Hello, my name is Jim Schall, and I'm an instructor
for Federal Highway Administration training
delivered under the National Highway Institute.
The National Highway Institute, or NHI, is the training branch
to the Federal Highway Administration.
The videos you're about to watch
are based on some of the training courses
developed by the National Highway Institute, in particular,
the Introduction to Highway Hydraulics course,
NHI course 135065, and the Culvert Design course,
NHI course 135056.
I've been an instructor for National Highway Institute
training courses for 25 years.
I completed my undergraduate engineering degree
at Purdue University and did my Masters and Ph.D
at Colorado State.
The videos are based on demonstrations and experiments
that we do primarily in these two training courses,
built around a portable flume.
The flume is six inches wide
and approximately five feet long,
and recirculates water from a 30 gallon sump.
The videos, there are six of them to watch.
The recommended order in which to watch those videos,
first, open-channel flow concepts,
then grate inlets,
culvert hydraulic concepts,
hydraulic effects of culvert liners,
aquatic organism passage design concepts,
and energy dissipators for culverts.
Thank you for your interest
in Federal Highway Administration training.
I hope you find this video series helpful
in completing highway drainage design projects.
This video will demonstrate the effects of liners
on culvert performance.
The purpose of the video is to see
how a liner changes hydraulic performance,
primarily by looking at the change in headwater
that will be detected by our stilling well.
I have for the model a double barrel culvert.
We'll only be using the rough barrel side,
which simulates a corrugated metal pipe
with an n value of .024.
So, I have a plug in the smooth barrel side.
I have two liner models to demonstrate.
The first one will model a slip liner.
My culvert model is a one to 12 scale.
I have a two inch diameter pipe in the model,
meaning a two foot diameter pipe in prototype.
This slip liner would be six inches smaller in prototype.
It's a 1 1/2 inch pipe, or 18 inches in prototype,
and that's a fairly common change to a slip liner
to allow grout to be pumped into the annulus
between the host and the liner pipe.
I also have what we might call a close fit liner,
which is a 1 3/4 inch pipe, or in my prototype dimension
equal to a 21 inch.
We'll be looking at the changes
in the roughness of the pipe.
We're going from my n value of .024
to a value in both liners of a smooth barrel,
with an n value of say, .012.
So, we're cutting the n value in half
and comparing how that change
interacts with the change in area that we see
when we put a liner into a culvert.
I have a couple different ways to terminate the liner.
The models have a headwall with a groove-end
to allow different things to be input to the headwall
so my liner model has a ring on it
that will allow it to recess into the socket
on the end of the headwall,
maintaining K sub e of about .2.
I also have some extenders that I can put on the headwall
to simulate what would happen
if we terminated the liner outside of the host,
which is not a preferred construction method
but I have seen it done.
That changes the K sub e from .2 to about .9
the way I'll be testing the model.
So, we'll run through this in outlet control, initially.
If you're not familiar with the concepts of outlet control
in culvert hydraulics,
please refer to the culvert hydraulic video,
the FHWA culvert hydraulic video
that goes through the differences
between inlet and outlet control.
Once the headwater stabilizes,
we'll mark it with one of the o-rings on our stilling well,
and then we'll proceed with the slip liner
which will be the pipe dropping down
from a two foot to an 18 inch in prototype dimension,
allowing enough space for grout injection
around the annulus of that liner pipe.
And the question is,
when I stick the liner in,
will the headwater go up or go down?
It's commonly believed that a liner
will improve the hydraulic performance,
that the headwater would go down,
because we're changing the n value so dramatically.
We're going from our .024 for our CMP pipe
to an .012 for the smooth barrel.
So let's see what happens.
As we can see, the headwater is rising quite a bit.
Once that stabilizes, I'll go ahead and mark that,
but what that tells us is that the change in area
on this particular model,
going from a 24 inch to an 18 inch pipe,
far outweighs the change in roughness,
that in fact, the hydraulic performance doesn't improve,
it gets worse.
This is with a K sub e,
the entrance coefficient
loss of about .2.
I can change that by putting my liner extension
on to a thin edge projecting
which has a K sub e of .9.
So my headwater's rising slowly,
but I think we're stable enough, we can try this.
And we see a little bit more
of an increase in the headwater.
We don't see a big change.
It was quite a change in the K sub e,
we went from .2 to .9,
but in culvert hydraulics, in outlet control,
the entrance loss is just one part of the energy loss.
