Abstract
The purpose of this paper is to investigate the horizontal stress evolution and soil collapse during the cement dissolution process using a combination of experimental and numerical methods. The experimental procedure was carried out using a modified oedometer cell with horizontal stress measurements and synthetic samples in order to simulate simultaneous cement dissolution, stress changes and sample deformation. The samples were loaded at a constant vertical stress and exposed to a reactive fluid which dissolved the cementation of the artificial soil. During the dissolution process, sample volume decreased and horizontal stress changes were observed. Initially the horizontal stress decreased due to grain mass loss and then increased due to solid matrix rearrangement. Numerical simulation of these coupled chemical and mechanical processes was performed using a general purpose finite element code capable of performing numerical analysis of engineering problems. The constitutive model adopted to reproduce the soil behavior is an extension of the Barcelona Basic Model for unsaturated soils including the cement mineral concentration as state variable. Some new features were incorporated to the original elasto-plastic model in order to represent the results observed in the experiments. In this paper a good agreement between experimental and numerical results was achieved.
Highlights
IntroductionThe recent development of experimental techniques, where measurements of variables of different nature (thermal, hydraulic, mechanical and chemical) can be performed simultaneously in the same experiment, allowed the incorporation of new variables and equations to the numerical procedures used to reproduce the behavior of soils and rocks
The recent development of experimental techniques, where measurements of variables of different nature can be performed simultaneously in the same experiment, allowed the incorporation of new variables and equations to the numerical procedures used to reproduce the behavior of soils and rocks. In geotechnical engineering, such models are mainly related to the effects of partial saturation and consequences of chemical actions on the porous media, where suctions and chemical concentrations were included as state variables of the mechanical problem (Alonso et al, 1990; Castellanza & Nova, 2004; Gens & Nova, 1993; Guimarães et al, 2013)
It is not easy to determine K0 when the soil or rock is simultaneously loaded and exposed to reactive fluids in the attempt to simulate diagenetic or weathering processes. Authors such as Shin and Santamarina (2009) and Castellanza and Nova (2004) have given some insights into this complex behavior of cemented soils and rocks. They developed modified oedometer cells to evaluate changes of horizontal stress caused by mineral dissolution
Summary
The recent development of experimental techniques, where measurements of variables of different nature (thermal, hydraulic, mechanical and chemical) can be performed simultaneously in the same experiment, allowed the incorporation of new variables and equations to the numerical procedures used to reproduce the behavior of soils and rocks. Authors such as Shin and Santamarina (2009) and Castellanza and Nova (2004) have given some insights into this complex behavior of cemented soils and rocks They developed modified oedometer cells to evaluate changes of horizontal stress caused by mineral dissolution. In the elasto-plastic model proposed by Castellanza & Nova (2004), the reference model for the unbonded material is based on the Critical State Theory and a new state variable to represent bonding is proposed This new variable affects the shear strength (cohesion) and pre-consolidation stress of the material and its evolution is a result of imposed mechanical and chemical loads. The mass balance equations for water and all chemical species (flow and reactive transport problems) and the balance equation for momentum (mechanical problem) are solved together in a fully coupled way according to Guimarães et al (2007)
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