Effect Of Saturation On Dynamic Response Of Footings In Sand

This investigation was undertaken to determine the effect of saturation of dense sand on the response of square footings to nuclear blast-type loading. Tests were conducted with footings on the surface and at a depth of burial equal to the footing width with a water table coincident with the plane of the footing. The results of these tests were compared with data from similar tests on dry sand from a preceding study. Saturation of dense sand had the effect of reducing maximum displacement. The displacements of surface footings were only about 30 percent of the displacement of footings on dry sand with equivalent soil density and loading condition, and the displacement of shallow buried footings was reduced by 50 percent. Empirical load-displacement curves developed from previous studies on dry sand were shown to be conservative when used to predict the response of footings on saturated dense sand. The primary difference in response occurred after peak reaction. The footings on saturated dense sand came to rest immediately, while footings on dry sand continued to displace for some short distance. This behavior was attributed to the development of transient negative pore pressures resulting from dilation of the sand. A similar laboratory investigation on a medium-density sand is recommended in order to determine whether or not any tendency toward liquefaction may occur at the lower end of the range of densities of interest for protective structure foundations. (Author).