An effective constitutive model for lime treated soils V. Robin a,b , A.A. Javadi a,⇑ , O. Cuisinier b , F. Masrouri b a Computational Geomechanics Group, Department of Engineering, University of Exeter, United Kingdom b LEMTA – UMR 7563 CNRS, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Université de Lorraine, France article info Article history: Received 16 June 2014 Received in revised form 30 November 2014 Accepted 18 January 2015 Keywords: Lime treated soils Structured soils Degradation Constitutive modelling abstract The effect of lime on the yield stress, and more generally the presence of structure in the soil, is usually not accounted for in the design of geotechnical structures. As a result the potential of lime treatment or of a structured soil has not been fully exploited. This paper presents a new formulation to account for the effect of structure on the mechanical behaviour for structured soils. A constitutive model is proposed in the framework of the Modified Cam Clay model to describe the behaviour of lime treated soils. The new formulation introduces a limited number of additional parameters, all of which have a physical meaning and can be obtained from an isotropic compression test. Due to similarity in behaviour of lime treated soils and naturally structured soils, the formulation can be applied to both types of soil. It is shown that the proposed model can successfully reproduce the main features of both structured soils such as max- imum rate of dilation at softening and degradation at yield. The model can be applied for any structured material regardless of the origin of cementation. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The use of on-site materials has become a central issue for civil engineering companies, but it is sometimes difficult to deal with all the resources available on site. For soils with low mechanical char- acteristics, lime treatment appears to be an efficient method to improve their mechanical properties and allow their use in geotechnical earth structures (e.g. [23]). The effects of the addition of lime on the soil parameters such as cohesion and friction angle have been extensively studied (e.g. [6]). Nevertheless, lime is still mostly used to dry soils with high water contents and increase the bearing capacity. However, it is also generally known that adding lime leads to a significant increase of the yield stress and modifies other mechanical parameters in compacted soils. In lime-treated soils, the modification of the mechanical behaviour results from several physico-chemical processes associated with the increase in calcium concentration and pH (i.e. cation exchange, pozzolanic reactions, etc.). From an economical point of view, it is becoming increasingly important to account for the properties of treated materials in the design of the geotechnical structures. However, despite its pro- ven efficacy, the use of treated materials suffers from several major drawbacks: there is no reliable method to account for the structure in the calculations. At yield, and for an increasing mechanical loading, treated materials experience what is called the ‘‘loss of structure’’, resulting in the degradation of the structure in different ways. To model the behaviour of these materials, a constitutive law describing the behaviour at yield is a requirement. Some studies [26,3,22,25,16] have shown that naturally structured soils and artificially treated materials have common mechanical features; artificial treatment appears to create a ‘‘structure’’ in the soil. In this paper, ‘‘structure’’ refers to Burland’s definition [7], and is seen as the combination of the fabric and the bonding of the soil skeleton. Fabric accounts for the arrangement of particles, which depends on the state of compaction and their geometry. Several constitutive models have been proposed for structured materials. Most of these models use the destructured state as ref- erence to describe the mechanical behaviour of structured soils. [24] proposed a constitutive model, based on the Modified Cam Clay model (MCC), by adding three additional parameters to the original MCC [36]. Since then, several enhancements (e.g. [18,40]) have been proposed. However, various modes of destructuration have been identified, and the original formulation fails to model some of them. A number of other formulations have been devel- oped [19,42,30,5,38,29] and some of which give good agreement with experimental results. However, it often comes at the cost of a larger number of parameters, or high computational resources (e.g. mapping rule). Parameters do not always have a physical meaning, and some of them can be difficult to determine. All these limitations make these models difficult to be used in engineering practice. http://dx.doi.org/10.1016/j.compgeo.2015.01.010 0266-352X/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Computers and Geotechnics 66 (2015) 189–202 Contents lists available at ScienceDirect Computers and Geotechnics journal homepage: www.elsevier.com/locate/compgeo