Volume 28, Issue 5 (September 2005)
Behavior of Embedded Footings Supported on Geogrid Cell Reinforced Foundation Beds
The results from laboratory model tests on an embedded circular footing supported on geogrid cell reinforced foundation beds are presented. The embedment depth of the footing (depth of placement of the footing with respect to the fill surface) was varied from zero to 0.6 times the footing width with foundation beds made of dry sand and saturated silty clay. The cellular mattress was prepared using a biaxial polymer geogrid, called a “Geogrid cell.” The various parameters studied in this testing program include the depth of placement of cellular mattress below the footing base, width, and height of the cellular mattress. The load carrying capacity of the geogrid-cell reinforced sand beds have improved up to about 9.5 times with increase in the embedment depth of foundation as against 6.5 times for surface footings. In case of cellular reinforced soft clay beds, a fourfold increase in the performance of the surface footing is observed against unreinforced bed, and it increases up to 5.5 with the footing embedment depth. In case of sand beds, the increased performance of the footing is observed with increase in footing settlement. In case of clay beds a sharp decrease in performance improvement of the footing at around 15 % of the footing settlement is observed at all embedment depths. The effect of embedment depth of footing becomes marginal in case of sand beds when compared with clay beds at higher embedment depths. The sand bed was instrumented with earth pressure cells, and strain gages were mounted on a strip of geogrid that was placed below the cellular mattress. The earth pressure cells embedded in the subgrade soil show that with insertion of the cellular mattress, the footing pressure is distributed more uniformly over a wider area with footing embedment depth. The strain measurements also show a fairly uniform strain in geogrid strip under footing contact pressure.