A combined Lattice Spring – Discrete Fracture Network method is applied as a numerical tool for 3D simulations of rock tunnel excavations in low in-situ stress environments, where falling of blocks is the main failure mechanism. In order to achieve a synthetic representation of the fractured rock mass, a Discrete Fracture Network characterization is attained by means of the Baecher Disk Model. In order to ascertain the competence of the method, two case studies are presented based on published data of rock tunnels excavated in Washington, DC and New York City. The rock tunnels are back-analyzed using the combined approach presented. From the analyses, it is concluded that the combined Lattice Spring – Discrete Fracture Network method is an appropriate numerical tool for the simulation of rock tunnels when block fall is the prevalent mode of rupture. Of note, the following advantages of the approach are highlighted in this research: blocks are modeled as deformable elements; rock may fracture in tension; mesh design is simple and does not present convergence issues; and 3D simulations can be achieved within reasonable times.

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