A four-phased system
yres Associates and GCI, Inc., in partnership with Kimley-Horn
and Associates, Inc., and STV Incorporated, recently earned a
National Recognition Award in the American Council of Engineering
Companies 2017 Engineering Excellence Awards competition for
their efforts evaluating scour for more than 1,500 Florida bridges
with unknown foundations. The following describes the four levels of
evaluation typically completed.
Phase 1 involves a field review of the bridge, looking at conditions, the
Bridge damage after flash flood in
Colorado Springs, Colorado
water’s angle of attack, its channel migration, and other field evidence
suggesting a scour problem.
Bridges appearing to look scour-susceptible advance to a
Phase 2 hydraulic evaluation where engineers complete
a channel survey and hydraulic modeling and calculate a
Undermining of abutment by scour
theoretical amount of bed material that the force of the water
will remove. If it’s doubtful there’s enough material left to
support the foundation, then a Phase 3 evaluation is performed.
This involves geotechnical and structural evaluations to check the
bridge’s stability and determine whether the predicted scour could
potentially cause it to become unstable in a major storm. If the
latter is the case, engineers then implement Phase 4 and develop
a plan of action. When working with unknown foundations, additional
steps, such as non-destructive evaluation or theoretical formulations to
estimate pile embedment, are required.
I mporting Innovation
n 2001, Ayres engineers Pete Lagasse and Paul Clopper traveled to Germany
to investigate and assess a partially grouted riprap technique that had been
developed and perfected there. They then adapted what they learned into
practice back in the United States.
Tidal surge at Shad Creek Bridge
near Jacksonville, Florida
“We routinely look at what the state of practice is not just in the United States but
all around the world – and then supplement that,” said Clopper, director of applied
technology at Ayres, who’s currently leading $800,000 worth of research projects in
conjunction with the National Cooperative Highway Research Program (NCHRP).
In 2010, Lagasse and Clopper proposed using the innovative and ultimately cost-
saving European technology on a scour-critical bridge in Colorado Springs, Colorado.
Permeable and flexible, it offered decided advantages over traditional, fully grouted rock
– including providing greater protection against storm events at a lower cost. The original
design with standard techniques was bid at $140,000 and provided protection up to a 50-
year flood. The change to partially grouted, or “matrix” riprap, cost $47,000 and provided
protection against a 500-year flood. Matrix riprap uses smaller rock and grout within
the riprap to provide stronger and more stable protection compared to traditional loose
(dumped) rock. The Colorado Springs project represented the first use of the partial grouting
technique in the United States for bridge scour protection.