161,019 research outputs found
Temperature response functions (G-functions) for single pile heat exchangers
No full textFoundation piles used as heat exchangers as part of a ground energy system have the potential to reduce energy use and carbon dioxide emissions from new buildings. However, current design approaches for pile heat exchangers are based on methods developed for boreholes which have a different geometry, with a much larger aspect (length to diameter) ratio. Current methods also neglect the transient behaviour of the pile concrete, instead assuming a steady state resistance for design purposes. As piles have a much larger volume of concrete than boreholes, this neglects the significant potential for heat storage within the pile. To overcome these shortcomings this paper presents new pile temperature response functions (G-functions) which are designed to reflect typical geometries of pile heat exchangers and include the transient response of the pile concrete. Owing to the larger number of pile sizes and pipe configurations which are possible with pile heat exchangers it is not feasible to developed a single unified G-function and instead upper and lower bound solutions are provided for different aspects ratios
G-Functions for multiple interacting pile heat exchangers
No full textPile heat exchangers – where heat transfer pipes are cast into the building piled foundations – offer an opportunity to use ground energy systems without the additional construction costs related to the provision of special purpose heat exchangers. However, analysis methods for pile heat exchangers are still under development. In particular there is an absence of available methods and guidance for the amount of thermal interaction that may occur between adjacent pile heat exchangers and the corresponding reduction in available energy that this will cause. This is of particular importance as the locations of foundation piles are controlled by the structural demands of the building and cannot be optimised with respect to the thermal analysis. This paper presents a method for deriving G-functions for use with multiple pile heat exchangers. Example functions illustrate the primary importance of pile spacing in controlling available energy, followed by the number of piles within any given arrangement. Significantly it was found that the internal thermal behaviour of a pile is not influenced appreciably by adjacent piles
Dataset for "The use of the hollow cylinder apparatus to study stress paths relevant to railway track foundations"
No full textDataset supports the paper :
A.Mamou, W. Powrie, J. Priest, C.Clayton
The use of the hollow cylinder apparatus to study stress paths relevant to railway track foundations
7th International Symposium on Deformation Characteristics of Geomaterials 26th – 28th June 2019</span
Thermal response testing through the chalk aquifer
No full textThermal conductivity of the ground is an important parameter in the design of ground energy systems, which have an increasing role to play in providing renewable heat to the built environment. For larger schemes, the bulk thermal conductivity of the ground surrounding the system is often determined in situ using a thermal response test. Although this test method is commonly used, its limitations are often not fully understood, leading to an over-simplistic interpretation that may fail to identify key facets of the ground thermal behaviour. These limitations are highlighted using data from an instrumented thermal response test carried out in a 150 m deep borehole in east London. It is shown that a single, unique value of bulk thermal conductivity may not be appropriate, as stratification of the ground can lead to differences in thermal performance, depending on the direction of heat flow. Groundwater flow within the Chalk aquifer is also shown to have an important effect on the long-term heat transfer characteristics
Pile heat exchangers: thermal behaviour and interactions
No full textThermal piles – that is structural foundation piles also used as heat exchangers as part of a ground energy system – are increasingly being adopted for their contribution to more sustainable energy strategies for new buildings. Despite over a quarter of a century having passed since the installation of the first thermal piles in northern Europe, uncertainties regarding their behaviour remain. This paper identifies the key factors which influence the heat transfer and thermal–mechanical interactions of such piles. In terms of heat output, pile aspect ratio is identified as an important parameter controlling the overall thermal performance. Temperature changes in the concrete and surrounding ground during thermal pile operation will lead to additional concrete stresses and displacements within the pile–soil system. Consequently designers must ensure that temperatures remain within acceptable limits, while the pile geotechnical analysis should demonstrate that any adverse thermal stresses are within design safety factors and that any additional displacements do not affect the serviceability of the structur
Comparison of two different models for pile thermal response test interpretation
No full textThermal response tests (TRTs) are regularly used to characterise the thermal resistance of borehole heat exchangers and to assess the thermal conductivity of the surrounding ground. It is becoming common to apply the same in situ testing technique to pile heat exchangers, despite international guidance suggesting that TRTs should be limited to hole diameters of 152 mm (6 in.). This size restriction arises from the increased thermal inertia of larger diameter heat exchangers, which invalidates the assumption of a steady state within the concrete needed to interpret the test data by traditional line source analysis techniques. However, new methods of analysis for pile heat exchangers have recently been developed that take account of the transient behaviour of the pile concrete. This paper applies these new methods to data from a multi-stage TRT conducted on a small diameter test pile. The thermal conductivity and thermal resistance determined using this method are then compared with those from traditional analytical approaches based on a line source analysis. Differences between the approaches are discussed, along with the observation that the thermal resistance may not be constant over the different test stages
Data set for "Modelling the effects of trafficking and tamping on scaled railway ballast in triaxial tests"
No full textData for the paper Aingaran, S., Le Pen, L., Zervos, A., & Powrie, W. (2018). Modelling the effects of trafficking and tamping on scaled railway ballast in triaxial tests. Transportation Geotechnics.</span
Dataset for: Train loading effects in railway geotechnical engineering: ground response,analysis, measurement and interpretation
No full textData generated for examples given the paper: Powrie, W., Le Pen, L., Milne, D., & Thompson, D. (2019). Train loading effects in railway geotechnical engineering: ground response, analysis, measurement and interpretation. Transportation Geotechnics.</span
The thermal behaviour of three different auger pressure grouted piles used as heat exchangers
No full textThree auger pressure grouted (APG) test piles were constructed at a site in Richmond, Texas. The piles were each equipped with two U-loops of heat transfer pipes so that they could function as pile heat exchangers. The piles were of two different diameters and used two different grouts, a standard APG grout and a thermally enhanced grout. Thermal response tests, where fluid heated at a constant rate is circulated through the pipe loops, were carried out on the three piles, utilising either single or double loops. The resulting test data can be used to determine the surrounding soil thermal conductivity and the pile thermal resistance, both essential design parameters for ground source heat pump schemes using pile heat exchangers. This paper uses parameter estimation techniques to fit empirical temperature response curves to the thermal response test data and compares the results with standard line source interpretation techniques. As expected, the thermal response tests with double loops result in smaller thermal resistances than the same pile when the test was run with a single loop. Back analysis of the pile thermal resistance also allows calculation of the grout thermal properties. The thermally enhanced grout is shown to have inferior thermal properties than the standard APG grout. Together these analyses demonstrate the importance of pile size, grout thermal properties and pipe positions in controlling the thermal behaviour of heat exchanger piles
Terzaghi's theory of consolidation and the discovery of effective stress. (Compiled from the work of K. TErzaghi and A.W. Skempton)
No full textTerzaghi's theory of consolidation, and the discovery effective stress of Compiled from the work of K . Terzaghi and A . W. Skempton by C. R. I. Clayton, H. Miiller Steinhagen and W. Powrie z;2;:t:; Engng, 1995,113, Oct., 191-205 Ground Board Geotechnical Engineering Advisory Panel Paper 10843 Die Berechnung der Durchlassigkeitsziffer des I5discussion 1995 closes Written December Tones aus dem Verlauf der hydrodynamischen Spannungserscheinungen A method of calculating the coefficient of permeability of clay from the variation of hydrodynamic stress with time By I n g ...<br/
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