development of forward works program and prediction …

DEVELOPMENT OF FORWARD WORKS PROGRAM AND PREDICTION OF DETERIORATION RATES ON UNSEALED

ROADS

Authors: Justin Weligamage1; James Erskine2

(1) Toowoomba Regional Council, Principal Engineer Asset Management, Toowoomba E:[email protected] P: +61 7 4688 6244

(2) Pavement Management Services, Senior Pavement Engineer, Sydney E:[email protected] P: +61 403 240 718

Abstract For most rural road agencies the unsealed road network is by length the biggest road asset and has the highest maintenance requirements. Developing sound strategic planning for this asset is vital to ensuring community access to rural and isolated locations is maintained. This paper looks at the strategic use of the data captured as part of the comprehensive survey recently completed on the Toowoomba Regional Council (TRC) unsealed road network. The data which included gravel depths and material type along with gravel depths, geometric profile, condition, and drainage/shoulder status was used to develop an Unsealed Condition Score (UCS) that was used to establish a priority with which works could be ordered. Subsequent annual condition data collected on the higher order roads across the network has been used to examine and provide initial deterioration rates of the unsealed road performance. The collected data was used to trigger works activities appropriate for the local conditions of each road segment and backlog of work was determined where the condition of the unsealed road network did not meet the Levels of Service. A three year program to address this backlog was developed based on the UCS. In order to project and justify long term investment needs of the unsealed network it is necessary to understand the deterioration rates for the condition parameters that trigger the works activities. Condition data collected from the second survey and utilised in this study will be combined with additional survey data to be collected in future years to improve the confidence of the deterioration rates and predictions made from this data. Introduction: The Toowoomba Regional Council (TRC) covers an area of 12,973km

2 and is uniquely

located in the south-east corner of Queensland, Australia. The TRC’s road network consists of a total of 8,087km of roads, 82 major structures (bridges/major culverts). Unsealed roads represent 4,865km and sealed roads the remaining 3,222km. TRC has responsibility for the delivery of safe and sustainable transport infrastructure and management of the unsealed roads network, which forms part of essential provision of access for rural communities. One of the biggest challenges facing Council is how to fund vital infrastructure projects. A key question which must be addressed in managing roads is whether the rate of improvement of the road network is keeping pace with the growth in road needs, including restoration of the ageing elements of the network. As a result, Council has developed an unsealed road network management strategy with the aim of creating a more positive cost

benefit ratio between investment and return and, in turn, optimise the road networks serviceability standard. The first step to developing the new management system was the identification of the characteristics and condition of the current road network. On this basis, TRC engaged Pavement Management Services (PMS, formerly Fugro PMS) to accomplish the data collection of pavement defects, road assets, pavement materials types, thickness of the pavement layer, condition of the shoulder and drainage of 3100km of the Toowoomba’s unsealed road Network. Toowoomba’s unsealed road network comprises of 3132km of gravel roads, 148km of formed and 1585km of unformed roads. The data collection was achieved by a post-survey visual assessment and the use of a Ground Penetrating Radar (GPR), which was integrated to the host vehicle to determine the existing pavement layer(s) and thickness(s). The survey system was mounted to a suitable and rugged host vehicle. Five cameras were fitted on the survey unit facing the front, rear, left and right side to cover all road assets, so data could be extracted for future references. Objective: The objective of this paper is to demonstrate TRC’s strategic approach with regards to the development of effective work programs as well as robust maintenance & renewal strategies, based on the pavement profile and the condition of individual road section. It allows the Council to obtain a better value for money solution with respect to maintaining and operating the unsealed road network. In addition, this paper shows the condition data extracted from current and future surveys will improve the understanding of deterioration and ensure confidence in prediction. Methodology: The area under study comprised of 3100km of unsealed roads. The following information was collected on each section that comprises the network: a) type of the gravel layer(s); b) condition of the pavement; c) condition of the shoulders and drains; d) road assets; e) length and width of the roads; f) pavement profile data from an integrated Ground Penetrating Radar (GPR), and g) GIS coordinates of all sections surveyed. The extent of unsealed pavement defects was determined through a video survey followed by post rating of the collected images. The video survey was conducted using a Four Wheel Drive mounted with five cameras orientated to provide full coverage of the road surface and immediate road reserve including shoulder and table drains. The survey recorded the extent, severity and location of the unsealed pavement defects found. The extent of pavement defects was assessed as the length affected by each defect, with the location where the condition of any defect changed recorded. Homogeneous sub sections were subsequently created from this information reflecting distinct changes in the underlying condition of the unsealed road segment and from which decisions relating to appropriate treatments can be made.

