Energy tunnels: concept and design aspects Barla, Marco; Di Donna, Alice
Tunnelling and underground space technology,
December 2018, 2018-12-00, 2018-12, 2018-12-01, Letnik:
3, Številka:
4
Journal Article
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Geotechnical structures are increasingly employed as energy geostructures in Europe and worldwide. Besides being constructed for their primary structural role, they are equipped to exchange heat with ...the ground and supply thermal energy for heating and cooling of buildings and de-icing of infrastructures. This technology can play a fundamental role in the current challenge of addressing the increasing need for clean and renewable sources of energy. This study investigates the possibility of thermal activation of tunnel linings. Particularly, attention will be paid on a new energy segment, which can be used together with tunnel boring machine tunneling to create so-called energy tunnels. Thermal and mechanical designs need to be developed by making effective use of computational methods to quantify the exploitable heat and assess the possible consequences on the surrounding ground and the structure itself. Guidance on how to proceed in this direction will be provided in this study, showing how thermo-hydro and thermo-mechanical numerical analyses can be used to achieve a proper and effective design of energy tunnels. Two examples of possible applications will also be presented.
Naturally occurring mass transport events can endanger human life and infrastructure integrity, especially in mountain areas often affected by landslides, debris flows, and avalanches. Currently ...available hazard detection systems can greatly help with the timely warning (within a few seconds) of ongoing, potentially dangerous events, but can often be inaccurate, unreliable and, due to the need for in-situ power supply, difficult to operate. Modern optical fiber sensing techniques, on the other hand, can provide exceptional accuracy but require longer measurement time and increased complexity and cost, which makes them unsuitable for such time- and cost-sensitive applications. In this paper, we present an on-field demonstration of a previously developed polarization-based optical fiber early-warning system. A mountain gully in the Valle d'Aosta region, in Italy, is used as a validation testbed to show the reliability of our approach in detecting anomalous vibration phenomena, and its robustness against the background noise associated, for instance, with car traffic or animal wildlife in the monitored area. Our findings show that the rate of variation of the state of polarization induced by real-life, hazardous rockfall events on the optical fiber is orders of magnitudes higher than the average variation rate recorded in normal conditions, thus making the proposed system a promising alternative in the mountain hazards sensors world. Moreover, we show that the system has great potential for increased accuracy in the monitoring of event dynamics by using different optical fibers in separate sections of the site, which can also be a source of additional cost reduction.
The mountain scenario is often subject to catastrophic events such as rockfalls and avalanches, potentially dangerous for both people and civil infrastructures. Early-warning alarm systems that in ...case of such events can immediately turn on a traffic light on a mountain road and send remote alarms to control rooms, have already been developed in the geotechnical engineering sector, but all have some limitations and/or very high costs. In this work we propose an immediate-warning monitoring system based on fiber polarization sensing. Anomalies such as rockfalls and avalanches would change the instantaneous birefringence of the fiber installed in the area to be monitored, and can be sensed by looking at the state of polarization at the fiber output. The novelty of our paper is the development of an algorithm that is able to detect dangerous events, which we experimentally emulated on a reduced scale physical model of a mountain slope, in which fibers have been buried in different configurations. Our findings show that the system can correctly sense all the experimentally generated rockfall phenomena and for all the installed fiber configurations, and it is also robust to false alarms, provided that the monitoring algorithm main parameters are properly set.
In this paper, we propose a wireless sensor network (WSN) designed for monitoring and risk management of landslides, where data collected by sensors are delivered through the network to a remote unit ...for online analysis and alerting. To ensure fast deployment, robustness in harsh environments, and very long lifetime, the sensor nodes and the communication protocol have been specifically conceived, so that the network is self-organizing, fault tolerant, and adaptive. The WSN has been installed on a landslide located in Torgiovannetto (Italy) for an experimental campaign of several months where performance metrics, such as radio link and path statistics as well as battery levels, have been collected. These metrics demonstrated the effectiveness of the network protocols to manage self-organization, node failures, low link quality, and unexpected battery depletion. With negligible human intervention during the pilot experiment, the WSN revealed a very high level of robustness, which makes it suitable to monitor landslides in critical scenarios.
Trenchless technology is often used in congested urban areas or river crossings to install underground pipelines to minimize disturbance to surface traffic or other activities. Pipe jacking is a ...typical technique applied to jack pipe segments between two working shafts. However, the design of the jacking force is usually implemented using empirical methods. It should be emphasized that the jacking force will change for each site, depending on the magnitude of overcut, lubricants, work stoppages, geology and misalignment. A particle method is proposed to estimate the jacking force along the pipe. The microparameters are calibrated for sandy soils in Shenyang, so that the macroscale material behavior can be reproduced using the particle model. Hence, the normal force around the pipe circumference can be derived in the particle model, after which the interface friction coefficient is applied to evaluate the friction resistance mobilized at the soil-pipe interface. A modified Protodyakonov’s arch model can be used to assess the magnitude of earth pressure acting on the shield face. In the end, the combination of friction resistance and face pressure provides the jacking force. The efficacy of the proposed particle method is demonstrated by comparing calculated jacking forces with those measured in the field for three types of jacking machines in sandy soils under the Hun River, Shenyang.
Energy linings are receiving great interest due to their potential to transform a tunnel into a smart energy system for enhancing thermal comfort of buildings and metro stations, as well as to absorb ...waste heat from the tunnel environment. Yet, besides their thermal performance, the impacts of equipping segments with a net of pipes are still challenging in the framework of energy tunnels structural design. Indeed, the thermal regime of the concrete members is altered due to heat carrier fluid circulation. Hence, the need to shed some light on the possible limit states attainment arises. In this paper, field monitoring of stresses and strains are presented for the first time in relation to a full scale monitored prototype of Enertun energy tunnel lining installed in Turin, Italy. Experimental data are compared to the results of a coupled thermo-mechanical numerical model, showing to be in good agreement. Criticalities from the ultimate limit state do not emerge, although a deeper analysis of serviceability limit states attainment should be performed.
•Energy tunnels design requires two additional stages: thermal and structural design.•Energy tunnels can exchange from about 10–20 W/m2 to 50–60 W/m2.•Best application of tunnels as heat exchangers ...is in urban areas.•Urban planning can optimize integration with distribution networks.•Up to 18,7 MW of thermal power can be exploited along the Turin ML2.
The use of renewable energies will be increasingly necessary to reduce carbon dioxide emissions. An important contribution can be provided by energy tunnels, which make it possible to draw on a form of clean, renewable and locally accessible thermal energy for heating and air conditioning of buildings. The paper describes the characteristics of an energy tunnel and the design aspects necessary for its conception. Explicit reference will be made to the studies conducted at the Politecnico di Torino which led to the development of an innovative energy segment then used to create an experimental prototype in the true size of an energy tunnel. The data collected allowed to evaluate the performance of the system and to study the possibility of thermally activating the tunnels of the future Line 2 of the Turin Metro, allocating the heat partly to the air conditioning of the stations and partly to external users. With a view to sustainable urban development, the possibility of integration with district heating systems and the possible creation of local heat distribution networks at different temperatures, directly connected to the underground infrastructure, is particularly attractive and promising.
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