Management of unpaved roads

Management of unpaved roads
Developing strategy and refining models SATC Pretoria Mervyn Henderson & Gerrie van Zyl

Acknowledgements and Focus
Mervyn Henderson Western Cape Government District Municipalities Focus Redevelopment of processes and systems for unpaved road maintenance Levels of service for the unpaved road network Demand-supply model for regravelling Materials Information Management System Continuous improvement of maintenance techniques and technologies

Background The Western Cape is a province of South Africa & is situated at the southern most part of Africa Area of km2 Bordered by the Atlantic coast on the west & the Indian Ocean in the south A Mediterranean climate Highest elevation m 6,2 million inhabitants About two-thirds of these inhabitants live in the metropolitan area of Cape Town, which is also the provincial capital

Introduction – the network
The Branch manages the unpaved road network, with the assistance of the five District Municipalities (DMs). The DMs carry out routine maintenance and periodic maintenance, i.e. regravelling. Only a fraction of the gravel loss per annum has been replaced during the last decade – average gravel thickness was approximately 22 mm in 2016

Provincial road network
Unpaved roads comprise 79% of the road network in the Western Cape – km A high proportion of roads with a low traffic volume, only 5% of VKT, 35% of maintenance budget Most unpaved roads fall into traffic categories S0, S1, T0 and T1

Introduction – network condition
There has been a significant increase in very poor roads since 2013 The Network Condition Number has a downward trend

Feedback from road users
“Fasten your bra straps and take out your false teeth. The road is stuffed!”

Introduction – objective for unpaved network
Imperative that available funding is used in the most effective and efficient manner through application of the best processes and technology for the maintenance of the network. The Branch’s objective for the unpaved road network is “to maintain and build high performance and cost effective gravel roads that will last much longer, provide a good average riding quality and have a safe riding surface, while reducing costs for the road user and the Branch”

Introduction - issues Issues contributing to the historically poor performance of the network using unsuitable material lack of an on-site investigation prior to construction full scope of the project not determined addressing only the most serious drainage deficiencies not shaping the roadbed and inadequate compaction inadequate breakdown of the gravel material and poor compaction limited leadership and governance best practice not always applied very few sources were legally compliant leading to a shortage of gravel diversion of funding to the upgrading of unpaved roads, etc.

Context of the Gravel Roads Maintenance System
Top left (light blue box) strategic level provides overall direction, the budget and the projects Top right (orange box) is the tactical and operational enablers – strategy & plan, manuals Bottom left (dark blue box) shows the tactical level processes to source material and manage the process of regravelling Bottom right (orange box) show the on-site work needed for regravelling – mining material, people & plant, control, optimised decision-making – cost, performance, risk and time

Context of the Gravel Roads Maintenance System
The Unpaved Road Network Maintenance Strategy and Plan was developed.

Strategy development Connecting operational work with strategic objectives – line-of-sight Critical to take a strategic approach and develop a strategy for maintaining unpaved roads in the long term to appropriate standards Strategy content: the vision, project selection process, activity & treatment selection process, principles for decision-making on maintenance treatments, safety requirements, levels of service, guidance on the use of out-of-specification materials and trade-offs involved in using these materials Vision for the unpaved network ‘A network that complies with the targets set for mobility, accessibility and safety, as described by the desired level of service. The Gravel Road Maintenance Management System will be used to support all aspects of the maintenance task’

Level of service Level of service Mobility Accessibility
Days accessible per annum [pa] Safety rating in terms of dustiness Proportion of the unpaved network [km] Intervention Roughness [p90 IRI] Minimum Speed [km/h] Target Average Roughness High 7,5 80 4 99,5%: In service for ≥363 days pa 3 2 516,7 Medium 10 60 5 99%: In service for ≥361,5 days pa 4 1 760,5 Low 13 40 6 3 013,2 Very low 15 20 5 3 090,4 LOS ito of mobility (target network roughness), accessibility, safety (dustiness)

