Numerical investigation of piezocone dissipation tests in clay: Sensitivity of interpreted coefficient of consolidation to rigidity index selection

Standard methods for interpreting the coefficient of consolidation (ch) from CPTu dissipation tests require an estimation of the soil’s rigidity index (Ir=G/su). For the Teh & Houlsby numerically derived dissipation solution, the values of shear modulus (G) and undrained shear strength (su) were straight forward to specify due to the use of the elastic-perfectly plastic Von-Mises soil constitutive model. However, estimation of appropriate G and su values is not as straight forward for field dissipation tests. The objective of this study is to examine the sensitivity of the interpreted ch to various approaches for estimating Ir. The study is performed with an axisymmetric direct cone penetration model to simulate piezocone dissipation. Simulations are performed with the MIT-S1 constitutive model calibrated for Boston blue clay behavior. Analyses examine how the sensitivity changes for normally to lightly overconsolidated clay, and slightly to strongly anisotropic hydraulic conductivities. The results indicate that ch interpretation is not highly sensitive to Ir estimation when Ir is within standard values for clay; however, the sensitivity appears to increase as the overconsolidation ratio increases.

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