Development of a practical heat of hydration model for concrete curing for geotechnical applications

Thermal integrity profiling (TIP) is a common non-destructive technique to evaluate the quality of construction of piles by analysing the temperature fields due to heat of hydration from freshly cast concrete piles. For this process to be accurate, a reliable concrete heat of hydration model is required. This paper proposes a practical and simple to calibrate four parameter model for the prediction of concrete heat of hydration. This model has been shown to be able to reproduce the evolution of heat of hydration measured in laboratory tests, as well as field measurements of temperature within curing concrete piles, as part of a thermal integrity profiling (TIP) operation performed at a site in London. With the simplicity of the model and the small number of model parameters involved, this model can be easily and quickly calibrated, enabling quick predictions of expected temperatures for subsequent casts using the same concrete mix

On the Thermal Activation of Turin Metro Line 2 Tunnels

The Turin metro Line 2 will extend for nearly 28 km and include 26 stations. It will connect the SW suburbs of the city to the NE ones. The excavation will be performed by means of TBM and Cut & Cover techniques and, once concluded, will host a fully automated driverless light metro. This paper will describe the feasibility study carried out to assess the energy potential of the thermal activation of the line by using an innovative tunnel lining segment (ENERTUN) recently patented and tested in real operating conditions. A novel methodology was adopted, involving thermo-hydraulic 3D FE numerical anal- yses to identify the geothermal potential for the different sections of the line. A study of the possible collectors for the thermal energy produced was also performed considering the planned stations, the existing buildings and the future urban developments

Energy performance of diaphragm walls used as heat exchangers

The possibility of equipping diaphragm walls as ground heat exchangers to meet the full or partial heating and cooling demands of overlying or adjacent buildings has been explored in recent years. In this paper, the factors affecting the energy performance of diaphragm walls equipped as heat exchangers are investigated through finite element modelling. The numerical approach employed is first validated using available experimental data and then applied to perform parametric analyses. Parameters considered in the analysis include panel width, the ratio between the wall and excavation depths, heat transfer pipe spacing, concrete cover, heat-carrier fluid velocity, concrete thermal properties and the temperature difference between the air within the excavation and the soil behind the wall. The results indicate that increasing the number of pipes by reducing their spacing is the primary route to increasing energy efficiency in the short term. However, the thermal properties of the wall concrete and the temperature excess within the excavation space are also important, with the latter becoming the most significant in the medium to long term. This confirms the benefits of exploiting the retaining walls installed for railway tunnels and metro stations where additional sources of heat are available

Effect of domain size in the modelled response of thermally-activated piles

The application of thermally-activated pile foundations has received significant atten-tion in the last decade with a number of large- and small-scale tests having been under-taken. Alongside these physical studies, a number of investigations utilising numerical analysis have been undertaken to examine the behaviour of single piles and pile groups. Focussing on studies examining single piles, it is apparent that a variety of dif-fering domain dimensions have been used. The work presented in this paper had the objective of systematically examining the influence of the domain size and how it af-fects the predicted thermo-mechanical response of the pile. It shows that the domain size has an important impact on the initial distribution of mobilised shaft friction due to applied mechanical load which then impacts on the subsequent thermo-mechanical re-sponse

Thermo-mechanical schemes for energy piles

Currently, schemes based on seminal empirical knowledge about energy piles subjected to mechanical and thermal loads are available to describe the response of such foundations. However, schemes based on theoretical principles may more closely reflect the predictions made for the analysis and design of energy piles. Looking at such challenge, this paper presents thermo-mechanical schemes based on thermo-elasticity theory to address the response of single energy piles to mechanical and thermal loads. The proposed schemes highlight a number of key aspects associated with the modelling of energy pile response to loading and may be considered in analysis and design. © Springer Nature Switzerland AG 2019

Numerical Analysis of the Thermo-mechanical Behavior of Energy Piles

A finite element model is developed to investigate the thermomechanical behavior of the energy pile in detail. In the model, soil is regarded as a kind of thermo-elastic-perfectly plastic material, and the interaction between the pile and soil is modeled by contact elements. In order to save the computing time, the U-tubes in the energy pile are simulated by line elements, which are proved to be suitable for calculating the temperature of the pile. To deal with the thermomechanical multi-field problem, the sequential coupling method is utilized. The simulation results show that the thermally induced stress and deformation in the pile can be significantly influenced by the properties of the soil, the applied mechanical load and the restraint condition at the pile head. Long-time simulations of the energy pile with cyclic heat injections and extractions indicate that the thermal cycles would induce an unrecoverable settlement of the pile, and the ultimate bearing capacity of the energy pile may need to be redefined in view of its longtime performance.Department of Building Services Engineerin