Predicting Erosion Impact on Highway and Railway Bridge Charles T. Swann, R.P.G. Mississippi Mineral Resources Institute 111 Brevard Hall University, Mississippi Christopher L. Mullen Department of Civil Engineering University of Mississippi P.O. Box 1848 University, Mississippi 2015 University Transportation Center Conference for the Southeastern Region Birmingham, Alabama March 26, 2015
Project Goals 1) To evaluate bridge condition and the present status of stream erosion beneath existing bridges. 2) Relate this erosion potential to the geological unit on which the bridge is founded. 3) To identify any additional factors that may accelerate stream erosion beneath the bridges. 4) To identify erosion sources other than stream erosion that may influence bridge well-being. 5) To evaluate any stream erosion mitigation measures. 6) Determine the implications present erosion may have during a major earthquake event in North Mississippi. 7) Transfer the results to engineering and geological professionals.
Study Area
Bridge Condition Survey Modern Construction *Appropriate amount of well placed rip-rap *Stream is located between piers *No structural discontinuities *Small-scale erosion features Older Construction *Some lack rip-rap mitigation *Piers within stream flow *Structural discontinuities are present *Erosion concerns are present to varying degrees, some significant * Construction dates back to the 1930 s
Stream Erosion Conditions Identified concerns include: 1) lateral migration of channel; 2) rapid downward erosion of stream channel; 3) local scour caused by debris dams; and 4) erosional vulnerability of the substrate.
Erosion and Geological Unit Some geological Units more vulnerable to erosion than others, most vulnerable are: Ripley Formation particularly the Transitional Clay, Coon Creek Members Least Vulnerable Units: Ripley Formation Chiwapa Member, Demopolis Chalk
Other Erosion Sources
Channelization Impact On Erosion Vulnerability
Vulnerability to Seismic Events FEA (ABAQUS) modeling Predicting effect of Earthquakes on eroded substructure Soil-Substructure Interaction (use of Infinite Elements)
Predicting Erosion Impact on Highway and Railway Bridge Soil Profile per Original Drawings (1936)
Predicting Erosion Impact on Highway and Railway Bridge Soil Profile per Current Field Observation (2014)
Predicting Erosion Impact on Highway and Railway Bridge Predicted Soil Profile (2045)
Predicting Erosion Impact on Highway and Railway Bridge Original Soil Profile and Current Observed Soil Profile Overlay
Preliminary Conclusions 1) Erosional concerns are time-dependent features. The Highway 178 bridges provide insight into the future concerns likely to develop on the new U.S 78 corridor. 2) Stream erosion, both lateral and vertical, is a significant stability factor at the older bridges. 3) Bridge drainage openings and expansion joints can initiate erosion in addition to the stream channel erosion. 4) Rip-rap provides only short term mitigation. Condition of the rip-rap should be monitored and renewed as needed. 5) Misalignment of channelized streams and bridge piers can initiate rapid scour and downcutting. 6) Erosion and geological units can be correlated providing geotechnical insight to future bridge design. 7) Bridges are frequently used well beyond its intended designed life span.
QUESTIONS?