Engineering Characteristics of Loose Silts and Impact on Foundation Design

Silt deposits provide the geotechnical engineer with a challenge by being at the borderline between cohesive clays and cohesionless sands for which separate design methodologies are established. Special care must be taken during the planning and exploration phase of the foundation investigation to obtain samples which have not been disturbed and to follow through with appropriate laboratory testing. Loose silts when combined with high water tables or pore pressures can behave like quicksand; slight disturbances triggered by vibrations and dewatering may result in flowing ground, piping into excavations and drilled shafts, or rapid settlement of embankments. Adequate description of silts requires notation of special properties including apparent cohesion, dilatancy, sensitivity, and the presence of organics or weak cementing agents. The geology of silt deposits should be considered to extend the understanding of the layering, possible age, compaction, diagenesis, and susceptibility of the deposit to liquefaction.