Auger Boring Trenchless Technology
A short history of Auger Boring informs us that it has evolved over a period of eighty years. We learn that horizontal Auger Boring began its existence in the coal mining industry in the 1930s. The first marketable Auger Boring Machine (ABM) was manufactured in 1941 by Kandal Motors and modified over time to meeting the widening demands of contractors for splitting the ABM along with the need to increase power and thrust so it could manage to deal with increasing pipe length and larger diameter jacking pipe. With the earlier versions of the ABM accuracy was not very exact as there was no technology that permitted steering. Since the pioneer manufacturing days of ABMs modern machines have a steering mechanism that is now guided. Laterally ABMs could only work in silts, sands and gravels above groundwater and in rocks of compressive strengths less than 4000 psi. Over the past 20 years new developments mean that more variable ground conditions can be overcome with Auger Boring. There are two distinct methods of Auger Boring, the Track method and the Cradle method. As far as conventional Auger Boring is concerned, ABM methods can be combined with specialised cutting heads permitting the installation of pipes ranging from .1 to 4 metres and is possible in a wide range of ground conditions.
Auger Boring is not compatible generally with soils that are not cohesive and are subject to a groundwater head. The largest pipe installed in the United States using the Auger Boring method was in Phoenix Arizona where the pipe was 170m long and 2.1m in diameter. An additional technology known as “pilot tube micro tunnelling” or “guided boring method” sees the horizontal Auger Boring technique used in conjunction with a multi-stage method of installing piping accurately.
PTM as it is called, depends on pilot head steering and can accommodate pipe laying up to a recommended 300 feet. Below ground soil conditions dictate how far the drive length can extend and sometimes rocky conditions can cause problems for advancing the pilot tube. Drive length also depends on underground conditions and pipe diameter. Specialised rock cutting heads, called (SBUs) or Small Boring Units have been used successfully with the ABM to cut rock efficiently with a (UCS) Unconfined Compressive Strength greater than 4000 psi. This rock cutting technology has been in existence for about 50 years on hard-rock cutting tunnel boring machines. SBUs are ideally used for cutting full-face rock but are not functional in soil conditions. Horizontal Auger Boring has developed immensely since its inception over 75 years ago and it can now complete 600 ft crossings in rock with strict guidelines. These boring methods commonly collectively known as Auger Boring are very effective but are not risk free like any other construction project. Risk is a potential downside with activities such as steering variability, long drives, groundwater conditions and operator experience.
Terra Solutions is a leading trenchless civil engineering contractor specilaising in Microtunnelling
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