Given the many smart advantages to vacuum excavation for a range of projects, there’s no mystery as to why this method has become so popular in the industry. Construction operators have increasingly opted to leverage this technology to keep their crews safe, optimize project plans, minimize risk and maximize profitability.
As the technology for employing vacuum excavation advances and evolves, so do the opportunities for utilizing it at a variety of construction and utility work sites. But even as the benefits gained from using this technology become clearer, there’s still much to be considered in the way of selecting the best deployment method.
When it comes to construction digging, vacuum excavation can be applied using one of two pressure sources: water or air. Hydro excavation—also referred to as hydrovac, hydro trenching or soft digging—leverages highly pressurized, heated streams of water to break up the soil before it’s suctioned out and stored in nearby debris tanks or trucks for transport. Air excavation—otherwise known as airvac, pneumatic or air-knife excavation—uses compressed air to break up the ground soil before siphoning it through a vacuum hose and potentially returning it as backfill later on.
There’s no doubt that understanding the distinctions between these two is critical to planning your vacuum excavation approach. The final decision of which to utilize will depend on a number of key factors that we’ve highlighted here for you:
One of the most integral elements to consider in deciding between hydro and air excavation is the size and scope of your construction or utility project. Knowing this information enables you to make a selection based on time and cost parameters.
Broadly speaking, hydro excavation is often the most ideal option for large-scale projects, mostly because it has proven to be a faster and more economical method. It is typically the more efficient way to move ground material, providing construction operators with the means to dig deeper into the ground—with both greater precision and higher levels of equipment capacity.
On the other hand, air excavation has been known to suit smaller work crews, as it can generally be managed with reduced manpower, trucks and equipment.
It’s no small point that as a resource, air is much less limited than water. This sometimes makes air excavation the preferred option.
Given that air compressors provide for an infinite supply of the pressure needed to dig, you don’t have to worry about “refilling” during the excavation process, as you would with water. This is a particularly important issue when there is a significant distance between the work site and the nearest applicable source of water.
Perhaps one of the most determinant factors of which type of vacuum excavation to employ is the soil conditions with which the work crew will be contending.
For projects that involve lower-temperature, more compact or tougher soil conditions, hydro excavation is the most ideal option. If you’re dealing with ground materials like frozen soil, clay or rocky earth, for example, water is a more formidable approach because it is more effective in terms of breaking up the area. That’s why it’s more often applied in colder climates and during winter seasons in northern locations.
This softer approach also avoids the potential sandblasting that can occur with air excavation, essentially reducing the potential for damage to underground utilities. Plus, the deeper you have to dig, the greater the probability of reaching colder, harder and wetter subsurfaces, which can render air excavation ineffective. These attributes make hydro excavation a more versatile tactic.
Even so, vacuum excavation may be better suited for projects involving less compact soil or sand.
Material Backfill & Disposal
Your needs for returning the ground material to its prior location versus hauling it off and disposing of it are another major area of consideration.
The process of air excavation has the unique ability to backfill dry soil and debris so there’s no need to transport or dispose of wet, muddy material after digging. Therefore, this is often the most ideal choice for projects that enable workers to reuse the ground material on site. In fact, many utility applications are leveraging this option more frequently than before, given the routine sequence of exposing the lines, performing the work and then putting the ground materials back in place.
Although it’s true that the use of air can be a somewhat slower process than that of water, cost-effectiveness hinges on more than just the time it takes to complete the job. There’s also the expense of having to transport vacuumed materials to a disposal site, as well as the high price of dumping fees. In addition, you must factor in state and local weight restrictions depending on your transport needs.
Because water is a natural lubricant, it is less harsh on excavation equipment, thereby minimizing wear and tear on the vacuum machinery.
Then again, hydro excavation trucks require distinct care in terms of being winterized. So this is an additional cost and management factor to keep in mind.
There are important safety and damage prevention realities to keep in mind. For instance, air excavation is often the better choice when working around live electrical wires, as air is nonconductive. It might also be the safer approach if there’s risk of water causing a chemical reaction with the ground materials.
It should be noted that air excavation generally operates under lower conditions of pressure and force than water, so it could be a more fitting option for fragile utilities or those incapable of withstanding direct contact from a highly pressurized stream of water.
Understandably, the array of advantages that both hydro and air excavation offer to construction and utility teams in a myriad of environments has given rise to these methods as broadly embraced best practices—and the future of construction digging. Comprehending the differences described here is one of the first fundamental steps to planning a successful, safe and cost-effective project.