Response of pavement foundations incorporating both geocells and expanded polystyrene (EPS) geofoam

The suitability of geocell reinforcement in reducing rut depth, surface settlements and/or pavement cracks during service life of the pavements supported on expanded polystyrene (EPS) geofoam blocks is studied using a series of large-scale cyclic plate load tests plus a number of simplified numerical simulations. It was found that the improvement due to provision of geocell constantly increases as the load cycles increase. The rut depths at the pavement surface significantly decrease due to the increased lateral resistance provided by the geocell in the overlying soil layer, and this compensates the lower competency of the underlying EPS geofoam blocks. The efficiency of geocell reinforcement depends on the amplitude of applied pressure: increasing the amplitude of cyclic pressure increasingly exploits the benefits of the geocell reinforcement. During cyclic loading application, geocells can reduce settlement of the pavement surface by up to 41% compared to an unreinforced case – with even greater reduction as the load cycles increase. Employment of geocell reinforcement substantially decreases the rate of increase in the surface settlement during load repetitions. When very low density EPS geofoam (EPS 10) is used, even though accompanied with overlying reinforced soil of 600 mm thickness, the pavement is incapable of tolerating large cyclic pressures (e.g. 550 kPa). In comparison with the unreinforced case, the resilient modulus is increased by geocell reinforcement by 25%, 34% and 53% for overlying soil thicknesses of 600, 500 and 400 mm, respectively. The improvement due to geocell reinforcement was most pronounced when thinner soil layer was used. The verified three-dimensional numerical modelings assisted in further insight regarding the mechanisms involved. The improvement factors obtained in this study allow a designer to choose appropriate values for a geocell reinforced pavement foundation on EPS geofoam

Subgrade equilibrium water content and resilient modulus for UK clays

The main functional requirement of the subgrade is to resist excessive deformations during construction and in service. Deformation is controlled by ensuring adequate foundation resilient modulus. UK pavement design currently relies upon the determination of long-term CBR values for subgrades, which results in conservative pavement foundation design. To allow more realistic design an analytical approach is required, including measured values of resilient modulus at anticipated short- and long-term equilibrium subgrade water contents. Resilient modulus is determined from repeated load triaxial tests with on-sample strain measurement. Results from these tests on samples adjusted to model the subgrade behaviour at various design conditions are presented. These results are discussed, highlighting problems both with measuring small strains on undisturbed soils and in predicting and modelling accurately long-term soil behaviour. RÉSUMÉ: Le critère principal d’une sous-couche est de résister à des déformations excessives en construction puis en service. La conception des chaussées au Royaume-Uni est actuellement basée sur la détermination de l'indice portant Californien (CBR) à longterme des sous-couches. Pour une conception plus réaliste, il est nécessaire d'adopter une approche prenant en compte des valeurs de module de résilience mesurées à des degrés d'humidité de sous-couches à l'équilibre simulés à court et long-terme. Le module de résilience est déterminé à partir d'essais répétés en charge triaxiale avec mesure des contraintes sur l'échantillon. Dans cet article les résultats de ces tests sur des échantillons simulant le comportement de la sous-couche sous diverses conditions de conception sont présentés. Ces résultats sont discutés, en soulignant les problèmes résultant de la mesure de faibles contraintes sur des sols non-perturbés, et dus à la prédiction et à la modélisation du comportement des sols à long-terme

A dynamic gradient ratio test apparatus

The soil-geotextile filtration mechanism is a complex process which depends on physical compatibility between the geotextile and the soil to be retained. Several methods have been proposed by researchers for assessing the filtration behaviour of soil-geotextile composite systems under steady state conditions. The Gradient Ratio (GR) test is the most commonly used method for measuring filtration compatibility of soil-geotextile systems. This paper describes the design of a modified GR permeability test apparatus to overcome disadvantages associated with traditional GR test devices. The apparatus can perform filtration tests under static and dynamic conditions and can be used to evaluate the filtration compatibility of fine-grained soils with geotextiles. The apparatus is incorporated within a triaxial testing system, hence representative field stress conditions can be applied to test specimens. Some exemplar GR tests performed on coarse and fine-grained soils with a non-woven geotextile are presented in this paper. Unidirectional dynamic loads are applied within the filtration tests to replicate highway traffic loading. Test results show that dynamic loading affects the filtration behaviour at the soil-geotextile interface by increasing the fine particles migration towards the geotextile, but that, for the soil evaluated here, this effect was small

