Numerical modelling of small-scale geogrid encased sand column tests

The use of stone columns as a ground improvement technique in soft cohesive soils is increasingly being extended to sites with poorer conditions. This is being achieved with the use of geosynthetic reinforcement which acts to provide additional lateral support to columns, preventing excessive bulging and column failure. Although the use of geotextile encasement has been investigated and implemented on numerous projects throughout Europe, research into the complex reinforced behaviour is ongoing. In addition, the concept of using other geosynthetic materials such as geogrid for column encasement is relatively new. In order to investigate the effect of geogrid encasement on stone columns, small-scale laboratory testing of model sand columns was undertaken. In conjunction with this, a numerical modelling study was undertaken to further understand the interaction between the geogrid, column material and surrounding soil. Particular emphasis was placed on comparing the behaviour of partially encased columns to fully encased columns. This paper describes the finite element modelling that was undertaken to replicate model sand column behaviour and predict the performance of further laboratory testing. Results of the numerical study indicate good correlation with the observed behaviour in laboratory tests.