Study On Multiscale Mechanical Analysis Method Of Stone-column Composite Foundations

Previous studies on stone column composite foundations have been usually concerned with few columns,which is far from realities for a big engineering site with a large number of columns.The mechanical properties and the multiscale analysis method of stone column composite foundations were studied.Centrifuge model tests were conducted to analyze the bearing and deformation behaviors of composite foundations in terms of macro responses,local properties and column-soil interactions.Accordingly,the multiscale analyzing method was developed and a novel method of parameter equivalence was proposed,which provided a new approach to the engineering practices.The main conclusions and new findings are as follows:1.The stone column composite foundations were analyzed on the basis of centrifuge model tests and corresponding FEM simulations.The quantitative range of bulging of group columns was given,i.e.bulging was found within the depth of 6 times the column diameter.The corresponding relationship of the deformation development and the bearing load was indicated,and the association relationship of column-soil interaction and bulging deformation was revealed.It was concluded that the bearing load increased as the settlement of the soil surface increased,and the bearing curves were nonlinear with no obvious peaks.The bearing behaviors of the composite foundation were closely associated with the bulging deformation.If the bearing load increased linearly as the settlement increased,the deformation localization was relatively small.However,deformation localization became more obvious as the bearing load increased nonlinearly.According to the distribution of column-soil stress ratio,the composite foundation was divided into a bulging deformation zone and a uniform deformation zone.2.The multiscale analyzing method was developed.On the basis of Asymptotic Expansion Method and Finite Element Method,a parallel multiscale analyzing system was developed on Abaqus software platform.The effectiveness of the developed system was validated by the results of the centrifuge model test of a loaded embankment and the corresponding fine-mesh FEM simulation.The column-soil interaction and anisotropy can be considered by the multiscale method.3.A novel method of parameter equivalence was proposed.The relationship of the equivalent elastic moduli of the representative volume element and the column-soil modulus ratio was analyzed by the multiscale method.Meanwhile,the relationship of the equivalent moduli and the area replacement ratio was received.Accordingly,a generalized form and the Duncan-Chang E-? form equivalence methods were deduced.The approximate expressions of the column-soil stress ratio were put forward.The effectiveness of the novel equivalence method was verified by the comparisons with the multiscale method.The anisotropy was reasonably considered by the novel method.The equivalent moduli by the traditional method were overestimated and only an isotropic homogenized modulus can be received.4.By employing the developed multiscale method and the method of parameter equivalence,the important projects of the box foundation and the rock-fill dam on stone column reinforced composite foundations were analyzed.The bearing capacity of the foundations reinforced by the stone columns was increased and the settlement was reduced.