We have the entrance loss,
we have the friction loss of the barrel,
and we have the exit loss.
The friction loss is typically the largest.
The entrance loss doesn't change
the hydraulic conditions too much in outlet control.
When we go to inlet control
we'll see something different,
but in outlet control,
this K sub e value wasn't a big change.
So let's take this out and put the close fit liner in.
We’ll give it a minute to stabilize.
And again, the close fit liner
will change my barrel diameter from 24 inches to 21,
not as much of a change in flow area as
we had with the slip liner.
And we'll see how that impacts this trade off
between area and n value change.
Federal Highways has done enough research on this
to know as a rule of thumb
that the smaller pipe sizes, like in my model,
my two foot barrel,
the area change is more important.
That continues up to about a 48 inch pipe.
The change in area is typically more important
than the change in roughness.
Above a 48 inch pipe,
what is commonly believed starts to happen
which is that the smooth liner,
particularly on a CMP pipe,
will improve the hydraulic performance
because in the larger pipe size,
even for a slip liner, that normal six inch reduction
in size to allow for grout injection,
is not as significant as it is at the smaller pipe sizes.
So we're pretty stable on the headwater.
Let's go ahead and put my close fit liner in
and see what happens.
And as expected, we see an increase,
or course, not as much as we had with the slip liner
because the area reduction is not as great.
So I'll mark this one, and again,
we'll put on the liner extension,
meaning that the liner is terminated outside of the host.
And there'll be a slight increase again,
but because we're still in outlet control,
we don't see as much of a change.
In outlet control we have all three energy losses,
the entrance loss, the barrel friction loss,
and the exit loss that account
for the headwater performance.
With the model in this configuration,
I'm going to go ahead and raise the slope up to inlet control
and we'll see these changes in inlet control,
starting with the liner extension.
I'm going to vent this pipe only to make it
transition into inlet control more quickly.
And again, this idea of terminating the liner
outside of the host is certainly
not a recommended design practice.
In addition to a hydraulic impact,
changing the K sub e,
you have what is typically a thin edge projecting pipe
projecting into the flow with assorted structural
and buoyancy related concerns.
So I'll start by marking this headwater,
and then what we'll do is transition from the K sub e of .9
to a beveled ring that will change the K sub e to .2.
So now we're in inlet control.
We're flowing super critical, we're on a steep slope,
super critical part flow inside the barrel.
The headwater is pretty stable.
Let's take the liner extension off,
slip the beveled ring into place,
and we immediately see a reduction in the headwater.
This is because in inlet control,
conditions at the inlet are critical.
That's why we call it inlet control
and changes we make at the entrance
can dramatically change hydraulic performance.
So it's clear from the demonstration,
there's two primary points to remember,
that the way you terminate the liner is important
in terms of how the culvert
will operate hydraulically in the field.
When you allow the liner to project from the host pipe,
beyond the headwall,
you change the K sub e value
and create this thin edge projecting entrance condition
that has a small effect in outlet control,
has a large effect in inlet control.
By far, the preferred construction practice
is to terminate the liner inside the host
and use that grout to form a bevel
at the entrance to the pipe.
The second important lesson to remember
is that while it's commonly believed that inserting a liner
will improve the hydraulic performance,
particularly on a rough barrel pipe
because you're changing the n value,
in fact, what we find is that's only true
on the larger diameter pipes.
If you're above a 60 inch pipe,
48 inch pipe on into 60 inch pipe,
a six inch change in pipe size, even for a slip liner,
isn't that much of a change percentage-wise
and therefore, the change in n value
becomes very important.
Smaller pipes below 48, and my model
was in a prototype dimension of 24-
a two foot diameter pipe,
we saw that the change in area
was far more important than the change in n value.
Thank you for your interest
in Federal Highway Administration training.
For additional information on culvert hydraulics
and the effects of liners on culvert hydraulics,
please refer to Hydraulic Design Series Number Five,
the Design of Highway Culverts
by the Federal Highway Administration,
and the accompanying NHI training course,
NHI course 135056 on culvert design,
and you can also use to do any of these calculations
and to evaluate these changes,
the Federal Highway Administration software, HY-8,
for culvert design, changing the barrel size,
the n value, the entrance coefficient
to evaluate how a liner might act in the field
before it goes into construction.