Assessment of Unsealed Defects – Pavement condition, Roadside assets and shoulders The pavement defects identified during the inspection are tabulated in figure 0-1, the severity assessed against each defect are summarised in Table 0-1 to 0-5 [1]. In addition, locations where the level of the shoulder with respect to the central pavement was higher were recorded.

Figure 0-1 Unsealed Pavement Defects

The road profile was rated on a scale of 1 to 5, where one is very good and the trafficked surface will shed water easily, and five is very uneven resulting in potential localised ponding and/or surface drainage occurring in a longitudinal direction.

Table 0-1 Cross-Sectional Profile Condition

Condition Description 1 (Very Good) Well formed camber (about 3 - 4 per cent)

2 (Good) Good camber (about 2 per cent) 3 (Flat) Some unevenness with camber mostly less than 2 per cent

4 (Uneven) Obvious development of irregularities that will impede drainage and form depressions

5 (Very Uneven) Development of severe irregularities impeding drainage and likely to cause extensive localised ponding. Water tends to flow to the centre of the road or individual lanes

Drainage from the road is rated on a scale of 1 to 5 where one indicates that the road is well above ground level and has effective side drains leading water away from the road formation and five is classified as a canal where the road acts as the drainage path in the area.

Table 0-2 Drainage Condition

Condition Description

1 (Well above ground level) Edges of road are at least 300 mm* above natural ground level with effective side drains

2 (Slightly above ground level) Road is between 50 and 300 mm above natural ground level. Side drains are present. Stormwater could cross in isolated places

3 (Level with ground) Road is generally at ground level with ineffective side drains. Stormwater could cross in most places

4 (Slightly beneath ground level) Isolated areas of the road are below natural ground level. No side drains are present and localised ponding of water will occur

5 (Canal) Road is the lowest point and serves to drain the entire area * If pipes are laid under the road for drainage, then the formation should be at least 500 mm above natural ground level

Potholes are rated on a scale of 1 to 5 where one indicates that depressions are only just visible and five is classified as large and dangerous requiring evasive action.

Table 0-3 Pothole Condition

Condition Description 1 Depressions just visible. Cannot be felt in the vehicle 2 <20 mm deep 3 Larger potholes affecting safety from 20 - 50 mm deep 4 50 - 75 mm deep 5 Large, dangerous potholes requiring evasive action >75 mm deep

Corrugations are rated on a scale of 1 to 5 where one indicates that corrugations are not felt or heard and five is classified as dangerous requiring motorists to drive very slowly and take a different path.

Table 0-4 Corrugation Condition

Condition Description 1 Not felt or heard in a light vehicle 2 Can be felt and heard, no speed reduction necessary 3 Can be felt and heard, speed reduction necessary 4 Significant speed reduction necessary 5 Drivers select a different path and drive very slowly. Safety is affected

Embedded stones are rated on a scale of 1 to 5 where one indicates that embedded stone are not felt or heard and five is classified as damaging requiring motorists to drive slowly and avoid stones that are protruding.

Table 0-5 Embedded Stones Condition

Condition Description 1 Seen, but not felt or heard in a light vehicle 2 Protruding stones can be felt and heard, but speed reduction not necessary 3 Speed reduction necessary 4 Protruding stones require evasive action 5 Vehicles avoid protruding stones or drive slowly

