The present paper is the result of the study of a specific railway in Brazil, with 70 Km of shallow turinels extension. These tunnels are located in different rock masses. Based on NATM principles, the various stabilization systems of excavation were already tested and approved in the 20 Km constructed section, because of their flexibility, rapidity and economy.
Die vorliegende arbeit entspricht dem vorge1egten vorschlag zum bau eines tunnels von unfefahr 70 Km lange fuer eine eisenbahnstrecke in brasilien. Diese tunne1 muessen in den verschiedensten felsigen gesteinstypen durchgefuehrt werden. Folglich muessen sie geplant werden, basierend auf den prinzipien der NATM, verschiedenen sicher heits systemen der ausschachtung, die schon getested und bewahrt sind durch die schon gebauten 20 Km tunnel, durchz ihre vielseitigkeit, schnelle ausfuehrung und wirtschaftlichkeit.
Ce travail ici est une consequence d'une proposition presentee pour la construction de 70 km de tunnels avec basse couverture, pour un chemin de fer au Bresil. Ces tunnels se developpent dans les plus varies typpes de massif rocheux: filites, quartzites, gnaisses. On a conçu, puis, avec base dans les principes du NATM, des systèmes de stabilisation, qui ont dejà ete eprouves et approuves, dans les 20 kilometres dejà construis moment, par sa versatilite, vitesse d'execution et economie.
The present paper has a defined purpose: to take to the international mileu some important informations about the successes obtained in Brazil, with a new approach in the sha1 low tunnel design and construction, where are Pointed out enormous advantages, in triple aspect: safety, rapidity and economy, face to the conventional or classic methods. This new approach for design and construction was implanted in Brazil in 1970 at the Immigrants Highway (important connection between Sao Paulo and Santos), where was built 4 km of tunnels. It is now been applied at the works of Ferrovia do Aço" (important railway connection between the three largest industrial centers in Brazil: Sao Paulo, Rio de Janeiro and Belo Horizonte) where are already built 16 tunnels (with a total extension of 20 Km) out of 97 tunnels (with a total extension of 70 Km). The figures 1 and 2 show the clearence diagrams for single and double track. The first one, doubtlessly, constitutes the initial mark in the first experience in Brazil and resulted in undisputed success. The second one availed itself of the maturaton benefitting from the technical conquests accumulated in the first and besides propitiating new improvements, in a rational adjustment of the geological and geotechnical dictates of the region crossed, with characteristics and parameters that situated in a large behavior range. The basis of this new approach of design and construction of tunnels are supported at the ideas given by Terzaghi (1946) and the principles of the "New Austrian Tunneling Method - NATM" conceived by Prof. L. von Rabcewicz (1964).
For us, the tunnel construction planning must consider the influence of various factors which can be assembled in 3 groups:
One must have knowledge, as complete as possible, of the conditions of the rock masses to be transposed, namely:
morphology, lithology and structures;
degrees of jointing and weathering;
geotechnical and geomechanical characteristics (E, c, φ, σc); -
initial stress state;
So, there is considerated the classes of rock mass nφs VII to I, in increasing order of geomechanical characteristics.
The excavation alters the initial state of stresses in the rock mass. Then, it is important to establish for each rock mass type, the adequated excavation method. Thus, this new concept of design and construction idealized the necessary proceedings to face efficiently the various situations founded. There is here a special remark for the orientation given by Mastropietro (1970–1975).
The excavation stability was the chiefest aim to, be reached. The stabilization devices will be the simpler so much better are the rock mass conditions, so much more adequate are the excavation method adopted, so much more careful are the excavation works and so much appropriate are the stabilization systems recommended. Therefore the excavation and stabilization operations shall not be considered independent stages, free from reciprocal entailments, but on the contrary they shall form an integrated system, allowing the establishment of adequate lines of direction for the optimization of in technical and economic terms. The collaboration of brazilian construction companies was very important for the success of the auspicious results reached.
The present design conceptualization has the concern of reducing the disturbance caused to the rock mass by the tunnel excavation and it is achieved with an adequate support able of making the rock mass reach a new tridimensional state of balance and therefore the desired stabilization.