| In the process of urbanization,the development of underground space led by tunnel engineering is an important means to save urban ground space and ease traffic pressure.Engineering construction in the complex and changeable urban environment will undoubtedly bring great safety risks.Therefore,the stability of the tunnel face in layered soil has attached much attention from scholars and become a hot issue in the field of engineering.In this paper,the evolution law of the unstable failure of the tunnel face in layered soil is taken as the research topic and the research method combining transparent soil model test and numerical simulation is used for research.Firstly,the preparation method of transparent soil and its factors affecting transparency are clarified,then the similarity between transparent soil and natural soil is verified.Secondly,the combination of transparent soil model test and numerical simulation is used to study the evolutional law of failure process under different stratum conditions,the threedimensional wedge models are modified according to the failure mode.Finally,the influence of soil parameters on the stability of the tunnel face is studied,in order to provide theoretical guidance for the shield construction.The results show that:(1)Using transparency as the evaluation index,the best ratio of transparent soil is determined.Through tests such as consolidation tests and direct shear tests,the results show that the basic properties of transparent soil are similar to those of natural soil,which verifies the feasibility of applying transparent soil to model tests.(2)The method of combining model test and numerical simulation is used to study the evolution law of unstable failure of the tunnel face in the homogeneous layers.During the failure process of the tunnel face in the homogeneous layer,the soil in front of the tunnel face experiences two stages,namely local failure and overall failure process,which is a gradual failure process.In the sand layer,the failure process appears as a vertical upward failure process;the failure mode of the tunnel face is chimney-like;the lower slip surface of the classic three-dimensional wedge model is modified to a logarithmic spiral and the upper part is modified to an elliptical cylinder.In the clay layer,the failure zone is continuously expanding during the failure process and there is no obvious failure boundary;the failure mode of the tunnel face is basin-shaped;the lower part of the classic three-dimensional wedge model is modified into an ellipsoidal shape and the upper part is corrected to an inverted elliptical stage.(3)The method of combining model test and numerical simulation is used to study the evolution law of unstable failure of tunnel face in the layered soil.During the failure process,the soil in front of the tunnel face experiences two stages of local failure and overall failure process.The failure process is close to the failure process of the clay layer.The slip angle of the soil in the overburden changes abruptly at the change of the stratum.The lower part of the classic three-dimensional wedge model is modified to an ellipsoidal shape and the upper part is modified to two inverted elliptical cones.The inclination angle of the inverted elliptical cone is related to the soil parameters.(4)Soil parameters have a significant impact on the tunnel face stability.When the ratio of the local layer is greater than 1,the face stability is greatly affected.Under shallow conditions,there are obvious settlement tanks on the surface.With the increase of the cover depth,the surface failure transforms into the overall settlement gradually;the internal friction angle and elastic modulus mainly affect the size of the vertical settlement of the surface. |