Ground Penetrating Radar (GPR) The GPR survey was carried out using a GSSI SIR30 digital GPR system connected to antennae operating at centre frequencies of 2.2 GHz, 1.5 GHz, 900 MHz and 400 MHz. These frequencies were selected to provide the best combination of thin layer resolution and depth penetration, resulting in information on materials 20 mm thick at the surface and penetration to a depth of approximately 2 m below ground level. The GPR survey was completed using a four wheel drive vehicle. The 2.2 GHz antenna was mounted to the rear of the vehicle on a 2 m long non-metallic arm positioned roughly 500 mm above the nominal ground surface. A sled containing the three remaining antennae was attached to the base of the vehicle, sitting approximately 25 mm above the nominal ground surface. Data was collected at a density of 10 scans per metre at normal traffic speeds, to gather a detailed dataset. The GPR system was connected to a hub encoder and dGPS to provide both linear offset and coordinate based relocation systems. For the GPR survey, the video which was collected at the same time was used to solve relocation issues and as an aid to selecting locations for targeting the boreholes used to calibrate the signal response for the types of gravel materials found throughout the network. The video was also used to assist with the GPR data interpretation, for material identification and pinpointing features of interest in the road. The depth of gravel for each sub-section identified from the visual inspection was averaged using the depths found from the GPR in order to provide a representative depth for reporting and modelling. The pavement condition assessment, roadside assets and shoulder ratings were conducted based on the captured videos using the LINSEVO software that has been developed by Pavement Management Services (PMS). The post rating of pavement defects was based on the Standard Visual Assessment Manual for Unsealed Roads (2000) prepared by Jones, D & Paige G.1 Considering the limitations of conducting a visual assessment based on video and the time and financial constraints of the project; defects have been selected from the manual for analysis and the definitions for degree of severity Development of Works Program The visual condition assessment of the unsealed road network and assessment of gravel depths from the GPR survey was incorporated into a register of the unsealed road network.

This information was utilised in the preparation of a forward works program that reflected the LOS of TRC and priority for allocation of funds. The available treatments described below were applied to all sub-sections that were determined from the 2012/13 survey where any defect was found to be in a condition of 5 or in the case of corrugations and embedded stones where the condition was a 4 and above. Once a sub-section was identified as requiring treatment the depth of gravel determined from the GPR survey was used to determine whether grading or gravel resheeting was required. Resheeting was triggered when the depth of gravel was less than 50mm for the sub-section. Drainage improvement was included as an associated treatment to clear and reshape table and offshoot drains within those sub-sections that displayed drainage condition greater than 3. The backlog of works was distributed over a three year period by prioritising the road sub-sections based on a ranking of the UCS from highest to lowest. A separate program for shoulder grading was also prepared for those sub-sections that were found to have a shoulder higher than the road. This treatment was undertaken where the visual condition did not trigger any of the treatments described. This work totalled a further $9.0 million of shoulder grading needed across the network.

Pavement Treatments The appropriate and applicable maintenance options considered in the analysis were determined in conjunction with the TRC representatives and are shown in Table 0-6 following.

Table 0-6 Selected Treatments

TREATMENT DESCRIPTION OF TREATMENT UNIT RATE

Grading Used to reshape the road profile or correct potholes and corrugations where there is sufficient existing gravel depth. $1/m2

Drainage Improvement Involves the clearing and reshaping of existing table and offshoot drains and where necessary provision of additional drainage. $5/m

Shoulder Grading Involves grading to remove and reposition excess granular material in the shoulder. $4/m

Gravel Resheeting Provision of additional granular material where there is insufficient gravel depth to provide the required service. $6/m2

These unsealed maintenance treatments or combination of treatments were triggered based on a combined consideration of the unsealed condition, depth of existing gravel and drainage conditions of each sub-segment. Subsequent Condition Survey

Visual inspections of the entire unsealed sealed network was completed between 2012 and 2013 and was the first time a comprehensive survey was undertaken and as such represented the first complete picture of the condition of the unsealed road network. Subsequent survey of the unsealed roads in 2014 focussed on class 4 to 8 roads and class 9 roads having a road width greater than 5m and totalled 500km to examine the performance of those roads and effectiveness of TRC’s unsealed maintenance regime. The 2014 survey covered all of the class 4 to 8 roads and totalled 208km allowing a direct comparison with the previous survey results. The remaining 292km of survey undertaken across the class 9 roads was distributed across the network and as such provides a fair representation of the condition of this class of road, allowing comparison with the 2012/13 results.

