Model Test Studies And Numerical Analyses Of The Vertical Bearing Behaviour Of Single Piles With Stem Shrinkage

Due to the reasons of construction technology, geological conditions and construction management and so on, various defects, such as stem breakage, stem enlargement, stem shrinkage and mud cake etc, are very likely existence in pile stems. And stem shrinkage is one of the most common forms of the pile defects. At present, researches of the shrinkage pile mainly focus on analysis of the causes, testing methods and treatment technologies, but the model tests of the piles with the load bearing characteristics is still rare. Therefore, in this paper a model test was made to single piles with stem shrinkage, to study them (the shrinkage pile) with the vertical bearing behavior, together with the analyses of the workings mechanism of piles with stem shrinkage through numerical simulation.In the model tests, firstly, some test equipments were designed in the model test of pile foundation, such as a displacement detection rod and a small touch the ground device, etc, and focused on research the method of realizing the stem shrink. And, based on this, pile load-settlement relationship was measured, through the normal piles and piles with stem shrinkage which shrink diameter was 0.5d and 0.75d defects in the pile model test. The tested results show that: (1) The defects of the stem shrinkage in the pile body can reduce the bearing capacity of the pile; (2) The two different degree defects of the shrink diameter affect the bearing capacity of the pile not too big; (3) The piles with stem shrinkage often happen the position of the damage at the upper in the shrink diameter section .In this paper, A 2-D finite element software Plaxis was used in the analyses the stem shrinkage pile with the load bearing characteristics and analyzes the different stem shrinkage degree, different stem shrinkage position and different soil parameters on the stem shrinkage pile bearing the influence law of the character. The calculated results show that: (1) The stem shrinkage defect in the pile make the pile side friction loss; (2) The degree of stem shrink effect the bearing capacity of the pile not too big; (3) Bearing capacity of piles are lower when the stem shrinkage position located in the bottom of the piles; (4) The influence of soil cohesion is most obvious to the bearing capacity of piles with stem shrinkage.The research reveals the regularity of the effect of the stem shrinkage defect contributing to the vertical load-bearing characteristic of single pile; it contains important guiding significance to the group of pile and related research and also gives certain guiding sense to the design and construction.