Mechanistic Load Restriction Decision Platform for Pavement Systems Prone to Moisture Variations
Project Start Date: July 25, 2019
Project End Date: July 31, 2021
At present, a majority of roadway seasonal load restriction (SLR) protocols in the National Road Research Alliance (NRRA) and state Departments of Transportation (DOTs) depend on either use of subsurface soil information or historic seasonal moisture data. Neither of these methodologies provide robust estimate of actual pavement structural load carrying capacity and both of these approaches lack in terms of climate variations and assessment of roadways in post-storm scenarios. Due to empirically driven nature of the SLR protocols there is potential for imposing either over- or under- restriction on roadways. Both of these result in substantial loss to general population of NRRA member state entities. When over-restriction is used it results in losses to businesses due to limits imposed on trucking and other mean of freight transport. When there is under- restriction scenario, it substantially limits the life-span of roadway infrastructure resulting in excessive pavement repair, rehabilitation and reconstruction costs. The proposed research will develop a mechanistic framework to improve robustness of the load restriction decision process. Through use of mechanistic relationships, the proposed research will enhance the pavement load capacity assessment and implement this methodology within a system dynamics framework. The system dynamics framework allows for a flexible platform that can incorporate multi-variant effects and provide a tool with ability for forecasting. This tool will allow transportation officials to plan for seasonal load restrictions into future and allow businesses to better plan freight transport. Finally, due to incorporation of both mechanics and climate data, the tool will also have ability to make decisions regarding post-flooding road opening. This ability will have tremendous impact on NRRA state DOTs’ taxpayers as it directly impacts access of emergency responders and other post-flooding aid to impacted areas.
Task 1: Initial Memorandum on Expected Research Benefits and Potential Implementation Steps
Key benefits have been selected to clearly define the benefits the state will receive from the results and conclusions of this research. This task will provide an initial assessment of research benefits, a proposed methodology, and potential implementation steps.
Task 2: Literature Review
The research team will conduct a thorough literature review regarding the state of the art and state of the practice related to the following topics: i) available seasonal load restriction protocols and guidelines; ii) moisture-dependent material characteristics including subgrade and base material; iii) moisture-dependent performance of pavement systems considering laboratory experimental, numerical, and field evaluation; iv) flooded pavement assessment practices and post-flooding evaluation; v) climate forecasting formulation and flow processes in unsaturated soils; and vi) other related and similar systems dynamic modules and approaches. The review will fill in the background knowledge needed for implementation of the proposed mechanistic framework and will be categorized under three major subjects: i) material needed to develop mechanistic pavement response; ii) material needed to perform the systems dynamic analysis; and iii) material needed to develop the load restriction protocol and module. A wide range of tools available at the University for literature review will be used for this task.
Task 3: System Dynamics Framework Development
In this task, the University will develop and populate a system dynamics framework with typical pavement base and subgrade materials, climate and loading inputs, and mechanistic equations. The goal will be to establish the platform and prepare the system linkable to the load restriction decision platform and toolkit in the subsequent tasks. To accomplish this task, the system dynamics software (such as Vensim or similar package) will be used to develop the framework that incorporates all stressors (such as, soil moisture state, vehicular loads and volume, climatic conditions etc.) and resulting components, all integral to overall mechanical response of pavement systems. Data from the literature review in Task 2 will be used to populate this pilot framework. Parameters such as surface deflection, subgrade stress distribution, induced vertical and horizontal strain, structural capacity, and relative damage will be assessed in this framework. Moisture-suction profile in depth will be predicted based on climatic and environmental forecasting and be related to mechanical properties and response of subgrade system.
Task 4: Sensitivity Analysis and Framework Refinement
In this phase, comprehensive sensitivity analysis and statistical modeling will be performed to fine-tune the system dynamics framework. The framework developed in Task 3 will be used to understand the significance of each stressor and pavement component on overall pavement response where each parameter will be ranked after the sensitivity analysis. Monte-Carlo simulations will be used to understand the impact of uncertainty within the system resulted from uncertainty of individual stressors and material properties. The framework will be fine-tuned based on the results of this task where the interaction among different stressors, material properties, and mechanistic relations will be modified. Specially, since most of available mechanistic formulations have been developed within a limited scope of testing conditions and material selections the suitability of each formula will be evaluated and corrected.
