Appraisal of the stability of a road tunnel based on microfracture distribution and total displacement of the rock mass

Abstract

Appraisal of the stability of a road tunnel based on microfracture distribution and total displacement of the rock mass. In tunnelling, instability is always a major concern for the safety of people and equipment. Tunnels are designed to maintain a specific profile; however, deterioration tends to occur over time due to factor such as age and wear, water infiltration, chemical attack, ground movements and poor maintenance. The main objective of this thesis was to predict the effects of fracturing on road tunnel stability. This was achieved through the application of finite element modelling approaches and linear regression analysis technique. A predictive model was developed using supervised machine learning algorithm. This was done to predict the fracturing along the road tunnels using the Hendrik Verwoerd tunnels as case studies. The predictive model showed that shallow tunnels can be classified into three zones based on the fracturing intensity. For road tunnels, the middle portion is characterised by little or no fracturing (Zone 1). The intensity of fracturing increases when moving outside of the tunnel. Moderately fractured zone was referred to as Zone 2 and highly fracture zone was referred to as Zone 3 in this thesis. The effect of fracturing for each zone was analysed and support lining was proposed to cater for the three zones. According to the suggested support lining strategy, zone 1 inside a new road tunnel should have lining that is 0.3 meters thick if the overall lining for the tunnel is intended to be 0.3 meters thick. Zones 2 and 3 should have linings that are respectively 0.4 (i.e., 0.3 + 0.1) and 0.5 (i.e., 0.3 + 0.2) meters thick. Each zone was assessed individually, and support capacity diagrams were used to validate the proposed support.