Vibration And Settlement Of Loess Due To Subway Moving Loads

No.2 metro line of Xi'an is the first route built in loess in China. Vibration and settlement of loess due to subway moving loads after operating must be urgently solved. In this dissertation, the dynamic properties and residual strain of saturated loess is investigated under cyclic loading with modest amplitude; The vibration and settlement of loess is calculated through numerical computation; The static stability, vibration and foundation settlement of Xi'an city wall are analyzed for undercrossing of No.2 metro line of Xi'an.The main contents in this dissertation are as follows:(1) Dynamic triaxial tests are designed and conducted to investigate the dynamic properties of saturated loess under cyclic loading with modest amplitude. And the effect of some key factors on dynamic elastic modulus of saturated loess is studied, such as dynamic strain, initial confining stress, over consolidation ratio, residual strain and effctive confining stress.(2) Cyclic triaxial tests are also designed and conducted to investigate the residual strain of normally consolidated saturated loess under cyclic loading with modest amplitude. And the effect of some key factors on residual strain of saturated loess is studied, such as initial confining stress, drainage condition, dynamic stress ratio, dynamic stress and its cyclic numbers.(3) A arc tangent function model with dynamic stress ratio and cyclic numbers as essential parameters is established based on cyclic triaxial tests'rusults of saturated loess. The model results coincide well with cyclic triaxial test data.(4) According to damage mechanics theory, a residual strain accumulative law of saturated loess under cyclic loading with different amplitude is proposed . Then a FORTRAN schedule is developed to calculate this residual strain. (5) Combining with infinite element, a finite element numerical model of tunnel-loess is built and calculated by direct integration method to figure out the vibration of loess under subway moving loads. Then the effect of tunnel depth, loading frequency, train running speed and dynamic elastic modulus on ground vibration is studied. A attenuation formula of ground vibration is established according to calculation results afterwards.(6) A CREEP user subroutine is scheduled based on the arc tangent function model of loess to modify the creep law in Drucker-Prager model. A plane strain model with dynamic stress from direct integration method is built afterwards to calculate the settlement of loess. And the effect of tunnel depth, inundated surface layer and soil static lateral pressure on loess settlement is also investigated.(7) For Xi'an No.2 metro line's undercrossing the city wall, the static stability, vibration and foundation settlement of the city wall are analyzed finally. First the stability of Xi'an city wall is analyzed by using strength reduction FEM. Then the vibration of the city wall is calculated by direct integration method. The foundation settlement of the city wall is also estimated taking the wall's initial consolidation into account. The effect of some important factors on the foundation settlement is also figured out.