Study on Influence to Compaction Effect of Jacked Pile by Dug Pile
|Keywords||foundation engineering jacked pile dug pile compaction effect numerical simulation|
In recent years, jacked piles have been widely used in urban infrastructure constructions because of its various advantages such as little pollution, vibrationless, noiseless, stable bearing capacity and fast construction speed. The pile driving effect of jacked piles can effectively improve the pile shaft resistance, as well as the bearing capacity of the soil. However, the squeezing effect has a great impact on the environment surrounding the construction site. When multi-channel process of construction is used, along with the step-by-step process, the squeezing effect of the former step will make the jacking force of the later step significantly increase, which leads to a much more difficult degree for construction, and even the phenomenon of pile explosion. Therefore, forming composite foundation by replacing part of the soil compaction piles with the soil displacement piles has been one of the most useful measures to reduce the difficulty of static pile construction as well as to mitigate the adverse environmental impacts of the construction process.In this paper, on the basis of previous studies, the status and key issues of the compacting effect of the jacked pile are elaborated. Besides, research methods of squeezing effect which are commonly used at present are summarized as follow:the cavity expansion theory, the strain path method, and the finite element simulation. Taking the construction process which makes the construction of the soil compaction piles earlier than the soil displacement piles into consideration, how stress field around the pile, displacement field and shaft resistance distribute and change during the static pile construction process in Henan Province typical sand of clay and silty loess conditions are researched using the method of numerical simulation. Thus, how the construction of the soil compaction piles influence the pile axial force and the shaft resistance of the soil displacement piles are illustrated. Conclusions of the study are as follow:(1) When the sinking process of the jacked piles comes to an end, the horizontal displacement of sand, clay and silty loess soil at the same depth decay exponentially along the radial direction, the closer from the pile, the faster it decays. For the friction between piles and soil, vertical displacement of the soil close to the pile within a certain range performs uplift, outside this range, the performance of the soil displacement sinks. Vertical displacement of the soil first increases and then decreases, the maximum vertical displacement occurs at a certain depth from the surface.(2)After the end of the sinking process, the radial stress and vertical stress of the jacked piles, sand, clay and silty loess along the radial decay exponentially. Due to the differences in the nature of the soil, the decay rates changes, silty loess decays fast while the sand decay slow, but they both rise with the increase of soil depth. Because of the splitting of the pile tip, stress in the the pile tip reaches the maximum value.(3)Ultimate bearing capacity of jacked piles ascends with the increase of the pile diameter and the pile spacing under certain pile length conditions. Axial force of the jacked piles changes little in the length range of the body of soil displacement piles, under this depth, it changes greatly. The corresponding pile shaft resistance above this site, for the construction process of the soil compaction piles which makes jacked piles stress of squeezing effect release, display a smaller degree. Under the depth of the soil displacement piles, shaft resistance increases linearly and reaches its maximum value at a certain distance away from the pile tip, and decreases sharply at the pile tip. Ultimate bearing capacity of the jacked piles ascends with the increase of the pile diameter of the soil displacement piles but decreases with the increase of its length under certain condition that the space between soil compaction piles and the soil displacement piles is certain. Corresponding shaft resistance, affected by the release of the stress from squeezing effect, display a small degree, and also reaches the maximum value in the part of the pile tip.(4)The construction of the soil displacement piles has a great influence on the shaft resistance of the jacked piles, before the construction process, the shaft resistance displays a big degree, after that, the tip resistance play a small degree.