Theory of partially drained piezometer insertion

A theory is presented to evaluate pore pressures developed as a result of insertion of an open-tipped standpipe into a saturated porous medium. An integral method is used whereby the advancing tip is represented as a moving point dislocation. Dimensionless standpipe pressure, [Formula Presents], is uniquely controlled in dimensionless time, t_D, by dimensionless penetration rate, U_D/E_D, and the modulus ratio, E_D(R₂/R₁)². The time lag to pressure buildup is controlled by the magnitude of the ratio of penetration rate, U, to consolidation coefficient, c, as embodied in U_D/E_D. The magnitude of the pressure differential between a closed-tip piezocone and the open standpipe piezometer is exacerbated as the parameter E_D(R₂/R₁)² is increased, reflecting the volume compressibility of the measuring system. At low relative penetration rates, the steady pore pressure response within the standpipe is subhydrostatic as fluid response is controlled primarily by the in situ hydrostatic pressure distribution with minimal contribution from generated pore pressures. As dimensionless penetration rate U_D/E_D is increased, the standpipe response becomes greater than hydrostatic, indicating the influence of high drivage-induced tip pore pressures on overall behavior.