Limits in determining permeability from on-the-fly uCPT sounding

Abstract

Limits are defined for the transition from partially drained to undrained penetration during uCPT testing. These limits prescribe the range of cone metrics for which coefficient of permeability magnitudes may be recovered from peak pore pressure data, on the fly. The transition from partially drained to undrained behaviour is defined through the traditional non-dimensional metrics of cone resistance Qt, sleeve friction Fr and pore pressure ratio Bq, together with the undrained shear strength Su, normalised by shear modulus G and in situ effective stress, σ′v0. For plausible ranges of Su/σ′v0 and G/Su, the lower bound for transition from partial drainage is defined by the uCPT metric products and ratios of BqQt = 1·2, QtFr = 0·3, and Bq/Fr = 4, with the first and last proving the best determinants of drainage condition. Standard (2 cm/s and 10 cm2 face area) uCPT data together with independently measured permeabilities identify the transition from partially drained to undrained conditions at permeability magnitudes of the order of 10−5 m/s. These results are used to define limits of partial drainage where peak tip pore pressures may be used to recover in situ permeability profiles. For conditions of partial drainage, a non-dimensional permeability KD is defined independently in terms of cone metrics as KD = 1/BqQt (with BqQt < 1·2), enabling permeability to be recovered during standard penetration for K > 10−5 m/s. Where undrained data are excluded, non-dimensional permeability KD is optimally defined as KD = 0·62/(BqQt)1·6.