Study Of Key Techniques Of Foundation Underpinning Using Steel Pipe Pile

With the progress of society and the change of the people's requirement, it is hoped to obtain larger space through the reconstruction of existing buildings. Simultaneously, with the rapid development of national economy, business investment is increasing, production scale is enlarging constantly. So the original factory buildings can not meet the requirements of products development, the existing structures face the issues of reinforcement and reconstruction. The detection, assessment, reinforcement and reconstruction are gaining people's attention more and more. It has become a new kind of knowledge in civil engineering, and also become a significant branch of building industry. Underpinning is an effective means for the reinforcement and reconstruction to the foundations, and is also an important research topic in up-to-date domain of structural engineering and geotechnical engineering. Pier underpinning is one of the most important foundation underpinnings and has gained more and more attentions of research and engineering personnel.Though there are many process methods and research findings about reinforcement and reconstruction based on pile underpinning, many key problems or difficulties have not been solved. Based on the research background, the dissertation aims to impel the study on the theory and application for underpinning, and makes the techniques of design and construction more normative to utilize and exploit urban hidden spatial resources fully. The results can be used in the practice for detection, assessment, reinforcement and reconstruction, and the application is significant theoretically and practically.In this dissertation, the following aspects are studied theoretically, numerically and experimentally, and some results are achieved:1) The application of foundation underpinning at home and abroad is introduced firstly, pile underpinning is discussed specially, including the application domain and virtues or defects of active and passive underpinning, the types and characteristics of pile for underpinning, the typical examples at home and abroad using pile underpinning, the characteristics and correlative techniques and the preparatory work before underpinning are stated. Simultaneously, some problems in foundation underpinning are elaborated, and combined with an actual engineering the problems which will be solved in the dissertation are brought forward.2) Combined with an actual engineering, some key techniques about pile underpinning are introduced. Firstly, its engineering general situation is introduced, then several key problems are dealt with, including slenderness ratio, lateral displacement and differential subsidence of adjacent columns, it can be seen that the three indexes all meet the code requirements.3) Considering the practical situation, bar-planting technique and heat-resisting concrete are applied successfully. The construction process of bar-planting is introduced and anchoring of bar-planting is calculated. Simultaneously, the mix rate design of concrete is carried through and applied successfully.4) The design philosophy and construction practice about bored cast-in-place steel pipe pile are probed into, checking computations of foundation underpinning using steel pipe pile are carried out, it can be seen that the bearing capacity, punching shear resistant performance, subsidence and horizontal displacement all meet the code requirements. In the end, the finite element models are set up based on ANSYS and the static analysis are carried out subsequently, in the analysis two different models are set up which consider different soil dimensions, the results also meet the code requirements, the feasibility of pile underpinning in the dissertation are validated theoretically.5) The monitoring was carried out, and its main items include the establishment of monitoring scheme, the observation of vertical settlement and horizontal displacement of the independent column foundation and the foundation pit supporting structure. In the end, the monitoring results are assessed according to displacement curve of field observation, it can be seen that the steel pipe pile underpinning is very successful and meet the requirement of the reinforcement and reconstruction.