Link to Report: Coming Soon
Background :
Changes in flooding patterns, temperature extremes, and soil moisture cycles are intensifying the environmental loads acting on bridge infrastructure. These changes often result in more frequent and severe hydrologic events, potentially heightened vulnerability to structural failure of bridges. Scour, the erosion of soil around bridge piers and abutments due to increased streamflow during heavy rainfall, is a leading cause of hydraulic-related bridge failures. Similarly, soil moisture variability caused by extreme temperature and precipitation swings can compromise pile capacity, as soil stiffness decreases significantly under saturated conditions. These issues are particularly critical for Accelerated Bridge Construction (ABC) projects, where rapid construction methods must ensure long-term performance and resilience. Scour and soil moisture variations can accelerate foundation deterioration, compromising the integrity and safety of ABC bridges. Therefore, the proposed study aims to incorporate hydraulic hazard effects into the assessment of bridge substructure performance. Specifically, it will develop a comprehensive understanding of how the increasing frequency and intensity of hydraulic events influence bridge vulnerability, particularly the risk of damage caused by scour and seasonal variations in soil moisture. The research team will evaluate multiple Global Climate Models (GCMs) using different Shared Socioeconomic Pathway (SSP) scenarios to project future temperature and precipitation trends at selected study locations. Hydrologic modeling tools will be used to develop calibrated streamflow models using historical datasets of precipitation, temperature, and flow rates. Also, scouring depths at bridge foundations will be estimated following the HEC-18 procedures. These outputs will be integrated into a finite-difference model to study how scour and variations in soil moisture affect the lateral load behavior of bridge piles. The results will quantify failure probabilities, providing a comprehensive understanding of bridge resilience under changing hydraulic hazard conditions.
Objectives :
This study will focus on using a probabilistic risk assessment framework for bridge substructure failure due to scour and seasonal variation of moisture influenced by severe hydraulic hazard conditions. The primary objectives of this study are:
- To use Global Climate Models (GCMs) for predicting future temperature and precipitation patterns under different scenarios: for this purpose, several locations will be selected in consultation with the IBT/ABC-UTC leadership. To estimate scour, developed relationship between basin rainfall and the predicted streamflow of the river using hydrologic models will be used. The soil seepage analysis will be used to estimate seasonal variations in soil moisture.
- To evaluate the impact of scour on bridge substructure considering increased hydraulic hazard conditions: in addition, the soil-structure interaction of bridge substructures under seasonal soil moisture variations combined with thermal cycles will be evaluated.
- To conduct a probabilistic risk assessment of bridge substructure failure from scour and seasonal moisture variations coupled with temperature: updates on design and maintenance specifications will be recommended.
- To conduct impactful workshops and webinars focused on this topic.
Scope :
Task 1: Document Current Practices
The team will conduct a literature search to document the failure mechanisms of bridge substructure considering different hazardous events. Research related to the use of GCMs for the prediction of environmental variables, such as precipitation and temperature will be studied. Also, studies related to the validation of GCM model outputs with historical data will be explored. Research related to the coupling of GCM data with hydrologic models will be documented. In addition, federal and state guidelines on bridge analysis due to scour and moisture variations will be examined and gap identified. Literature related to risk evaluation and probabilistic design will be documented.
Task 2: Prediction of Temperature and Precipitation
In this study, multiple models that provide regional temperature and precipitation projections will be evaluated. The focus will be on models from the NASA Earth Exchange Global Daily Downscaled Projections Coupled Model Intercomparison Project Phase 6 (NEX-GDDP-CMIP6). This archive includes over 35 models from the CMIP6 collection and features downscaling to an approximately 25 km × 25 km grid, making it well-suited for analyzing environmental hazards in US. Several locations will be selected in consultation with the IBT/ABC-UTC leadership and stakeholders and used for these analyses. The selection will depend on the availability of relevant data, vulnerability to hazardous conditions and presence of a suitable bridge. The team plans to use three GCMs with multiple Shared Socioeconomic Pathways (SSPs) scenarios for this study. The model outputs will be bias corrected to enhance the reliability of the projections. The data will then be compared with historical data from local weather stations to assess the accuracy and reliability of the selected models. These outputs will be used to determine the changes in severe temperature (both high and low), precipitation events and seasonal variation in soil moisture conditions over the next 100 years.
