Study On Design Theory And Construction Technology Of Cast-in-Place Expanded Pile With Hammer Driven Casting

Cast-in-place expanded pile with hammer driven casting is widely used in the foundation engineering because of its convenient construction, large bearing capacity of single pile and remarkable economy benefit. However, the researches on it make slow progress with complex bearing mechanism and various effect factors. Thus it is significant in engineering application and latent economy benefit to study the destruction model, compaction mechanism and the design theories and methods of rammed expanded pile.Firstly, this paper studies the compaction mechanism of rammed expanded pile deeply based on the expansion theory about sphericity pore of Vesic, discusses the possible destruction models on which points out that the destruction model of rammed expanded pile is transitional and it is more appropriate to make static analysis on the vertical bearing characteristics of rammed expanded pile with the slid surface theory of Janbu, and then, educes the formula about the eigenvalue of vertical compressive resistance bearing capacity of single pile considering the influence of energy on the pile tip shape in different layer and the effect of compaction, and the local experiment of single pile load shows that the result of theory is identical with practice perfectly. Secondly, this paper discusses the pull resistance characteristic and the calculation method of pull resistance bearing capacity of rammed expanded pile with the static analysis method, studies the pile group effect of rammed expanded combined with the load distribution characteristic and factor of pile tip earth, discusses the selecting principle of the technics and its properties (such as pulling height, penetration and casting height) with the experience of foundation engineering in Hengyang Hunan province, and proposes the corresponding design properties and control criteria. Besides, proposes the reinforcing design method using thin stiff stratum as bearing layer considering the melioration effect on earth of compaction process. At last, the achievements are used in several projects and obtain nice society benefit and economy benefit, which can be used as reference for design and construction of similar projects.