Uplift Mechanism Of Bolt And Its Application In Self-anchored Loading Test Technology Of Pile Foundation

With the increasing request of the superstructure to bearing capacity and settlement of the foundation, pile foundation has extensive application in engineering practices because of its much merit. Using an economical and effective method to test the vertical bearing capacity of pile, is not only the requirement of existing criterions, but also the topic of important theoretical and practical significance in the area of pile foundation. Presently, self-anchored loading test technology of pile foundation is a new application technology. There is a deficiency of systematic and thorough research on the mechanics property of the anchoring bolt under pile toe and the pile-soil-bolt interaction. By integrating with the Construction Technology Projects of Hunan Province(NO.200403), this paper discussed the uplift mechanism and design method of bolt, also the bearing capacity of pile foundation, in the self-anchored system.Mainly research and investigation are done as the following:Firstly, Through comprehensive analyses of the domestic and world related references and experimental data, an in-depth study and summarization of the pile-soil load transfer behavior and the uplift mechanism of bolt is obtained. Based on the analyses of linear deformation, an estimated formula for critical anchorage length of normal bolt is derived. According to the mechanical characteristics of rock-socketed anchoring bolt under pile toe in the system of vertical load-bearing capacity test of pile foundation by the self-anchored technique, a new load transferring function suitable for anchoring bolt under pile toe are set up based on the dilatancy effect between anchorage-body and surrounding rock, and an analytical solution of the critical anchorage length are obtained as well. Then, the distribution of frictional resistance along the anchorage length and the influencing factors are discussed in detail. In order to fully research the uplift mechanism of rock-socketed anchoring bolt under pile toe, the mechanics property and the elastic solution of normal stress of anchorage-body will be considered, and the Hoek-Brown strength criterion is carried out to understand the calculation method of frictional resistance. Integrated with the result of pull-out test of the anchoring bolt under pile toe that has ever been made till now, it gives a general discussion on the physico-mechanical nature of the rock, the characteristic of the anchorage-body and the load level, then the influence those factors carried out is analyzed. In order to fully discussing the calculation method of the uplift capacity of anchor in engineering practices, the existing research of anti-uplift pile with enlarged bottom is referred after the discussion on load transfer mechanism and failure mechanism on the bolt with enlarged bottom. A new calculation method of the ultimate uplift bearing capacity of the bolt with enlarged bottom is introduced, which is based on un-run- through shear failure model and the effect of plastic zone on the top of enlarged bottom. A general pulling calculation method that can consider different failure models also have been developed. In addition, according to the comparison of the bolt pull-out test P-s curve and the pile dead load test Q-s curve, forecasting uplift bearing capacity of bolt is proofed to be feasible, and the optimal combination forecasted model of uplift bearing capacity based on Hyperbola curve model and Index curve model is discussed with its application.Furthermore, based on the in-depth analyses of the pile-soil load transfer behavior and the uplift mechanism of bolt, the theoretical explanation of pile-soil-bolt interaction in the self-anchored system is obtained. And the enhanced action mechanism that the bolt under pile toe do to the pile end bearing capacity and the pile side resistance have been researched on the base of Meyehof presumption and Touma's arch-formation theory.