Experimental Study On Anti-collision Of High-elevated Pile Foundations And New Anti-collision Design Methods

With the rapid development of global economic, the number of structures in water such as bridge piers, transmission towers and oil or gas drilling platforms increase drastically in the world. As a result, the possibility of ship collision on these structure is also increase. It is significant to study the problem of their anti-collision which has been paid much attention by governments, scholars and engineers recently.The anti-collision structure using elevated piles as the foundation, such as the pile group anti-collision pier and the flexible pile-supported anti-collision system, is one of most normal one in engineering application. Presently, the anti-collision design method of the bridge pier with a very large lateral stiffness is widely used for structures in water, but it is not suitable for the anti-collision structure taking elevated piles as the foundation which will be large deformed during the collision. So the study on anti-collision of these structures especially the impact model tests and the new design methods are required for engineering design.In this thesis, the soil types in all tests were silt and clay which often appear in offshore area and rivers in China. Both lateral static and impact tests were carried out to study the anti-collision mechanism and dynamic interaction between the pile and soil, based on which several simplified design methods for anti-collision structures on elevated piles were proposed. The main work and innovations are listed as follows:(1) A large-scale model facility was developed for impact model tests, and both lateral static and impact large-scale model tests of a single elevated pile subjected to different impact energy were carried out. The anti-collision mechanism and dynamic interaction between the pile and soil were studied, and a proposed structural impact model considering the dynamic large lateral deflection of the pile has been validated. Further, a simplified anti-collision design method for the elevated pile was proposed.(2) The lateral static tests of in-situ large-diameter piles in soft clay were also carried out. The behaviors of the horizontal displacements, pile shaft moments, and the soil reaction as well as their relationship were studied, based on which some guidelines were given for large lateral deflection analysis of the elevated pile.(3) Both static and impact model tests were carried out for a single-row and a two-row flexible pile-supported anti-collision structures. The horizontal displacement of piles and axial force of the connecting beams were measured. This work has revealed the complicated characteristics of spatial force and deformation of the structure and validated the proposed energy-control based design method. In addition, some guidelines and suggestions for engineering application were presented.(4) By introducing a reasonable interaction model of ship and anti-collision pier and dynamic p-y curve method, the dynamics model of elevated pile impacted by ship is established. Through the systematic analysis of the influence to impact process by different parameters, such as bow strength, weight of concrete pier, shear strength of soil, and so on, we found the bow strength just affects the impact load-time curve, not the maximum horizontal displacement and the maximum bending moment of the pile. While the internal forces and deformation are only relevant to initial energy and pile diameter. Base on these, a new energy-control based design method was proposed for the anti-collision pier on elevated piles.