Assessment of Design Procedures for Vertical Borehole Heat Exchangers

The use of ground source energy systems is a well-established method to provide low cost heating to buildings, diversify the energy mix and help meeting increasingly stricter sustainability targets. However, considerable uncertainties remain over their efficient design, with several standards, guidelines and manuals being proposed over the last few years. This paper aims at providing insight into the implications to the design of a vertical borehole heat exchanger of the adoption of different design procedures. The hypothetical case of a typical dwelling located in London, UK, is analysed in order to highlight the impact on the final design of the chosen methodology. Moreover, a parametric study using an analytical design procedure was performed to point out the influence of various factors, such as borehole characteristics and thermal properties of the ground. It is shown that there are considerable discrepancies between design methods and that uncertainties in some input parameters, such as the thermal properties of the ground, which for relatively small systems are often selected from tables rather than measured in situ, may have a substantial influence on the length of borehole required

Numerical interpretation of the coupled hydromechanical behaviour of expansive clays in constant volume column tests

© The authors and ICE Publishing: All rights reserved, 2015.Experimental and numerical studies of the behaviour of expansive clays have been attracting increasing interest, due to their good sealing properties, which render them ideal to be used as engineered barriers (buffers) in both active (e.g. nuclear) and non-active waste disposal facilities. Both large scale and laboratory scaled experiments indicate that the sealing capabilities of the buffer are fundamentally governed by its volumetric behaviour when wetted. In this paper, a constant volume column infiltration test, performed under isothermal conditions on compacted MX80 bentonite, is modelled numerically using the Imperial College Finite Element Program (ICFEP). A modified version of the Barcelona Basic Model is used to simulate the behaviour of the buffer, which is inherently partly saturated. The numerical results agree well with the observed experimental data, especially with regard to the advancement of the wetting front. A detailed interpretation of the computed evolutions with time of stress state, suction and void ratio at different elevations along the samples axis is carried out, providing insight into the complex hydro-mechanical response of the buffer during the experiment. Indeed, even though the overall volume of the sample was kept constant, a region of localised dilation, which induced the contraction of other zones of the material, was observed to advance simultaneously with the wetting front along the height of the soil column

Dissipated energy in undrained cyclic triaxial tests

Energy-based methods are an emerging tool for the evaluation of liquefaction potential. These methods relate excess pore water pressure build-up to seismic energy dissipated per unit volume. Further development of these methods require their validation through laboratory testing. In this paper, a comprehensive study of energy dissipated during cyclic triaxial tests is undertaken. Results of undrained cyclic triaxial tests performed on air-pluviated samples of Hostun sand prepared with different initial densities and subjected to several confining pressures and loading amplitudes are presented. The energy dissipated per unit volume is estimated from the experimental results and correlated to the generated excess pore water pressure. The correlation between those quantities appear to be independent of the initial relative density of the sample, isotropic consolidation pressure and cyclic stress ratio used in the tests. Moreover, the relationship between observed doubleamplitude axial strain and the energy dissipated per unit volume is examined. It is found that this relationship is greatly dependent on the relative density of the sample

Planning travel as everyday design

This paper examines the implications of conceptualising planning as a type of design activity. This is explored through results from a two-month field study that investigated the planning and decision making behaviour of people engaged in preparing for multipoint, international air travel. Planning travel is a type of ill-structured complex problem that is characterised as being temporally sporadic, sometimes synchronous, often asynchronous, frequently collaborative, and spatially varied with participants at different times co-located and in separate places. Research participants were professional travel agents and non-professional but experienced travel planners. Ancillary material collected included photographs of the planning situation and drawings and notes made by participants. In contrast to the formalised prescriptive planning models common in cognitive science and operations research, the everyday planning activity featured in this study is situated and naturalistic. This research is undertaken with a view to designing systems to support the design and decision making activity of travel planners. Copyright the author(s) and CHISIG

A study of email and SMS use in rural Indonesia

This paper describes a two-year research study that piloted and evaluated the use of low-cost, low-bandwidth Information and Communications Technology (ICT) to support meetings between agricultural researchers and farmers in rural Indonesia and researchers in Australia. We found that the primary constraints to ICT use in rural Indonesia are rarely technical, but rather relate to the knowledge, social and economic systems within which they are used. This study revealed how different local appropriations of email and mobile phone SMS clash, which often resulted in misunderstanding, frustration and reduced team cohesion and performance. This research contributes to understanding the role of ICT to enhance social inclusion of those in remote parts of developing countries. © ACM 2009

Investigating soil-water retention characteristics at high suctions using Relative Humidity control

A technique for controlling relative humidity (RH) is presented, which involves supplying a sealed chamber with a continuous flow of air at a computer-regulated RH. The desired value of RH is achieved by mixing dry and wet air at appropriate volumes and is measured for servo-control at three locations in the chamber with capacitive RH sensors and checked with a sensitive VAISALA sensor. The setup is capable of controlling RH steadily and continuously with a deviation of less than 0.2% RH. The technique was adopted to determine wetting soil-water retention curves (SWRC) of statically compacted London Clay, under both free-swelling and constant volume conditions. The RH within the chamber was increased in a step-wise fashion, with each step maintained until vapour equilibrium between the chamber atmosphere and the soil samples was established. Independent filter paper measurements further validate the method, while the obtained retention curves complement those available in the literature for lower ranges of suction

On the assessment of energy dissipated through hysteresis in finite element analysis

The accurate reproduction of the hysteretic behaviour exhibited by soils under cyclic loading is a crucial aspect of dynamic finite element analyses and is typically described using the concept of damping ratio. In this paper, a general algorithm is presented for assessing the damping ratio simulated by any constitutive model based on the registered behaviour in three-dimensional stress-strain space. A cyclic nonlinear elastic model capable of accurately reproducing a wide range of features of soil behaviour, including the variation of damping ratio with deformation level, is chosen to illustrate the capabilities of the proposed algorithm. The constitutive model is described and subsequently employed in two sets of finite element analyses, one involving the dynamic response of a sand deposit subjected to different types of motion and another focussing on the simulation of a footing subjected to cyclic vertical loading. The application of the presented algorithm provides insight into the processes through which energy is dissipated through hysteresis