Showing papers by "T. G. Sitharam published in 2005"

Model studies of a circular footing supported on geocell-reinforced clay

Abstract: The potential benefits of geocell reinforcement in soft clay foundations have been studied by a series of laboratory-scale static load tests on a rigid circular footing placed on a fill surface. Parameters of the test program include depth of placement of the geocell layer, width and height of the geocell layer, and influence of an additional layer of planar geogrid at the base of the geocell mattress. With the provision of geocell reinforcement, the load-carrying capacity of the soft clay foundation can be improved by a factor of up to 4.8 times that of the unreinforced soil. Heaving of the soil can be reduced substantially by providing geocell reinforcement of sufficient height and width. Further improvement in performance could be obtained with the provision of an additional layer of planar geogrid at the base of the geocell mattress.

Behavior of Embedded Footings Supported on Geogrid Cell Reinforced Foundation Beds

Abstract: 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.

Seismic hazard studies using geotechnical borehole data and gis

Abstract: Seismic Hazard Analyses of Bangalore city has been done based on the local soil conditions using a geotechnical data. Seismic hazard analyses parameters are evaluated in terms of amplification rating, peak ground acceleration and factor of safety against liquefaction by considering hypothetical earthquake. Amplification rating is done based on soil profiles by using Finn (1991) recommendation. The peak horizontal ground acceleration in Bangalore is predicted using Boore. et. al (1994). The theoretical PGA curve was developed using different methods by considering Ramanagara fault, which is about 48Km away from Bangalore. The factor of safety against liquefaction was determined using Seed and Idriss (1983) simplified approach. The seismic hazard maps for these three parameters have been prepared in 2-dimension by using AutoCAD and Geographic Information System (GIS), ARCINFO packages. The seismic hazard maps of amplification rating, peak horizontal ground acceleration and factor of safety against liquefaction by considering earthquake magnitude 6 and 7 in Richter scale have been prepared for Bangalore city. These seismic hazards maps are the first level microzonation maps for Bangalore city.