Experimental And Theoretical Study Of Capped Rigid Pile Composite Foundation In Soft Soil Area

Rigid pile composite foundation has been widely used in deep soft soil Foundation. However, due to rigid pile composite foundation under large loads the pile is easy to produce thorn phenomenon, affecting the foundation reinforcement effect. So the capped rigid pile has been introduced, it not only can reduce the pile of thorn phenomenon, but also can improve the bearing capacity of the soil between piles, which greatly improved the bearing and deformation behavior of rigid pile composite foundation. However, despite the capped rigid pile has been widely used in engineering practice, but the mechanism of pile caps and bearing mechanism of rigid piles are still in the primary stage.So under the support of National Natural Science Foundation of China“Work mechanism and differential-settlement-based optimal design of composite ground with two-directional reinforcements in shore(51278186)”, a thorough study on capped rigid pile composite foundation reinforced soft roadbed technique is made in this dissertation.Based on the analysis of existing rigid pile composite foundation model test, the similarity theory is introduced in model test against the arbitrariness of parameters choosing. In this paper, the relevant principle of similarity theory is adopted, then, the similarity criterion of rigid pile composite foundation model test is obtained by using dimensional analysis method. Experimental phenomena has been revealed that the hard soil under the horizontal tilt of capped rigid piles under load pile pressure distribution presents a large pile in the middle, both sides of the pile smaller. Through experimental and theoretical research, it is found that upward penetration occurs at the pile top, and it causes negative friction to a specified depth, so the maximum axial stress occurs no longer at the pile top, but at the point of about one third of the pile length below pile top.Based on the upper plastic limit analysis theory and failure modes of rigid piles, kinematically admissible velocity field was established. According to the energy balance principle and unified strength theory, ultimate bearing capacity limit solution of rigid piles considered the intermediate principal stress calculation formula was derived. Meanwhile through parametric analysis, the variation of ultimate bearing capacity of rigid piles with different pile cap size, soil cohesion and internal friction angle have been found. It is found that there is a large increase in the upper limit considering the main stress of capped rigid piles solutions. It is reasonable to chose unified strength theory parameters 0.1 to 0.2 in capped rigid piles bearing capacity calculation. It can be also found that with the increase in the size of pile cap the capped rigid piles bearing capacity increases, and when the diameter of the pile and pile cap diameter ratio is D / d> 2, the bearing capacity of the increasing trend is more obvious. With the increased of soil cohesion and internal friction angle, the bearing capacity increases By comparison with the existing theoretical methods and test results, the proposed method was not only in theory more closely, and to obtain a more realistic calculation.