Deep Foundation Retaining Structure With Double-row Piles Work Resistance Properties

With the widely use of deep excavations in high-rise buildings and subway engineering and Municipal Engineering, the safety issues due to the deeper depth have become significantly noticeable. Ways to ensure the safety in construction of deep foundation and nearby structures are the key points to the construction of high-rise buildings. The double-row piles, as one type of the bracing projects of deep foundation pit, have drawn general attention from the engineers owing to its unique advantages. Under the background of the excavation of Qingdao North Metro Station Project, the paper reviews the researches of the research achievement of excavations both at home and abroad, and a FLAC3D numerical computation model based on finite difference method considering either theoretical or numerical analysis has been presented in this paper to study the effects of stress and deformation of the structure of double-row piles. The following main conclusions can be drawn from the study.1. The main parameters that influence the mechanical properties of bracing structure of double-row piles are the depth and diameter of a pile, the spacing between the piles and two rows, top beam stiffness and ground improvement in the active earth pressure zone.2. Remaining a constant depth of the back-row pile, the lateral displacement of the pile top decreases with the increasing length of the front-row pile until the minimum value is reaches at the length of16m; after that it then increases. Furthermore, the internal forces and the surface settlements both achieve the minimum vales, simultaneously when displacement appears a minimum.3. Keeping a constant length of front-row piles, the deformation of the pilebolck varies with the length of back-row pile changs from14m to24m behaviors as the previous one for the same reason, and also reaches a minor value at16m together with the internal forces and the surface subsidence.4. Keeping other parameters constant, both the front and the back rows of piles have a relatively small displacement of the pilebolck spacing varies from lm to2m, and the top displacements reach a minimum at16m together with the internal force and the surface subsidence.5. Comparing the results of different pile diameters varying from0.5m to2m on the deformation with keeping the other parameters unchanging, both the rows of piles are found to a minor displacements at the top as it is2m, including the internal force and surface settlement.6. The lateral displacement of the pilebolck in front and back rows reaches a minor value when the spacing between the two rows reaches4m and other parameters stay the same. Similarly, the internal forces and the surface deformation also reach a minor value.7. The reinforcement of soil in the passive zone is beneficial to the stability of supporting structures and the decrease of the displacement of the pilebolck as well as the surface subsidence.