EN-1997 Geotechnical Design - referred to here as EC7 - is a limit states design (LSD) standard that allows application of the Observational method (OM). However, to date, it has not been shown how the OM satisfies the requirements of LSD. In this paper, we investigate this issue. We assume the OM in rock engineering can be regarded as a series of measurements of structural responses when the structure and loading system are uncertain. We rationalize this by examining the behaviour of a beam whose bending stiffness and support conditions are only partially known, as a simple analogue to the OM applied to roof stability of an underground excavation. Our results show that unambiguous definition of the structural mechanism is essential, and hence the current presentation of the OM in EC7 is generally insufficient to allow verification of limit states. Moreover, we discuss strength and time dependent aspects of design in the context of application of the OM within the LSD paradigm. We make suggestions for critical areas which require further research and development in order to allow the OM to be used in rock engineering design and construction such that it permits limit state verification.
