Finite Element Analysis And Research On Deformation Forewarning Of Foundation

Excavations works are carried out under the variety of foundation soil and complex environment. And the depth of pit is digged deeper and deeper, and the instability of pit happened frequently. Therefore, it is very great significant to study the stability of the deep pit.(1) The pile building enclosure with one bracing pieces is particularized as example in this paper. Simulate and Calculate the foundation pit project with the planar finite element method. The moment and deformation with braced structure, surface subsidence and the distribution of active earth pressure are studied. After comparing the data calculated with measured data, the results show that the finite element method which is adopted in the paper is reasonable and feasible. Simultaneously, influencing factors of pit deformation and the distribution of earth pressure are researched, such as the stiffness of the retaining structure (pile diameter), the depth of the pile on the braced structure, expansion angle with the soil and soil behavior. It is shown that the depth of the pile into soil is equal to the depth of digged pit in the region. Expansion angle with the soil is remarkable to deformation of pit. The diameter of bracing pile and the cross-section of the support (stiffness) should be in an appropriate ratio in order to make the deformation of supporting structure more reasonable; simultaneously make the cost of structure construction acceptable. The behavior of soil has tremendous influence on deformation of pit and earth pressure. It is suggested that the clay soil pressure distribution is designed according to the triangle design for the future excavation, which the maximum value is at the bottom of the pile. For the sandy soil, it is designed according to trapezoidal earth pressure distribution, which is above the surface of foundation pit is the triangle distribution and under the surface of foundation pit is the rectangular distribution.(2) The concept of permissible distortion coefficient is proposed, which is based on a large number of unconfined compression strength tests. And permissible distortion coefficient table with different tangent modulus has been given. And then the allowable value of deformation of different soil can be derived according to the limit displacement. In addition, the permission of deformation coefficient is obtained by doing direct shear test which the vertical pressure (confining pressure) is considered.The allowable value of deformation is calculated using an engineering example. It is proved to be the stability of the foundation pit which is compared with the measured values. And it is tested to be the feasibility of methods of using allowance deformation coefficient to predict stability of pit. This study in the article has a good reference value for the foundation pit design and early warning.