Study On Bearing Mechanism Of Squeezed Pile With Expanded Branches And Plates

Squeezed pile with expanded branches and plates (being DX pile) is a new type pile that has been developed in recent years. Based on common cast-in-place pile, it adequately avails itself of the bearing capacity of each soil hard layer. According to the difference of design bearing capacity and engineering geological condition, it consists of some branches and plates by the squeezing equipment of hydraulic pressure in the different parts of DX pile. DX pile is a sort of change-section pile and is priority to shaft resistance between friction pile and shaft pile. Making use of the tip resistance of breaches and plates and shaft resistance around the branches, in order to add the shaft resistance and tip resistance.DX pile was applied in Dongying in late 1999. As the application mechanism of DX pile at the exploration period in soft soil presently, there are no uniform regulations for design account. The local experience and the correlative theories were applied in practice. There are a lot of such as unreasonable, insecurity and uneconomical factory. In view of the engineering examples, the load transfer mode and numerical value model of DX pile has been proposed by analyzing the movement mechanism of extrusion-expansion device. Based on soil engineering test and loading test, the compaction effect and load characteristic around DX pile have been seriously explored, and, the load mechanism has been theoretically analyzed, and, the character and mechanism of load transfer has been perfected in some degree. At the same time, the account formula of ultimate bearing capacity in Dongying is proposed from a great deal of engineering practice. This provides the theoretic evidence for the development of DX pile in soft soil.The conclusion as fllows:(1) The branches setting and bearing plates in DX pile by utilizing the anisotropism of foundation soil, especially the change of soil character in vertical direction, in order to add the ratio of load share beyond the bound of pile. Under the action of extrusion-expansion device of hydraulic pressure, the soil around bearing plates is reinforced in the level direction, so that the region was formed of extrusion and reinforce from inside to outside of the around pile.Proved in practice, it can enhance the bearing capacity of hardness soil around bearing plates and increase the stabilization of pile.(2) The bearing plates and branches are formed with the effect of extrusion-expansion device of hydraulic pressure, in the same time the engineering performance of soil is changed. The effect is obviously to molding and extrusion-expansion. The range of molding and extrusion-expansion is apart from the outside brim of pile in one meter in the lever direction, is apart from in half meter in vertical direction. The maximum percent of dry density may be enhanced in range of about 15 to 20.(3) DX pile is suitable for the quite great load of pile top and reduces the settlement calculation, the curve of load-settlement is more gently than the pile of the same diameter, and the settlement calculation is also far smaller than the same diameter. The vertical resistance of pile bottom has the character of both tip resistance and shaft resistance, and it is lean to the latter.(4)The angle of extrusion-expansion ( 9 ) is smaller, and the pile is more propitious to the load and transmutation. The optimum angle of extrusion-expansion may be adopted between 60 and 90 degree in engineering, the suggestion value ( ) is 70 degree in soft soil district of Dongying.(5)For DX pile, the vertical space between branches or plates cannot be too close, the branches cannot be overmuch set. If the amount is too much of branches and plates, the quality of formed branches and plates will be affected, at the same time, the redundant branches and plates cannot take effect, for the superposition effect (being stress superposition) of soil. It is indicated that the vertical space between branches and plates cannot be less than 3D, simultaneity, cannot be less than 6d.(6)The constrained modulus of b...