Study On Bearing Mechanism Of Closed Diaphragm Wall As Bridge Foundation

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.