Mechanical And Deformation Performance Of Composite Foundation With Geosynthetics Encased Columns

Granular columns, such as stone columns and sand columns, are widely used to deal with soft and weak foundation for supporting flexible structures such as embankments and storage tanks. However, inpractice, bulging failure of the columns can occur due to a lack of lateral confinement. It makes Granular columns can be difficult to apply in soft soils with undrained shear strength of<15kPa. Using a geosynthetic which provides the desired lateral support for the granular materials to encase the columns, a new ground treatment technology, Geosynthetics Encased Column (GEC), was presented. Geosynthetics Encased Column extends the application scope and field of granular column. In addition, Geosynthetics Encased Columns can improve the bearing capacity, deformation capacity and integrity of the composite foundation, reduce construction time and costs. At home and abroad, it is applied widely and successfully in engineering area.As a new-style and effective ground treatment technology, the performance of the composite foundation with geosynthetics encased columns is recently a research highlight in the world. Now the research on theory, experiment and numerical analysis are still have some deficiencies. Deformation is important index to evaluate the performance of the composite foundation with geosynthetics encased columns. In this paper, we studied the deformation performance of the composite foundation with Geosynthetics Encased Columns in detail from points as follows:(1) The static stair-cased loading tests for the unit cell model of the foundation with geosynthetic-encased stone column (GEC) and ordinary granular column (OGC) were carried out and also material parameters were given out in laboratory. The settlements, stresses of the column and soil at the top of the model and stresses of the geotextiles under different loadings were recorded. The results of experiment were also compared with results of existing elastic analytical solution to provide reference basis for further theoretical analysis.(2) The large scale triaxial tests for the unit cell model of the foundation with geosynthetic-encased stone column (GEC) and ordinary granular column (OGC) were carried out, and the results ware compared.(3) To develop a more reasonable calculation method for a GEC composite foundation, based on an axial symmetrical unit cell model, by assuming yielding occurs in columns while the surrounding soil and the geosynthetic remain elastic, this paper presents a more applicable analytical procedure under the equal strain conditions. Subsequently, parametric analyses based on the elastoplastic solution were carried out to study the effect of various factors on the performance of composite foundations with GECs.(4) To study the effect of various factors on the performance of composite foundations under the case of multi layered soil, a finite element model that consider the case of multi layered soil penetrated by GECs was built and the performance of the composite foundation with GECs was studied.(5) To consider the case that columns were partially encased, an improved elastoplastic analytical procedure for composite foundation with partially Encased Columns was presented. And the effect of the effect of the length of encasement on the performance of the composite foundation was studied.The innovation of this paper is that an elastoplastic analytical procedure for composite foundation with Geosynthetics Encased Columns was proposed and the effect of the length of encasement on the performance of the composite foundation was considered. In comparison with the existing analytical methods, this procedure was more close to actual situation and has a more widely application, thus providing a reliable theoretical basis to the design and construction of the composite foundation with Geosynthetics Encased Columns...