Activities and treatments
The LOS is associated with appropriate work activities and treatments that are constrained by the limited budget Level of service Activities and Treatments High and Medium Blading maintenance Reshape Rework Drainage work Spot regravel Regravel based on priority (economics, social factors and risk) Low and Very Low Reshape only where essential to maintain LOS requirements Drainage work only where essential to maintain LOS requirements Spot regravel only where essential to maintain LOS requirements

Demand-supply model A demand-supply model was developed that models the current demand for gravel using the gravel loss model required supply of gravel regravel teams needed to construct the layer of wearing course Variables Parameters Outputs Traffic Regravelling thickness Quantity of gravel required Weinert N-value (measure of macro-climate) Average thickness of gravel desired on the network Time to reach a steady state thickness of gravel on the network Gradation Number of regravel teams Number of regravel teams required to sustain the steady state thickness of gravel Plasticity

Demand-supply model Model results for an average gravel thickness of 60 mm and the quantity of material required A demand-supply model models the current demand for gravel using the gravel loss model of Paige-Green, the required supply of gravel and the regravel teams to construct the layer of wearing course. The variables are traffic, Weinert N-value (a measure of macro-climate), gradation and plasticity. The parameters are regravelling thickness, the average thickness of the gravel on the network, & the no. of teams. Outputs are the quantity of gravel required, the time to reach a steady state thickness of gravel on the network, and the number of regravel teams required to sustain the steady state thickness of gravel. The model simulates the ongoing process of gravel loss for each road section. This process continues until the gravel thickness reaches a trigger thickness, where the road should be regravelled in order to facilitate blading maintaince. The model prioritises roads for regravel by sorting them firstly by LOS, and then by gravel loss, and lastly according to the thickness of gravel left on the road. A road can be regravelled after it has been triggered, but only if there are sufficient resources (regravel teams) available. When resources are depleted, i.e. the total production by a limited number of teams is consumed, the model ends the regravelling activities for that year and new regravelling projects will only commence the following year. Figure shows results for an average target network gravel thickness of 60 mm, a regravel trigger of 40 mm, a 150 mm regravel layer, and a 25% reduction in gravel loss for high quality construction and good quality gravel wearing course. The number of regravel teams is constrained to 10 and the quantity of material required is determined by the rate of production of the 10 teams With the current limited number of regravel teams and very little gravel left on the network, about 580 km of road that have very high gravel loss consume most of the resources, requiring frequent regravelling, and preventing roads with a lower gravel loss from being regravelled. Consequently, a large part of the network cannot be regravelled with the limited number of available regravel teams.

Scenarios Various scenarios were tested in the spreadsheet and the results are shown in Figure. The scenarios covered the current situation, reduced gravel and upgrading of unpaved roads. Two thicknesses of gravel wearing course were modelled, i.e., 100 mm and 150 mm, as well as The impact of upgrading to paved standards for 120 km and 240 km of unpaved road that have high traffic volumes and high gravel loss. The scenario where a thicker layer of gravel wearing coarse (150 mm) is applied enables more of the roads with a high rate of gravel loss to retain sufficient gravel for a number of years, allowing more km of road with a lower demand for gravel to be regravelled in the years that follow. When a thin 100 mm layer of gravel is applied, it initially results in gravel being spread over more roads, but the demand for regravel from the high gravel loss roads eliminates regravelling on the lower gravel loss roads in the years that follow. By applying a 150 mm layer of gravel, the demand for regravel from the high gravel loss roads is delayed, and this enables a steady state target thickness on the network to be reached sooner.

