Nomographs to obtain three dimensional (3D) elastic displacements for deep circular tunnels

Abstract

Finite element (FEM) based software is frequently used in practice for tunnel design, alongside the traditional analytical and empirical solutions. Design is not the only challenge in this kind of projects, there are other important factors such as considering what is necessary to develop an efficient construction plan under a schedule and foreseeing possible changes that modify the original design. The use of two-dimensional (2D) FEM is one of the main tools used in the industry. However, 2D results yield not an entirely accurate analysis, since the behaviour of the infrastructure is considered as threedimensional (3D). This paper presents nomographs and a 3D  and 2D relationship, to rapidly  estimate values of elastic 3D and 2D displacements produced in the periphery of a deep circular tunnel, inside soils of different rigidities. Graphics given correspond to five different radii and for a 100 m  excavation length. Nomographs were obtained from RS3© and RS2© FEM simulations and according to the elastic theory. Geotechnical parameters correspond to a constant friction angle, cohesion and soil specific weight. FEM analysis was made using the Mohr-Coulomb model, considering sotropic conditions.