We’ve had considerable rain over the last week or so, and of course now the roads are full of potholes, some quite large so they pose a bit of a threat to drivers and their cars.
Yesterday I was at a mall shopping centre that was a number of hectares, fully paved. Yet in one of the parking drives there was a hulking great pothole, at least 12" deep and 24" across.
How does the water get UNDER the road to wash away the soil to create the pothole? I can understand it on the narrow roads that don’t have sidewalks and proper gutters, but in the scenario above, what is the mechanism for the pothole formation?
I don’t think the freeze/thaw cycle applies where I live. It’s rare to even get a frosty morning, never snows, and rarely gets down to 3-4c even overnight.
Colorado Springs is currently going through a multi-year re-paving effort–catching up, or trying to, on the deferred street maintenance from the recession years. When the city is getting ready to repave a street, the first thing they do is replace any cracked curb and gutter segments. If the curbs and gutters are in poor condition, that lets water down below the asphalt, and rather dramatically shortens the lifespan of the new pavement.
Parking lots are not subjected to the same DOT regulations since they are private property. So it doesn’t get the proper void testing and the performance grading can be much more lax.
Commercial jobs often are either dumping grounds for poor quality asphalt like 70-10 or testing grounds for high RAP (reclaimed asphalt pavement) projects. Some regions like the northeast get gov’t kickbacks based on how much RAP they use so there is high incentive to use it.
There is a major interest in asphalt rejuvenation right now and the Transportation Research Board (TRB) are still ironing out official testing between diluents and rejuvenation.
Lastly asphalt is like a sheet of glass, one crack propagates thru the entire section. Thats why cracks often appear in a rhythmic periodic fashion. There’s minor strain that accumulates in asphalt from each axle loading (ESAL’s) and even moreso from parked vehicles. If the asphalt has a poor m-value (relaxation parameter) which commonly get used in commercial jobs the lifespan is often less than 7years.
Sometimes cracks happen because the wrong binder was used in the asphalt design for the traffic load/temperature range of a location. Asphalt design is a big deal. You can also get the gravel mix wrong, but it seems like it’s easier to choose the wrong binder.
There’s also alligator cracking, which sometimes happens because the sub-base isn’t strong enough for the load the road is carrying. If the sub-base is weak or has been damaged, just repairing the surface asphalt won’t solve the problem. The asphalt will still be still be subjected to too much flexing and the cracks will come back.
Unfortunately, evaluating and reinforcing the sub-base is expensive, so you’ll often see the same area patched and re-patched.
Alligator cracking can also be caused by the asphalt or base sections being too shallow. That usually shows over a wider stretch of road, rather than as a single location.
The secret to potholes, on asphalt, is oil. Any type of oil will do - gasoline, diesel, engine oil … Once a bit of oil is “spilled” , a soft spot is created. A car or truck drives over that and it gets deeper and it propagates the same way from then on.
I think a lot of people don’t know that roads require routine maintenance. You can’t just install one and expect it to stay drive-able for all time. Entropy will have its way. All roads will crack and deteriorate eventually.
Ideally, when an agency or municipality installs a road, they add it to their maintenance schedule. If you don’t keep up with sealing and with overlays, your system will degrade and you risk base and sub-base damage. Then it’s going to be even more expensive to fix. I think people would be shocked to discover how many millions it takes just to keep roads drive-able. And if you get behind, you’ll be spending millions to watch your roads decay, just not as fast.
A related, smaller, budget thing in our area is landscaped medians. After water prices rose, and after much screaming from the Parks Department, Public Works instructed all engineers not to include a landscaped median in a project unless Parks has confirmed that they have the budget to water and maintain another one.