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 sample 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. Encouraging agreement has been found concerning the validation of the proposed formulation.
1. INTRODUCTION
Some geotechnical problems that are likely to require new approaches or, at least, extension of the classical ones are as follows: collapse and expansion of active soils, subsidence due to oil and gas extraction, dissolution, degradation and weathering of soils and rocks and CO2 sequestration [1]. For instance, the large-scale injection of CO2sub> and other gases into geological formations may induce complex interaction of multiphase flow, diffusion, convection, mineral and gas dissolution, mineral precipitation, and other chemical reactions. Depending on the composition of the rock and fluids and CO2 injection strategy, the rock-fluid interactions may have a significant impact on safety and reservoir storage capacity [2].
