Three-dimensional Mechanical Model And Influence Factors Analysis Of Retaining Structure With Double-row Piles Of Foundation Pit And Its Engineering Applications

Double-row piles as a new bracing structure are developed in recently years. Because of their advantages, such as the ability to resist lateral displacement and significant economic benefits, they were more and more applied in foundation engineering, But their mechanism of force is more complex, computational theory and foundations of design are also imperfect. All of these become restrictions on their development. So it is important to study the type of bracing structure.This paper gives a brief introduction about double-row piles in features and nowadays status. Some analysis models that commonly used at present were summed up. The advantages and shortcomings of theirs were illustrated: Three-dimensional model is set up on the basis of former work. The main factors of double-row piles were analyzed by ANSYS. We should research the working condition of supporting structure after the factors of them changed; getting some conclusions that are good for engineering practice. The main work includes the following respects:1. During the research of interaction between double-row piles and soil, the working condition of double-row piles is analyzed from three-dimension when they were applied in foundation. Piles,beams and soil were simulated by corresponding models. A new model of touching is set up where the different characteristic of interaction between the piles and soil:1) In those region, such as bottom of piles,back of front row piles,front of back row piles and beam, where the bracing structure touches the soil, the structure and soil will be made as a kind of continuous medium that is studied .2) In the region, such as back of back row piles and front of front row piles, we will install contact model. Because extrusion,friction,even gap may arise between the piles and soil when the piles occurred lateral displacement.2. Firstly we set up a basic example by ANSYS based on the model that is set up in 3D in the paper, and then we study the influence of parameters by changing them. The parameters involve distance between front piles and back piles,stiffness of beam and the depth of foundation. During calculating by ANSYS, the results were expressed as graphs. The main regular conclusions were listed as follows:1) The lateral displacement in double-row piles' top is less than one half of single row piles' on the basis of equivalent stiffness. So we should adopt double-row piles in the situation that the depth of foundation is in the range of 5 to 10 meters if the demand of displacement is strict.2) The moment curve of double-row piles show as "S", and it is distributed well-balanced. The peak of moment is greatly reduced comparing with single row piles'. The reinforcement rate is reduced.3) When the distance between the two ends increases, the lateral displacement in piles' top is reduced, but the trend is more and more weak. So it is not effective all the time to reduce lateral displacement by increasing the distance of two ends.4) The stiffness of beam has significant influence on lateral displacement. Based on the situation of unchanged width of beam, the connection of piles' top with beam changes from rigid connection to hinge with the thickness of beam reduced. The moment of theirs is reduced, but it has not obviously effect to increase the thickness of beam all the time. So it is supposed to make the range of beam's thickness from 0.5 to 1 meter.5) The curves of double-row piles are similar as single row piles' when the distance between the two ends is 2 meters, and the moment distribution of piles is unreasonable. When the distance of that is 8 meters, the effect that back row piles pull front row piles back during beam between them is obvious. When the distance of two ends is 4 meters, the interaction between piles and soil is obvious. The moment of piles is reasonable and the value of displacement is to meet the requirements.3. One project in Qingdao that applies double-row piles is analyzed by ANSYS. During the comparison between the calculated data and monitoring data, the results show that the two sets of data is closed. So the 3D model of double-row piles constructed in the paper is reasonable.