Three-dimensional numerical tests have been conducted to investigate the failure process of surrounding rock mass around circular and U-shaped tunnel at depth. Different failure modes of deep underground openings have been reproduced. The influence of different shapes and sizes of tunnel section, as well as the direction of the maximum principal stress, on zonal disintegration was analyzed. Numerical simulations show that failure modes and load-bearing capacity of tunnel depend on the direction of the maximum principal stress. The zonal disintegration around deep underground openings is a phenomenon that only occurs under some special conditions. Firstly, there must be a higher horizontal tectonic stress along the axial direction of tunnel; secondly, the radius of curvature of tunnel should be large enough to induce the tensile stress higher than tensile strength of rock mass. Therefore, the direction of tunnel axis as well as the direction and the size of tectonic stress should be carefully considered during tunnel design.
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