Abstract: To investigate the relation among the stress, deformation, rupture, and stratigraphic effects of surrounding rocks of the supported and unsupported TBM tunnelling in deep mixed strata, the experimental investigation was conducted by a similarity model test system in biaxial plane strain. The stress and strain measurement devices and the self-developed refinement digital photogrammetric measurement system PhotoInfor were applied in this study. The results show that the stress distribution and failure mode are quite different between the upper-soft and lower-hard strata, indicating an obvious non-uniformity stratigraphic effect. The stress in hard rocks is larger than that in soft rocks. As the confining pressure increases, the internal stress of the surrounding rocks also increases in general, but it first increases and then decreases along the radial direction for both supported and unsupported tunnels. Under the unsupported condition, the complete process of the deformation, fracturing, and the relaxation zone of the surrounding rocks have been reproduced. During the failure process, the upper-soft rocks is dominated by structural collapse and the lower-hard rocks is mainly fractured into fragments. The development stage of radial displacement for surrounding rocks can be obtained. The supporting structures can effectively improve the stress redistribution, reduce the unloading speed, and enhance the self-bearing capacity of the surrounding rocks and the global stability of tunnels.

Key words: deep tunnel, mixed strata, TBM, model tests, support