Tunneling in squeezing rock is one of the most challenging tasks in tunnel engineering. Nowadays, Tunnel Boring Machines (TBMs) used in tunnel excavation are increasing. This trend is even observed in tunnels excavated under challenging conditions such as squeezing grounds. Tunneling with TBM under squeezing ground conditions is confronted with many challenges because of the large time- dependent and usually anisotropic ground convergences. This behaviour is observed in argillite, tuff, flysch, mudstone, gneiss, and schist rock masses submitted to a high-stress state. The squeezing ground encountered in Tunnel Boring Machine (TBM) Tunneling presents significant challenges and may trigger potential hazards without warning. Large tunnel deformation in squeezing ground may cause support failure, raveling, or collapse. This paper illustrates the squeezing ground phenomenon through the Zagros tunnel’s case study excavated under the Zagros Mountains. The second part of the Zagros tunnel’s length is 25.7 km with a diameter is 6.7 meters and excavated by double shield TBM. Squeezing accompanied by the support failures have occurred at 18.39 to 18.6 km of Zagros tunnel, where the overburden exceeded 750 m. The lithology of the squeezing zone is composed of thick-layered Shale with thin limestone layers of Surmeh Formation. Evidence for convergence in this zone before completely jamming the TBM included changes in thrust and torque, high thrust force of the auxiliary jacks, and cracking in the roof concrete segments. The method of releasing a jammed shield TBM included providing access to the space behind the shield by cutting part of the shield, excavating the rock materials surrounding the shield, supporting the excavated space, and finally filling the excavated space with polystyrene and foam.

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