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

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 Q_t, sleeve friction F_r and pore pressure ratio B_q, together with the undrained shear strength S_u, normalised by shear modulus G and in situ effective stress, σ′_v0. For plausible ranges of S_u/σ′_v0 and G/S_u, the lower bound for transition from partial drainage is defined by the uCPT metric products and ratios of B_qQ_t = 1·2, Q_tF_r = 0·3, and B_q/F_r = 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 K_D is defined independently in terms of cone metrics as K_D = 1/B_qQ_t (with B_qQ_t < 1·2), enabling permeability to be recovered during standard penetration for K > 10⁻⁵ m/s. Where undrained data are excluded, non-dimensional permeability K_D is optimally defined as K_D = 0·62/(B_qQ_t)^1·6.