Lyesse Laloui

An Improved Volume Measurement for Determining Soil Water Retention Curves

The complete determination of soil water retention curves requires the sample volume to be measured in order to calculate its void ratio and degree of saturation. During drying in the pressure plate apparatus, cracks often appear in the sample altering its deformation and evaporation patterns. Consequently, this causes a significant scatter in the volume measurement when using the volume displacement method. This paper proposes a simple method to avoid cracking, by limiting friction and adhesion boundary effects, to allow for unrestrained shrinkage of the sample. Such modification of the technique decreases the measurement error by a factor of three.

Geotechnical analysis of heat exchanger piles

There is currently a lack of established calculation method for the geotechnical design of heat exchanger piles, although the technology is experiencing a fast expansion. Instead of quantifying the effects of temperature changes on the static behavior of heat exchanger piles, the common geotechnical practice is to apply a large overall security factor. This is done in order to be on the side of safety with respect to thermal effects. The few existing in situ experiments show that applying a thermal load induces a significant change in the stress-strain state of a pile. This paper presents a geotechnical numerical analysis method, based on the load transfer approach, which assesses the main effects of temperature changes on pile behavior. The method is validated on the basis of two in situ measurements of the loads and deformations experienced by heat exchanger test piles. The occurrence of critical design situations is further discussed. Some conclusions are formulated on concrete failure and the full mobilization of the pile shaft friction and base resistance during the operation of the heat exchange system.

Thermodynamically based mixture models of saturated and unsaturated soils

Note: Sols Reference LMS-ARTICLE-1999-004View record in Web of Science Record created on 2006-11-09, modified on 2016-08-08

A thermo-viscoplastic constitutive model for clays

Note: Sols Reference LMS-ARTICLE-1997-002doi:10.1002/(SICI)1096-9853(199705)21:5 3.0.CO;2-5View record in Web of Science Record created on 2006-11-09, modified on 2016-08-08

ACMEG-T: Soil Thermoplasticity Model

This paper addresses an advanced and unified thermomechanical constitutive model for soils. Based on experimental evidence showing the nonlinear and irreversible thermomechanical responses of saturated soils, the constitutive equations of the developed model, Advanced Constitutive Model for Environmental Geomechanics-Thermal effect (ACMEG-T), are presented. In the context of elastoplasticity and critical state theory, the model uses the multimechanism plasticity and bounding surface theory. Nonlinear thermoelasticity is joined with two coupled thermoplastic dissipative processes. The yield functions, the dissipative potentials and the plastic multipliers are introduced. Attention is particularly focused on the coupling between both plastic mechanisms, an isotropic and a deviatoric one, which are in agreement with the consistency condition for multiple dissipation. As far as isotropic mechanism is concerned, a unique thermomechanical yield surface reproduces the thermoplasticity observed at low and intermediate overconsolidation ratios, as well as the plasticity under mechanical loading in an framework unifying mechanical and thermal hardenings. Finally, the efficiency of ACMEG-T is proven by validation tests on drained and undrained thermomechanical paths.

Thermo-mechanical behaviour of soils

ABSTRACT Research interest in the thermo-mechanical behaviour of soils is growing as a result of an increasing number of geomechanical problems involving thermal effects. It is, therefore, necessary to understand thermally induced effects on soils and then to use the appropriate constitutive models for the numerical simulation of such phenomena. This paper addresses various issues concerning the thermo-mechanical behaviour of soils. Starting from experimental evidence of non-linearity and hardening that heating causes in soils, thermodynamic considerations are then introduced for the derivation and the discussion of the general form of the constitutive equations. After that, constitutive modelling is presented and treated in the context of elasto-plasticity based on the LTVP model, which includes the evolution of yield surfaces with temperature. Numerical simulations support the theoretical aspects of the paper by showing performances of this constitutive law, especially for undrained and cyclic paths.

Desiccation cracking of soils

ABSTRACT The scope of this paper is to present the global mechanisms of soil desiccation, including drying shrinkage and cracking. The paper first reviews the basic processes that are beneath the word “desiccation”. Then the results of an experimental study of desiccation are presented, in which strains, suction, water content, degree of saturation and crack geometry are investigated. The results show that cracking initiates close to the onset of de-saturation. Insights into the micro-scale are proposed to explain this observation. A scenario for the processes leading to crack initiation is further established in terms of the macroscopic variables: an assessment of the stress building up is proposed, until a critical point at which the tensile strength is met. Desiccation crack pattern formation is finally discussed.

Effective stress in double porous media with two immiscible fluids

Note: Sols Reference LMS-ARTICLE-2005-006doi:10.1029/2005GL023766View record in Web of Science Record created on 2006-11-09, modified on 2016-08-08

Structural characterization of unsaturated aggregated soil

Despite the recent experimental studies of soil structure, a comprehensive understanding of the macroscopic response of a soil in relation to its structure has not yet been achieved. This lack of understanding reveals the need for further assessments of soil structure and its evolution under loading. In this work, the structure of an aggregated soil under various conditions of saturation and mechanical loading is studied. We also compare the aggregated soil structure, which shows a double porous fabric, with that of the same soil when reconstituted. The experimental methods selected for this study are a combination of mercury intrusion porosimetry (MIP), environmental scanning electron microscopy (ESEM), and neutron computed tomography (CT). Using MIP and ESEM, we first examine the soil fabric at the intra-aggregate scale. Then, we quantify the structural evolution of the soil using neutron tomography and link it to the macroscopic response of the soil. Based on the experimental evidence, the main features of the soil structure and its evolution are outlined for unsaturated aggregated soil under different loading conditions.

Behavior of a dual-purpose pile as foundation and heat exchanger

The behaviour of a pile subjected to thermo-mechanical loads was studied in situ with the aim of quantifying the thermal influence on the bearing capacity of heat exchanger piles. To accomplish this, a pile situated in a building under construction was equipped with a pipe system to inject heat into it using a special heat pump. Load cells, deformation gauges, and thermometers were installed to evaluate the behaviour of the pile during seven tests with coupled thermo-mechanical loads. The temperature variations applied to the pile were of the order of 15degreesC and the mechanical load reached 1300 kN. The results permitted the quantification of three significant effects brought about by the temperature increase: (i) pile uplift, (ii) mobilization of skin friction due to the relative displacement of the pile with respect to the ground, (iii) additional load generated in the pile by constrained dilation.The behaviour of a pile subjected to thermo-mechanical loads was studied in situ with the aim of quantifying the thermal influence on the bearing capacity of heat exchanger piles. To accomplish this, a pile situated in a building under construction was equipped with a pipe system to inject heat into it using a special heat pump. Load cells, deformation gauges, and thermometers were installed to evaluate the behaviour of the pile during seven tests with coupled thermo-mechanical loads. The temperature variations applied to the pile were of the order of 15degreesC and the mechanical load reached 1300 kN. The results permitted the quantification of three significant effects brought about by the temperature increase: (i) pile uplift, (ii) mobilization of skin friction due to the relative displacement of the pile with respect to the ground, (iii) additional load generated in the pile by constrained dilation.