【作者】 宋章；

【导师】 程谦恭；

【作者基本信息】 西南交通大学 ， 防灾减灾工程及防护工程， 2008， 博士

【摘要】 闭合型地下连续墙(以下简称闭合墙)整体刚度大,承载能力高,作为一种新型的桥梁基础,不仅具有良好的竖向承载性能,而且还具有很好的水平承载特性。然而,由于墙内土芯受力变形十分复杂,基础承载性状的影响因素众多,到目前为止,对闭合墙桥梁基础的承载机理这一问题尚未得到很好的解决。为此,本文结合交通部西部交通科技项目,采用现场荷载试验、数值计算和理论分析的方法对单室闭合墙基础的荷载传递机理及其承载性状进行了系统的分析和研究。主要研究内容和成果如下:(1)通过闭合墙现场竖向载荷试验,对黄土层中闭合墙的荷载-沉降特性、墙身轴力与墙侧摩阻力的发挥性状、墙侧摩阻力和端阻力荷载分担比的变化规律进行了分析。结果表明:闭合墙具有端承摩擦墙的特性;竖向承载力由墙侧摩阻力和端阻力共同承担;侧摩阻力和端阻力的发挥取决于墙周土性参数的变化及墙土之间相对位移量的大小。(2)考虑墙内土芯的承载作用,通过数值计算和分析,对竖向荷载作用下闭合墙基础的荷载传递机理,墙身内、外侧摩阻力的发挥机制,以及各荷载分量及其荷载分担比随墙顶荷载变化的分布规律等进行了研究;并探讨了墙身截面形状及尺寸、土体物理力学特性等因素对闭合墙承载性状的影响。(3)研究了墙端附近墙内土芯的受力变形规律。采用土拱理论,基于平面应变假定,确定了土拱的合理拱轴线为二次抛物线形式,并对土拱的最不利受力截面位置、土拱出现及保持稳定的条件进行了详细探讨。指出:存在于土芯端部附近范围内的“应力锅状拱”效应有利于墙身内侧摩阻力及端阻力的发挥。(4)通过水平荷载作用下闭合墙基础的三维数值计算,研究了闭合墙基础的水平受力变形破坏特征,以及墙身变位、内力及墙侧地基横向土抗力变化的分布规律。并探讨了不同加载方向下矩形闭合墙基础其水平屈服强度的方向性。(5)斜向荷载作用下闭合墙基础的承载机理与单一的竖向或水平向荷载分别作用情况不同,其受力变形特征包括了竖向或水平向荷载单独作用下的各种可能情况。数值计算表明:斜向荷载作用下闭合墙基础的极限承载力与墙项荷载的倾斜程度及墙身侧摩阻力的发挥性状有关;其极限承载力应综合考虑地基土体的竖向承载能力、基础上部结构允许的位移量、地基横向土抗力、墙身材料强度特性等方面的要求。(6)利用荷载传递法,推导出了闭合墙竖向荷载—沉降关系的弹塑性半解析公式,并求得了任意截面墙身轴力及墙身侧摩阻力计算表达式。通过计算分析,表明此公式能较好的分析竖向荷载作用下闭合墙基础的荷载传递机理及其承载性状。(7)基于地基系数m法,按照弹性地基上有限长梁的方法,建立了地基横向土抗力、墙身变位与内力关系的微分方程,采用幂级数求解的方法,导得了水平向荷载及斜向荷载作用下闭合墙墙身内力与变位的关系公式。并初步验证了此计算公式的合理性。更多还原

【Abstract】 Because of the characteristics of whole large stiffness and high bearing capacity, as a new form of bridge foundation, the closed diaphragm wall (called the closed wall) has good both vertical and horizontal bearing capacity. However, owing to the complexities of the deformation of soil core within the closed wall, and the influencing factors for the load transfer mechanism and bearing behavior of the closed wall, the study on the bearing mechanism of the closed diaphragm wall as bridge foundation is in the air yet up to now.In this dissertation, by the methods of the in-situ loading test, numerical computation and theoretical analysis, the load transfer mechanism and bearing behaviors of the simple closed diaphragm wall as bridge foundation were studied systematacially. The main contents and results are as follows:(1) By the method of the in-situ vertical loading test of the closed wall, the characteristic of load-settlement, the working characters of axial force and skin friction, and the variational laws of the load-sharing ratio of skin friction and end resistance of the simple closed wall were studied in loess subsoil. The results indicated that the bearing characteristics of the closed wall present the properties of end-skin friction wall, the bearing capacity of the closed wall consisted of the skin friction and end resistance; and the working of skin friction and end resistance of the closed wall were related to the factors, such as the physical and mechanical characteristics of loess, the relative displacement between the diaphragm wall and loess, etc..(2) According to the numerical computation, considering the bearing action of soil core within the closed wall, the load transfer mechanism of the closed wall foundation subjected to the top vertical loading, the working mechanism of the inside and outside skin friction, and the distributing law of the various load components and its load-sharing ratio varied with the loading on top of the foundation, etc. were studied, respectively. Besides, the influencing factors, such as the section shapes and sizes of the closed wall, the physical and mechanics characteristics of soil, for the bearing behavior of the closed wall were discussed in detail also.(3) The arch theory was introduced to study the deformation characters of soil core nearby the toe of the closed wall, the form of quadratic parabola as the reasonable arch axial line of soil arch was determined. In addition, the most disadvantageous forcing position of soil arch, and the condition of appearing and keeping stability of soil arch were discussed carefully. The results showed that the effect of "stress dome shape arch" nearby the toe of the closed wall is advantageous for improving the inside skin friction and end resistance.(4) The deformation behavior of the closed wall foundation, displacement, internal forces of the closed wall and the horizontal soil resistance of subsoil were studied by the method of three-dimensional numerical computation, when the horizontal loading was acted on the top of the closed wall. And the orientation of horizontal yielding strength of the closed rectangular wall, which subjected to the various loading, were analyzed systematacially.(5) The deformation mechanism of the closed wall subjected to the inclined loading is different from that of the closed wall subjected to the vertical loading or horizontal loading only, and its deformation characters may include different kinds of the deformation characters subjected to the vertical loading or horizontal loading only. The results of numerical computation presented that the ultimate bearing capacity of the closed wall subjected to the inclined loading rest with the inclined degree of inclined loading and the working characters of skin friction, and the factors of the vertical bearing capacity of subsoil, the allowable displacement, the horizontal soil resistance of subsoil, the material strength of the wall, and so on, should be considered.(6) Based on the load transfer method, a set of elastoplasticity analytical formula for the axial load-settlement of the closed wall were deduced. Furthermore, the calculational expressions of the random sectional axial force and the skin friction were derived. By the computational analysis, the load transfer mechanism and the bearing behavior of the closed wall subjected to the vertical loading were analyzed commendably by these expressions.(7) According to the theory of finite-length beams on the elastic foundation, the differential equations of the horizontal resistance, the deformation and the internal forces of the closed wall have been established. Based on the subsoil coefficient m method, the formulae of the internal forces and the displacement of the closed wall subjected to the horizontal loading or inclined loading were deduced. And the calculated results indicated that the formulae were reasonable.更多还原