Prólogo escrito por el Profesor Z.T. Bieniawski (Versión original en inglés)

I am pleased to be requested to preface this computer program and wish its developers and users every success in their professional endeavours.

Excavability is defined as the ease of excavation and was investigated as early as Kirsten (1982). TBM excavability or performance prediction models were studied by Barton (2000), Alber (2000), Bieniawski (2004), Blindheim (2005) and others.

When one considers the history of tunneling technology, its development and the major milestones, the emergence and increasing use of modern tunnel boring machines (TBMs) provided both spectacular advantages and achievements, as well as complex challenges and problems to designers and constructors who faced significant shortcomings in our understanding of the interaction of rock mass conditions and TBM design and performance.

Even the subsequent modern rock mass classification methods (Wickham et al., 1972; Bieniawski, 1973, and Barton, 1974) were predominantly directed to drill-and-blast tunnels, independent of TBM characteristics.

Today, this is no longer the case. Tunnel boring machines have increased in power and size to such an extent that they directly influence tunnel design.

This situation led to recent successful applications of a combination of drill-and-blast and TBM methods, leading to a revival of the concept of rock mass excavability (which goes back to the early 1980s).

Nevertheless, one problem remains: how to assess effectively the interaction between rock mass conditions, as described by the RMR or Q classification systems, and the design and performance characteristics of the TBM.

The purpose of the Rock Mass Excavability (RME) indicator which the authors found effective in predicting excavability by TBMs, using a quantification of TBM performance, and to provide a tool to choose the tunnel construction method.

The RME is based on five parameters specifically related to rock mass behaviour and TBM characteristics. A number of statistical correlations have been established between RME and such relevant output parameters, as Average Rate of Advance (ARA).

The computer program GeoTopo XXI offers the possibility to calculate the performance prediction in four different ways: Bieniawski(RME), Barton(Q_TBM), NTNU y CSM, it is always a good engineering practice to cross‑check one's results.

But, like with every computer program, two issues are important: 1) the reliability of the input data, and 2) clear understanding of what and how is being calculated ‑ so that all the assumptions and procedures are properly considered.

And with these words, all it remains for me is to wish all the users: Good luck!

Z.T. Bieniawski. Arizona, USA, september, 2006.