Influences on the thermal efficiency of energy piles

Energy piles have recently emerged as a viable alternative to borehole heat exchangers, but their energy efficiency has so far seen little research. In this work, a finite element numerical model is developed for the accurate 3D analysis of transient diffusive and convective heat exchange phenomena taking place in geothermal structures. The model is validated by reproducing both the outcome of a thermal response test carried out on a test pile, and the average response of the linear heat source analytical solution. Then, the model is employed to carry out a parametric analysis to identify the key factors in maximising the pile energy efficiency. It is shown that the most influential design parameter is the number of pipes, which can be more conveniently increased, within a reasonable range, compared to increasing the pile dimensions. The influence of changing pile length, concrete conductivity, pile diameter and concrete cover are also discussed in light of their energetic implications. Counter to engineering intuition, the fluid flowrate does not emerge as important in energy efficiency, provided it is sufficient to ensure turbulent flow. The model presented in this paper can be easily adapted to the detailed study of other types of geothermal structures

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

Characterisation of ground thermal and thermo-mechanical behaviour for shallow geothermal energy applications

Increasing use of the ground as a thermal reservoir is expected in the near future. Shallow geothermal energy (SGE) systems have proved to be sustainable alternative solutions for buildings and infrastructure conditioning in many areas across the globe in the past decades. Recently novel solutions, including energy geostructures, where SGE systems are coupled with foundation heat exchangers, have also been developed. The performance of these systems is dependent on a series of factors, among which the thermal properties of the soil play one of major roles. The purpose of this paper is to present, in an integrated manner, the main methods and procedures to assess ground thermal properties for SGE systems and to carry out a critical review of the methods. In particular, laboratory testing through either steady-state or transient methods are discussed and a new synthesis comparing results for different techniques is presented. In-situ testing including all variations of the thermal response test is presented in detail, including a first comparison between new and traditional approaches. The issue of different scales between laboratory and in-situ measurements is then analysed in detail. Finally, thermo-hydro-mechanical behaviour of soil is introduced and discussed. These coupled processes are important for confirming the structural integrity of energy geostructures, but routine methods for parameter determination are still lacking

The role of frictional heating in the development of catastrophic landslides

In this work, a new thermo-mechanical model is developed by improving on an existing one, applicable to large deep seated landslides and rockslides consisting of a coherent mass sliding on a thin clayey layer. The considered time window is that of catastrophic acceleration, starting at incipient failure and ending a few seconds later, when the acquired displacement and velocity are such that the sliding material begins to break up into pieces. The model accounts for temperature rise in the slip zone due to the heat produced by friction, leading to thermoplastic collapse of the soil skeleton and subsequent increase of pore water pressure. This in turn drastically decreases the resistance to motion and allows the overlying mass to move downslope ever more freely.The proposed model is implemented numerically and validated by back-analysing the two well-documented catastrophic landslide case histories of Vajont and Jiufengershan. The model is then employed to carry out a parametric study to systematically investigate the development of catastrophic failure in uniform slopes. It was found that the most influential parameters in promoting catastrophic collapse are (1) the static friction-softening rate a1, (2) the slope inclination ?, (3) the soil permeability kw, (4) the dynamic residual friction angle rd ? and (5) the overburden thickness H. The most dangerous situation is when a1, ? and H are very large and kw and rd ? are very low. Of the above, the ‘thermo-mechanical parameters’ kw and H deserve more attention as they have been introduced by the thermo-mechanical model and are not normally considered in standard stability analyses of uniform slopes. A second parametric study was performed to demonstrate that thermo-mechanical parameters alone can make a difference between a relatively non-catastrophic event and a catastrophic one. Hence, further insight into the design of landslide risk mitigation measures can be gained if, in addition to the standard site investigations, the permeability of the soil is measured and the depth of an existing or expected failure surface is measured or estimated respectively