Task 3: Hydrologic Modeling and Prediction of Scour Risk
This task involves using hydrologic modeling tools developed by the U.S. Army Corps of Engineers’ Hydrologic Engineering Center (e.g., HEC-HMS and HEC-RAS), to develop a calibrated streamflow prediction model through statistical analysis of historical precipitation, temperature, and streamflow data. The established model will enable estimation of future streamflow conditions using projected temperature and precipitation scenarios derived from various GCMs. Model performance will be assessed by comparing simulated streamflow results with observed data to evaluate its predictive accuracy. Scour at bridge piers is influenced by factors, such as bed material properties, channel bed configuration, flow dynamics, fluid properties, and the shape and size of the pier and its foundation. Therefore, scour modeling entails significant uncertainties from natural variability in soil characteristics, bridge geometry, and river discharge conditions. Several empirical models are available to estimate scour depth at bridge piers. In this study, scour depth at bridge piers will be estimated following the HEC-18 guidelines as proposed by Arneson et al. (2012), while the time-dependent progression of scour will be calculated using the multi-flood accumulation framework proposed by Briaud et al. (1999). Other models can be used if time and resources allow.
Task 4: Evaluating the Effects of Scour and Soil Moisture Variability on Bridge Substructure
In this study, the effects of scour and soil moisture variability on the lateral loading behavior of bridge substructure will be evaluated using a finite-difference modeling software. For this purpose, representative bridge substructure commonly used in the abovementioned locations will be considered. The selection of these substructure elements will be based on the recommendations of the local transportation agencies. The finite-difference modeling software, LPILE, will be utilized to model the bridge substructure elements and estimate the change in lateral loading capacity subjected to varying levels of scour. Scour prevalence and depths estimated in the previous task will be utilized for these analyses. Scour depth will be incorporated into the model by removing soil which is subject to scour from the model resulting in a greater unsupported length for a given foundation element. In addition, varying soil moisture conditions based on anticipated seasonal moisture from the previous task will be incorporated into the model. For example, a severe heat wave will likely be associated with drought conditions which will impact the lateral loading behavior of the foundation element. The effects of varying soil moisture content will be incorporated into the model through modification of soil strength parameters within LPILE. The effects of thermal cycles will be incorporated into the model as pile top displacement. Pile top displacement in the model will be a function of lateral bridge deck movement in excess of the allowable expansion joint width for a given bridge span in conventional bridges. For multispan integral bridges, pile top displacement will be a function of bridge deck expansion for a given span.
Task 5: Conduct Risk Assessment of Bridge Substructure
In this study, risk assessment of bridge substructure will be conducted using methodologies proposed by Khandel and Soliman (2019). To assess the failure probability of a bridge substructure considering scour and seasonal moisture variations, several simulations will be conducted by varying the temperature and precipitation events. The probability distribution function (PDF) of the lateral load capacity from these simulations will be generated. The probability of failure of the bridge substructure will be calculated. The risk of structural failure will be determined as a product of cumulative annual probability of failure and monetary value associated with the bridge failure.
Task 6: Provide Recommendations for Updating Bridge Design Specifications
The findings of this study will be used to recommend changes in the bridge design specifications. Also, the process of risk analysis will be documented. The consideration of hazardous events will be important to ensure long-term durability of bridge infrastructure.
Task 7: Organize Workshop and Webinar
With assistance of ODOT and other stakeholders, at least one workshop and one webinar will be organized as part of this task. The goal is to share the findings of this project with the stakeholders. In addition to ODOT, assistance of the Southern Plains Transportation Center (SPTC) & IBT/ABC-UTC will be sought to make these events successful.
Research Team :
Principal Investigator: Syed Ashik Ali, Assistant Professor of Civil Engineering and Environmental Science
Co-Principal Investigator: Tommy Bounds, PhD, PE Assistant Professor of Civil Engineering and Environmental Science, Musharraf Zaman, Ph.D., PE. David Ross Boyd Professor and Aaron Alexander Professor of Civil Engineering, Alumni Chair Professor of Petroleum and Geological Engineering