Log-Log Method for Determination of Preconsolidation Pressure

A new method called the “log-log method” has been proposed for a more accurate determination of preconsolidation pressure. The method consists of plotting both the pressure p and corresponding void ratio e in logarithmic scale. The log e - log p plots result in two distinct straight lines. Series of conventional consolidation tests were carried out on saturated specimens of five different soils with a wide range of physical properties, keeping the initial water contents equal to their respective liquid limits. In order to have a preknowledge of the preconsolidation pressure, specimens were loaded to certain selected sustained pressures, unloaded to seating pressure, and then reloaded to the full extent. It has been found that the proposed method can predict the preconsolidation pressure accurately. The results given by the log-log method were then compared with those given by conventional Casagrande method, and it was found that the new method gave values closer to the chosen sustained pressures, assumed as the real pc values for the purpose of comparison. Specimens subjected to specified pressures with duration varying from 2 to 90 days showed the presence of quasi-preconsolidation pressure increasing with duration. The results show that the log-log method gives more consistent values for pc. The newly proposed method is devoid of human errors, consistent, simpler, safer, and faster.

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