SOME OBSERVATIONS ON THE OEDOMETRIC CONSOLIDATION STRAIN RATE BEHAVIORS OF SATURATED CLAY

Abstract

Data obtained from laboratory incremental loading (IL) oedometer tests are evaluated to study the consolidation strain rate behaviors of saturated clay. Soil consolidation is a time-dependent volume change (compression) process induced by both dissipation of excess pore water pressure and reorientation of mineral grains. As most consolidation test setups are not equipped with pore water pressure transducers, the process of consolidation is most frequently monitored by measuring specimen compression and consolidation time during both primary consolidation and secondary compression. Strain rate values can readily be computed from data of specimen compression at different times of consolidation. Of particular interest is the relationship between end-of-primary strain rate and consolidation pressure, since this information provides some insights on the issue of strain rate selection in the constant rate of strain (CRS) consolidation test. The CRS consolidation test is usually carried out using a strain rate reasonably higher than the end-of-primary strain rate, so that only small excess pore water pressure is developed at the bottom of specimen. Information on the range of strain rates during primary consolidation is beneficial for assessing the CRS test for studying the strain rate effect on the compressibility of clays. Effects of sample disturbance, stress history, load increment ratio, and consolidation on the end-of-primary strain rate are evaluated by comparing end-of-primary strain rates of undisturbed and disturbed samples, and at normally-consolidated and overconsolidated conditions.