Coefficient of consolidation from the linear segment of the t1/2 curve

Abstract

The coefficient of consolidation is commonly determined by fitting the Terzaghi theoretical time factor, T, versus average degree of consolidation, U, relationship to the measured oedometer consolidation curve. A simplified version of the Taylor t1/2 method is proposed in this paper. Since the theoretical T1/2 versus U relationship is linear up to 60% consolidation, the measured t1/2 consolidation curve may also present a linear segment that ends at 60% consolidation. Samples of 10 natural soft clays with liquid limits ranging from 40 to 152% were used to carry out conventional oedometer tests with consolidation increments in the recompression range, spanning the preconsolidation pressure, and in the compression range. Based on the oedometer test results, the effects of secondary compression on the shape of the t1/2 consolidation curve are evaluated and found limited between 60% and 90% consolidation. In the proposed simplified t1/2 method, the time of 60% consolidation is recognized from the lower end of the linear segment and is used together with the Terzaghi theoretical time factor of 0.286 and the maximum drainage distance of the oedometer specimen to determine the coefficient of consolidation. A large amount of the oedometer coefficient of consolidation data obtained from the simplified t1/2 method are in good agreement with those from the Taylor t1/2 method and are within one to two times those from the Casagrande logarithm of t method.Key words: laboratory tests, coefficient of consolidation, curve fitting method, settlement.