* Corresponding author: peter.bourne-webb@tecnico.ulisbosa.pt Effect of thermal boundary conditions on the response of thermally-activated floating piles in a cohesive material Peter Bourne-Webb 1,* , Martina Zito 2 , Teresa Maria Bodas Freitas 1 , and Donatella Sterpi 2 1 CERIS, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal 2 Politecnico di Milano, Milano, Italia Abstract. The application of thermally-activated foundations has received significant attention in the last decade with a number of large- and small-scale tests having been undertaken. Alongside these physical studies, a number of investigations utilising numerical analysis have been undertaken. The majority of analyses are transient with durations from a few hours up to 10 years. A broad range of thermal boundary and initial conditions have been applied in these analyses, and only a limited number of studies have explicitly considered the surface boundary imposed by an overlying structure, let alone considered what effect variations in the operational temperatures of the structure might have on the foundations. The work presented in this paper had the objective of systematically examining these assumptions and the effect they have on the predicted response of a thermally-activated pile foundation, and if important, which is the most appropriate set of conditions to use. 1 Introduction The application of thermally-activated foundations has received significant attention in the last decade with a number of large- and small-scale tests having been undertaken. Alongside these physical studies, a number of investigations utilising numerical analysis have been undertaken, some of which, [1] to [20], are tabulated in Table 1. The majority of analyses are transient with durations from a few hours [6] where small-scale tests have been analysed, up to 10 years [18]. Examining the side and bottom boundary conditions applied, adiabatic (no flow) or constant temperature conditions have been used more-or-less equally. Generally, the centreline condition is adiabatic, except in some pile group studies where constant temperature conditions were applied to all boundaries. Surface temperature boundary conditions are in most cases defined using either a constant temperature [3, 9], often the same as the initial temperature [1, 4 to 8, 11, 13, 15, 17, 20], or in a few cases an imposed temperature harmonic representing the change in average air temperature across the year [16, 18]. Only, a limited number of studies have explicitly considered the surface boundary imposed by an overlying structure [2, 3], let alone considered what effect variations in the operational temperatures of the structure might have on the foundations [9, 21]. The pile thermal load has in most cases been applied across the elements forming the pile, either as a stepped or ramped temperature change or a prescribed heat flux [2, 3, 7]. In some analyses, the thermal load has been applied along lines within the pile body (ring in 2D analysis), again either as temperature change [6, 13, 16, 20] or a heat flux [15, 19]. This illustrates the broad range of assumptions that can be made in initialising the analysis of thermally- activated foundations. Using steady-state analyses, Bodas Freitas et al. [1] showed that the choice of either a constant temperature or adiabatic surface condition could have a profound effect on the predicted temperature field and hence, the response of the pile during subsequent thermal loading, Fig. 1. This was further expanded upon by Bourne-Webb et al. [9] and [21] under similar conditions, however the effect in a transient thermal loading condition was not explored. Fig. 1. Effect of surface boundary assumption on the response of thermally-activated piles, [01] Bodas Freitas et al. 2013. E3S Web of Conferences 195, 04013 (2020) E-UNSAT 2020 https://doi.org/10.1051/e3sconf/202019504013 © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).