SUMMARY:

This article presents a methodology for creating 3DEC block models of tunnels constructed in fractured (blocky) rock masses, based on the Terrestrial Laser Scanning technique (TLS) and Discrete Fracture Networks (DFN). Several aspects of discontinuity mapping using TLS, discontinuity analyses by window-sampling methods and DFN modeling are discussed. The Monte Seco tunnel (Vitória-Minas Railway), located in the State of Espirito Santo (Brazil), is used as an example. Three discontinuity sets (two fractures sets, F1 and F2, and the rock foliation, Sn) were mapped (with TLS) and analyzed to obtain the probability distributions of the discontinuity diameters and orientations. Next, the volumetric intensities (P32) were calculated and DFNs were generated to create the 3DEC block model of an 8 m long section of this tunnel.

1 INTRODUCTION

Several old tunnels in Brazilian roads and railways were constructed in hard rock masses without any support system. Recently, some of these tunnels are presenting localized problems of rock falls mainly related with rock discontinuities distributions and some punctual weathering processes. The Vitoria-Minas Railway (VMR), owned by VALE SA, is one of the oldest railways in Brazil and has about twenty tunnels in this condition, requiring geological and geotechnical investigations to provide parameters and evaluate the stability state. Considering this problem, a partnership between Escola Politécnica of the University of São Paulo and VALE SA was initiated to propose a methodology and study of these tunnels. The lengths of these tunnels vary from hundreds of meters to a few kilometers, which makes conventional field discontinuity mapping a strenuous and time-consuming task since considerable detail is required. In addition, it is difficult to obtain the actual position and geometrical parameters (generally described as orientation, frequency and size) of all the discontinuities in tunnels with the conventional geological mapping, mainly in the higher regions of the tunnel section.

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