Numerical analysis of the geotechnical behaviour of energy piles

Abstract

Summary Energy geostructures are rapidly gaining acceptance around the world; they represent a renewable and clean source of energy that can be used for the heating and cooling of buildings and for de‐icing of infrastructures. This technology couples the structural role of geostructures with the energy supply, using the principle of shallow geothermal energy. The geothermal energy exploitation represents an additional thermal loading, seasonally cyclic, which is imposed on the soil and the structure itself. Because the primary role of the piles is the stability of the superstructure, this aspect needs to be ensured even in the presence of the additional thermal load. The goal of this paper is to numerically investigate the behaviour of energy pile foundations during heating–cooling cycles. For this purpose, the finite element method is used to simulate both a single and a group of energy piles. The piles are subjected to a constant mechanical load and a seasonally cyclic thermal load over several years, imposed in terms of injected–extracted thermal power. The soil and the pile–soil interface behaviours are reproduced using a thermoelastic‐thermoplastic constitutive model. The thermal‐induced stresses inside the piles and the additional displacements of the foundations are discussed. The group model is used to investigate the interactions between the piles during thermo‐mechanical loading. The presented results are specific to the studied cases but lead to the conclusion that both the thermal‐induced displacements and stresses, despite being acceptable under normal working conditions, deserve to be taken into account in the geotechnical design of energy piles. Copyright © 2014 John Wiley & Sons, Ltd.

Analysis and design methods for energy geostructures

“…cyclic loading [108], soil thermal response [109,110,111], or the behaviour of groups of piles [79,80,112,113].…”

Numerical modelling of thermo-active piles in London Clay

“…For example, Knellwolf et al (2011), McCartney andRosenberg (2011) and Suryatriyastuti et al (2014) used the load transfer (t-z) approach, which includes the effect of thermal expansion and contraction of the pile. The finite-element method has been employed by Laloui et al (2006), Suryatriyastuti et al (2012), Bodas Freitas et al (2013), Dupray et al (2014), Di Donna and Laloui (2015), Rotta Loria et al (2015), Salciarini et al (2015), Bourne-Webb et al (2016) and Di Donna et al (2016), among others. Such studies focus on reproduction of the experimental data and/or investigation of various aspects of the soil-structure interaction, including the effects of the soil's thermal expansion coefficient, pile length, ground surface temperature, thermal loads, as well as cyclic heating and cooling.…”

Thermally induced group effects among energy piles

“…Notable variations in the behaviour of friction energy piles may consequently arise because of the marked sensitivity of these foundations to the response of the pile-soil interface . These variations may increase for cyclic thermal loads applied to the piles with time (Di Donna & Laloui, 2014;Ng et al, 2014;Yavari et al, 2014;Saggu & Chakraborty, 2015;Suryatriyastuti et al, 2015;Ng et al, 2016;Vieira & Maranha, 2016), such a consideration suggesting the unsuitability of an elastic approach of analysis in those situations. Thermo-elastic analyses can be considered unsuitable also for situations that involve mechanisms and phenomena inducing plastic strain in the soil surrounding the piles irrespective of the magnitude of the applied loads.…”

“…Several in situ tests (McCartney & Murphy, 2012;Murphy et al, 2014;Mimouni & Laloui, 2015) and numerical analyses (Di Donna & Laloui, 2014;Jeong et al, 2014;Salciarini et al, 2015;Di Donna et al, 2016;Suryatriyastuti et al, 2016) have recently investigated this problem for energy pile groups. To date, however, knowledge of the development and impact of thermally induced group effects among closely spaced energy piles on their thermo-mechanical behaviour has been limited due to the lack of field data about the exploitation of energy piles that either partially or entirely operate as geothermal heat exchangers for timescales that are typical of practical applications.…”