A mechanistic evaluation and design of tunnel support systems for deep level South African mines.

Abstract

The design of support systems, comprising rock bolt reinforcement and fabric containment components for tunnels in deep level mining environments does not currently cater well for adverse rock mass conditions. This often results in periodic failure of the support system, particularly under dynamic (rockburst) conditions with the potential for total collapse of the excavation. The design of support systems is currently based either on empirical design guidelines often not applicable to this environment or simple mechanistic models. This thesis details a methodology for the rational design of tunnel support systems based on a mechanistic evaluation of the interaction between the components of a support system and a highly discontinuous rock mass structure. This analysis is conducted under both static and dynamic loading conditions. Due to the highly complex and variable nature of the rock mass structure and the dynamic loading environment, a large component of the practical work on the evaluation of the mechanisms of rock mass deformation and support interaction is based on rockburst case studies. The understanding gained from these investigations is further evaluated by means of laboratory testing of the performance of the components of the support systems and numerical modelling of the interaction of the components of the support system with the rock mass. Due to the complex nature of this design environment the methodology developed in this thesis is but a step towards our greater understanding of the behaviour of the rock mass, and the interaction of support systems in the stabilisation of tunnel excavations. However, in comparison to the current design, this methodology now allows the design engineer to make better estimations of the anticipated demand on the different components of the support systems, under a defined rock mass environment on engineering principles. This understanding will give the design engineer greater flexibility, and confidence to design the appropriate tunnel support system for a specific rock mass and loading condition based on the often limited availability of different support units in the underground mining environment.