TDD Trenchless Technology Specialists Horizontal Directional Drilling (HDD) offers a cost effective alternative for the installation of new small to medium sized pipes and ducts.  No vertical shafts are required as drilling commences from the surface. Directional Drilling is a surface launched technique.  Drilling from a small entry pit at one end of the bore and pulling the product pipe back through the ground from the reception pit at the exit end. A pilot bore is drilled between the entry and exit pits.  The drill head contains a transmitting device (sonde) which sends information to the digital tracking devise on the surface.  On completion of the pilot bore the drill head is removed and replaced with a reamer of the appropriate size for the pipe being installed.  For pipe with a larger diameter (usually > 180mm) a series of pre-reams with increasing size reamers will be required to cut the bore big enough to allow  for the larger pipe. Environmentally friendly, biodegradable drilling fluids are used throughout the drilling process to lubricate and remove cuttings from the bore.  When the bore is cut to the required size a swivel and towing head are attached to the product pipe and the pipe is pulled back through the bore hole as the drill string is being removed. Applications: Rivers, Motorways, Railways, Runways, Highways, outfalls. Benefits: Reduced costs, Shorter completion times, Less traffic disruption,                Reduced environment disruption, Less waste to landfill sites.