RSM and FORM for elastic-strain-softening rock mass excavation

Analytical solutions are often not available due to the complexity of engineering conditions. Circular tunnels are special cases which have analytical solutions and can be used for preliminary analysis of underground excavations and to guide the design. It is more logical to regard the properties or input data of geomaterials as random variables rather than constant values because of their uncertainties. In this paper reliability analysis of a circular tunnel in elastic-strain-softening rock mass subjected to a hydrostatic in situ stress field is conducted. Computational procedures for the response surface method and first-order reliability methods (RSM/FORM) are used in the reliability analyses of the elastic-strain-softening model. System reliability-based design of support pressure to achieve an overall target reliability index is carried out. The positive correlation between the compressive strength and the elastic modulus, are also investigated.