ABSTRACT
In back analyses, input data are measured values, such as displacements, strains, stresses and pressures, while the output results are the mechanical parameters of rock masses, such as Young's modulus, Poisson's ratio, strength parameters, permeability, and even the initial state of stress. This analysis procedure is entirely a reverse calculation of an ordinary analysis, so that it is called "back analysis", while an ordinary analysis is called "forward analysis". In forward analyses, it is obvious that any sophisticated computer program can be used, no matter how many input data are needed, as long as all the data can be determined by laboratory and in situ tests, while in back analyses only a limited number of measurement data are available. In a probabilistic approach, the determination of a probability density function for the mechanical parameters of rock masses is extremely difficult. The Fuzzy Set Theory must be a potential tool for solving rock mechanics problems in probabilistic approaches.
