The effect of different footages on tunnel face stability and failure mode was studied based on the strength reduction finite element method.Tunnel face deformation morphology

crown settlement characteristics and surface settlement trough shape under different footages were analyzed

as well as the stress transmission path

arch effect characteristics and stress evolution process of the place in front of tunnel face

excavation footage and supporting section.The results were compared with numerical simulation and Vermeer formula and a parametric analysis was performed at last.The main conclusions are as follows:the influence of footage on the tunnel stability is nonlinear.The stability safety factor is reduced and the plastic displacement distribution range is increased with the increase of footage in the whole.The influence range of displacement is also increased and gradually extended to the excavation section from the tunnel face.The displacement vector angle is increased nonlinearly

namely the proportion of vertical displacement is increased.The arch effect exists in front of the tunnel face and excavation section.The vertical arch effect is larger than the transverse arch effect;the horizontal arch effect is the weakest.Hence

the stability of the surrounding rock at the bottom of the tunnel face and the strength of the supporting section should be reinforced.According to the different distances from the vertical stress to the tunnel face

the stress can be divided into three sections.Specifically

a section near the tunnel face being the stress relaxation area

namely the unloading area

a section in front of the tunnel face being the stress increasing region

namely the stress bearing area and the arch effect zone

and a section far from the tunnel face being the protolith stress zone.