Determination of the Coefficient of Consolidation Using the Inflection Point on the Pore Pressure Dissipation Curve

It can be shown that the theoretical plot of time factor (T-v) versus the degree of dissipation (U-ub) from Terzaghi's consolidation theory has an inflection point of maximum slope at 53.4% of dissipation progress. Using this characteristic feature, a method is proposed to determine the vertical coefficient of consolidation (c(v) ). The method requires identifying the inflection point on the semilogarithmic plot of excess pore water pressure versus time. The time corresponding to the inflection point was used to compute a free from the effects of initial and secondary compressions value of c(v) . Laboratory end-of-primary (EOP) tests with pore water pressure measurements were carried out on three remolded clays. The c(v) data obtained from the pore pressure inflection point method was in good agreement with those from the quasiconstant criterion and was systematically lower than those from methods using settlement data. Moreover, the time at EOP determined based on the settlement data was smaller than that specified by the pore pressure dissipation data. It has also been observed that some amount of consolidation degree happens within the period from the time at the EOP consolidation determined by the settlement-time curve to the time at the EOP consolidation identified by excess pore water pressure dissipation.