Woodbury Park Apartments

A Flexi-Pave sidewalk was installed at Woodbury Park Apartments in Arlington, VA on April 14, 2014.  Chosen Flexi-Pave color was Mossy Slate.  For this job, preparation included installing a stone base and soil excavation using the super sonic air tool (SSAT) around tree roots.  For more information on the super sonic air tool click on www.supersonicairknife.com.Check out the link above as their website has a great description of the device and lots of technical info: The supersonic air knife is a “Hand held tool that converts compressed air from a portable compressor to a supersonic jet stream that is used to dig safely in the ground, without damage to buried gas pipe lines, tree roots, sewer pipes, and other non-porous objects…Applications of the supersonic air tool include:

-Trench Rescue
-Tree Root Arborculture
-Locating Buried Utilities
-Oil Spill Abatement
-Locating Septic Tanks
-Cleaning Earth Moving Equipment
-Shallow, Small Pipe Placement

The technology behind the air knife: “Compressed air, typically 90 to 100 psi, is converted to a supersonic jet while flowing through a nozzle especially designed for the purpose. The maximum jet velocity that can be achieved is determined by the pressure available from the compressor. Exit velocities in the range of mach 1.6 to mach 1.7 are typical for most portable compressors. Since the determining limit on mach number for the exiting jet stream is the available pressure, higher mach numbers can only be achieved by using higher compressor pressures. Since the emerging jet stream diameter is the same as the nozzle exit diameter, the air stream is initially the same diameter as the nozzle exit. For this reason, some refer to this characteristic as being laser-like. But as soon as the stream leaves the nozzle, it expands concentrically, since it is surrounded by atmospheric air. High speed video shows this rapid expansion, but it also shows that this high velocity air penetrates the ground to a depth of about a foot, creating a momentary cavity of about a foot in diameter, in which the dirt is crumbled. As the jet leaves that location or the air blast is ended, the dirt falls back on itself if the tool barrel is held close to the vertical. If the Air Knife barrel is inclined away from the user, the dirt can be blasted out the ground to a depth of one to two feet, depending upon technique. Since buried pipes, cables and tree roots are not porous, the dirt is removed from them and they are not damaged.”

Woodbury Park Apts Plan
Flexi-Pave Over Critical Root Zone Detail