Research On Composite Foundation Of Lime Cushion And Seepage Control Membrane In Collapsible Loess Areas

Collapsible loess is widespread in China, especially in Northwest of China, where the loess is integral, well-grown, complete, and thick. Collapsible loess whose thickness is greater than10meters is distributed widely in east and west of Gansu Province. The loess where the foundation located has higher grade of collapsibility, usually grade Ⅲ or Ⅳ. It constrains the development of economy in Gansu seriously. At the same time, it is a great threat for the foundation of transformer substation which locate in the district of Gansu collapsible loess. Solutions of general collapsible loess foundation have some limitations when dealing with heavy thick collapsible loess transformer substation. Usually, it can damage the bearing characteristics of natural loess in different degrees. However, cost of the project will get higher, and construction will be more complex and the foundation will have lower reliability. In addition, owing to the influence of objective factors, methods of lime soil cushion or compaction are used mainly to eliminate the collapsibility of the loess. Therefore, in this paper, research about composite foundation of lime soil cushion and seepage control membrane has been developed to solve the collapsible loess problem in Gansu. It aims to provide some theoretical and practical reference for the construction and design of transformer substations that lie in these areas in Gansu. The specific contents are as follows:(1) Based on the present research, the characteristics, mechanism, influence factors of the collapsible loess, and the application of seepage control membrane and composite foundation are analyzed. Compared with the advantage of lime soil cushion and seepage control membrane, a new method which combines lime soil cushion and seepage control membrane has been presented.(2) By analyzing finite difference software calculation principle, on the basis of one specific static load test and FLAC3D simulation, the bearing and stress-strain characteristics of lime soil cushion are analyzed.(3) Using finite difference software, the mechanism of collapsible loess reinforced by seepage control membrane and its stress-strain characteristics are discussed. In addition, its function and application has also been analyzed and evaluated, and the feasibility evaluation is provided.(4) Finally, the feasibility and range of application of lime soil cushion and seepage control membrane composite foundation treatment method has been discussed, and the results shows that when E1/E2≤3, the characteristic of compound foundation is gentle, and the reinforcement effect is not obvious, and when3<E1/E2<10, the characteristic is transitional, while E1、E2≥10, the characteristic is sensitive, and the reinforcement effect is significant. Lastly, the characteristics of stress-strain and bearing of composite foundation in the collapsible loess area are discussed, and the influencing factors, including the composite foundation matrix properties and the effect of enhanceosome, are also analyzed.