Mechanically Stabilized Earth. Are there any words more thrilling to the human soul?

Honestly? Probably. More likely? Absolutely.

But that doesn’t change the fact that Mechanically Stabilized Earth plays an important role in ADOT infrastructure.

In fact, there’s a good chance you’ve passed by an MSE wall and were none the wiser!

You start by acquiring high quality soil. That soil gets compacted inside retaining walls and reinforced with steel rods. Other material can be, and sometimes is, used instead of steel. But why mess with a reliable compound?

These pieces (wall face, soil, rods) are assembled sort of like a jigsaw puzzle or building blocks. They are then sewn together, if you will, using steel straps.

Not only are they a safe and stable choice, but Mechanically Stabilized Earth walls are also cost effective! Another main draw to MSE walls is that they can be constructed quickly and relatively easily.

Recent projects that have utilized MSE walls include the Loop 202 South Mountain Freeway (photo bottom right) and the latest Grand Avenue/Bell Road interchange project (photo top right). And it’s not just these ventures that use MSE walls. In fact, ADOT’s been using this approach since the 1970s! 

But its history goes back way further than that, perhaps even to the dawn of civilization. Segments of the Great Wall of China have been found to employ a rudimentary reinforced soil technique. And that's held up quite well!

Next time you’re driving around Arizona’s highways, impress your friends! Tell them that you know all about Mechanically Stabilized Earth Walls.

A sharp-eyed driver spotted something like the photo to the right on the Loop 101 Pima Freeway near the State Route 51 interchange earlier this year and took to social media to ask us what it is.

And we are glad they did because it gives us the opportunity to talk about batch plants.

Batch plants, or the more august-sounding onsite materials plants, are used to provide paving materials, such as asphalt or Portland cement concrete pavement, that any given project will need. The photo at right is a batch plant in the northwest Valley in 2017.

When it's part of their plans, contractors seek permission to set up batch plants on land at or adjacent to projects. Having a batch plant on site producing materials is much more efficient and cost-effective than having concrete or asphalt made elsewhere and trucked to the work zone. To answer the question raised on social media, the batch plant they saw was helping produce pavement for the widening of the Loop 101 between Interstate 17 and Pima Road.

After a project is completed, the batch plant will be removed and the land it sits on will be restored to how it was before.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

What do the Loop 202 (Red Mountain, Santan and South Mountain freeways), State Route 347 north of Maricopa and Interstate 40 near Seligman all have in common?

The answer is they have all benefited recently from today's topic: fog sealing. 

Fog sealing is a pavement preservation technique used to add life and extend the longevity of pavement. "Fog" just means a coat, which is how the treatment gets its name, according to Mohammed Elomeri, with ADOT's Central Engineering and Maintenance District.

A fog seal normally contains an emulsifying agent – or diluted asphalt – and a rejuvenator and is designed to seal narrow cracks and restore lost flexibility to the pavement surface, Elomeri said.

You can see the results from these photos taken on State Route 89A last year, and from fog seals done on Loop 101 (Agua Fria Freeway) in Glendale two years ago and many other stretches where fog sealing has been used to extend the life of pavement.

Doing regular pavement preservation such as a fog seal or a chip seal, which we mentioned in this blog from 2018, is an important part of maintaining highways. Mainly because it proves the old saying that an ounce of prevention is worth a pound of cure. It costs $3,000 per lane mile for a fog seal, while to mill down and replace the asphalt surface of the same mile would cost $300,000. 

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

By David Rookhuyzen / ADOT Communications

You may have noticed we’ve been busy this summer improving State Route 88 east of Apache Junction. There’s been rock blasting, curve adjusting, bridge replacing and, recently, a chip seal to keep the road surface in good condition.

For those who don’t know, a chip seal is a type of road surfacing when aggregate, or crushed gravel, is combined in layers with asphalt cement. The individual layers of asphalt cement – the black, gooey stuff, as Transportation Engineering Specialist Roger Vial explained – are known as tack oil or a tack coat.