Simple statistical uncertainties will be incorporated to capture the reliability of the relations and include the risk level that user would be willing to take. Risk factors will be included in terms of using probabilistic distribution of input variables.
Task 5: SLR Toolkit Development
To implement a SLR protocol a user-friendly toolkit will be programmed and automated. In order to reliably evaluate pavement performance and to provide tools for pavement engineers to assess vulnerability to damage and make traffic allowance decision during and after periods of excessive moisture, this should be a real-time load restriction decision- platform. As a result, by combining the performance criteria, hydraulic analysis outcome, and risk and reliability choice a load restriction duration post-inundation or spring thaw that is required to avoid major damage to the pavement structure would be recommended. Such decision-platform should not only involve a mechanistic system assessment but should also be policy informed. Inputs of transportation agencies and users should be incorporated in the systems-based decision model to facilitate its implementation and to realize the cost-effectiveness of such mechanistic approach. Decision process within this toolkit will be modeled flexible enough so public and private agencies be able to incorporate their risk level in decision making process. Load limits here are defined in terms of axle load, tire load and, axle and tire configuration. To facilitate the access to the coupled hydraulic and mechanistic analysis process developed in this study a user-friendly computer code will be developed. Practitioners with different expertise, resources, and input data would be able to benefit from this user interface. The input data could be inputted in multiple hierarchical levels, such as, Inexperience User/Limited Data, Experienced User/Average Data and, Experience User/Detailed Data. The users can choose their performance assessment criteria and look at various plots. However, a less-detailed level of output, i.e. time to open the road, would be shown for the given input, risk, and damage criteria. A recordable report would be also generated and save upon the user’s request.
Task 6: Calibration and Preliminary Validation of the Toolkit using MnROAD Data
In this phase, available climatic and load-deflection data from MnROAD and other state agencies (archived and ongoing) will be collected and used to calibrate and validate the developed framework. The performance of such road sections under various decisions will also be evaluated using the developed toolkit. Leveraging the existing MnROAD test sections that are already instrumented and monitored for pavement performance would be beneficial to performance assessment of this toolkit. It is also anticipated that there are existing roadway segments, which experience seasonal and/or extreme weather event flooding, on the state and local road systems. The University welcomes a select number of these field validation opportunities into this research project as desired by the agency owners. In addition, to further enhance the developed decision framework with more detailed mechanistic pavement performance data, incorporate systematically controlled and monitored pavement response, and fully validate the procedures a subsequent project phase would include series of physical modeling and testing of scaled pavement sections.
Task 7: Out-of-State Conference Travel
This task is for the preapproval of the “Travel Authorization Form” required from NRRA before travel occurs. Travel to Washington DC to present research results at TRB in January 2021.
Task 8: Final Memorandum on Research Benefits and Implementation Steps
During earlier phases of the project, key benefits were selected to clearly define the benefits the NRRA states will receive from the results and conclusions of this research. This task will produce a final memorandum that clarifies and documents the methodology used to calculate benefits, including any assumptions and steps required. In addition to quantitative calculations (when feasible), this task should also include a qualitative discussion of the estimated benefits. The memorandum should also include key steps that agencies could take to implement the research. The memorandum will also include recommendations on the project’s next phase involving physical modeling and testing of scaled pavement sections.
Task 9: Compile Report, Technical Advisory Panel Review, and Revisions
The PI will prepare a draft final report, following NRRA publication guidelines, to document project activities, findings and recommendations. This report will be reviewed by the Technical Advisory Panel (TAP), updated by the PI to incorporate technical comments, and then approved by the Technical Liaison before this task is considered complete. If possible, a TAP meeting will be scheduled to facilitate the discussion of the draft report.
Task 10: Editorial Review and Publication of Final Report
During this task, the PI will work directly with NRRA’s contract editors to address editorial comments and finalize the document in a timely manner. The contract editors will publish the report and ensure it meets publication standards.
Principal Investigator: Majid Ghayoomi,University of New Hampshire, email@example.com
Co-Principal Investigator: Eshan Dave, University of New Hampshire, firstname.lastname@example.org
Technical Liaison: Ben Worel, Research Operations Engineer, Minnesota Department of Transportation, email@example.com
Project Technical Advisory Committee (TAP) – email the TAP
Terry Beaudry (MN)
Raul Velasquez (MN)