【作者】 张柯；

【导师】 吴敏哲； 胡卫兵；

【作者基本信息】 西安建筑科技大学 ， 结构工程， 2011， 博士

【摘要】 西安地铁是我国首次在黄土区域建设的地铁线路。地铁行车荷载作用下黄土地层的振动响应和沉降是亟待解决的问题。本文以西安地铁为背景,就小幅值循环荷载作用下饱和黄土的动力特性和残余应变进行了试验研究;就地铁行车荷载作用下黄土地层的振动响应和沉降进行了模拟分析;针对西安地铁二号线下穿明城墙的具体情况,进行了城墙的静力稳定性、振动响应和地基沉降计算。主要研究内容包括:(1)进行了饱和黄土的振动三轴试验,探讨了小幅值循环荷载作用下饱和黄土的动力特性,研究了动应变、初始固结围压、超固结比、残余应变和有效固结围压对饱和黄土动弹性模量的影响。(2)进行了饱和黄土的循环三轴试验,探讨了小幅值循环荷载作用下正常固结饱和黄土的残余应变,研究了初始固结围压、排水条件、动应力及其循环次数,以及动应力比对饱和黄土残余应变的影响。(3)根据饱和黄土循环三轴试验结果,以动应力比和循环次数作为基本参数,建立了饱和黄土残余应变的反正切函数模型,模型计算结果与试验数据吻合较好。(4)根据饱和黄土残余应变的反正切函数模型,考虑前期动应力历史和前期残余应变硬化的双重影响,提出了不等幅值多级动应力作用下饱和黄土残余应变的累加方法,并编制了相应的Fortran程序。程序计算结果与饱和黄土排水循环三轴试验吻合较好,可用于小幅值循环荷载作用下饱和黄土残余应变的计算。(5)基于振动三轴试验得到的饱和黄土动力参数,建立了有限元和无限元结合的隧道-地层数值模型,采用有限单元法模拟了地铁行车荷载作用下黄土地层的振动响应,研究了隧道埋深、荷载频率、列车运行速度和地层动弹性模量对地面振动响应的影响。(6)基于黄土残余应变的反正切函数模型,二次开发了接口于Drucker-Prager粘弹塑性模型的CREEP子程序。通过定义初始场变量,综合考虑地层的初始固结围压和动应力。采用大型有限元程序ABAQUS建立了隧道-地层的二维平面应变模型,计算出地铁行车荷载作用下黄土地层的沉降,研究了黄土地层沉降的发展过程和空间分布,探讨了隧道埋深、上部地层浸水和地层固结围压对黄土沉降的影响。(7)针对西安地铁二号线下穿明城墙的具体情况,应用强度折减有限元法分析了城墙的静力稳定性;建立了考虑瓮城侧墙影响的二维平面应变模型,采用有限单元法计算了瓮城侧墙的振动响应;考虑城墙重量对地层的先期固结作用,计算了地铁振动可能引起的城墙地基沉降,并分析了隧道埋深、上部地层浸水和地层固结围压对城墙地基沉降的影响。更多还原

【Abstract】 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.更多还原