Balancing Urban Development and Water Conservation
 

Posted Under: Paving

Basing the Driveway. Why its Important to Get it Right.

Posted March 16, 2021 @ 8:51am | by Tori

Basing the Driveway. Why it’s important to get it right.

If you happen to notice Spring’s heave and pothole haven around town you begin to understand the importance of a good foundation. Not only is a good foundation vital to a home’s structural soundness, it’s also vital to a pavement’s longevity.

Preparing a good foundation for a driveway involves a few things. 

First, understanding what native subsoils exist. Yep, back into the soil type discussion. Certain types of soil can be more problematic than others. Soil type can be broken down into silt, sand and clay, and most likely your property is a blend of two or all three. Below is a fun visual to understand the 3 main catagories and mixtures within. 

 

Now how do soil particles play out with your driveway’s structural soundness?

Spring is one of the times that you’ll see a great deal of movement on the pavement surface. As the frozen ground is unfreezing, the moisture has to go somewhere. If the soils are not well-draining for the water molecule to move down (or the frost is still in the ground), then there will be movement of that moisture going up. Aye, there’s the heave.

 

In clay soils, this can be extremely noticeable particularly when the ground is thawing, still freezing or doing the thaw and refreeze action.

Sandy soils present less complications as this soil type drains quicker. 

So if you had to choose the perfect soil type of your property, sandier soils would be the way to go. That is as long as the surface grades are working right for drainage on the property, but that’s an entirely different issue.

 

However, an important item to note are layers. Generally your property doesn’t have the same soil type 20’ down. So what might appear to be sandy for the first 12” may change below that and of course what’s below can play a role in things too.

So how does this discussion of soil types relate to installing a driveway?

Well, the pavement surface needs to be supported properly. And what does this mean exactly? Yeah, think of it as two things; 1. The shock absorber to all the movement that’s happening below ground with freeze/thaw conditions and 2. The structural stabilizer of what’s on top. 

 

The base layer is composed of aggregate. In a driveway this generally means a ¾” minus aggregate meaning that it’s a rock of a ¾” diameter and smaller. By incorporating fines (the smaller) allows for compaction. Another important factor is for the aggregate ideally to be fractured or angular to allow for maximal density. 

 

There are certain circumstances where it may be reasonable to install a layered aggregate base in really unstable soils. This might be a 1-3” aggregate below a ¾” for instance. 

     

How deep should the base layer be?

Yeah. This isn’t set in stone. The standard in the Twin Cities Metropolitan area for driveway construction is  4-6”. Is that enough in clay? No. Enough in sand? Yes. But again, no property has the one soil type 20’ down so how exactly do you know how deep is deep enough?

 

Without involving a civil engineer to analyze and design - ‘cause that can add to the cost of things - one of the best ways is for a driveway contractor to proof roll. Why? Because it’s specific to your site and is the best approach to know enough is enough...and without doing too much (‘cause that can get costly too). Over-engineering, or over-compensating on designing, is a thing too and more trucking, labor and materials in and out means more expense.

 

How is proof rolling done?

A loaded truck drives on the surface to see how much displacement (aka “rutting”) occurs. If significant, that area is dug out and a new base aggregate layer, potentially geotextiles as well, installed to reinforce that “soft spot.” It could be limited to one location, several or the entire length of your driveway.

If you really want to geek out on proof rolling, Purdue has a great research publication. find it Here  

 

Images by Indiana DOT and Purdue University Here

 

 
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Asphalt Seams/Joints

Posted September 3, 2020 @ 2:44pm | by Stacy

Asphalt Seams/Joints

Asphalt seams, or joints, occur as a result of the paving process. The standard size paver that lays the asphalt generally ranges from 8’ – 14’. Most driveways are a double car (16’ -24’) or a 3 car garage (~ 36’).

 

Laying the asphalt occurs in passes, where there are mats that are laid up against one another. This can be a weakness in the product if it’s not “sewn” up properly. Think of it as pieces of fabric that need to be joined (sewn) to stay together. If the seam isn’t joined well it can unravel or separate in the case of asphalt. You will see this happening on roadways.

 

One important process is the temperature of the two mats. When the asphalt leaves the plant it is between 300 and 350 degrees Fahrenheit. Depending upon how far away the plant is from the jobsite, the ambient air temperature, and how the project is staged with pulling passes the asphalt temperature will be affected. 

 

Other factors that allow a good seam construction are the paver and roller operators. Ensuring that the side of the paver is overlapping/abutting the adjacent mat properly and the seam is compacted at just the right time also are major contributors. 

