| With the continuous development of highway and railway transportation in China,and the continuous expansion of project construction area and scale,more and more transitional rock and soil between soil and rock have become the unavoidable key and difficult points in tunnel construction design.The formation rock mass is often poor cementing properties,high water content,the construction process of the excavation disturbance sensitive,apparent strain softening phenomenon,tunnel after excavation disturbance intensity reduced quickly,easily happened landslide in the construction,large deformation and other disasters,for engineering design and construction of excavation caused many difficult to solve the problem.Based on the Zhongtiaoshan Tunnel of Menghua Railway,this paper studies the softening characteristics of Tertiary weakly consolidated aggregates after construction disturbance.Through field sampling,laboratory tests,microscopic observation and numerical simulation,the excavation stability of this type of tunnel face is systematically studied.At the same time,under different conditions of Zhongtiaoshan Tunnel,The seepage field and displacement field around the tunnel,the stress characteristics of the primary support and the stability of the tunnel face in the construction process are studied,which can provide a reference for tunnel construction under similar conditions.The thesis mainly obtains the following research results.(1)Through large-scale laboratory shear tests,the deformation and strength characteristics of weakly consolidated conglomerate are systematically studied,and it is found that weakly consolidated conglomerate has obvious strain softening phenomenon.According to the stress-strain curve and the analysis of the mechanical properties of weakly consolidated conglomerate,the strain softening model was selected for numerical simulation.(2)By comparing and analyzing the difference between the calculated results of the strain softening model and the ideal elastoplastic model,it can be found that the calculation of the ideal elastoplastic model is more conservative than that of the actual engineering,and the strain softening model can better reflect the deformation characteristics of weakly consolidated conglomerate.At the same time,in order to study the influence of the value of strain softening model parameters on the engineering,the relevant significance of the strain softening model parameters was studied in this paper.(3)Several commonly used quantitative evaluation methods for the stability of tunnel face are studied and analyzed,indicating that the strength reduction method is not applicable to the stability evaluation of tunnel face in strain-softened strata.The realization method of load reduction method for solving the stability coefficient of tunnel face in strain-softened strata is introduced in detail.The stability of tunnel face in strainsoftening strata with or without seepage is analyzed with the cusp catastrophe theory.(4)On the basis of the strain softening model and combined with the actual engineering situation,this paper studies the influence laws of the initial head height,the increase of permeability coefficient of rock and soil mass,the lateral pressure coefficient of surrounding rock and the step length on the displacement field,seepage field,the stress of the initial support and the stability of the tunnel face in the process of tunnel construction.When the head height increases,the displacement around the hole increases,and the stability of the palm surface decreases.With the increase of the lateral pressure coefficient,the settlement deformation of the vault decreases obviously,the lateral deformation of the side wall increases significantly,and the safety factor of the palm surface decreases gradually.With the increase of step length,the convergence displacement of surrounding rock increases significantly,the stability of surrounding rock decreases,and the stability of the tunnel face increases. |
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