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  The use of umbrella arch method and rebars spiles, in the same road rock tunnel

  The Morro Agudo is a road single tunnel, built in the south of Brazil, on the BR-101 federal highway, as showed in Fig. 1. With two lanes plus shoulder, and 1,007 m of extension, this tunnel was a key part to increase the capacity of that highway. In geological point of view, the tunnel is in a granitic rock mass, with presence of mature soil from weathering, with variable thickness at about 3 meters. Since the design phase, was expected the presence of some faults along the tunnel alignment, for what was planned special tunnel supports looking for the safety of the jobs. During the excavations, was confirmed the granite rock mass, partially altered, presented 3-4 main families of discontinuities, with fracturing rates ranging from 6 to 20 fractures per meter. The discontinuities presented slightly rough surfaces, eventually with centimetric clayey infillings. The granite, in this tunnel portion, hosts several diabase, rhyolite and hybrid dykes. In the final segment of this part of the tunnel, groundwater occurred in spots with dripping and small spurts During the job, when the faults appears, was availed the benefits of observational methods of tunnel design, and adopted the rock tunnel support in way to security standard, but with saves of time and money.

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