Study on the interaction mechanisms between the fissure arrays and circular tunnels by physical experiment and meshless numerical method

Abstract

Fissure arrays, which commonly develop in surrounding rock masses, exert a significant adverse influence on tunnel stability. However, current research on the interactions between fissure arrays and tunnels are limited. In this study, specimens with fissure arrays and central holes are prepared using sand-three-dimensional printing (S-3DP) technology, with variations in fissure angles, lengths, and numbers. The crack propagation experiments are subsequently carried out, in which the propagation of fissures is monitored and recorded by employing Digital Image Correlation (DIC) methodology. Then, the developed smooth particle dynamics method is used to simulate and analyze crack evolution processes as a comparison. The results demonstrate that an increase in fissure inclination angle leads to an enhancement in specimen peak strength, whereas increases in fissure length and number result in a reduction in peak strength. Four basic crack types, namely tensile cracks (T-Ⅰ and T-ⅠⅠ), shear cracks (S), and tensile-shear mixed cracks (TS), are quantitatively identified using DIC technology. In addition, the rupture modes can be categorized into four distinct types: horizontal splitting damage mode, stepped damage mode, “Y”-shaped damage mode, and tensile-shear mixed damage mode. Distributions of tensile and compressive stress concentration areas should be responsible for the crack initiation and the final failure modes, because these stress concentration areas not only trigger the initial formation of cracks, but also guide the crack propagation paths. This study provides novel insights into the fracture mechanisms of tunnels containing fissure arrays, while also offering valuable references for the safe construction and long-term operation of tunnel engineering projects.