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The experience of the last ten years in using numerical methods in the design of underground constructions allows several conclusions to be made, which, without making any claims regarding their general validity, are summarized here. A clear formulation of the particular problem facing the engineer is first required if a computer solution is to be sought. On the basis of this formulation of the problem suitable computational models can be established and the variations in the required input data can be defined by giving the values of the upper and lower bounds. The real purpose of the computations is mostly a parameter analysis. However, in order to keep the number of computed cases within practical limits, only those data combinations can be considered, which the engineer thinks to be the most important in the light of his experience. It is readily shown that even the problem of a single tunnel in a two-layered elastoplastic material may easily lead to over 100 computations, if proper choice of combinations of input data is made (e.g. material properties, initial state of stress, support measures for the opening). Computational results should be presented in the form of diagrams which give a good summary of the results and enable various computed cases to be easily compared. For conclusions affecting constructional decisions the computed deformations in the rock and stresses in the lining are of particular . value. Rock anchors introduced as a safety measure can also be included in the computational model. However, their doubtlessly useful effect cannot, in general, be verified numerically due to the many simplifications in the model. A clear and thus a useful definition of the safety factor for underground openings does not exist even today despite the emergence of numerical computational methods. It is doubtful whether, in such a complex structure as a tunnel, a definition of safety can be reasonably expressed by a single figure.
Index Terms:rock; TunnelingGroup
Further Information:Date published: 1977