Water retention properties of perlite as a material with crushable soft particles M. Jamei a, ⁎, H. Guiras a , Y. Chtourou a , A. Kallel a , E. Romero b , I. Georgopoulos c a Civil Engineering Laboratory, National Engineering School of Tunis, BP.37, 1002, Belvedere Tunis, Tunisia b Department of Geotechnical Engineering and Geosciences, Universitat Politècnica de Catalunya, Barcelona, Spain c Laboratory of Geomaterials, Section of Mechanics, Faculty of Applied Mathematics and Physics, National Technical University of Athens, Greece abstract article info Article history: Received 23 August 2010 Received in revised form 1 June 2011 Accepted 11 June 2011 Available online 30 July 2011 Keywords: Perlite Particle crushing Evolution of water retention characteristics Predicting The purpose of this study is to present and discuss the experimental results of the water retention properties of an unsaturated material with crushable soft particles. Perlite was used as an artificial material due to its highly crushable behaviour on loading. In this study an approach including crushing and soft behaviour of the particles and its effect on water retention characteristics is specially proposed. The crushing effect of perlite grains is shown by the evolutions of the grain size distribution curves. The usefulness of the Weibull theory for perlite material, in order to predict the grain-size curves after the crushing, is highlighted. Using different experimental techniques on partially saturated perlite, a first insight into the water retention characteristics of the material is presented. The effect of the double porosity on water retention curve of the material is also highlighted. The evolution of the water retention characteristics with crushing is analysed, by using the Aray and Paris model in conjunction with the Weibull distribution predictions. Predicted and experimental results are compared and discussed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The hydraulic behaviour of unsaturated materials can be expressed by means of the water retention curve (WRC), as a relationship between the negative pore pressure (suction) and the water content (or degree of saturation). It is also linked to the relative water permeability (permeability of unsaturated material), which is often deduced from WRC results by using different empirical models. Experimental results and WRC models for soils have been proposed by neglecting mechanical aspects (Basile and D'Urso, 1997; Arya et al., 1999; Zeiliguer et al., 2000; Vaz et al., 2005). However, the importance of the mechanical response on the water retention characteristics have been recently highlighted, specially by studying the influence of the compaction on the WRC and by coupling the hydraulic and mechanical behaviour (Delage et al., 1996; Romero et al., 1999; Vanapalli et al., 1999; Cuisinier and Laloui, 2004). The conclusions of these studies clearly indicated that when uncoupled hydraulic paths were applied, an important influence of the initial water content and the hydraulic history (drying and wetting) was identified in the water retention properties. On the other hand, when coupled hydraulic and mechanical actions were considered, the loading conditions reflected a larger influence on the water retention characteristics. For unsaturated compacted soils, it has been shown that the microstructure of a given soil is not unique, and strongly depends on the compaction and hydraulic paths followed (Birle et al., 2008). The initial water content and dry density have an important influence on microstructure, and as a consequence on both the soil water retention and the relative water permeability. Birle et al. (2008) studying Lias-Clay showed a strong influence of compaction water content at values larger than 11–12.5%. This is consistent with the lower permeability detected on soils compacted wet of optimum and usually interpreted by the microstructural changes undergone by the material at elevated water contents (Cuisinier and Masrouri, 2005; Delage, 2006; Romero and Simms, 2008). This is why; understanding microstructural features on water retention properties have gained relevance (Delage et al., 1996; Romero and Simms, 2008), particularly for geo-environmental earth structures design such as landfills, engineered barriers, embankments and dams. Based on the previous discussion, there is a need to investigate the loading actions and their effects on the evolution of microstructure and their consequences on engineering properties, such as water retention curve, compressibility, water permeability and shear strength (Penumadu and Dean, 2000). In this sense, selecting a proper material with a highly sensitive microstructure to mechanical actions is very useful. However, to the authors' knowledge, most of microstructure investigations have been carried out with undeformable material particles, in which loading actions on microstructure are of limited action affecting only the porosity. In the case of soft and crushable grains, loading actions have a strong influence on both macro and micro voids (Lade et al., 1996). Particularly, the present paper addresses the evolving nature of the water retention properties of a highly crushable material with soft particles when undergoing loading paths. Engineering Geology 122 (2011) 261–271 ⁎ Corresponding author at: Civil Engineering Laboratory, National Engineering School of Tunis (ENIT), B.P. 37, Le Belvédère Tunis, Tunisia. Tel.: +216 71 874 700; fax: +216 71 872 729. E-mail address: mehrez.jamei@enit.rnu.tn (M. Jamei). 0013-7952/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2011.06.005 Contents lists available at ScienceDirect Engineering Geology journal homepage: www.elsevier.com/locate/enggeo