Research On Bearing Capacity Behavior And Influential Factors Of Pre-stressed Concrete Pipe Piles

The pre-stressed concrete pipe piles have a lot of virtues, such as high bearing capacity, credible quality, fast construction, little environmental pollution, convenient detection and so on. In recent years, the pre-stressed concrete pipe piles are widely used in actual engineering. But the time when the pre-stressed concrete pipe piles are applied in loess area is short and the study is not sufficient. The mechanism of pile bearing capacity and its influential factors need to be studied further.Firstly, we widely analyse the current research situation of the prestressed concrete pipe piles and point out some shortcomings of existing research. Secondly, we illustrate the mechanism of pile driving of static pressure pile and the mechanism of load transfor form. Lastly, according to the contrast between the data of static load and the value of current standard, we correct the coefficient of pile bearing capacity in Xi'an. The main conclusion in this paper are given as follows:(1) The transfer process of the pile bearing capacity is divided into three stages: 1)The elastic stage of pile-soil interaction; 2) The plastic stage of pile-soil interaction; 3)The failure stage of pile-soil interaction. When the piles are on the elastic stage, the growth of pile bearing capacity is determined by the side friction of pile body; When the piles are on the plastic stage, the growth of pile bearing capacity is determined by the effective area of pile-end.(2) The influence of the soil plugging effect on the pile bearing capacity is important. The soil plugging effect can make the vertical load of pile-end diffuse effectively and improve the pile bearing capacity. And it decrease strain of soil, improve the stability of the pile body and increase the ultimate load.(3) The increase of elastic modulus of pile soil plug can make the effective area of pile-end increase. And then, it can improve the pile bearing capacity. When the modulus of soil-plug reaches to a certain value, it can be calculated according to the closed pile. (4) Through the studies of the length-diameter ratio, we found that the increase of the length-diameter ratio can make the bearing capacity increase singificantly.(5) Through the analysis of the test data of prestressed concrete pipe piles in eight engineering projects in xi'an, we found that the calculated value of the code formula is lower than the value of the actual bearing capacity andαrepresents correction coefficient of pile bearing capacity whose value is between 1.1 and 1.2.