Study On The Mechenical Behavior Of Double Row Pile Supporting Structure System Of Deep Foundation Pit

Double row pile supporting structure refers to two parallel rows of piles settings in the soil in which piles are distributed into a rectangular or plum-shaped layout and a rigid or a tie beam on the top connect piles in different rows. Double row pile form a gate-shaped space supporting structure along a direction parallel to the edge of pit. It is mainly applied to shallow pit,deep pit and other pits requiring different security levels.Double row pile also can be used when the anchorage, supporting type and cantilevered structure are not applicable,also the pit with precipitation or curtain.Currently,double row pile are mainly used in soft soil area and the maximum deformation can be controlled within 4-6 cm in the case of pile bottom embedding in relatively stiff strata and shallow excavation.In the existing research results,the double row pile supporting structure performs frame effect, pile-soil interaction and tie beam effect in the work process.Some scholars study on the system by simplying it as a plane frame with earth press loading on it or by model test or by numerical methods.The author mainly study the mechanism of the system through the existing theoretical algorithm and 3D FEM,and the main contents are as follows.The specification algorithms of this system are systematic collated and analyzed and the applicability of the calculation method is also analyzed in this article which applies to row piles with the same layout like latticed piles or other cases of symmetry and eplicative piles.2D and 3D models are conducted based on specification algorithms and FEM software Sap84 and the results are analyzed.Displacement in deep direction shows a decreasing trend and a turning point appears in the displacement line of the front row piles.The maximum moment of the front row piles are larger than the maximum of back row piles but the maximum moment positions show at the top of the piles.The results also show that the maximum displacement of 3D model has an increase than the 2D model.According to the practical engineering,the material constitutive model are selected in the FEM software ABAQUS and the reference condition 3D FEM model of the double row pile of deep foundation pit is conducted.Moreover,different levels of the main influence factors of mechanical properties of double row pile supporting structure are analyzed in this article such as soil properties,concrete elastic modulus of double row pile structure,the designed insertion ratio of piles,distance of different rows piles,stiffness of connection beam.Post processing results of the above models are detailed analyzed from many aspects of the models as follows:the horizontal displacement and the earth pressure of the front and back row of piles,sharing ratio of the front row piles and the moment of the piles.The effect law of the factors are drawed and the mechanism of stress of double row pile structure in excavation of deep foundation pit are studied.