Study On Pile-Soil Stress Ratio Of Bi-Axially Reinforced Composite Foundation

The composite foundation method has been extensively used at home and abroad in the past decades. The bi-axially reinforced composite foundation method has been more applied in ground treatment, but the mechanism and design theory has seldom studied. This thesis deals with the pile-soil stress ratio of bi-axially reinforced composite foundation (pile-supported geosynthetics-reinfoeced embankment).Firstly, the stresses of geogrid in pile-supported geogrid-reinforced composite foundation were analyzed. The geogrid covering four piles was taken as a simple model, the constituent of stresses was discussed and the analytic solution of geogrid stress was obtained. The influence of all parameters on geogrid stresses was investigated. The following conclusions were drawn: the stresses of geogrid increase when the values of tensile strength of geogrid E_g, the maximum settlement S_m, unit weight of embankment soilγ, the equalivent height of embankment H increase, decrease when the pile spacing l increases, and some suggestions were made.Secondly, the pile-soil stress ratio had been studied. The composite soil mass within the influence scope of single pile was taken as a simple model, and the assumption that the geosynthetics above the soil between piles deformed as a paraboloid after the loading of the overlying soil was made. After taking the action of the geosynthetics to the pile top into account, by establishing the global equilibrium equation, the analytic solution of the pile-soil stress ratio of pile-supported geosynthetics-reinforced composite foundation was obtained. The influence of all parameters on the pile-soil stress ratio was analyzed, and the following conclusions had been drawn: the pile-soil stress ratio increases when the pile spacing l , the maximum settlement S_m, the equalivent height of embankment H , unit weight of embankment soilγincrease, and decreases when the radius of pile r , efficiency factor of soil between pilesλ, the standard value of bearing capacity of ground f_sk increase. Finally, based on the measured data in the practical project, the analytic solution of pile-soil stress ratio was validated, and the ranges of the coefficientαin the formula were recommended according to the two different cases, large and small pile spacing, respectively.The results in this thesis can be valuable reference for the research and application of bi-axially reinforced composite foundation method.