Thomas Mimouni

Design tools for thermoactive geotechnical systems

Abstract This paper presents a review of current design tools used for thermoactive geotechnical systems, along with validation efforts. The capabilities of available analytical methods used for the thermal and thermomechanical design of these systems are evaluated and shortcomings of the existing methods are identified. Although the analytical methods permit accurate prediction of the thermal stress and strain response of thermoactive piles from readily available soil and concrete properties, current shortcomings consist of the ability of the methods to simulate cyclic heating and cooling effects, transient pore water pressure generation and dissipation, and the effects of radial stress changes. Recommendations are provided on how to properly address the current design requirements and the efforts to overcome shortcomings with the development of constitutive relationships from further full scale and laboratory scale experimental studies on thermoactive piles. Furthermore, the need for the development of both simplified analytical tools and advanced finite element models is emphasized. In addition, the existing analytical tools should be validated using field data from recently available case studies of thermoactive piles in varying soil deposits. An urgent need for an extensive design guide for energy geostructures was identified. The guidelines should be targeted towards practitioners and include field observations and measurements, as well as laboratory and numerical studies.

New technologies and applications: materials and equipment in near surface geothermal systems

Abstract This paper presents an overview of new technologies and applications on thermoactive geostructures. A discussion session on issues involved with near surface geothermal systems is presented, focusing on opportunities for developing new technologies to address these issues. In addition, opportunities for new applications of geothermal heat exchange in geotechnical engineering were discussed. Progress on the development of new materials and equipment that may be used to enhance the rate of heat transfer or heat storage capacity was discussed.

On Using Tunnel Anchors and Bolts as Heat Exchangers with the Ground

Heating and cooling of the buildings represent an important area of energy consumption in the developed countries. Furthermore, a large part of this demand is still satisfied with fossil resources such as oil or gas. Therefore, developing alternative and renewable heat sources for buildings is a major challenge for future energy policies. But because of the congestion of the urban underground, conventional ground source heat pump systems need new heat exchangers with the ground. Therefore, embedding absorber pipes within foundation and underground structures represent a great opportunity while it saves the cost of dedicated drillings for boreholes. Shallow tunnels are numerous in large cities for roadways and metro lines. Therefore, using them as heat exchanger with the ground could provide an efficient heat source for the overlying buildings. Different solutions were identified and among them, heat exchanger anchors are the less investigated because of the emerging technology. The present paper investigates the potential of using tunnel anchors as heat exchangers for ground source heat pumps. The study is based on thermo-hydro-mechanical finite element analyses of a cut and cover tunnel and a bored tunnel. Different conditions are tested as well as the efficiency of seasonal heat storage and its mechanical implications.