The importance of displacement prediction

Tunnel construction in faulted and/or heterogeneous rock mass is in general associated with
stability problems, high deformations and frequently changing stress conditions. Depending on the encountered conditions, different strategies for excavation and support of the tunnel must be applied. The decisions on site thereby are widely influenced by the magnitude and development of the tunnel displacements.
To allow for a reliable and relatively accurate prediction of displacements, the program GeoFit® was developed. GeoFit® is based on analytical functions which simulate the face advance effect and the time-dependent behaviour of the rock mass and support. Several parameters are used to describe the complex system behaviour. The program allows considering several options, including the installation of supports, sequential excavation, and non-steady tunnel advance. It provides several options of displaying measured and
predicted data, thus allowing a continuous control of the “normality” of the displacements, and reacting in time in case the measured values deviate from the predicted ones. In addition the follow-up of trends of function parameters and displacements enables for short term prediction of the geological condition ahead of the face. This again increases the quality of decisions on site, increases safety and economic efficiency, and reduces the uncertainties.
The paper will show some basic principles of the displacement prediction and methods of data evaluation. Selected case histories will be used to illustrate the evaluation techniques and the benefit gained from these methods.