Cyclic Undrained Behavior of Nonplastic and Low Plasticity Silts

Keywords: Geotechnology, Soil Liquefaction, Clay Silts, Fine Grained Soils, Non-Plastic Silts, Foundations, Dynamic Soil Properties, Low Plasticity Silts, and Pore Pressure.

Abstract: This report describes dynamic testing carried out on plastic and non-plastic silts. The plastic silt was prepared by mixing nonplastic silt with controlled amounts of Kaolin clay. Testing was carried out using a quasi-static resonant column/torsional shear device, capable of measuring dynamic properties over a wide range of strain amplitudes. The main parameters investigated were the effects of cyclic shear strain amplitude on the potential for pore pressure generation, and the variation of shear modulus and damping ratio for different specimen plasticities. Results showed that the general dynamic response of the silts was similar to that of sands. In particular, pore pressure generation response with varying strain level resembled closely that of a sand of similar relative density. This indicates that silt, despite having a grain size distribution outside the generally accepted boundaries for soils susceptible to liquefaction, has a potential for liquefaction very similar to that of sand. Increasing plasticity was found to reduce the silt's level of pore pressure response. This reduction, however, was not significant for plasticity indices of 5 or less.