Lateral Displacement Analysis Of Retaining Structure With Double-row Piles In Deep Foundation Pit

Double-row piles as a new bracing structure of foundation pit are developed recently, and it has bigger lateral stiffness, its construction is convenient, its stability is better. But the mechanism of double-row piles is very complex, and few design theory and analysis method is mature.Many calculation models known well in engineering field are introduced, and those advantage and disadvantage are discussed in this dissertation. On the basis of that, a new double-row model calculation is brought forward. The method basis on finite element method theory, considers piles-soil interaction, contact surface theory is applied to solve piles-soil interaction of double row piles, which is used briefly parameters of model is chosen easily, and concept is very legible. Moreover, correctness of this testified by a example of project.Calculating double-row piles correlative parameters using large-scale finite element software. Supporting structure type, spacing of rows, pile-pile distance, pile spacing, strength of soil between piles, stiffness of top beam, embedded depth are studied. Then many correlative conclusions are given such as the problem of optimization spacing of rows. Those can be consulted in design of engineering. The major research results are as follows:1. The change of supporting structure type of double-row piles has greater influence to the internal force distribution of the support structure, and relatively smaller to displacement. Relative to the rectangular pile supporting structure form, front and back row pile positive and negative bending moment are more homogenous in plum-blossom pile supporting structure form, which gives full play to the supporting structure work performance; plum-blossom pile supporting structure is more suitable for application in foundation pit supporting project.2. Increasing the row spacing can control the deformation effectively, but supporting structure internal force will increase relevantly. It is rational that row spacing is between2/5L0～4/5L0, when row spacing is larger than L0, the uniformity of front and back row pile internal force distribution will increase, maximum bending moment of front row pile is much larger than back row pile. 3. Increasing pile spacing of double-row piles supporting structure, lateral displacement of supporting structure will largen, internal force increases significantly. Although, the smaller of pile spacing is, the better to supporting structure, but in practical projects, we need to consider engineering cost, project construction period etc. various comprehensive factors. In meeting the requirements of deformation control, we should minimize the time and reduce project cost to the greatest extent. When pile spacing is between1.5and2.5times the pile radius, the internal force difference between front and back row pile is small, which gives full play to the structure work performance.4. Appropriately increasing soil modulus between piles can effectively control lateral displacement of the double-row pile supporting structure, and internal force of double-row pile supporting structure has not changed much.5. When crown beam stiffness is more than critical stiffness, increasing crown beam stiffness can not reduce deformation of structure; Oppositely, when crown beam stiffness is less than critical stiffness, increasing crown beam stiffness can improve the integral stability effectively, and is in favor of deformation control.6. In meeting the minimum embedded depth request, adding front and back row pile length can improve the integral stability effectively, can control structure deformation effectively too.7.Internal force and deformation of double-row piles in the designed project foundation engineering are calculated using finite element software ABAQUS, and compared with observation date of site. According to observation date, internal force and deformation of calculating result conform result of site. Therefore calculating result using finite element software ABAQUS is believable, and some available suggestion of design and construction is put forward.