(logo whooshing)
- [Presenter] To prevent soil
and sand erosion around bridge foundations.
It's common practice to place stone rip rap on bridge piers
or abutment slopes,
even so, scour is the major cause of bridge failure.
Case histories and surveys conducted
as part of this project indicate
that in about 5% of the cases,
rip rap covered slopes fail.
As part of the project, researchers
with the Texas A&M Transportation Institute tested
the filters commonly used between the rip rap layer
and the soil surrounding bridge foundations.
- Bridge scour,
erosion of soil around bridge supports
is one of the leading causes of a bridge failures.
So in order to protect against a big holes
around the bridge supports,
we put rip rap,
those big rocks around the bridge supports.
- Even within our stone protection,
we've seen local and global failures.
And so what this research aim was aiming to,
was aiming to look at is how can we influence
the design of our stone protection
to be able to try to mitigate some of these failures
and something that the researchers looked at really closely
was the filter material between the existing embankment
and the stone protection.
- There are two types of filters.
One of them is granular filter
the other one is geotextile.
It's a fabric that we place under the rip rap
and over the sand or the soil in general.
And that also prevents the sand from eroding.
- They looked at it from a literature review standpoint,
they looked at it from a survey standpoint
with the use of those intermediate filter materials.
And then they also looked
at it from an analytical standpoint,
long-term stability analysis using slope stability programs,
as well as numerical modeling
to kind of look at how slopes potentially could affect
the critical velocity of stone protection
and the determination that they came
to is that in all cases except for when replacing
of this material in an underwater application,
that filter fabric from a cost standpoint
and from an installation standpoint,
turned out to be the better option.
- One of the questions in the project
was how steepest slope can you have to put the rip rap
on top of it.
And we found that if the slope is too steep,
1.5 to one rip rap is likely to fail,
but the two and a half to one is the maximum you can allow
and still have the rip rap on top of it.
And we found that when you start increasing the slope,
then the rock cannot resist the same velocity.
And this was one of the causes of failure
in some of the case histories that we analyzed.
So I think we should look into that.
- [Presenter] For more information
and to find the publications for this project,
please visit the TxDOT Research Library
at the link shown below.