SPECIALIZED CIVIL Construction
Soil Nail Launcher Cannons
Initially developed by the British military to launch chemical weapons, the launcher cannon utilizes compressed air to accelerate a 1.5-inch diameter, 20-foot-long steel or fiberglass tube into the ground at 250 miles per hour in a single shot. The nail’s dynamic installation results in distinct benefits over conventional nailing techniques. First, as these high-speed projectiles enter the earth, they generate a shock wave that causes the soil particles to elastically deform or “jump away” from the nail tip. The bars enter the ground without significant abrasion or loss of exterior corrosion protection. The soil particles then collapse onto the bar in a relatively undisturbed state, yielding pullout capacities up to 10 times that of driven or vibrated rods or tubes. In contrast, conventional open-hole drilling techniques allow the soil to relax before nail installation, adversely affecting bond capacity.
Launched Soil Nails also can be perforated to allow for horizontal drainage and pore water pressure relief and are the only technology available that provides continuous axial capacity and drainage with the same element. The perforated nails can be pressure grouted with various materials to increase bond capacity and soil properties throughout the nailed region. When used in landslide repair, the launched soil nails immediately increase soil density in the targeted area where they accept shear loading upon insertion.
Dyer mounts the launcher cannons on their walking excavators for ingressing into rugged terrain and reaching limited-access sites. Because these rigs can “walk” rather than use tracks, they can even launch nails in active streambeds. The launcher unit has full articulation, allowing it to work around overhead wires, underground utilities, and guard rails.