0

1

2

3

4

5

4. Highway 5. Regional Arterial 6. Sub-Arterial 7. Distributor 8. Collector 9. Local

Cross-Section Profile Condition

Con

ditio

n

2012/13 2014/15

Unsealed Pavement Condition Comparison

Cross-Sectional Profile The profile of an unsealed road influences the performance of the road such as how well it is able to shed water, which in turn, minimises the development of potholes, and potentially impassable conditions. Flat profiles tend to pond water in localised depressions resulting in a weakening of the wearing course and the development of potholes and other distresses such as rutting. Table 1-1 shows the length of road within each condition by road hierarchy across the network in 2012/13 with the average condition in that period and again after the latest survey and shows an improvement of the network from 3.2 to 2.3. Figure 0-1 compares the condition of the network over the two time periods.

Table 1-1 Cross-Sectional Profile Condition by Hierarchy (km)

1 2 3 4 5 Average Condition

Condition (Very Good

Shape) (Good Shape) (Flat) (Uneven) (Very

Uneven) 2012/13 2014

4. Highway 0 0 3.54 0 0 3 2

5. Regional Arterial 0 0 10.762 0.43 0.21 3.1 2.2

6. Sub-Arterial 0 0 5.546 0.166 0.252 3.1 2.2

7. Distributor 0 7.384 73.214 2.126 2.81 3 2.1

8. Collector 0.729 16.622 82.348 0.438 1.617 2.9 2.2

9. Local 23.774 122.352 2163.884 304.615 259.557 3.2 2.4

Total 24.503 146.358 2339.294 307.775 264.446 3.2 2.3

Figure 0-1 Cross-Section Profile condition over time

0

1

2

3

4

5


Drainage Condition

Con

ditio

n

2012/13 2014/15

Drainage Drainage relates to the removal of standing water away from the wearing surface and underlying pavement structure of the road. This occurs through the provision of effective side and offshoot drains which enable the removal water from adjacent to the road. Table 1-2 shows the length of road within each condition by road hierarchy across the network in 2012/13 with the average condition in that period and again after the latest survey and shows an improvement of the network from 3.2 to 2.7. Figure 0-2 compares the condition of the network over the two time periods.

Table 1-2 Drainage Condition by Hierarchy (km) 1 2 3 4 5

(Well above (Slightly

above Ground)

(Level with Ground)

(Slightly below

Ground) (Canal)

Average Condition Condition

Ground) 2012/13 2014

4. Highway 0 0.542 2.998 0 0 2.8 3

5. Regional Arterial 0 0.524 10.772 0.106 0 3 3.5

6. Sub-Arterial 0.026 3.468 2.248 0.222 0 2.4 3.1

7. Distributor 0 10.796 67.672 4.256 2.81 3 2.6

8. Collector 3.811 19.329 45.605 16.931 16.078 3.2 2.6

9. Local 34.774 357.019 1734.999 480.436 266.954 3.2 2.8

Total 38.611 391.678 1864.294 501.951 285.842 3.2 2.7

Figure 0-2 Drainage condition over time

0

1

2

3

4

5


Potholes Condition

Con

ditio

n

2012/13 2014/15

Potholes Potholes are round or elongated depressions in the road surface and arise from issues relating to the road profile and drainage, compaction, deformation or material quality. Potholes contribute significantly to the development of roughness on unsealed roads and have the potential to cause damage to vehicles if allowed to develop and increase in size. Once potholes have initiated the drainage will deteriorate as water is able to pond in the depressions. Table 1-3 shows the length of road within each condition by road hierarchy across the network in 2012/13 with the average condition in that period and also after the latest survey and shows an improvement of the network from 1.9 to 1.2. Figure 0-3 compares the condition of the network over the two time periods.

