Assessment of the coefficient of consolidation with Queensland data

Established relationships between the coefficient of consolidation (cv) and index tests are used during both preliminary design and as a cross check during detailed design. The laboratory oedometer test provides compressibility parameters and a lower bound of cv, while the coefficients of consolidation are preferred from the field dissipation tests. However, cv is dependent on the method used to determine its value, stress level, and over-consolidation ratio. In practice, the coefficient of consolidation values obtained from dissipation tests are used to predict settlement time, while oedometer tests are useful in obtaining the parameter required to predict the magnitude of settlement. However, dissipation tests measure the horizontal coefficient of consolidation (ch) which needs to be related back to the vertical value. These standard approaches are discussed using test data from Queensland sites. Inconsistencies in correlations are used to show that design should consider the wide variability in interpretations that can occur, and correlations of cv with index tests should not be used in detailed design. Additionally, the cv values obtained from oedometer testing is a poor predictor of time for consolidation. This could also be due to the size of samples being not large enough for the soil structure. Monitoring data from construction sites are used to assess a “moderately” conservative design value from dissipation and lab tests.