Strategies Various scenarios were tested in the spreadsheet and the results are shown in Figure. The scenarios covered the current situation, reduced gravel and upgrading of unpaved roads. Two thicknesses of gravel wearing course were modelled, i.e., 100 mm and 150 mm, as well as The impact of upgrading to paved standards for 120 km and 240 km of unpaved road that have high traffic volumes and high gravel loss. The scenario where a thicker layer of gravel wearing coarse (150 mm) is applied enables more of the roads with a high rate of gravel loss to retain sufficient gravel for a number of years, allowing more km of road with a lower demand for gravel to be regravelled in the years that follow. When a thin 100 mm layer of gravel is applied, it initially results in gravel being spread over more roads, but the demand for regravel from the high gravel loss roads eliminates regravelling on the lower gravel loss roads in the years that follow. By applying a 150 mm layer of gravel, the demand for regravel from the high gravel loss roads is delayed, and this enables a steady state target thickness on the network to be reached sooner.

Resource optimisation system - dTIMS®
Future development will be to customise the Branch’s resource optimisation system (Deighton Total Infrastructure Management System - dTIMS®) by including the LOS demand-supply model This will enable us to optimise the supply side teams, staff and construction plant for delivering periodic maintenance under a constrained budget - Budget - Borrow pits - Teams - Manpower - Plant Spreadsheet/ dTIMS Demand – Supply Optimisation of budget & resources

Materials Information Management System
Borrow Pit Module Financial Guarantee Module Expropriation Module Document Repository Workflow & communications layer Material Information Management System Borrow Pit Risk Register The impact of environmental and mining regulations on the legalisation of gravel sources led to the creation of new functionality in the Materials Information Management System The new business processes supporting the implementation of the mining regulations were documented, & once incorporated in MIMS, this will enable all the processes involved in legalisation of materials sources, including environmental, water, heritage, mining, and financial guarantee approvals to be monitored approval of the rehabilitation of gravel sources and the return of the financial guarantee assist risk assessment and mitigation of risks during the investigation, mining and closure stages of a borrow pit

Gravel Road Maintenance Management System
Tablet/ paper capturing of defects Network roughness report Gravel Roads Management System Costing System Project Management System Materials Information Management Geometric & Structures Designs Project Scheduling Materials Selection & Mix Design Project Scoping, Packaging & Programming, Plant utilisation utility Process & Acceptance Control Project Review Gravel Roads Maintenance Management System - Project scope - Specifications - Design plans - Treatment plan - Programme of projects - Materials sources - Mix design Project Risk Register Layer Quality Risks & mitigation measures Project Progress Defects Register Defect strip chart Tactical Planning Phase Operations Execution Phase Blading Optimisation Module Blading Programme Blading Programme Review Cost Report Reports Green is the tactical planning phase Yellow is the operations execution phase External systems in grey boxes

The registration of projects is controlled by the Branch’s Project Management System Projects are scheduled in the project scheduling module MIMS supplies the Materials Selection and Design module with information on the position of gravel sources, the quantities and quality of the gravel or binder & processing requirements, enabling the utilisation of gravel for periodic maintenance to be planned Ravel & Corrugate B E D Slippery A Erodible C Ravel Good (Dusty)

Trade-off between cost, performance and risk
A new risk based assessment sheet was developed to assess the trade-offs for the gravels not meeting the specification Factor Categories Climate Wet, temperate, dry Climate risk High, medium, low Average cost of material delivered to the road per m3 By comparison Shrinkage Product, Sp 0-100, , Grading coefficient, Gc 0-16, 16-34, 34-48 Performance Classification A- Erodible, B- ravels & Corrugates, C- ravels, D- slippery, E- good Performance Risk (compare deviation of Sp and Gc from category E) CBR of Gravel Wearing Course, % <9, 9-15, >15 Traffic, AADT <150, , >300 % Heavy vehicles 5, 5-10, >10 Subgrade CBR, % 3, 3-5, >5 Load spreading risk Hardness, Treton IV 20, 20-65, >65 Hardness risk Oversize % <5, , >10 Oversize risk Low, medium, high Cumulative risk L <10, 10M14, H>14 Comments and Recommendations

