In tunnelling through heterogeneous rock masses, such as the flysch, it is important to attempt to obtain reliable estimates of potential tunnelling problems as early as possible. This enables the tunnel designer to focus on the selection of optimum routes and to devote the appropriate resources to the investigation of those areas in which tunnelling problems are anticipated.  In the following text, a methodology is presented for estimating potential tunnel squeezing. This methodology does not provide the tunnel designer with a final design of the tunnel excavation sequence and support system to be used – these require additional analyses, which are not covered in this paper. However, the end product of the analysis presented gives a reliable first 

estimate of the severity of potential squeezing problems and an indication of the types of solutions that can be considered in overcoming these problems. Part 1 of the paper deals with estimating the strength and deformation properties of weak heterogeneous rock masses while Part 2 deals with the prediction of tunnel squeezing problems.