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Submerged soils may be considered as an unsaturated porous medium containing gas, water and solids. By using a three-phase model, the mechanical behaviour of such soils can be described by an extended consolidation equation in order to calculate transient pore water pressures, induced by external pressure changes. Microscopic gas bubbles embedded in the pore fluid of the soil skeleton may play a key role in soil behaviour due to the increased gas-water mixture compressibility. Pressure changes applied on such unsaturated submerged soils may cause soil structure deformations such as heaving, settling or even fluidisation. Rapid external pressure reductions such as excavations, draw down loading or ground water level lowering are followed by a delayed pore water pressure propagation. Transient pore water pressures may therefore cause embankment sliding, hydraulic failure and unacceptable deformation. Case studies concerning geotechnical applications are presented. Results from numerical simulations based on Biot’s consolidation equation are compared with computations based on Richards equation. The results are discussed towards formulation of protection measures in order to improve stability requirements.

Field and theoretical efforts indicate that the presence of entrapped gas bubbles below the water table may influence the propagation dynamics of excess pore pressure caused by load changes. The process of pore pressure propagation depends on the volume of the occluded gas phase and on the relation between hydraulic conductivity of the dynamics of (hydraulic or mechanical) loading changes at the boundary. In the context of safety considerations the estimation of excess pressure dissipation dynamics may be essential. Based on Boyle-Mariotte and Henry principles predictions on water saturation versus pore pressure were established and the soil-water characteristic curve was extended from the unsaturated zone throughout the zone of air occlusion. Analogous to unsaturated zone concepts a pore pressure dependent water-capacity relationship was derived for the zone of the residual gas phase and set in 2D FE-model based on Richards equation. The extended model accounting for gas entrapment was evaluated against an explicit 2-phase model, laboratory experiments and field observations. The approach presented enables the inspection of the effect of gas entrapment on pressure propagation considering the transition from saturated to unsaturated state.

The computer code CODE-BRIGHT has been applied to simulate thermal-hydro-mechanical (THM) experiments on clays being considered as host rock and as buffer/backfill for the disposal of radioactive wastes. In this paper, two modelling exercises will be presented: (1) prediction of the hydration of bentonite, and (2) scoping calculation of large-scale heating tests to be performed with a bentonite-filled clay cylinder in order to study coupled THM processes taking place in the near-field of heat-generating wastes in drifts and boreholes. The results suggest that the coupled THM phenomena observed in the laboratory can be well represented and interpreted by numerical simulation with the code.

In this paper we evaluate a number of model equations for the soil-water characteristic curve (SWCC), provided a relationship exists for each relevant soil. The models are with two parameters and relate suction to volumetric water content for values of suction higher then air entry value. Logarithmic tranformations are applied to the variables in order to find linear patern. Most of generally used models are also discussed and compared to the proposed. An example is given how to assess the experimental data to define the variable transformation and how to choose the most proper model. The procedure for estimating the air entry value is also presented.

An extension of the Distinct Element Method (DEM) in corporated with a capillary water (CW) contact model proposed is used to obtain an insight into the effective stress in the unsaturated granulate from the viewpoint of strength. The disappearances of menisci and air bubbles were numerically simulated in the wetting process. DEM biaxial compression and hydric tests showed that: with the description of net stresses, peak strength envelopes move parallel to each other in the direction of increases of peak shear strength nonlinearly with the increase of suction. There appears a unique peak/residual strength line if it is described with generalized effective stress (called GES here). The GES due solely to CW (called GESS here), is a nonlinear function of suction on a wide range of values suction. GESS vs. suction curve appears to be analogous to the water-retention curve, and to be correlated with the particle gradation.

The statistical grading entropy of soils S (Lörincz, 1986) consists of two terms: the base entropy arising from the difference in the width of the statistical cells in the conventional grading curve and, the entropy increment ΔS due to the mixing of the fractions. The aim of this ongoing research is to examine which part of the entropy plays the role of the “true” entropy in thermodynamic sense (i.e. undergoes an increase during irreversible thermodynamic processes).

Object-oriented (OO) methods become more and more important in order to meet scientific computing challenges, such as the treatment of coupled non-linear multi-field problems with extremely high resolutions. This two-part paper introduces an object-oriented concept for numerical modelling multi-process systems in porous media (Part 1). The C++ implementation of the OO design for process objects (PCS) as a class is described and illustrated with several applications. Due to the importance of the encapsulation of processes as individual PCS objects we denote our concept as an process-oriented approach.

The presented examples (Part 2) are dealing with thermal (T), hydraulic (H), mechanical (M) and componental processes (C) in bentonite materials, which are used as buffer material for the isolation of hazardous waste in geologic barriers. In particular, we are interested in coupling phenomena such as thermally induced desaturation, non-isothermal consolidation, swelling/shrinking phenomena as well as in a better understanding of the coupled, non-linear THM system.

Part 1 of this paper is about design and implementation of processes in an object-oriented way. Here we give numerical examples to show the variety of problems which can be treated based on the process-oriented approach.

The prior objective of the present paper is to predict the formation of desiccation cracks in a mineral liner for landfills. Therefore, a coupled pore water diffusion and stress analysis is made using the finite element method and the numerical program ABAQUS. For this analysis, test results of hydraulic soil relations and tensile behaviour of the investigated cohesive soil are needed. Also the inelastic mechanical properties must be given and implemented in the used numerical model. The present paper shows these test results, the used plasticity model and the geometry, loading and results of the numerical model.

This paper presents a modelling work of the “El Infiernillo” dam which was built in Mexico in the 60’s. A recently developed constitutive model for rockfill has been implemented in a coupled finite element program, which solves the hydromechanical problem for general unsaturated conditions. The performance of the dam during construction and impoundment has been analysed. The agreement between calculated and measured displacements indicates that the capabilities of the constitutive models and computational tools used.

In shallow tunnelling below the groundwater table compressed air can be used for preventing water inflow into the tunnel. Using this method air loss takes place through both the unsupported tunnel face and shrinkage cracks of the shotcrete lining. Until today it is difficult to correctly estimate the amount of air loss during the design phase of a project, although this is a significant factor concerning the total costs of a tunnel. For solving the problem the multi-phase flow in the soil above the tunnel has to be considered. The aim of the conducted research project was to develop a numerical simulation of the air flow in the soil, based on existing unsaturated soil constitutive models. In the first stage large scale laboratory tests were conducted at the Institute for Soil Mechanics and Foundation Engineering in Graz to simulate the air-permeability of the shotcrete lining and the soil. Additionally, the experimental results were simulated numerically. In a second stage the numerical model was extended to a three dimensional simulation of tunnel advance under compressed air. In this contribution the results of the tunnel advance model with respect to the air flow into the soil through the cracked shotcrete lining and the tunnel face are presented and discussed.