The Research On Settlement Of Two-dimensional Reinforced Composite Foundation

In recent years, with the development of the freeway construction, the treatment of soft soil foundation becomes increasingly important, which triggers the development of various soft foundation treatment technologies. The double direction reinforced composite foundation method is a new soft foundation treatment technique. This new foundation treatment is widely applied for engineering constructions such as freeway subgrade improvement, filling in the back of the abutment strengthening and widening of existing roads with unfavorable geological conditions. However, the theory about double direction reinforced composite foundation remains immature. This paper researches on bearing characteristic of double direction reinforced composite ground, which includes pile-soil stress ratio, settlement and consolidation of this composite foundation from several aspects of theoretical analysis, numerical simulation and model experiment under the supports of High Technique Research and Development Program of China (863 program)——"The Treatment Technique of Double Diretion Reinforced Foundation Based on The Settlement Control for Large Area and Non-uniform Soft Soil Foundation in Highway Construction" (2006AA11Z104).At first, based on the fact that the composite modulus of composite foundation is a key parameter in settlement calculations, but it is hard to obtain precise solutions that are completely conformed to reality. the composite modulus of gravel pile composite foundation and its disadvantages were calculated based on the discussion of the existing method, the calculation formula of the limit value of the composite modulus is obtained, applying the minimum potential energy principle and the principle of minimum complementary energy, and the gravel pile composite foundation is treated as a composite material composed by pile and soil in this process in order to avoid the analysis of complex interaction between piles and soil. Moreover, several factors which affect the limit value of the composite modulus such as compression modulus of pile and soil, Poisons's ratio of soil, replacement ratio were analyzed.Based on the virtual work theory and the Winkler elastic foundation model, considering non-linear deformation of sheet and net materials and composite foundation cushions as an overall net pad as well as taking the role of the level of resistance into account in the calculation, a formula for calculating the settlement of two-direction reinforced composite foundation was deduced in this paper. The deduced formula reflects the effects of load magnitude, the replacement ratio of composite foundation, rig ties of mattress and the surrounding soil, pile-soil stress ratio and etc. Besides, four groups model tests of composite foundation are designed and a large amount of data about the load-settlement, pile-soil stress ratio are obtained.Finally, four comparative model tests including "soft soil foundation model test" "gravel pile composite foundation model test" and "multi-layer geosynthetic+gravel pile composite foundation model test" were designed and carried out under the guidance of similarity theory and similarity criterions. The test results showed that, the multi-layer geosynthetic-reinforced can diffuse and homogenize upper load, the non-uniform settlement was also reduced effectively. The double direction reinforced composite foundation formed by multi-layer geosynthetic-reinforced and gravel pile composite foundation can be used to enhance the bearing capacity of the foundation and reduce its total and non-uniform settlements effectively, the lateral deformation of the embankment was restricted. The multi-layer geosynthetic-reinforced and gravel pile constituted a perfection draining system, which was propitious to drainage consolidation of soil around piles. The theoretical results of the settlement coincide with the results from tests.