In-situ Tests And Numerical Simulation Study On Deep Foundation Supported With Pile-anchors

With the rapid development of urban construction, subway Project, a large number of municipal Projects and increasing the scale of underground space develop-ment, which generated a lot of deep excavation. And the pile anchor supporting, with its unique advantages, is applied more and more in excavation supporting work. However, there are still many problems in engineering applications, such as the theory lags behind the engineering practice, in view of the above, studies on force and de-formation of pile-anchor supporting structure are of great significance in the improve ment and develo-pment of foundation pit theory.Take the the sewage treatment plant of Buji foundation pit in Shenzhen as an engineering background to study the pile-anchor supporting structure in deep founda-tion pit. Through analyzing the field measured data, we obtained the changes of pile lateral earth pressure, pile stresses, bending moment, anchor force and deformation during excavation. And on this basis,using finite difference sotware of FLAC to do th e numerical simulation studies to the soil and foundation support structure, then rese archthe soil stress, soil displacement, the force and deformation of pile and anchor wit h different depth of the excava-tion. Comparison between this result and field experim ental data has been obtained internal force distrihution of soil and supporting structure.Through the studies of the project we got that:(1)During the stage of unexcavation, the initial stress of the soil was a trapezoid and evenly. During the stage of excavation, with the excavation depth increases under the influence of soil unloading, both sides of the supporting piles to withstand the ear th pressure caused by the supporting structure of horizontal displacement, which led t o the pit at the top settlement produced; support structure horizontal displacement sho wed dynamic changes, along with the pit the entire excavation process, affect the ran ge of about2-3times the excavation depth, the excavation is completed, the horizont al displacement curve showed a "bow " shape, and a period of time to stabilize.(2)The maximum deformation of the pile anchor supporting was appeared on the upper part of the Pit, about0.5-0.7H of the deepth. The value of the teinforced stress o f the pile growed quickly with time. The distribution curve closed to the bending mo ment of the pile and also showed the "S" shape(3)The anchor was very important in the pile-anchor supporting, it could control the deformation of the soil after with prestressed.(4) During excavation, the horizontal displacement of the supporting structure gr adually increased with the increase of the excavation depths The pile has the maxim um of bending moment near the second floor of the anchor, while gains the zero bendi ng moment at the upper part in pit bottom. Along the length of the anchor, its force g oes down gradually and appears the largest change in the free section.