Research On The Methodology And Itsapplication Of Active-underpinning For Bridge Piers Under The Moving Trains

Along with the urbanization and urban upgrading, the infrastructure constructions have been continuously improving. More and more new-constructed projects have to pass through the space where the basis of the original structure exists. The foundation underpinning is the best choice because of the importance of the underground structures and the function immutable nature of the existing structure. The underpinning projects have the most difficult and the greatest risk for the complex geological and dynamic load conditions.The project of the bridge pier underpinning for Jin-bin mass transit is a typical example of dynamic load underpinning. The bridge pier underpinning and the tunnel construction have a certain influence on the upper bridges, rail lines and train operations, at the same time, the vibration of the operating rains also have an impact on the underpinning construction, and the two aspects are coupled together. And therefore the operation safety and the construction quality need to be taken into account in the construction. The relatively systematic researches are made on this underpinning project in this thesis, based on the theories for time-varying structures, from several ways, such as the risk identification and preventive measures, structural system design, construction techniques, modeling calculations, experimental research, monitoring, and assessment on the bridge after the construction, etc.First of all, after analyzing the potential risks of the project implementation comprehensively, the risks control measures are proposed for all participations, and the emergency contingency plans are designed to care for the risk that may be occur in the construction. The above all will lead to the implementation of the project safely. Then, the scheme selection, the design ideas and the designed results are introduced for the underpinning project, respectively. The quality assurance measures are interpreted in detail for every construction steps, such as drilling holes of the new piles, constructing the lattice beams, hosting jack loading, cutting the replaced piers and load conversion, excavating pit, constructing tunnel, and mixing the piles and lattice beams, etc.Based on the analysis of the time-varying process and features for the underpinning architecture, a detailed description is made on how to consider the effects from the various time-varying factors. The Ansys and the Midas Civil software are employed to simulate the stress state of the underpinning-node and the mechanical behavior of the underpinning architecture in the construction. The active measures are proposed to ensure the construction quality and the safety of mass transit operations.The pilot programs and results closely related to the project are given. The monitoring plan, which is throughout the construction process and covers the full range, are designed in detail, including monitoring indicators, layout of the measuring points, monitoring frequency, equipment, control standards, etc. A real-time monitoring system is established by using of the wireless data transmission technology, and the monitoring results are combined with the numerical simulations to realize information construction. The monitoring implementation and of results are focused on.Finally, a comprehensive assessment of the bridge after the construction is made, from the static mechanical properties, dynamic behavior and the using performance. This not only gives the bridge manager a specific judgment for the maintenance and management, but also makes an improvement in the foundation underpinning theory. The assessment shows that the bridge pier underpinning does not affect the normal operation of mass transit. The static bearing capacity of the bridge decreased slightly, while the dynamic performance was enhanced, and the adverse impact on the surrounding landscape can be weakened by greening.The successful implementation of the project plays a catalytic role to the theories and practices of the active-underpinning for bridge foundation by complex structure under the moving vehicles.