Table 1-3 Pothole Condition by Hierarchy (km) Average

Condition Condition 1 2 3 4 5 2012/13 2014

4. Highway 3.54 0 0 0 0 1 1

5. Regional Arterial 11.18 0.072 0.116 0.022 0.012 1 1.1

6. Sub-Arterial 3.352 0.154 2.376 0.066 0.016 1.9 1.1

7. Distributor 55.442 7.212 14.5 2.36 6.02 1.8 1

8. Collector 30.458 25.478 40.312 5.444 0.062 2.2 1.2

9. Local 1499.911 425.301 658.648 192.097 98.225 1.9 1.3

Total 1603.883 458.217 715.952 199.989 104.335 1.9 1.2

Figure 0-3 Pothole condition over time

0

1

2

3

4

5


Corrugation Condition

Con

ditio

n

2012/13 2014/15

Corrugations Corrugations occur in materials that have a low plasticity especially those with a high level of fines such as sand. Corrugations are caused when the material is dry and there is some level of wheel bounce associated with some irregularity in the road. This results in a kick-back of non-cohesive material which is followed by compression and redistribution of the wearing course as the wheel regains contact with the road. Corrugations are one of the most severe defects that occur on unsealed roads, contributing to excessive roughness and poor vehicle stability. They more frequently occur in areas of acceleration, deceleration and cornering where vehicle control is required most. The wavelength of the corrugations is a function of the travel speed of the vehicles using the road, with longer wavelengths formed at higher speeds. Table 1-4 shows the length of road within each condition by road hierarchy across the network in 2012/13 with the average condition in that period and also after the latest survey and shows a slight improvement of the network from 2.9 to 2.7. Figure 0-4 compares the condition of the network over the two time periods.

Table 1-4 Corrugation Condition by Hierarchy (km) Average


4. Highway 0 0.614 1.46 1.466 0 3.2 3

5. Regional Arterial 2.506 2.641 5.704 0.551 0 2.4 2.6

6. Sub-Arterial 2.696 1.362 1.906 0 0 1.9 2.5

7. Distributor 1.262 30.403 43.311 8 2.558 2.8 2.6

8. Collector 2.586 20.079 60.624 17.231 1.234 2.9 2.6

9. Local 209.892 700.416 1371.528 487.042 105.304 2.9 2.7

Total 218.942 755.515 1484.533 514.29 109.096 2.9 2.7

Figure 0-4 Corrugation condition over time

0

1

2

3

4

5


Embedded Stones Condition

Con

ditio

n

2012/13 2014/15

Embedded Stones Embedded stone refers to the amount of stones embedded in the road that is larger than a recommended maximum size (usually 37.5 mm). Excessively stony roads result in unnecessarily rough roads that are difficult to grade and compact; often a thick layer of loose material is needed to cover the stones which can lead to the development of corrugations. Embedded stones have the potential to cause vehicle damage and result in unsafe driving conditions. Table 1-5 shows the length of road within each condition by road hierarchy across the network in 2012/13 with the average condition in that period and also after the latest survey and shows a slight deterioration of the network from 2.9 to 3.0. Figure 0-5 compares the condition of the network over the two time periods.

Table 1-5 Embedded Stones Condition by Hierarchy (km) Average


4. Highway 0 0 3.54 0 0 3 3.6

5. Regional Arterial 1.302 2.502 7.522 0.076 0 2.6 3.3

6. Sub-Arterial 0.16 3.904 1.81 0.024 0.066 2.3 3.1

7. Distributor 0.321 7.96 52.589 15.56 9.104 3.3 2.8

8. Collector 2.964 45.65 43.347 8.812 0.981 2.6 2.8

9. Local 123.292 637.942 1556.844 483.794 72.31 2.9 3.1

Total 128.039 697.958 1665.652 508.266 82.461 2.9 3

Figure 0-5 Distribution of Embedded Stones Condition

15

20

25

30

35

40

45

50

55

60

65

70

75


UCS Condition

Con

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n

2012/13 2014/15

Unsealed Condition Score The Unsealed Condition Score (UCS) provides a representation of the health of the unsealed road network to be provided by a single number from 15 to 75 with 75 being considered an unserviceable condition and 15 being an as new condition. The UCS is a weighted index of each distress with the distress items perceived to be of most importance given the highest weighting. The following weightings have been used and each distress item as shown in table 1-6. These weighting values were applied equally across all road classes as the class 9 roads comprise 93% of the network and any consideration for the hierarchy of the road would be negligible under the current hierarchy structure.

