Monotonic and dilatory pore-pressure decay during piezocone tests in clay

During a pause in cone penetration in fine-grained soils, pore-water pressu re dissipation tests are performed to evaluate the coefficient of consolida tion. For standard piezocones with shoulder filter elements, soft clays and silts show a monotonically decreasing response with time; however, dissipa tion tests performed in heavily overconsolidated silts and clays show dilat ory behavior, with the pore-pressure behavior increasing from the initial m easured value to a maximum, and then decreasing to hydrostatic values. This paper presents a theoretical framework which combines cavity-expansion the ory and critical-state soil mechanics with an analytical solution to the ra dial consolidation equation. The method is able to describe the pore-pressu re response curve for dissipation tests performed in soils which demonstrat e either monotonically decreasing or dilatory pore-pressure behavior.