For many years trenchless crossings or roads and railways have been carried out by auger boring techniques. Typically a steel sleeve pipe is pushed forward into the ground by hydraulic jacks whilst the spoil is excavated by a cutter head. Spoil removal is via a continuous auger flight within the steel pipeline. This method, now referred to as Conventional Auger Boring, relies upon the rigidity of the steel pipes for its dimensional stability. It offers an economical way of constructing short trenchless crossings in dry soils.Guided Auger Boring is a development of the conventional technique which offers a high degree of accuracy for line and grade. This makes the technique suitable for gravity sewers. The alignment is maintained by the use of a theodolite set to line and grade. A camera mounted to the instrument allows the operator to easily see the illuminated target at the front of the bore.
Guided Auger Boring is generally carried out in a three step process.
- The pilot bore is installed by jacking a steel tube through the ground to line and grade. The front of the tube has a steering head inside which is an illuminated target array. No excavation takes place when the tube is installed, the ground being compacted by the action of installation.
- Once the pilot tube has been installed between drive and reception shafts a reamer head follows it. The reamer head and auger casings are fixed to the pilot tube and driven forward from the drive shaft. A full line of auger casings is eventually installed between both shafts as the pilot tube is gradually removed from the reception shaft.
- The final stage is to push out the auger casings with the product pipe. Typically the pipe installed will be a purpose made jacking pipe from either pre-cast concrete or clay.
The technique offers one of the most cost effective ways of installing small diameter trenchless pipes to a high degree of accuracy.Terra Solutions can offer both conventional and guided auger boring in diameters ranging from 150mm to 1200mm using equipment which can install pipes in a wide range of ground conditions including sands, silts, clays and even rock.