Modelling the behaviour of unsaturated non-active clays in saline environment

Giulia Scelsi,Gabriele Della Vecchia,Wojciech T. Sołowski,Guido Musso,Ayman A. Abed

doi:10.1016/j.enggeo.2021.106441

Abstract

The chemical composition of pore fluid and matric suction rule the mechanical behaviour of soils. In case of clays, their fabric changes in line with those variables. Since both the increase in matric suction and salinity cause a transition from an open to a close microstructure of low and medium activity clayey materials, a unique framework could tackle problems where salinity and saturation changes are expected.This paper presents a simple elasto-plastic model capable of reproducing the behaviour of unsaturated clayey soils in saline environments. Changes in the pore fluid composition are addressed through the use of osmotic suction as a variable. The proposed model extends the Barcelona Basic Model for partially saturated soils to consider the effect of osmotic suction.The model, implemented in the Thebes code, is calibrated for Boom Clay. The reproduced tests include mechanical loading at different matric and osmotic suctions in oedometric conditions, as well as more complex chemo-mechanical stress paths. Despite the simplicity of the formulation, the agreement between the experimental results and the simulations is encouraging. It seems that the modelling approach addresses the most important features of partially saturated soils with saline pore fluid which are slightly or moderately expansive.

Highlights

The chemo-hydro-mechanical response of clays is of significant importance in many geotechnical applications
The model introduces the effect of the osmotic suction in the Barcelona Basic Model (BBM) as an equivalent matric suction
Based on the analysis of the microstructural changes of clay materials, the model assumes that the equivalent matric suction in the BBM causes the same effects on void ratio as those caused by the osmotic suction in the chemo-mechanical model

Summary

Introduction

The chemo-hydro-mechanical response of clays is of significant importance in many geotechnical applications. A paradigmatic example is provided by sealing barriers for nuclear waste disposal During their operational life, the clay barriers will likely be saturated by fluids having a chemical composition different from the compaction one (Castellanos et al, 2008; Musso et al, 2013). Swelling pressure development upon saturation, as well as shrinkage upon desiccation and upon salinization are anticipated; changes of clay hydro-mechanical properties such as compressibility, permeability and shear strength may occur (Bolt, 1956; Mesri and Olson, 1971; Sridharan, 1991). Pore fluid salinity and water content vary in natural environments, such as in the Scandinavian ‘quick clays’. These are marine clays deposited in salt water and emerged in relatively recent geological times. The following desalinization and increase in water content can lead to volumetric collapse and decrease of shear strength (Bjerrum, 1955; Torrance, 1974)

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