APPLICATION OF FULLY GROUTED BOLTS IN YIELDING ROCK

Presently, displacement monitoring plays an important role in the observational design approach for underground openings such as tunnels. In particular, tunnel convergence measurements are considered as the primary component of the design-as-you-go approach. Tunnel convergence is not only easily obtainable and hence, universally measured, but its magnitude constitutes a most useful parameter for the evaluation of tunnel stability. Consequently, the control of wall convergence by alternative support systems can be considered as a key component for the design of underground excavations.;The application of fully grouted bolts as a passive support system in underground openings is analyzed in this thesis. At present, design decisions related to fully grouted bolts are often empirical, based on experience, or are justified after an interpretation of convergence data. An analytical method based on the concepts of elasto-plasticity, has been developed to predict the displacement and strain field of the reinforced rock mass surrounding a circular tunnel opening. The method considers the influence of grouted bolts on the extent of yielding. Results from laboratory simulations and field measurements provide convincing evidence to support the theoretical predictions. In addition, it has been attempted to describe potential failure mechanisms associated with both unsupported and reinforced tunnels. The influence of discontinuities on the tunnel behaviour has also been investigated by physical modelling. In the analytical model, reduced strength parameters describing the equivalent rock mass properties were chosen for comparison with the measurements. The practical application of the proposed displacement controlled design approach is discussed in detail and is illustrated by an analysis of one case history.