ANALYSIS OF PIEZOCONE DISSIPATION DATA USING DISLOCATION METHODS

The theory of a moving point dislocation is applied to the rational determination of permeability and consolidation coefficients from piezocone-sounding data. Motion of the process zone in following the penetrometer tip is shown to result in important differences in behavior between static and undrained analogs to penetration. A distinction is drawn between pressure buildup and postarrest dissipation behaviors recorded both at the tip and along the shaft. Tip pressures are shown to become steady within approximately 1 s following drivage initiation at a standard rate of 2 cm/s. Shaft pressures within 10 radii of the tip equilibrate within 10 s. Postarrest pressure dissipation at the tip enables consolidation coefficient, c, to be determined independently. Nonuniqueness in pressure-dissipation response along the shaft is shown to preclude independent determination of consolidation behavior for consolidation coefficients less than about 20 cm2/s, under standard penetration. Hydraulic conductivities, k, are directly evaluated from induced pore pressure magnitudes recorded either at the tip or along the shaft, given a priori knowledge of consolidation coefficient, c. Piezocone-derived magnitudes of consolidation coefficient enable conductivities to be determined independently of laboratory or material-specific empirical determinations. Relationships are developed for net cone end bearing (q(n)) as a linear function of elastic parameters and for pore pressure ratio (B(q)). Pore pressure ratio is shown to be an insensitive index in low c soils. Results from well-documented field investigations in both normally consolidated and overconsolidated materials are used to independently establish the applicability of the proposed parameter determination techniques. Satisfactory correspondence is obtained.