Pavement temperature mitigation by the means of geothermally and solar heated air

In this article, a novel method to mitigate pavement temperatures by the means of air convection is presented. The technique introduced here is based on a new type of experimental setup called a ground source heat simulator, which is able to feed air at a controlled temperature to a set of pipes embedded under a test pavement surface. The air at the chosen temperature can flow through the designed system by natural convection. The air heated by the simulated geothermal source can mitigate the pavement temperature in winter and summer conditions in order to avoid freezing and overheating of paving surfaces in an urban environment. In particular, during winter the geothermal air warms up the pavement, while during summer the pavement is cooled down. Laboratory tests of the ground source heat simulator allowed the collection of a high amount of data, which is here analysed statistically and computationally. This article shows that the use of geothermal energy to preheat the inlet air in pavements where an array of pipes is installed can provide a measurable contribution for the mitigation of pavement temperatures in both winter and summer conditions. Furthermore, the experimental data gathered successfully proved the effectiveness of computational simulations for the study of buoyancy powered air flow through channels buried under pavements and increased the understanding of the physical phenomena happening in the system under analysis. Finally, preliminary testing in the environment showed that the concept is effective and works as expected

Predicting and measuring vertical track displacements on soft subgrades

Several analytical models can be used to predict the propagation of bending waves in the track/embankment system. A model of a Euler beam on a Winkler foundation is studied and used to demonstrate how the magnitude of displacements are dependent on train speed and track damping. The methods by which the model parameters may be calculated are discussed and their relative advantages and disadvantages are considered. From this study it is possible to form practical suggestions on methods by which the design of rail tracks can be adjusted to limit the maximum transient deflections as a train passes. This paper compares results from a predictive method with the results of in-situ assessments

Bhutanese road and bridge resilience to floods and landslides – first suggestions for assessment and response

Bhutan is a country with one of the lowest per capita incomes and very limited financial and industrial resources. Situated in the Himalayan foothills and mountains, its road transport network must negotiate very challenging terrain in terms of topography, rainfall and earthquake propensity with a widespread risk of flooding and landslides. For the majority of communities, there is only a single road or bridge by which markets and services may be accessed. If such roads or bridges are cut by flood or landslide, communities upstream of the cut will, effectively, become isolated. The paper describes the initial conclusions drawn from an investigatory visit to assess the current vulnerability of such lifeline roads and to propose simple means of evaluating problems before roads become impassable and improving remedial responses. It is concluded that small-scale activities could be undertaken to improve preparedness and to speed repairs but that locating resources would need careful planning given the uncertainties of the time and location of future eventsPapers Presented at the 2018 37th Southern African Transport Conference 9-12 July 2018 Pretoria, South Africa. Theme "Towards a desired transport future: safe, sufficient and affordable"

Experimental and numerical investigation of the uplift capacity of plate anchors in geocell-reinforced sand

Plate anchors are frequently used to provide resistance against uplift forces. This paper describes the reinforcing effects of a geocell-reinforced soil layer on uplift behavior of anchor plates. The uplift tests were conducted in a test pit at near full-scale on anchor plates with widths between 150 and 300 mm with embedment depths of 1.5–3 times the anchor width for both unreinforced and geocell-reinforced backfill. A single geocell layer with pocket size 110 mm × 110 mm and height 100 mm, fabricated from non-perforated and nonwoven geotextile, was used. The results show that the peak and residual uplift capacities of anchor models were highest when the geocell layer over the anchor was used, but with increasing anchor size and embedment depth, the benefit of the geocell reinforcement deceases. Peak loads between 130% and 155% of unreinforced conditions were observed when geocell reinforcement was present. Residual loading increased from 75% to 225% that of the unreinforced scenario. The reinforced anchor system could undergo larger upward displacements before peak loading occurred. These improvements may be attributed to the geocell reinforcement distributing stress to a wider area than the unreinforced case during uplift. The breakout factor increases with embedment depth and decreased with increasing anchor width for both unreinforced and reinforced conditions, the latter yielding larger breakout factors. Calibrated numerical modelling demonstrated favorable agreement with experimental observations, providing insight into detailed behavior of the system. For example, surface heave decreased by over 80% when geocell was present because of a much more efficient stress distribution imparted by the presence of the geocell layer

