We treat parking lots a lot like many of us treat our health; we typically wait to call the professional and have them take a look until an issue becomes visible. As a parking lot contractor, we receive many calls throughout the season regarding actual sinkholes which have formed within our customers’ lots and the majority of them occur within close proximity to a catch basin(sewer) designed to remove water from the lot.
When these issues occur, in the same way we want a doctor to approach our health, we want to inform our customers on the actual root of the problem and how to fix it; rather than apply a band-aid that will need to be applied again down the road. I think everyone would agree, let’s put forth the right resources the first time so we don’t have to deal with it again!
Why do you have a hole in your lot?
The sinkhole which has formed in your lot is NOT simply an issue that can be treated by filling in the hole and patching the asphalt around the catch basin. The reason why the hole has formed in the first place is due to erosion of the drainage structure and the surrounding base material(stone) within your lot. The actual issue is a hole in the concrete structure or a cracked/deteriorated concrete adjusting ring which makes up the basin which is then allowing water to flow through an area not designed to have water flow through it. This break down in the integrity of the concrete structure makes water flow through the stone surrounding the catch basin, washing it out from underneath the asphalt and into the bottom of the drainage structure. This creates a pocket between your asphalt and the stone underneath. Now imagine cars, garbage trucks, and delivery trucks driving over asphalt which has nothing underneath it for support; and so forms your sinkhole!
What is the solution?
You can see why simply patching the asphalt surface will not be enough for a long term fix. Even adding a bunch of stone to replace that which has washed out into the basin is not enough. The structure needs to be patched in some capacity, cleaned out of the stone which has made its way in as it is not designed to work properly with the added debris, and in some instances, the structure needs to be replaced completely prior to patching anything on the surface. Please make sure the contractor you choose to 
assess the situation addresses these issues referenced prior to making a recommendation on fixing the asphalt and ensure they are equipped to provide the necessary solution. Do not choose the cheaper band-aid over the actual solution to the issue. you will end up paying the difference when you have to repair it again.
Is there anything I can do to prevent this?
Don’t wait for the sinkhole to form! I have pulled up on many of my customers’ lots where cones and barricades are within and surrounding a sinkhole which has already formed. This causes redirection of traffic within their lots, closures of docks, and loss of time and money for their operation. In some instances, these sinkholes have led to damage of cars and trucks prior to the discovery of the sinkhole!
Preventative maintenance minimizes these issues! Some of us will never go to see a doctor for regular check-ups, however studies will show the benefits in doing so outweigh the inconveniences and costs. Invite a paving contractor that you trust to assess your lot annually so you can spot some of these occurrences before they become an issue. Check around the catch basins you have in your lot. Do you have any major depressions in the asphalt within a 3-5 foot radius surrounding the cover? These indicate an area where a sinkhole may 
form and it may be time to call that reliable parking lot contractor.
As a property manager, you can’t become an expert in everything, there is simply not enough time in your day. However, we are #pavingitforward by providing education so you are equipped with some of the basics to apply to the properties you manage. If you find value within, please feel free to forward along, like, comment, or share!
-Nate Olson | Pavement Consultant | nate@rayaf90fa62d447.wpcomstaging.com | Connect with Nate on Linked In
