Tunneling works are inherently complex and there are plenty of variables to consider. The answer lies in the hydraulic breaker’s versatility. There are many situations where a TBM (or Tunnel Boring Machine), one of the most widespread and best-known methods, cannot be used for a variety of reasons (such as size and location of the tunnel, curve radius, logistical challenges, lack of flexibility of use) that would involve excessive costs or risks.
The choice of excavation method is based on geological considerations (RMR, RQD, GSI, etc.) regarding problems relating to advancement (cycle of excavation - chisel-finishing - consolidation) as well as logistical and economic assessments, relating to numbers of operators, machinery and equipment, jobsite accessibility, environmental constraints, etc. In order to carry out a preliminary rough analysis of the best excavation method, FocusOn proposes a “criteria matrix” assessment method which takes into account a whole series of factors used when selecting the right excavation method.
The first publication on tunnelling, written in conjunction with Bari Polytechnic, shows how hydraulic breakers can be used when excavating tunnels, which is a particularly strenuous use of this type of equipment.
“The idea to share the knowledge and experience we’ve been building up over 40 years of business in tunneling first gained ground in early 2013”, says Indeco Marketing Manager Michele Vitulano. “We’ve realized that the experience we’ve gained in that time working here in Italy alongside a variety of excavation firms could be a great treasure for demolition operators around the world. That’s because we’ve had to develop flexible solutions (i.e. our hydraulic breakers) for contractors who have to deal with Italy’s geology”.
“Yes, Italy’s geology is extremely varied”, says Prof. Alessandro Reina who wrote one section of the guide. “Indeed, it’s so complex that choosing the right tunnel-digging technology is crucial if contractors are going to achieve a balance between costs and benefits. Using AHP (Analytic Hierarchy Process), we worked together with the research team to identify a system that would consider several different factors when coming up with selection criteria”.
Indeco Engineer Mauro Amato adds: “Even though it’s not totally comprehensive, AHP is essentially a user-friendly tool for dealing with the complexity of the problem. It can provide project teams with initial assessment criteria as to the best excavation method to use. Of course, when working on inherently complex projects such as tunnels, decisions need to be based on a whole range of tools that together provide a full overall picture.”
“But Indeco’s response to these situations lies in the versatility of its hydraulic breaker” claims INDECO engineer Alessandro Ciccolella. “Whereas the tunnel-boring machine (or TBM, for short) is currently regarded as one of the most efficient and best-known excavation methods, there are various situations (unusual size and/or position of the tunnel, curve radius, logistical challenges, etc) where using a TBM would be either inefficient or inadvisable, due to its lack of flexibility, and to the excessive costs and risks it would involve.
By contrast, the hydraulic breaker is a versatile, economical and efficient method that has proven without doubt to be an ideal complement, mainly to drill and blast, when excavating tunnels whose geological and geometrical profiles make other excavation methods risky, difficult or uneconomical”.
The A3 Salerno-Reggio-Calabria highway runs a total of 442.9 km. The tunnel was built between 1966 and 1974 in an area where road construction is historically a challenge due to its orography, geology and seismicity.
Since 2001, the A3 has been the subject of major works as part of a project entailing both the incorporation and upgrading of the old highway and the definition of a new and parallel route.
To date 339 km of road have been successfully completed, while the remaining 68.5 km are under construction.
For the excavations, a combination of drill and blast and hydraulic breakers were used, both due to the nature and unevenness of the geological profile and because at the southern end both tubes were designed to come straight onto a viaduct under construction, a situation which in itself was enough to rule out the use of a TBM.