Project Scoping Defects are assessed and recorded in GROMAMAS The Project Scoping module associates the defects with treatments, such as regravel, spot regravel, reshape, drainage, etc., or activities, such as cleaning of a pipe culvert A periodic maintenance project is scoped and includes a treatment plan, a costed bill of quantities for projects and details of the utilisation of gravels from the associated gravel sources in MIMS

The Risk module provides a standard risk profile that covers the investigation, mining and closure of gravel sources, and the operations on the road for periodic maintenance Risk profiles can be adjusted to match the circumstances Mitigation measures are provided The Process and Acceptance Control module is used for quality control and acceptance of the final gravel wearing course Project review is enabled by reports on cost and performance in terms of progress and quality of the final product The risk associated with these factors can be evaluated and mitigation measures implemented Project Review Reports enables the District Roads Engineer to the control scope of work for a project control scheduling control risk with appropriate mitigation measures Assess progress, quality and cost of the work

Integration of systems
Legend Data flow Output Borrow Pit Module Financial Guarantee Module Expropriation Module Document Repository Workflow & communications layer Material Information Management System Borrow Pit Risk Register - Budget - Borrow pits - Teams - Manpower - Plant Spreadsheet/ dTIMS Demand – Supply Optimisation of budget & resources Resource Optimisation System Geometric & Structures Designs Tablet/ paper capturing of defects Network roughness report Gravel Roads Management System Costing System Project Management System Project Scheduling Materials Selection & Mix Design Project Scoping, Packaging & Programming, Plant utilisation utility Process & Acceptance Control Project Review Gravel Roads Maintenance Management System - Project scope - Specifications - Design plans - Treatment plan - Programme of projects - Materials sources - Mix design Project Risk Register Layer Quality Risks & mitigation measures Project Progress Defects Register Defect strip chart Tactical Planning Phase Operations Execution Phase Blading Optimisation Module Blading Programme Blading Programme Review Cost Report Reports

Improving techniques and technologies
Ongoing effort to improve the techniques and technologies of work activities and the monitoring and control of the quality A number of experiments have been set up across all DMs with the objectives of improving maintenance techniques and developing new and/or calibrating robust HDM-4 deterioration models. The scarcity of materials and its effect on maintenance and material specifications with respect to the different levels of service is an ongoing challenge in achieving the best performance Data from the experiments and also data collected on the network will assist in the application of appropriate gravel specifications

Blading optimisation The current best practice applied in two Districts and TRH 20 Requires an initial estimate of the blading frequency to maintain the target road roughness set for a selected LOS

Blading optimisation process
Define network Define Uniform Maintenance sections Define Minimum & Target LOS Feedback Select maintenance strategy – treatment blading type and sequence per section Determine frequency, blade passes, blade km per maintenance section per annum & adjust Appropriate Funding Requirement Unit Costs Fund allocation Determine/ allocate grader productivity per road/ area Combine maintenance sections to obtain balanced distribution per Maintenance Area Grader/ equipment requirement Distribute blading requirements through year to balance cycles: Blading Schedules Recalculate affordable blading frequency per maintenance section Verify monthly program on site & issue Monitor performance

Performance models Investigations into different performance models and the ability to calibrate the local conditions and blading type resulted in the selection of the HDM-4 version 2 models The “steady state” of roughness, is a function of traffic material properties climate road geometry blading type and frequency Testing the recommended default values of HDM-4 did not provide acceptable answers, highlighting the need to calibrate the models for local conditions

Defining blading methods
Due to the high variability in climate and material properties throughout the Western Cape, different blading methods are applied light, dry blading using motorised graders or towed graders heavy, wet blading using normal blades or serrated blades tyre dragging and sand cushioning The applicability and cost-effectiveness of the different methods, currently applied under different conditions, are not defined well enough to establish optimum maintenance strategies

Calibrating the HDM-4 model
Some factors being investigated for calibration of the HDM-4 model Steady state IRI per Blading Frequency (BF) Time IRI BF=4 BF=8 BF = 24 LOS BF=12 Calibration required for Western cape

