The practice of microtunneling continues to make strides roughly a decade after the maturation of existing technologies, as engineers acquire greater experience in their application under more challenging circumstances.
According to civil engineer David Abbott, a member of the American Society of Civil Engineers (ASCE), microtunneling is defined by the modern engineering profession as the excavation of tunnels with dimensions up to 3 – 3.5 metres in diameter.
While the smaller scope of tunnels can involve technical challenges that differ significantly from those of larger excavation projects, their reduced dimensions can also facilitate tunnelling under more difficult ground conditions.
“Where microtunneling differs from other tunnelling techniques is the ability to operate systems remotely from a control room on the surface,” said Abbott. “This is particularly the case for smaller diameters of less than 2 metres, and tunnels that are too small to permit the operation of microtuneling machines by human-beings from within.
“Another major difference is the ability of almost all microtunneling machines to both balance the external groundwater pressure and provide support to the excavation face as tunnelling proceeds.
“This permits tunnelling under both considerable groundwater heads, and in poorer conditions where the ground is soft – something which would be almost impossible or very expensive under similar conditions using simpler techniques like open faced tunnelling.”
According to Abbott the basic technologies used for microtunneling have already reached a state of maturation following several decades of development in industrialised countries over the last century.
“Microtunneling is now a mature technology that has been in use for nearly 40 years,” said Abbott. “The major microtunneling manufacturers are in Japan, Germany and the U.S. In the past decade there have not been any major technological advances as the use of computers and modern signal and controlling techniques such as PLC had been adopted by the industry in the preceding decade.”
While the core technologies involved in microtunneling may have temporarily plateaued, the practice of microtunneling itself has nonetheless continued to evolve and advance as engineers acquire greater experience in the usage of existing methods.
This is particularly the case for microtunneling in challenging circumstances that involve difficult terrain or underground obstacles.
“Significant advances have been made in the use of microtunneling techniques to successfully complete more challenging projects with greater confidence and at minimal risk,” said Abbott.
“Microtunneling is being undertaken in more difficult ground conditions, involving poor soils, larger stones or even boulders, longer tunnel lengths, greater depths below the water table, as well as sea outfalls and intakes.
Abbott notes, “These types of projects have been constructed for a number of years, but experience and the volume of successful projects have led to them becoming more common.”
In future, Abbott sees engineers taking on even more difficult microtunneling projects, as well as the adoption of sophisticated techniques that are currently applied to larger tunnels.
“The likely direction of future developments is longer and deeper microtunneling in both harder and softer conditions, as well as improved ability to tunnel around curves, even at smaller diameters.
“Perhaps some of the monitoring and mapping operation techniques used for more sophisticated large diameter tunnel projects may come into use with microtunneling machines.”
To learn more about current microtunneling standards and best practice, ASCE have a three-day Design and Construction of Microtunneling Projects course run by Engineering Education Australia.
David Abbott is the facilitator of ASCE’s Design and Construction of Microtunneling Projects course run in partnership with EEA. David has nearly 40 years of experience in underground construction and has been actively involved in the design and construction of tunneling, pipe jacking, microtunneling and other forms of trenchless technology.