A piezocone dissipation test interpretation method for hydraulic conductivity of soft clays

An alternative approach is developed in order to estimate the hydraulic conductivity of soft fine grained soils, based on numerical simulation of the full penetration and dissipation process for piezocones. Unlike previous methods of analysis, the process of penetration and dissipation has been explicitly simulated, thus eliminating several of the simplifications inherent in existing interpretation methods such as geometric approximations, predefined stress fields or neglecting material compressibility. The presented method is not established upon a particular set of data leading to limited applicability, but is rather developed using a more general approach and can be extended to other datasets if intended. Given the time to 50% consolidation and a number of influencing soil parameters, a single estimate of the soil horizontal permeability can be obtained via a single-run piezocone sounding using pore pressure measurements taken at the shoulder filter element (u2) located immediately behind the cone.The proposed interpretation method embodies many of the key parameters (namely the soil shear strength, soil rigidity, and soil confining stresses) likely to influence the soil behaviour and thus the parameter to be interpreted. Numerical analyses demonstrated that the rate of dissipation increases as the soil rigidity or the soil confining pressure increases, which is a consequence of higher excess pore pressure gradient at higher depths or at larger rigidities. The method, which involves a new excess pore pressure normalisation technique, is applicable to both monotonic and dilative dissipation data. The proposed interpretation method is compared to a series of experimental data including two recent field tests. Although the method was calibrated against only a select few cases, its applicability to a wide range of clayey soils was verified.