“There are different tack coat materials that are used for asphalt pavement, Portland cement pavement and chip seal,” Vial said. “The type, grade or designation, and the rate of application for the specific usage are specified by the engineer."

On State Route 88, this coat was also topped with wet sand that acts with the tack oil to seal the road.

And even before all that, a tack coat was also put down on the existing pavement to prepare for the coming layer of fractured rock chips.

We doubt you’ll be thinking of this bit of highway engineering next time you drive up for a day at Canyon Lake, but as long as you get there it’s done its job.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

By David Rookhuyzen / ADOT Communications

If you’ve driven Interstate 10 in Casa Grande recently, then you probably noticed work going on to expand the freeway to three lanes in each direction near Interstate 8. That includes expanding bridges carrying I-10 over Jimmie Kerr Boulevard and the Union Pacific Railroad tracks.

Next year cars will use the larger bridge on a wider I-10 without giving much thought to the engineering behind it. But for now they can see the new vertical supports known as piers capped by what are known as – wait for it – pier caps. Pier caps creating the horizontal section in the picture above will eventually support bridge girders.

Erin Kline, an engineer on the project, explained the role these vertical concrete beams will eventually play.

“Pier caps transfer the loads from the superstructure to the piers. They hold the bridge girders on bearing pads and disperse the loads from the bearings to the piers. Bridges with piers will all have pier caps to transfer the load from the superstructure. I would say majority of the bridges in Arizona are like this,” Kline said.

We’ll have more to say about the anatomy of this project moving forward. For now you can read more about the coming improvements at the project's website.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained...leave a comment here on the blog or over on our Facebook page!

The word for today is rustication. Know what it means?

If you do, you might be thinking it’s a word not typically associated with transportation. But rustication actually is something you regularly encounter as a driver on Arizona’s highways.

ADOT’s Chief Landscape Architect LeRoy Brady gives us the definition…

“Rustication is a repetitive pattern or texture added to a wall, so it’s not just a smooth wall,” Brady said, adding that the pattern can be as simple as a series of grooves or textures.

As you can see in the photos above and below, ADOT uses rustication on many of the walls, bridges and structures surrounding its freeways.

ADOT uses rustication and graphic elements or designs to help create visual interest and a sense of place.

“It provides visual interest,” Brady said. “The rustication makes it so that everything’s not the same, so it helps create a sense of place also.”

The rustication patterns are decided on during the design process, Brady said. Contractors then cast the different patterns into the concrete by using forms during construction.

Besides rustication, ADOT also uses graphic elements or designs – like tortoise, cacti, gecko, mountains, water and wave icons – to also help create that visual interest and sense of place.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

If you’ve driven recently on the Loop 202 Red Mountain Freeway, you might recognize the structure pictured to the right.

It sits near the Val Vista Drive exit, spanning westbound travel lanes, and while it’s not something you might see on every work site, it serves an important function on this project.

Referred to as a Bailey Bridge, which according to the Federal Highway Administration, is a temporary, prefabricated steel bridge that’s easy to transport, the structure shown above utilizes a conveyer belt to transport freshly mixed concrete from the batch plant just off the freeway to the median where crews are working to add an HOV lane.

It’s sort of brilliant because using the conveyor belt to move concrete over the freeway to the work zone saves countless truck trips. If the structure wasn’t there, trucks would have to be loaded up with concrete at the batch plant, get onto the freeway, and cross over several lanes to the work zone in the median.

Now, trucks can be staged within the work area without having to impact traffic – the concrete comes to them!

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Dirt has been a pretty popular topic for us.

We’ve let you know how we test it, move it, water it and even why we sometimes “paint” it green.

Now we want to explain why we bench it. More specifically, why we minibench it.

Does this topic sound familiar? We've actually covered minibenching before, but today we're taking a closer look...

When ADOT constructs a new road, makes an adjustment to a current road alignment or takes on a major road construction project, there’s often quite a bit of earthwork that happens. Soil and rock material can get dug up, cut into, moved around or filled in. The resulting roadside slopes are the product of precise planning and calculation (but that’s a blog post for another day!).