Dense circumnuclear molecular gas in starburst galaxies

We present results from a study of the dense circumnuclear molecular gas of starburst galaxies. The study aims to investigate the interplay between starbursts, active galactic nuclei and molecular gas.We characterize the dense gas traced by HCN, HCO and HNC and examine its kinematics in the circumnuclear regions of nine starburst galaxies observed with the Australia Telescope Compact Array. We detect HCN (1-0) and HCO (1-0) in seven of the nine galaxies and HNC (1-0) in four. Approximately 7 arcsec resolution maps of the circumnuclear molecular gas are presented. The velocity-integrated intensity ratios, HCO (1-0)/HCN (1-0) and HNC (1-0)/HCN (1-0), are calculated. Using these integrated intensity ratios and spatial intensity ratio maps, we identify photon-dominated regions (PDRs) in NGC 1097, NGC 1365 and NGC 1808. We find no galaxy which shows the PDR signature in only one part of the observed nuclear region.We also observe unusually strong HNC emission in NGC 5236, but it is not strong enough to be consistent with X-ray-dominated region chemistry. Rotation curves are derived for five of the galaxies and dynamical mass estimates of the inner regions of three of the galaxies are made. © 2016 The Authors.This project was supported by the Brother Vincent Cotter Award for Physics (UNSW). LVM has been supported by Grant AYA2011-30491-C02-01 co-financed by MICINN and FEDER funds, and the Junta de Andalucia (Spain) grants P08-FQM-4205 and TIC-114. WAB acknowledges the support as a Visiting Professor of the Chinese Academy of Sciences (KJZD-EW-T01). The research leading to these results has received funding from the European Community's Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No 229517.Peer Reviewe

Magnetic fields and Sunyaev-Zel'dovich effect in galaxy clusters

In this work we study the contribution of magnetic fields to the Sunyaev Zeldovich (SZ) effect in the intracluster medium. In particular we calculate the SZ angular power spectrum and the central temperature decrement. The effect of magnetic fields is included in the hydrostatic equilibrium equation by splitting the Lorentz force into two terms one being the force due to magnetic pressure which acts outwards and the other being magnetic tension which acts inwards. A perturbative approach is adopted to solve for the gas density profile for weak magnetic fields (< 4 micro G}). This leads to an enhancement of the gas density in the central regions for nearly radial magnetic field configurations. Previous works had considered the force due to magnetic pressure alone which is the case only for a special set of field configurations. However, we see that there exists possible sets of configurations of ICM magnetic fields where the force due to magnetic tension will dominate. Subsequently, this effect is extrapolated for typical field strengths (~ 10 micro G) and scaling arguments are used to estimate the angular power due to secondary anisotropies at cluster scales. In particular we find that it is possible to explain the excess power reported by CMB experiments like CBI, BIMA, ACBAR at l > 2000 with sigma_8 ~ 0.8 (WMAP 5 year data) for typical cluster magnetic fields. In addition we also see that the magnetic field effect on the SZ temperature decrement is more pronounced for low mass clusters ( ~ 2 keV). Future SZ detections of low mass clusters at few arc second resolution will be able to probe this effect more precisely. Thus, it will be instructive to explore the implications of this model in greater detail in future works.Comment: 20 pages, 8 figure

Discrimination, labour markets and the Labour Market Prospects of Older Workers: What Can a Legal Case Teach us?

As governments become increasingly concerned about the fiscal implications of the ageing population, labour market policies have sought to encourage mature workers to remain in the labour force. The ‘human capital’ discourses motivating these policies rest on the assumption that older workers armed with motivation and vocational skills will be able to return to fulfilling work. This paper uses the post-redundancy recruitment experiences of former Ansett Airlines flight attendants to develop a critique of these expectations. It suggests that policies to increase older workers’ labour market participation will not succeed while persistent socially constructed age- and gender- typing shape labour demand. The conclusion argues for policies sensitive to the institutional structures that shape employer preferences, the competitive rationality of discriminatory practices, and the irresolvable tension between workers’ human rights and employers’ property rights