Rate effects in circular footing penetration in saturated sand

This study investigates rate effects in the penetration resistance of a circular footing into saturated sand using laboratory 1g and centrifuge tests. A model circular footing of 40 mm diameter was pushed at various penetration velocities
into fine silica sand saturated with either water or a highly viscous pore fluid. The highly viscous pore fluid, water with MethocelTM cellulose ether, with a dynamic viscosity of 480 mPa.s was used to reduce the Darcy permeability of the sand
sample in order to achieve partially drained and undrained conditions. The 1g model tests were conducted in sand with a relative density of 45% to provide appropriately scaled dilational properties as compared with those obtained from centrifuge tests at 50g in the same sand at a typical field relative density of 76%. The 1g test results showed an increasing penetration resistance with increasing penetration velocity as the response became increasingly undrained. The observed rate effects in the penetration resistance are captured using a backbone curve framework. However, comparison between the 1g and 50g
tests reveals difficulty in matching the response between the two stress levels, revealing uncertainty in existing stress scaling approaches.