Slab pumping is one of the major causes of failure in concrete pavements. It's caused by free water that seeps into the pavement subbase through joints and cracks. During pavement construction, adequate subbase compaction and installation of a drainage system or impermeable membrane helps to prevent pumping. A recently patented transverse drainage system allows retrofit installation of slotted drain pipe in the pavement subbase beneath major water-entry points - transverse joints and cracks. A special ground-piercing tool bores a tunnel in the subbase, spanning the pavement width, and pulls the drain pipe behind it. Once installed, the pipe collects water that enters the joint and drains it onto the pavement shoulder. Because water can no longer accumulate in the subbase, pumping and other moisture-accelerated damage is prevented.
The ground-piercing tool is a torpedo-shaped device about 4 feet long powered by an air compressor. An internal piston drives the tool forward through the subbase by successive impacts. Because the tool forms the tunnel by compaction rather than excavation, it compacts the subbase along its path and helps repair existing erosion. The tool takes about 30 minutes to bore the tunnel and does the job without damaging the pavement or disrupting traffic. The drain pipe can be coupled to the tailpiece of the piercing tool so it's pulled behind the tool as it forms the tunnel or they can push the drain pipe in by hand after the tunnel is formed.