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(logo whooshing)

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- [Presenter] To prevent soil

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and sand erosion around
bridge foundations.

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It's common practice to place
stone rip rap on bridge piers

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or abutment slopes,

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even so, scour is the major
cause of bridge failure.

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Case histories and surveys conducted

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as part of this project indicate

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that in about 5% of the cases,

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rip rap covered slopes fail.

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As part of the project, researchers

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with the Texas A&M
Transportation Institute tested

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the filters commonly used
between the rip rap layer

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and the soil surrounding
bridge foundations.

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- Bridge scour,

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erosion of soil around bridge supports

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is one of the leading
causes of a bridge failures.

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So in order to protect against a big holes

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around the bridge supports,

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we put rip rap,

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those big rocks around
the bridge supports.

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- Even within our stone protection,

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we've seen local and global failures.

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And so what this research
aim was aiming to,

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was aiming to look at
is how can we influence

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the design of our stone protection

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to be able to try to mitigate
some of these failures

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and something that the researchers
looked at really closely

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was the filter material
between the existing embankment

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and the stone protection.

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- There are two types of filters.

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One of them is granular filter

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the other one is geotextile.

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It's a fabric that we
place under the rip rap

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and over the sand or the soil in general.

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And that also prevents
the sand from eroding.

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- They looked at it from a
literature review standpoint,

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they looked at it from a survey standpoint

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with the use of those
intermediate filter materials.

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And then they also looked

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at it from an analytical standpoint,

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long-term stability analysis
using slope stability programs,

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as well as numerical modeling

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to kind of look at how slopes
potentially could affect

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the critical velocity of stone protection

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and the determination that they came

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to is that in all cases
except for when replacing

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of this material in an
underwater application,

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that filter fabric from a cost standpoint

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and from an installation standpoint,

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turned out to be the better option.

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- One of the questions in the project

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was how steepest slope can
you have to put the rip rap

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on top of it.

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And we found that if
the slope is too steep,

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1.5 to one rip rap is likely to fail,

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but the two and a half to one
is the maximum you can allow

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and still have the rip rap on top of it.

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And we found that when you
start increasing the slope,

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then the rock cannot
resist the same velocity.

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And this was one of the causes of failure

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in some of the case
histories that we analyzed.

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So I think we should look into that.

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- [Presenter] For more information

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and to find the publications
for this project,

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please visit the TxDOT Research Library

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at the link shown below.