| The tunnel’s expansion and deformation caused by the flooding of the surrounding rock in the loess-paleosoil stratum will seriously threaten the safety of the tunnel during the operation period.Therefore,it is a great significance to study the mechanical properties of the paleosol and the interaction between the tunnel support structure and the surrounding rock.In this paper,the mechanical properties and microscopic structural characteristics of loess-paleosoil are studied from the laboratory mechanics test and meso-test,and related mechanical parameters are obtained.Taking the Yinxi High-speed Railway Zaosheng No.3 tunnel as the engineering background,using Midas-GTS software and FLAC3D finite difference method software,a three-dimensional model was established,and the thermal-mechanical coupling algorithm was applied to analyze the effect of paleosol expansion on the internal force of the tunnel lining structure.Based on the determination of the equivalent load of the expansion force,the stress and deformation of the surrounding rock of the tunnel,the load arch,the stress distribution of the base,and the failure mode of the solid lining are studied under different expansion loads.The analytical solution of the compressive stress of the foundation under different expansion loads is derived.(1)Mainly by studying the mechanical characteristics of loess-paleosoil,it is determined that the expansion force of the paleosol is about 40kPa;the logarithm of the expansion deformation and the logarithm of the compressive stress have a linear relationship.The mesoscopic test determined that the expansion deformation of paleosol was mainly caused by clay mineral illite.The microstructure was mainly intergranular voids.The soil particles were in surface-to-surface contact.Compared with Q3 loess,the paleosol structure was dense.(2)The GTS load-structure method is used to numerically calculate the tunnel supporting structure with a depth of 50m.Considering the effect of different positions without using large and small expansion forces,the results show that the expansion force is the most unfavorable,and the plastic expansion force is the smallest;when the base expansion force exceeds a certain value,the deformation of the center of the upward arch accelerates;the settlement of the dome It is linearly related to the expansion load of the vault.(3)The numerical calculation of FLAC3D thermal-mechanical coupling shows that after tunnel excavation,additional stress appears within a certain range on both sides of the arch waist;the internal and external boundary values of the surrounding rock bearing arch under initial conditions and different expansion loads are obtained;According to the analysis,the plastic zone of the lining gradually penetrates from the arch top to the outside,and gradually develops from the inner side of the arch foot to the center of the invert arch.Compared with the calculation results of the load structure method,the results tend to be consistent.(4)By applying a circle of expansion load model around Flamant and the tunnel,the distribution function of the base pressure under different expansion loads is determined,and the analytical solution of the additional stress of the base under the expansion load is obtained,and verified by the center of the invert arch,which proves that the analytical solution is reliable in a certain range The additional stress caused by the swell load only affects the soil layer 10m below the base.t. |
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