A Simple and Unified One-Dimensional Model to Describe Various Characteristics of Soils

• Published in: SOILS AND FOUNDATIONS Vol. 51; no. 6; pp. 1129 - 1148
• Main Authors: Nakai, Teruo, Shahin, Hossainmd, Kikumoto, Mamoru, Kyokawa, Hiroyuki, Zhang, Feng, Farias, Marciom
• Format: Journal Article
• Language: English
• Published: Tokyo Elsevier B.V 01.12.2011; The Japanese Geotechnical Society; Japanese Geotechnical Society
• Subjects: aging; Applied sciences; bonding; Buildings. Public works; clay; consolidation; constitutive equation of soil; deformation; density; elasto-plasticity; Exact sciences and technology; Geotechnics; IGC: D5/D6; one-dimensional condition; overconsolidation; rheology; sand; Soil investigations. Testing; Strength of materials (elasticity, plasticity, buckling, etc.); Structural analysis. Stresses; structured soil; suction effect; temperature-dependent behavior; time-dependent behavior; overconsolidation; one-dimensional condition; rheology; density; consolidation; suction effect; time-dependent behavior; clay; sand; IGC: D5/D6; elasto-plasticity; bonding; deformation; aging; temperature-dependent behavior; constitutive equation of soil; structured soil; Constitutive equation; Sand; (time-dependent behavior) (IGC: D5/D6); Modeling; Consolidation; Elastoplasticity; Oedometer; Strain rate; Clay; Rheology; Property of soil; Overconsolidated soil; Simulation; Soil test; One dimensional model; Application
• ISSN: 0038-0806; 1881-1418
• DOI: 10.3208/sandf.51.1129

A simple and unified constitutive model for soils, considering various effects such as the influences of density, bonding, time dependent behavior and others, is presented in this paper. The elastoplastic behavior of over consolidated non-structured soils under a one-dimensional stress condition is firstly presented by introducing a state variable that represents the influence of density (stage I). To describe the one-dimensional stress-strain behavior of structured soils, attention is focused on density and bonding as the main factors that affect the response of this type of soil, because it can be considered that soil a skeleton structure which is in a looser state than that of a normally consolidated soil is formed by bonding effects (stage II). Furthermore, a simple method is presented which allows for other soil characteristics to be considered, such as time and temperature dependency, and the effect of suction in unsaturated soils. Experimental observations show that the normally consolidated line (NCL) in the void ratio—stress relation (e.g., e-ln σ curve) shifts depending on the change of strain rate, temperature, suction and others (stage III). The validation of the model at stages I and II is demonstrated by simulating one-dimensional consolidation tests for normally consolidated, over consolidated and natural clays. The applicability of the model at stage III is verified not only by the simulations of time-dependent behavior of clays in one-dimensional element tests but also by the soil-water coupled finite element analysis of oedometer tests as a boundary value problem. The extension from one-dimensional models to three-dimensional models is easily achieved by defining the yield function using stress invariants instead of one-dimensional stress ‘σ’ and by assuming an appropriate flow rule in stress space. The details of the modeling in general three-dimensional stress conditions will be described in another paper (Nakai et al., 2011).