Interpretation of Field-Measured and Simulated Non-Monotonic CPTu Dissipation Tests: Fid-Bau Portal

Interpretation of Field-Measured and Simulated Non-Monotonic CPTu Dissipation Tests

Huffman, Andrew P. E. / Moug, Diane M.

The piezocone penetration test (CPTu) is a commonly used method for geotechnical and environmental engineering site investigation. CPTu dissipation tests, which can be classified as monotonic or non-monotonic depending on the type of pore pressure dissipation they exhibit, provide data from which a soil’s coefficient of consolidation and hydraulic conductivity can be estimated. However, there remain limitations in interpreting CPTu dissipation tests—e.g., simplification to a one-dimensional problem, or applying methods developed for monotonic tests to analyze non-monotonic data—that affect characterization of interpreted soil properties. To examine the performance of interpretation methods and limitations of their assumptions, CPTu dissipation responses at the cone shoulder position (u₂) from field-measured and numerically simulated dissipation tests are analyzed and interpreted, according to four published methods. Numerical simulations of u₂ dissipation tests were performed with a direct axisymmetric penetration model and the MIT-S1 constitutive model for a range of overconsolidation ratios and hydraulic conductivity anisotropies. Interpreted values from each of the applied methods are compared for both field-measured and simulated data. Additionally, the performance of these methods in interpreting assigned model properties from numerically simulated data is examined. This study investigates two factors that affect interpretation of coefficient of consolidation from u₂ dissipation tests: non-monotonicity and two-dimensional pore pressure migration (radial and vertical). The results indicate that two-dimensional pore pressure migration contributes to CPTu dissipation, which is inconsistent with most interpretation methods’ assumption that vertical pore pressure migration is negligible, and that non-monotonic dissipation behavior is affected by vertical pore pressure migration. Additionally, the results indicate that non-monotonicity in dissipation responses negatively affects interpretation of assigned properties.