

pp.2477-2486.

• Martin, T. and Choummanivong, L., 2018, May. The benefits of long-term pavement

performance (LTPP) research. In ARRB International Conference, 28th, 2018,

Brisbane, Queensland, Australia.

• Paige-Green P., 1989, The influence of the Geological and Geotechnical Properties on

the Performance of Materials for Gravel Roads', Ph.D. Thesis, University of Pretoria,

Pretoria.

• Pardeshi, V., Nimbalkar, S. and Khabbaz, H., 2020. Field Assessment of Gravel Loss

on Unsealed Roads in Australia. Frontiers in Built Environment, 6, p.3.

• Pardeshi, Vasantsingh, Sanjay Nimbalkar, and Hadi Khabbaz. "Theoretical and

Experimental Assessment of Gravel Loss on Unsealed Roads in Australia." In

Sustainable Civil Engineering Practices, pp. 21-29. Springer, Singapore, 2020.

• Road Infrastructure Management Support (RIMS), 2015, Unsealed Roads Tactical

Asset Management Guide, RIMS, New Zealand.

• Scenic Rim Regional Council (SRRC) (2018), 2018-19 Community Budget Report

Scenic Rim Regional Council, 2018-19, Scenic Rim Regional Council, Beaudesert,

Australia

• Thew, C., 2009, 'Gravel Loss Monitoring Project Summary Presentation', presented at

REAAA low Volume Roads, Napier, NewZealand