The Research Of The Reinforced Composite Subgrade Under The Strip Foundations

Because the soft soil has a lot of characterisitics such as the low strength, high deformability and low permeability, the soft grounds have to be treated with some kind of method so as to improve their engineering properties to meet the standard of constraction. Earth reinforcement, which may be defined as the inclusion of resistant element in a soil mass to improve its mechanical properties, has been greatly increased in use. It is so well suited to the needs of high way construction or reconstruction of embankment, and probably one of its most useful applications is for retaining walls.Sand is the premier to select and has been used in most reinforced earth engineering by reason of its high permeability and making greater friction. So, in this paper, the characterisitics of sand is introduced; the interaction characteristics of sand and geogrid are summarized.In the paper, the author sums up the main calculation methods of reinforced earth structure, and points out the disadvantages of methods in being and advantages of FEM. It also introduces the design theories and methods of the reinforced earth composite foundation in the meantime.In the paper, the finite element analysis software ANSYS is used to analyse the foundations with the different loads that one is only sand blanket , another is three layer Geogrid reinforced sand blankets . The results of displacement, stress and reinforcement tension and so on are analyzed . All the results show : (1) the main function of the reinforced sand blankets reduce the lateral deformation of the foundations and the shallow layer soft grounds, the restraint of vertical settlement is not obvious. (2)Because the work of stress diffusivity, reinforced sand blankets reduce the differential settlement on the bottom of the foundations. (3)The reinforced sand blankets can availably reduce shearing expansion . (4)It's availability to reduce vertical stress on the boundary between the blankets and the soft subsoil, it can make vertical stress level off degree.The method of FEM can not only meet force equilibrium, but also can take into account the relationship of stress and strain, the reciprocity of the filling and geogrid, besides, it can get the distribution of stress and strain under load. This paper analyzed the reinforcement effect and the reinforcement mechanism, which provids some reference values for design calculations and further research.