The single-shield TBM is generally used for excavations in weak rock masses to prevent excessive deformations and falls of the ground. During the excavation with shielded TBM, excessive ground pressure imposed on the shield causes the jamming. Pre-determination of deformation and pressure, which will impose on the roof of the shield, provides basic information to overcome the jamming problems during the excavation with a single-shield TBM. It is possible to determine the pressure on the shield by numerical modelling. But it requires expertise in numerical modelling and time-consuming and tedious design tool for each case. In this paper, tunnels excavated in weak rock masses with single shield TBMs were modelled by using finite difference method-based numerical modelling software FLAC3D. Multiple regression analyses were carried out on model results for different weak rock mass conditions, tunnel depths, and tunnel and TBM parameters. An equation was suggested for predicting the ground pressure at any point starting from the contact point of the ground with the shield to the end of the shield roof. The suggested ground pressure equation acting upon the shield roof was a function dependent on TBM length and first contact point of ground with the shield. An equation was also suggested for determining the first contact point. The general equations for predicting the maximum ground deformation and roof pressure on the shield were suggested based on some rock mass, tunnel and TBM parameters normalized with other independent parameters. The suggested equations were verified by means of the analysis of variance.