MSCA-COFUND-CLEAR-Doc-PhD Position #CD22-33: Climate Change Vulnerability and Risk Assessment of Urban Pavements

Changing climatic patterns necessitate adaptation to current practices for design, maintenance, and management of urban roadways (Jacobs et al. 2018, Stoner et al. 2019). Urban roadways are often more prone to climatic stressors due to their age, lack of proper structural designs and interdependencies with other infrastructure elements. The financial burden of damage to road infrastructure due to major storms, floods, and excessive summer heats are much higher in urban regions as compared to those for rural regions. Also, impact to general population is significantly greater due to higher population densities in urban areas.

To ensure quality of life and safety of residents, there is an urgent need to adapt existing urban road infrastructure to climate change. While newer technologies (such as, solar pavements and electric roads) are underway, their usage and implementation are decades away. Further, costs to adopt such technologies will be an impediment for majority of urban entities. Climate change is already well underway, and this is resulting in more road closures and catastrophic failures (such as sinkholes and washouts). Recent flooding events in France are a prime example of vulnerabilities of urban roadways due to changing climate. At present, life cycle assessment-based decision tools that fundamentally embed a system level thinking, are not accessible to urban road managers and decision makers. Roadways are a system where pavements, subsurface features, ambient and climatic conditions, other infrastructure features (such as, water and electric utilities) and road-users constantly interact with each other. Recent efforts have been undertaken to use system dynamics models to assess pavement vulnerabilities and model post-flooding recovery efforts (Mallick et al. 2017, Mousavi et al. 2021). The effects of climate change on the pavement system and corresponding vulnerabilities and durability challenges need to be studied to ensure transportation system resiliency in the future.

A system-dynamics informed mechanistic pavement analysis tool for making load restriction decisions on pavements with excessive moisture states (such as, post-flooded pavements) called PaveSafeTM (https://mypages.unh.edu/pavesafe/home) has been developed by the mobility partner, the University of New Hampshire (Mousavi et al., 2020; Ghayoomi et al. 2021). This tool integrates a hydrological soil-moisture movement model with geotechnical property prediction and pavement structural response models. The soil-moisture movement model uses a degree of saturation dependent permeability response and soil water retention curve characteristics and meteorological forecasts as boundary conditions. The geotechnical model predicts mechanical properties of pavement layers and subgrade (variable with depth) as function of saturation level in each layer. The pavement response model conducts the mechanistic analysis for various vehicle configurations and corresponding load levels. Validation of PaveSafeTM has been conducted using in-situ measurements from two pavements before and after flooding. While this tool is already developed and validated, several attributes need improvement and new development. For example, the tool does not specifically address roadway demand and design attributes that are specific to urban areas and effects of climate change are limited to moisture. Further, adverse soil response is only considered in terms of excess moisture, whereas the drying shrinkage effects due to extended dry spells and draught for pavements with clayey subgrade needs to be assessed.

The primary contributions of the proposed doctorate thesis will be to fill current knowledge gaps on understanding key climate change related stressors (precipitations, temperatures, flooding, subsurface water table rise) as they impact structural conditions, durability, and remaining service lives of urban roadways through a systems-based analysis approach. The proposed Ph.D. research will also develop necessary methods and models for integrating future climate forecasts with system-based pavement evaluation techniques. The outcomes of this research effort will be realized in form of identification of critically deficient aspects in the currently developed methodologies and propose necessary changes to the current approaches to ensure resiliency of urban roadways to changing climate. Some deficiencies that have been identified include, effects of changing temperatures in future climate, shrinkage potentials of clayey pavement subgrades under extended draughts and use of effective stress-based pavement capacity limits. Scope of evaluation will include existing data sets on pavement and geotechnical materials, use of forecasted future climate inputs (for example, using CMIP6 projections, Eyring et al. 2016), data from actual pavement sites in France and United States.

Expected applications of this doctorate work will include risk and vulnerability assessment framework for urban roadways, improvements to the current French pavement design procedures with considerations of future climate, life-cycle assessment-based decision tools to support load restriction protocols for post-flooded pavements and for future flooding, and design of pavements for regions with high shrinkage potential soils.

The Ph.D. candidate will be within the LAMES laboratory of Université Gustave Eiffel at Nantes campus, this laboratory has led the French pavement structural evaluation and design efforts. World famous facilities, such as the largest European accelerated pavement testing facility, at LAMES will allow Ph.D. candidate to have access to the necessary testing equipment. Ph.D. supervisor has been involved in the development of the French pavement design software called Alizé and pavement design guide. Recently, Ph.D. supervisor was contributor of a project on effects temperature changes on pavement design (AdaptClim project, Kotronis et al., 2019). The Nantes campus has a staff of about 250 researchers and technicians, consist of multi-disciplinary teams, allowing the Ph.D. candidate to have access to experts in life cycle assessment, geotechnics, hydrology and hydraulics and processing of climate data.