SUMMARYThe geothermal use of concrete geostructures (piles, walls and slabs) is an environmentally friendly way of cooling and heating buildings. With such geothermal structures, it is possible to transfer energy from the ground to fluid-filled pipes cast in concrete and then to building environments. To improve the knowledge in the field of geothermal structures, the behaviour of a pile subjected to thermo-mechanical loads is studied in situ. The aim is to study the increased loads on pile due to thermal effects. The maximum thermal increment applied to the pile is on the order of 218C and the mechanical load reached 1300 kN: Coupled multi-physical finite element modelling is carried out to simulate the observed experimental results. It is shown that the numerical model is able to reproduce the most significant thermo-mechanical effects.

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 15°C 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.Key words: heat exchanger pile, in situ test, loading test, thermo-mechanical loads, mobilization of skin friction.

Many geotechnical problems are conditioned by the coupling effects between the solid matrix and fluid transport, in particular in unsaturated zones: construction of embankments, cyclic loading of road foundations, environmental engineering, etc. An understanding of the behaviour of saturated/unsaturated soils is therefore important for the design and analysis of those geostructures. In this paper, the Svendsen–Hutter thermodynamic theory of a mixture of isotropic visco‐elastic materials is summarized and applied to the formulation of field equations for saturated/unsaturated, compressible/incompressible soils. Emphasis is on the presentation of differences in the formulation, the roles of thermodynamics and configurational as well as saturation pressures. The theory is illustrated by studying (1) viscous mixtures (saturated binary/ternary mixtures and unsaturated binary mixtures) and (2) the statics of elastic soils. Several variants of this modern thermodynamic theory are presented. We establish a thermodynamic basis for well‐known concepts of effective stress in saturated and unsaturated soils. Copyright © 1999 John Wiley & Sons, Ltd.

SUMMARYThis paper addresses various issues concerning the modelling of solid-liquid-air coupling in multiphase porous media with an application to unsaturated soils. General considerations based on thermodynamics permit the derivation and discussion of the general form of field equations; two cases are considered: a three phase porous material with solid, liquid and gas, and a two phase porous material with solid, liquid and empty space. Emphasis is placed on the presentation of differences in the formulation and on the role of the gas phase. The finite element method is used for the discrete approximation of the partial differential equations governing the problem. The two formulations are then analysed with respect to a documented drainage experiment carried out by the authors. The merits and shortcomings of the two approaches are shown.

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.