Minibenches can be cut into the soil on those slopes, and the result is a sort of stair-step design that you can see in the drawing above.

Taken on SR 188, these photos show an example of mini-benching. At left, the mini-benched slope just after construction. At right, the same slope several yeas later. Photos by Luis Colon.

Wondering why ADOT does that? Well, there is a good reason, and it has to do with establishing vegetation and preventing erosion.

ADOT’s Chief Landscape Architect LeRoy Brady explains that decades ago, cut slopes were left smooth, but rain would run right down, often bringing dirt and rock with it.

Today, many steps are taken to help prevent erosion and minibenching is just one of several grading techniques used.

Minibenching works like this: When a slope is first graded and shaped, it is cut into a series of benches or stair-steps. Once the grading is complete, the minibenched slope is seeded with vegetation that's indigenous to the area. The stair-step design initially works to slow the flow of rain water down the slope, but it also captures or harvests the rainwater to help establish the native seeding. The minibench helps to keep the seed up on the slope and create a planting area that allows the seed to germinate and take root to re-establish vegetation on the slope. The graded minibench provides the short-term erosion protection – while well-established vegetation provides long-term natural erosion control and protection.

“The fact that the vegetation has been established on those benches … it helps for the rest of the life of that slope,” said Brady, adding that, after a few years, the slope fills in and drivers don’t see the minibenches anymore.

Minibenching reestablishes the native vegetation along the highways so the roadside is more visually pleasing, but it’s not all about looking pretty. There’s a cost-savings factor too.

“A stable slope that stays there and doesn’t erode means you’re not having to clean the ditch, you’re not having equipment along the roadway and you’re not having that maintenance cost,” Brady said.

Visit our website to learn more about ADOT’s Roadside Development section.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

When someone hears the word “asphalt,” they might picture the road that they drive on, but asphalt is actually one component of that surface...

We recently dropped by ADOT’s binder lab and learned all about asphalt and the testing that ADOT conducts. We’ll share that information with you soon, but for today, we thought we’d start off by showing you a couple photos of asphalt – the thick, sticky, black substance that acts as a binder when mixed with aggregate.

Asphalt, which is basically the residual hydrocarbons that are left over when oil is distilled, has multiple uses. At ADOT we use it for road paving.

You’ll notice the photo at left looks smooth and the one at right looks a little chunky. That’s because the sample on the right is rubberized asphalt and already has the crumb rubber mixed in (you can watch this video to get a detailed look at how rubberized asphalt is made).

Stay tuned … we’ll have more on asphalt coming up soon. 

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

While their name might sound somewhat morbid, Deadman Anchors are actually nothing to be afraid of. In fact, they’re very handy on a project site...

Primarily used as anchors (as the name implies), a deadman anchor can also be used to resist forces acting in tension or compression.

Take the photo at right as an example – it was snapped on the Loop 101 widening project and shows a deadman anchor in use.

What you see is a wall form (kind of like a mold that is used to shape the wall). Concrete is poured into the form and, once it hardens, the forms are removed to reveal the finished wall.

Another view of the anchors at work.

But, before the concrete sets, it is in a liquid state and that liquid naturally wants to push outward, equally in all directions. The greatest lateral forces acting on the wall are at the bottom (due to gravity), but because the wall forms are pinned into the concrete footer, blowouts are prevented. That deadman anchor (along with the rod anchor) is actually preventing the wall from overturning before it sets.

These things are very durable and contractors typically have a steady supply they can use for projects. They can be built to suit the needs of the contractor and come in a variety of sizes (the one above is roughly 4,000 lbs.). They’re fairly easy to construct (as long as you have some extra concrete). Contractors will create a box form, into which concrete is poured. The next day, the form is removed and the anchor is complete.

Deadman anchors are primarily utilized to aid in the construction process, though you might see them used at special events to close off a public street and prevent vehicle access.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!