Mechanical behaviour of silty soils of the Venice lagoon as a function of their grading characteristics

The main feature of the shallowest quaternary basin of the worldwide known historic city of Venice, Italy and its surrounding lagoon is the presence, apparently without any regular trend in depth and site, of a predominant silt fraction. This is always combined with clay and/or sand, forming a chaotic and erratic interbedding of different sediments, whose mineralogy is however variable in a relatively narrow range due to a unique geological origin and a common depositional environment. After a brief description of the basic soil indexes of the Venice lagoon soil, the present study, based on a comprehensive geotechnical laboratory investigation, describes the range of variation of the most relevant time-independent geotechnical properties. Moreover, a new grain size index, combining the geometrical characteristics of the particle distribution, is introduced. It is shown that the soil response at large and very small strains can be related to this grain size index, that appears to be able include the influence of the soil grading on the description of the overall mechanical behavior.