ANALYTICAL CAVITY EXPANSION-CRITICAL STATE MODEL FOR PIEZOCONE DISSIPATION IN FINE-GRAINED SOILS

Susan E. Burns and Paul W. Mayne

ABSTRACT: After the arrest of cone penetration in clays and silts, excess porewater pressures decay with time until Du = 0 and hydrostatic conditions prevail. A dissipation model is developed and initial porewater pressures are formulated in terms of cavity expansion theory and critical-state components, indicating the derived coefficient of consolidation (c_h) is a function of stress history (OCR), effective friction (M), and rigidity index (I_r), as well as the probe diameter. Both OCR and I_r are assessed theoretically from the CPTu results. The governing rate of dissipation can be expressed by a second order differential equation and solved explicitly in closed-form. The framework is unique in that both monotonic decay and dilatory response (initial increase and then decrease of Du with time) are handled by the approach. The model results show good comparison with laboratory data, as well other currently accepted methods of c_h determination.

Key words: clays, cone penetration, consolidation, dilatory, dissipation, in-situ, permeability, pore pressures (IGC: C3/F4)