An Interpretation of Mechanical Properties of Bentonite as a Non-linear Elastic Material

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are discussed based on the experimental data obtained from triaxial tests under a drained condition. However, in the case of bentonite materials, available experimental data on the compression and swelling characteristics obtained from triaxial tests under the drained condition are neither sufficient nor reliable. The primary data used to justify constitutive models have come from oedometer tests. Compression and swelling behavior of bentonite materials obtained from the oedometer tests are not directly applicable for discussing compression and swelling characteristics under isotropic confining pressure, because the lateral stress cannot be measured in the oedometer tests. If the lateral stress could reliably be estimated, more intensive discussion and more strict interpretation on the compression and swelling characteristics of bentonite materials would have been possible. In this paper, we cite experimental data on bentonite materials where lateral stress was measured with a special oedometer test apparatus by Sasakura et al. (2003). We also discuss the compression and swelling characteristics of bentonite materials under isotropic confining pressure, which are the fundamental mechanical properties for constitutive modeling. ABSTRACT: Bentonite is usually modeled as a geo-material with elasto-plastic isotropic compression/expansion and plastic dilatancy characteristics. In this paper, fundamental considerations of elasto-plastic constitutive modeling for fully saturated bentonite are investigated. According to uniaxial compression test data by Sasakura et al. (2003), where lateral earth pressure was measured, it was found that the hysteresis response between loading and unloading processes does not appear. It suggested that bentonite is an elastic material in which the swelling line corresponds to the normally consolidated line in the 'e-logp' relationship. Also, according to triaxial CU test results of bentonite, it was seen the effective mean stress remains almost unchanged during shearing. This implies that bentonite does not have dilatancy characteristics as defined by the critical state theory. Similar interpretation can be derived from the experimental results obtained from a series of triaxial CD tests by Cui et al. (2006).