Physical modelling and PIV analyses of an underground tunnel heading

Predicting surface and sub-surface movement upon tunnel heading failure is essential for safety and contingency planning. This paper presents the results of a 2D physical modelling experiment of tunnel heading failure in cohesionless soil. By modelling six overburden to diameter ratios, the research seeks to investigate the behaviour, magnitude and failure mechanism of a tunnel heading. The physical model uses displacement control to simulate tunnel heading movement. The use of transparent faced modelling containers allows video capture of the soil movement as the tunnel heading is displaced. From the captured video, Particle Image Velocimetry (PIV) was then utilised to analyse soil movement. PIV examines and monitors groups of pixels based on colour variability, thus small amounts of coloured sand were added to ensure accurate tracking. This then allowed close monitoring of the soil movement, which allows verification of settlement results and examination of failure behaviour. It is concluded that the current experimental procedures produce qualitative results that can be used to compare with results obtained from numerical experiments. FLAC modelling with FISH programing is recommended for this purpose in the future