The Research On Influence To The Behavior Of Adjacent Excavation By Existing Composite Foundation

In recent years, with the acceleration of urbanization process, the rapid development of high-rise buildings, the consumption of city’s land resources, resulting in limited ground space is difficult to meet the people’s growing material and cultural needs of life, which makes underground engineering especially excavation engineering obtain unprecedented space for development. In medium-sized cities, a large number of high-rise, high-rise buildings grow rapidly, the proposed excavation pit of these buildings are generally in dense buildings, narrow construction site, and conditions of the surrounding environment is extremely complex. The influence of existing buildings should be taken into account in design and construction of the actual excavation, especially the control of excavation pit deformation impact when the presence of existing buildings around foundation, although many scholars and experts have been researching into the deformation control design of foundation excavation for recent years, but the control that existing buildings to the deformation of adjacent excavation still has shortcomings during excavation. In this paper, based on previous theories and research results, and combined with the engineering example, a three-dimensional finite element model of structure-soil is established by finite element software ANSYS to simulate and analyze the impact on horizontal deformation and earth pressure of adjacent excavation by existing buildings used composite foundation, and at the same time make an exploratory study about the influence to horizontal deformation of excavation by adjacent composite foundation when changes pile conditions, and draw relevant conclusions.(1) By comparative analysis, under the same conditions, model parameter selection and foundation pit excavation are the same, the maximum horizontal displacement value of the composite foundation pit is of about20%less than that of the natural foundation, the maximum soil pressure of the retaining pile above the excavation face is to be reduced by about30%to35%.(2) Pile length changes have an impact on neighboring foundation pit, when the pile stiffness of the composite foundation is bigger. As the composite foundation pile length increases, the earth pressure of the supporting piles decreases, the maximum horizontal displacement is correspondingly smaller, and there is a critical length of pile, the degree of influence of the supporting piles traits slows down when the pile length exceeds this value.(3) Pile diameter changes have an great impact on neighboring foundation pit, when the pile stiffness of the composite foundation is bigger. The larger diameter of piles, the lateral displacement of the foundation pit support pile and the earth pressure value are smaller. The decreasing trends of the supporting piles horizontal deformation and earth pressure are slower, when the pile diameter reaches to600mm and then increases.(4) The change of modulus of elasticity E of composite foundation pile could produce greater impact on adjacent foundation pit. The horizontal displacement and soil pressure of supporting pile of adjacent foundation pit supporting pile are continuously smaller with the increase of the pile stiffness of the composite foundation.(5) Under the pile stiffness of existing composite foundation is larger case, the impact from both the composite foundation and the distance between adjacent foundation pit for the supporting pile are mainly in the range of excavation depth. As the distance increases, the horizontal displacement of the supporting piles and soil pressure values continue to decrease, and when the distance is more than twice the excavation depth, the impact of existing buildings on the adjacent pit is no longer obvious.(6) Additional load P of existing buildings is adverse effect to adjacent foundation pit, and it could be revealed from the beginning of excavation pit. And with the building load increases, horizontal deformation and soil pressure of the adjacent foundation pit are increased accordingly, and it is also more consistent with the actual situation.