Effect of Confining Pressure, Relative Density and Shear Strain on the Poisson’s Ratio of Clean Sand

In comparison to other dynamic properties of soil, Poisson’s ratio is mostly considered as an elasti\ud c \ud constant. The effect of \ud different para\ud meters on the Poisson’s ratio of soil is neglected in most of the\ud available\ud literature. \ud Proper estimation of the Poisson’s ratio is required as it signifies the stress and \ud deformation characteristics of the soil. \ud In \ud this study a series of resonant column tests were performed to \ud determine the variation of Poisson’s ratio with confining pressure, relative density and shear strai\ud n. \ud Clean \ud sand free from fines content\ud was used in this study\ud . The tests were performed on sa\ud nd sample of \ud size 50 \ud \ud 100 mm compacted at relative densities \ud of \ud 30%, 50% and 75\ud %. \ud The sample preparation \ud was\ud done\ud by \ud using a split mold. \ud B\ud y using a funnel\ud ,\ud t\ud he sand \ud was\ud gently poured into the split mold. Then each \ud layer \ud was\ud compac\ud ted by means of a tamping rod which weighs 150\ud g. The sample preparation \ud was\ud done \ud in 5 equal thick layers. By \ud performing\ud few trial sample pre\ud parations\ud , the number of blows required per \ud layer for a desired relative density \ud was\ud determined. \ud A fixed free type \ud of resonant column was used in this \ud study\ud . By performing the resonant column test in torsional mode as well as flexural mode of excitation\ud , it\ud is possible to estimate the Poisson’s ratio of the soil. The confining pressure \ud was\ud varied from 100 kPa to \ud 800 kP\ud a. The shear strain \ud vari\ud ed\ud from 10\ud -\ud 4\ud % to 10\ud -\ud 1\ud %. \ud Figure 1 gives the variation of Poisson’s ratio with confining pressure for various relative densiti\ud es. From \ud the figure i\ud t is observed that there is \ud a \ud continuous decrease in Poisson’s ratio of the soil wit\ud h \ud an \ud increase \ud in\ud the\ud confining pressure as well as relative density. The percentage reduction in Poisson’s ratio obtained\ud for the soil subjected to a confining pressure of 800 kPa as compared to soil subjected to 100 kPa \ud confining pressure is \ud 19 %, 21 % an\ud d 22\ud % for 30 %, 50 %, 75 % relative densities of the soil.\ud In addition,\ud the percentage\ud s\ud reduction in Poisson’s ratio of sand prepared at 75 %\ud relative density\ud as compare \ud to \ud 30 % \ud relative density \ud are\ud 14 %, 15.7 %, 16.7 % and 17.6 % \ud for sand subjected to 100\ud kPa, 400 kPa, 60\ud 0 kPa \ud and 800 kPa respectively\ud . It \ud can be concluded \ud that the percentage reduction in Poisson’s ratio increases \ud with the increase in confining pressure as well as relative density