Design tools for thermoactive geotechnical systems

Abstract

This paper presents a review of current design tools used for thermo-active geotechnical systems, along with validation efforts. The capabilities of available analytical methods used for the thermal and thermo-mechanical 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 thermo-active piles from readilyavailable 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 thermo-active 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.

Parameterization of a calibrated geothermal energy pile model

“…A state of practice paper by Bourne-Webb et al (2014) emphasized the current need for advanced finite element models in addition to field studies to improve existing design guidelines for geothermal energy piles. Existing energy pile design guidelines are contained within GSHPA (2012), however these guidelines focus on sizing and installation "best practices".…”

Analysis and design methods for energy geostructures

“…About 70 individuals from both research and industrial backgrounds attended the workshop, and this paper results from the discussions relating to the issue of the validation of design tools for energy geostructures, see [9] for a report on this particular session and the same issue of the DFI Journal for reports on the other sessions of the workshop.…”

Reviewing the Modeling Aspects and Practices of Shallow Geothermal Energy Systems

“…Although analytical methods allow for an accurate prediction of the thermal stress and strain response of EGS (see Section 8), the methods exhibit shortcomings in their ability to simulate effects of cyclic heating and cooling, of transient pore water pressure generation and dissipation, as well as of radial stress changes [4]. Major drawbacks of current analytical tools consist in their inability to take account of the short-term thermal energy storage and thermal resistance of EGS, the effect of ground water flow and real surface boundary conditions [77], which might all affect significantly the mechanical response of EGS (see Chapter 4) whose geometry differs significantly from BHE.…”

“…Regarding numerical modeling, while there exist a number of published thermal response modeling case studies, as presented in Section 2, publications reporting the thermomechanical response of EGS are largely absent. Still, the thermomechanical analysis of EP has attracted certain attention [4,5,26,145,149,150] while detailed thermomechanical analysis of other EGS remains rare [50,151].…”

“…The empirical rules are based on assumptions of maximum changes in axial load and maximum deformation caused by heating/cooling cycles. They generally lead into overly conservative design [4]. On the other hand, load transfer models, which represent pile-soil interaction by load transfer rules, are much more accurate and widely used.…”