Investigation of the effect of the intermediate principal stress component for tunnel stability – Case study: Northern Collector Tunnel, Kenya

Many underground structures, such as water tunnels, are designed using empirical, analytical, and numerical methods. However, these approaches overlook the significance of the intermediate principal stress component, which can lead to inaccurate assessment of tunnel stability. In this paper, tunnel plasticity response is investigated by considering the effect of the intermediate principal stress component using the Northern Collector Tunnel (NCT) in Kenya as a case study. A newly developed three-dimensional elasto-plastic model, known as 3DHB, an extension of the classical Hoek-Brown model, is implemented in the FLAC 3D framework to describe and capture the complex response of rock mass under varying stress states. The simulation results using the 3DHB model show a significant reduction in the volume of plastic zones in the tunnel, compared to the classical HB model. These findings demonstrate the critical importance of considering the intermediate principal stress component to accurately and realistically assess safety and stability in rock engineering design.