Practical method to estimate parameters of elasto-plastic constitutive model for unsaturated soils from compaction curve

Abstract

The input parameters for the hardening law for the elasto-plastic constitutive model of unsaturated soils are generally fitting parameters that control the degree of hardening response and cannot easily be determined without the results of experimental tests in which the changes in suction, water content, and volume are measured or controlled. However, it is next to impossible to complete such precise experimental tests on all the geomaterials comprising the earth structure to be analysed, such as an embankment. It is important, therefore, to establish a method for determining these parameters from more easily attainable data on the material. This paper presents a practical method for estimating the input parameters related to hardening/softening due to desaturation/saturation in the elasto-plastic constitutive model proposed by Ohno et al. (2007a) from a compaction curve, which is frequently obtained and widely used in engineering practice. In the proposed method, the input parameters are estimated by simultaneously solving three theoretical equations, each of which holds for a different point, indicating the statically compacted state on the dry side of the compaction curve, while the approximately represented compaction curve is used instead of a hand-drawn one. The paper demonstrates that the proposed method enables the estimation of the input parameter values within a range small enough so as not to affect the results of the simulation, irrespective of the way in which the points on the represented compaction curve are selected. The validity of the estimated parameters is verified and then discussed through a series of static compaction test simulations.