Research On Calculation Theory And Its Application Of Deep-mixing Pile In Composite Ground

As a new soil improvement technology, deep-mixing pile has a number of merits. With the construction of a great number of foundation engineering, it gets much wider application. However, application and development of this technology is greatly confined as academic research still lags behind practice. In order to provide valuable method for analysis of composite ground, emphasis has been put on study of its character and investigation of longitudinal interaction mechanism between soil and pile. The main contents are as follows:1. Numerous monitoring data have been got through field tests, which makes it possible to know the stress distribution law and deformation character of soft ground reinforced by deep-mixing pile group, and provide useful proof for subsequent researches. At the same tune, precious experiences of design and construction are accumulated.2. Considering spatial axial-symmetry, Finite element method (FEM) is used to analyze the behavior of pile-soil unit (also called "unit cell"), such as the distribution of the stress and deformation in reinforced regions and substratum. The law of load transfer between pile and soil is further revealed through the numerical analysis.3. Considering the longitudinal interaction between soil and single pile, theoretical solution for settlement of the unit cell is obtained. In order to make it convenient for engineering application, the variability of parameters on different work conditions is discussed. As a result, a simplified formula is derived.4. The effects of pile group are analyzed with the plane strain FEM, the results of which show great consistency with the monitoring data. Thus, conclusion is drawn that the predicted settlement of ground surface is reasonable and correct. The future settlement also meets the requirement of the project.5. A method to settlement of composite ground has been put forward. The key point is that the additional stress field should be obtained by applying both Mindlin solution and Boussinesq solution. By calculating the real project, it is proved that the method has good precision and can be widely used in foundation engineering.