The Research Work About The Bearing Capacity And Deformation Characteristic Of Two-layered Ground

The practical value of the crust in engineering has been paid attention to by engineers so long ago. But unfortunately, because of not grasping the spirit of the crust overlying soft ground, lacking credible basis and being affected by the traditional ideas, engineers treat the ground as pure soft soil with the methods such as "drainage by consolidation". Using a lot of money, it makes the curst destroyed, and the settlement of the ground still happens when it has been put to use. Instead of expanding such large amount of money without any return, people are eager for making full use of the crust. The research work to understand the bearing capacity and deformation characteristic of the curst has become the essential point in the study of soft ground, while finding the reasonable methods to use the crust is also on the agenda of the investigation.The overlying crust has two kinds of effects on soft soil below. The crust under the load has stress dispersion effect, while the crust outside the area of the load has closure effect. The following research work has been done on the bearing capacity and deformation characteristic of the curst with such two effects:1. Orthogonal experimental method has been used to design the indoor model test, whose main aim is to find out important factors about the bearing capacity of the foundation. The thickness of the crust overlying soft mucky soil stands below one fourth of the loading's width. The Chinese code for design of building foundation (GB50007-2002) doesn't consider the stress dispersion effect of the crust in such condition. The result of the model test provides suggestions to design and make full use of the crust as reference ideas.2. Because being limited by current experimental condition, the horizontal and vertical stress of one point in ground couldn't be measured at once. It makes difficulty for the further analysis of the closure effect. PFC software is used as a tool to establish mechanical model for the analysis of stress distribution in soft soil in elastic stage considering the closure effect. 3. Based on the analysis of stress distribution in soft soil in elastic stage, the thesis uses stress path method to clarify the way in which the closure effect affects the critical edge pressure and deformation characteristic of the two-layered ground. And the critical edge pressure formula of soft clay foundation involving the two effects is derived. At the same time, it is pointed out that the conventional elastic mechanics theory couldn't consider the closure effect of the dry curst.4. Inspired by the results of the model test and field test which show that the semi-logarithm relationship between settlement and load is made up in the form of two linear parts, one dimensional consolidation model with constitutive model in the form of fold beelines is built up. This model is based on Terzaghi's one dimensional consolidation theory, and is treated as an empirical model to predict the settlement of the two-layered ground in two-dimensional condition. The model's ability to predict is tested by three field examples.