Free fall impact penetration tests on soils

The hydrosphere which is still the unexplored frontier of our planet is receiving the special attention of scientists and engineers because of its vast potential. A comprehensive knowledge of the properties of marine sediments is essential for most engineering activities in the oceans. A free fall penetrometer designed and developed at Memorial University is a potential tool for a quick and economic evaluation of the geotechnical properties of the top few metres of surficial ocean sediments. -- In addition to measuring the cone resistance and sleeve friction, the deceleration is measured by an accelerometer mounted within the penetrometer. These quantities are then used for correlating the shear strength of the soil at different depths of penetration. Laboratory experiments were conducted with two types of soil targets. -- Test results show that an increase in soil strength and roughness of the penetrometer cone material would cause a substantial increase in cone resistance and decrease in maximum penetration depth. Cone angles and weight per unit area of the penetrometer have also significant influence on the cone resistance and penetration depth. The effect of all these parameters on penetration behavior are discussed. -- The mode of soil failure at low velocity penetration was assumed to be similar to a conventional quasi-static case as proposed by Meyerhof (1961). It was observed that results of free fall penetration tests showed a greater penetration resistance, compared to the standard quasi-static tests. However, when the results were translated into computation of the angle of shear resistance, the difference was insignificant. For cohesive soils penetration resistance is dependent on the penetration velocity. ‘Strain-rate effect’ was found to influence the results. ‘Static’ strength for clays from ‘dynamic’ strength profiles can, however, be obtained taking the ‘strain-rate effect’ into account.