Piuro Landslide: 3D Hydromechanical Numerical Modelling of the 1618 Event

The Piuro 1618 landslide represents a well-known case history of a large Alpine landslide. It destroyed the ancient village of Piuro (Italian Bregaglia Valley), renowned as an important trading center between the Mediterranean region and Northern Europe. The event had a significant impact among communities of all Alpine regions and was well documented by chronicles and paintings during subsequent decades. However, some aspects, such as the geometry reconstruction of the landslide body, the location of the landslide scarp, and its dynamics, remained undefined in previous studies, and a geomechanical characterization of the failure area is completely missing. Using field and laboratory analysis followed by stress–strain numerical modelling, this work develops a 3D conceptual geomechanical model of the slope considering its complex geological framework. The aim is to back-analyze the 1618 event, defining predisposing and triggering factors of the sliding event, and providing verifications on the geometry and location of the failure scar, as well as on the landslide dynamics. A coupled hydro-mechanical analysis with a 3D numerical approach is presented, assuming a rainfall scenario as a possible triggering factor. Simulated displacement and the development of a deep region of shear strain localization at a depth roughly corresponding to that of the detected Piuro sliding surface, allow us to highlight the mechanical role of geological elements outcropping along the slope and to validate the proposed scenario as a likely triggering factor for the 1618 event

Static and seismic numerical analysis of a shallow landslide located in a vulnerable area

L’articolo presenta le analisi svolte per studiare il comportamento di un movimento franoso classificabile come “molto lento” e “poco profondo”, situato sul versante laterale di un invaso artificiale. Il lavoro comprende la descrizione di un’ampia campagna geotecnica per la caratterizzazione dei terreni, l’elaborazione dei dati di monitoraggio e la modellazione numerica 2D del versante sia in condizioni statiche che dinamiche mediante analisi agli Elementi Finiti. I risultati dello studio numerico dimostrano che le possibili riattivazioni del movimento sono per lo più guidate da fattori idrologici, mentre i fenomeni sismici possono accelerare i movimenti e produrre spostamenti aggiuntivi che rimangono tuttavia limitati se confrontati con l’estensione complessiva del movimento. Nell’analisi presentata è stata studiata l’importanza di considerare le due componenti spaziali, orizzontale e verticale, del terremoto ed è stato osservato che, per il caso esaminato, considerare la componente verticale non produce incrementi di spostamento significativi. Al contrario, il metodo adottato per la definizione dell’azione sismica può produrre differenze significative nei risultati della simulazione. Lo studio dimostra, infatti, che definire l’input sismico a partire dalla “pericolosità sismica di base” o da uno studio sismico-tettonico specifico per il sito in esame conduce a importanti differenze nella scelta del terremoto di riferimento da usare nelle analisi sismiche e, di conseguenza, negli spostamenti previsti per la frana.The paper summarizes the work carried out to study the activity of a shallow, slow-moving landslide located on the lateral slope of an artificial reservoir. The work includes the description of an extensive geotechnical campaign to characterize the soils, the elaboration of monitoring data, and 2D numerical modeling of the slope in static and dynamic conditions using Finite Element Analysis. The results of the numerical study demonstrate that possible re-activations of the movement are mostly driven by hydrological factors, while earthquakes can accelerate the movements but bring about additional displacements within tolerable limits. The relative importance of the two spatial components of the earthquake has been investigated suggesting that, for the examined case, considering the vertical component does not produce appreciable displacement increments. On the contrary, the method adopted to define the seismic action causes significant differences in simulation results. Starting from the ‘basic seismic hazard’ or from a site-specific seismic-tectonic study brings about important differences in the selection of the reference earthquake for the seismic analyses and, consequently, on the predicted landslide displacements

Chlamydia trachomatis detection in a population of asymptomatic and symptomatic women: correlation with the presence of serological markers for this infection

A study of 371 women (261 asymptornatic and 110 symptomatic subjects with clinical PID) was performed to detect the presence of Chlamydia trachomatis (C.t.) and to correlate the serological markers against this microrganism, such as antibody to chlamydial bsp60 (Ab-Chsp60) and different levels of IgG, IgM and IgA, with epidemiology, pathology, sexual habits, age, diagnostic methods in the groups of women with and without pelvic inflammatory disease (PID). We found a statistically significant difference between the asymptornatic and symptomatic women regarding the presence of C.t. (3.4% versus 20%; p < 0.0001). This presence was affected by the age of women (more in the group:525 years old), by having sex with new partners mainly if they did not undergo an antibiotic treatment. The association of antibody Chsp60 with the presence of clinical PID was quite striking. We also found a strict correlation between the detection of Ab-Chsp60 and previous chlamydial infection as well as between Ab-Chsp60 and elevated serum chlamydial IgG or IgA levels. Due to these findings, we can say that the use of serological markers for C.t. in clinical practice may be an important tool for an early screening and diagnosis of women at high risk of chlamydial infection