Table 1-6 UCS Weighting Values

Distress Weighting

Cross-Sectional Profile 3

Drainage 2

Corrugations 5

Embedded Stone 4

Potholes 1

Table 2-1 UCS by Road Class

Unsealed Condition Score

Network Average Class 4 Class 5 Class 6 Class 7 Class 8 Class 9

2012/13 44 44 38 35 44 42 44

2014/15 38 42 41 39 34 37 40

Figure 0-6 Distribution of UCS

The Council Application Toowoomba Regional Council (TRC) utilised the analytical findings in a three stage program that will be executed in the short, intermediate and long term. The first stage involved identification of roads/ sections that require urgent maintenance & improvement needs (due to extremely low current service standards, where one or more KPI’s fall way below minimum).This process enables assessment of the effectiveness of TRC’s current maintenance strategy. The stage 1 has focused on rectification work and identified deficient sections. The intermediate stage (stage 2) spanning 1-3 years involves the development of a robust maintenance strategy that is dependent on road characteristics, such as traffic volumes, composition and geometry, to optimise the outcome and increase the overall level of service of the unsealed road network. This may be subject to funding restrictions. The strategy will be developed by assessing and recording the performance unsealed road pavement following maintenance and/or renewal. Long term (beyond 3 years) in stage 3, TRC intends to implement a more robust & holistic approach with respect to renewals, maintenance & operation of the gravel road network. TRC’s pavement asset management team is currently looking at a number of different options in this regard, including suitability of materials for respective situations. A workshop was organised and conducted to disseminate and discuss the work program and strategy with all stakeholders. A three year work program was mapped and distributed during the workshop. This will assist management in how best to allocate funding for implementation. Further stakeholder consultation and ground truthing exercises were conducted to confirm the work program. Conclusion and Recommendation The process adopted by TRC using this reliable data forms part of an effective control and governance system embraced by the council. TRC’s asset management better practice is a part of overall framework of decision making in the organisation, striving to integrate its asset portfolio within the council’s strategic goals which in order to achieve balance of cost, risk and performance of the road network. The attributes that have been considered by TRC provide a thorough overview of the current condition of the unsealed road network. These attributes allow the TRC Assets Management Team to review and improve gravel network maintenance strategy, inclusive of drainage and profile maintenance, short and medium term renewal program and specification of the revised intervention levels. These documents provide Council with an overview of the condition of the network, the works required in the renewal of the network to an adequate serviceability and the identification of maintenance requirements specific to the material, environment, traffic volume and geography. The survey equipment and the methodology that has been applied, allowed PMS to collect the pavement condition data with a reasonable degree of accuracy for a network level pavement investigation.

Material types were largely as predicted across the unsealed network, with the majority of road surfaces consisting of gravel in various forms, with small sections of bare subgrade and others of sealed materials. The process also identified backlog of works based on road condition and gravel thickness. Also it provides senior management with sufficient information to assist their investment decision making. A dissemination workshop was conducted with all stakeholders within the council to influence district staff when undertaking their maintenance prioritising processes. Subsequent surveys and their comparisons with previously assessed conditions of the network will provide the Asset Management team with an understanding deterioration of the gravel layer in the local environment. Referenced Documents Jones, D & Paige G. “Draft TMH12 Pavement Management System: Standard Visual Assessment Manual for Unsealed Roads”, Council for Scientific and Industrial Research Transportek, Pretoria, South Africa, 2000. “Toowoomba Unsealed Road Network, Ground Penetrating Radar Survey for PMS on behalf of Toowoomba Regional Council” Fugro Aperio. Author Biography Justin Weligamage Justin Weligamage is currently a Principal Engineer (Asset Management) with the Toowoomba Regional Council, in Australia. He has over 25 years of consulting, research and industry experience in the areas of road and civil infrastructure. Over this time Justin developed and implemented road asset management initiatives, including the publication of “Asset Maintenance Guidelines” and “Skid Resistance Management Plan”, the strategic application of the Highway Development and Management System (HDM4) for the Queensland Department of Transport and Main Roads. He has written a number of research papers and technical reports, and has published and presented at various refereed international conferences. Justin holds a MBA, Master’s degree in Engineering Science and bachelor degree in Civil Engineering. He is a former Manager (Road Asset Strategy) with Department of Transport and Main Roads and has 20+ years of experience in the Asset Management area. James Erskine James is a Senior Pavement Engineer based in Sydney with fifteen years of pavement engineering experience specialising in road network management and project level pavement investigations. James has been and is currently the Project Manager for various significant and varied projects throughout Australia providing advice to Local and State Governments as well as a number of Construction companies. He has specific expertise in the development of network optimisation and multi-year forward works programmes, pavement design and investigation as well as network condition monitoring.