UC Davis

The effects of soil plasticity and penetration rate on cone penetration resistance in low-plasticity fine-grained soils are evaluated. A series of centrifuge tests with in-flight variable rate cone penetration soundings was performed on models of four slurry deposited mixtures of nonplastic silica silt and kaolin clay (0%, 2.5%, 5%, and 20% kaolin by dry mass) with plasticity indices ranging from 0 to 6. Cone penetration resistances for an effective overburden stress of 100 kPa ranged from 26 to 40 MPa (260 to 400 atm) in the nonplastic silica silt to 0.4-1.8 MPa (4-18 atm) in the silt-clay mixture with a plasticity index of 6. The addition of a small amount of clay (as little as 2.5% by dry mass) to nonplastic silt resulted in an order of magnitude decrease in drained penetration resistance. Faster penetration rates produced partially drained and undrained conditions, with negative excess pore pressures developing in the nonplastic silica silt and positive excess pore pressures developing in the mixtures with 5% and 20% kaolin.