Crushing of materials The predominant defect is oversized aggregate in the wearing course Two roads were selected where road sections were constructed using material from the same borrow pits to compare the performance of the material processed on the road and the same material crushed to minus 26 mm before it was processed on the road Monitoring these sections over a period of 4 months showed that the crushed material sections could be maintained at an International Roughness Index (IRI) of 1 less than the uncrushed sections with far less effort, i.e. 5 light blades versus 10 heavy blades over the width of the road and at least one less blading per annum At an Average Annual Daily Traffic (AADT) of 150, the savings for the Road Authority amounts to R per km per annum and the Vehicle Operating Cost (VOC) savings are R per km per annum, giving a total of R25 000/km pa, or R /km pa over 10 yr

Effect of crushed material
1 IRI extra improvement after blading Cost difference 5 blades vs 10 blades

Rolling after blading Blade & Roll systems are used in several countries with good results highlighted by different organisations No results could be obtained to quantify the cost-effectiveness of the system Based on a number of experiences in the Western Cape using pneumatic tyred rollers (PTR) for final compaction after regravelling, an experiment was designed to simulate the “blade & roll” system by using a six ton PTR after the wet blading action 3 sections were selected on the same road, but with different material properties Half of each section was rolled after the wet blading activity and the performance in terms of roughness deterioration and gravel loss was measured over periods of 54 and 65 days The intention is to increase the mass of the roller during the follow-up process to quantify the effect of contact stress All three sections showed a slower rate of deterioration in roughness on the rolled sections with the average savings in VOC per vehicle pass

Savings in VOC – Rolled versus Not rolling

Effect of rolling on gravel loss

Tyre dragging 7 road sections have been selected and prepared to compare the effect of tyre dragging with light grader blading on different thicknesses and properties of the sand cushion as well as the rate of roughness deterioration, mainly the formation of corrugations, after treatment Although too early at this stage to report conclusive information, it has been confirmed that the tyre drag, at a cost of less than 40% the cost of light grader blading, is just as effective in the immediate improvement of roughness through removing the loose corrugations The effect of tyre dragging is minimal when hard corrugations have formed

Effect of tyre dragging
Hard & soft corrugations Hard corrugations Soft corrugations

Blading maintenance strategy development
Variability in materials, climatic conditions, topography and traffic volumes require different strategies, i.e. rules for the sequence and frequency of maintenance activities, to maintain a specific LOS at the lowest possible cost The first challenge is to select the “package” and sequence of activities appropriate for a set of conditions, e.g., very low traffic, dry area, low cohesion materials and high percentage of oversize Incorporating sequential activities such as in-line crushing for reworking, different blading types and reshaping into calibrated performance models for this scenario would assist with determining the required frequency of activities to achieve the minimum and target LOS

Construction and maintenance strategies evaluated
From previous study Effect of Reshaping Effect of Regular light blading Effect of Material selection Proper compaction PTR rolling

Example of a maintenance strategy
Typically low volume, West coast with availability of sand Time IRI (m/km) Minimum LOS Steady state target LOS Rework/ Regravel Towed/ motorised grading Tyre dragging Reshaping

Findings The significance of this work lies in the development of a strategy, which Enables the connection of tactical planning and operational maintenance activities on the unpaved road network with the strategic objectives and Encourages discussion on cost, performance and risk in the time period considered, spurring on improvements that should lead to better network performance HDM-4 performance models can be adjusted and calibrated to incorporate the quality of construction, specific blading methods as well as other treatments The study confirms that the optimum maintenance strategy could consist of Different treatments during the maintenance life-cycle and Different strategies are required depending on materials, climate, topography and traffic

Conclusions In conclusion, the approach taken by the Branch to develop and implement a turnaround strategy that includes the refinement of HDM-4 prediction models is expected in the medium term to lead to More effective management Better network performance Improved outcomes for the community

Cape Town and Table Mountain
Thank you!

Management of unpaved roads

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