 

When the seam is noticeable you see a strip or shadow where the mats join. This doesn’t mean that the adherance is insufficient but it can be an aesthetic issue for some homeowners. Using a propane torch, skilled looters to loot (or rake) the larger rock and smaller fines as well as talented roller operators will lessen the look. Unfortunately weather, especially cool fall days, will make it rather difficult. 

 

If your driveway shows too much of that seam for your preference or any other minor surface variation, a simple emulsion sealcoat will unify your surface. Make sure to use an asphalt-based sealer only. Not a coal tar sealer. Not only is an asphalt-base a smarter enviromental choice but your asphalt will appreciate it too. As the asphalt wants to expand and contract with changes in temperature, the sealant needs to move with it. A coal tar sealer is a rigid product and on a flexible material such as asphalt that means hairline cracks.

 

Enjoy your asphalt driveway!

 

 

 

 

 

 

 

 

 
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Greening up your driveway

Posted May 1, 2014 @ 3:08pm | by Earth Wizards

Greening up your driveway

Driveways are conduits for runoff.  Not only do our impervious driveways shed stormwater but often portions of our home, garage and even lawns direct runoff onto the driveway. Hence, why the driveway becomes an ideal design feature to rethink how it's constructed.

Generally there are three methods of thought in making a driveway more "green."  

  1. Decrease the extent of pavement,
  2. Reroute stormwater from the driveway to available green space for a rain garden or native-planted filter strip (one of my favorite methods as it provides habitat), and
  3. Make the pavement permeable, pervious, porous - somewhat interchangeable terms depending upon the surface type used.

Starting with decreasing pavement surface, think about where your car tires actually go. Oftentimes we think the driveway needs to extend all the way along the house to the back of the garage or for it to be three cars wide the full length of the driveway. Consideration of the vehicle's path will help determine what really needs to be a solid hard surface, what can be a secondary pavement type (both turfstone, a grid structure or concrete runners can work well) and then green space of course.

Rerouting can entail contouring the surface if slopes are relatively slight or installing a diverter structure, such as a trench drain.  In Minnesota, contouring can be tricky as winter conditions need to also be considered.  When we're snowbankless that's one thing but take 2014 winter's deluge and that means overflows need to be working well to prevent major ice dams.  Here are two examples of driveways showing a contour versus a steeper slope necessitating a trench drain (also see the main photo of this blog).

Lastly, most expensive but sometimes the most appropriate, are permeable pavements.  In order of the photos are; porous asphalt, porous concrete, permeable pavers, permeable stonework (not generally recommended for driveways but great for patios).

Keep in mind the entire surface doesn't need to be permeable.  Setting a design goal, such as a 2" rain event capture, helps to determine how much of your driveway surface needs to be permeable (that means less cost, less maintenance and less of a carbon footprint with material export/import). I hope this helps in considering what approach may work best for you and feel free to give us a call or email if you'd like us to visit and provide some options for you. Thanks for rethinking your driveway.

 
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Concrete, Blacktop or What?

Posted April 1, 2014 @ 7:33am | by Earth Wizards

Concrete, Blacktop or What?

How do I choose a driveway surface?

 This is a great question and requires additional information before deciding on the product or products that are right for you and your situation. There are a number of factors to consider when choosing a driveway surface, so lets go through them.

1) Cost

Obviously cost is a big consideration in your decision. Don’t make the mistake of going with the lowest price simply because it is the lowest price. There is usually a reason for the lesser price. Just like anything, “you get what you pay for”. At the same time, the most expensive may not mean better quality either. Do your research and find out who is a quality contractor and get multiple quotes.

2) Existing soil type

This is probably the single most important and often overlooked item in the decision making process. What soil type is in the driveway area? Sand, loam and clay are common soils in the upper Midwest and react differently during the freeze/thaw cycles. Sand is very forgiving, provides good drainage and doesn’t require extra excavation. Clay retains moisture and can move greatly as it expands and contracts during freeze/thaw. If you are in a green/grey clay soil that is wet, you can expect to pay more to have additional excavation, additional base material and possibly stabilization fabric installed. It is critical to have a stable base course for the driveway surface to have a long lasting driveway. This may not be an issue in other parts of the country.

3) Appearance

This is your preference. There are more choices than ever and it’s really exciting! Asphalt, concrete, trap rock, gravel, runners, flag stone or even grass (grass is planted inside a turf stone or plastic which supports the vehicle weight and doesn’t flatten out). How about a combination of two or more of those?

4) Usage

In other words, will there be heavy loads or frequent vehicles using the driveway on a regular basis? This is often not considered in choosing the driveway surface.
 

 
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I have already recommended you! Our consultant, Shelly, was extremely knowledgeable. She explained (the process) in technical detail. She is the reason I chose Earth Wizards over the other 5 bidders. Installation crew was terrific and exceeded my expectations.

- Don P.
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