Mechanisms of root reinforcement in soils: an experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation.

Vegetation on railway or highway slopes can improve slope stability through the generation of soil pore water suctions by plant transpiration and mechanical soil reinforcement by the roots. To incorporate the enhanced shearing resistance and stiffness of root-reinforced soils in stability calculations, it is necessary to understand and quantify its effectiveness. This requires integrated and sophisticated experimental and multi-scale modelling approaches to develop an understanding of the processes at different length scales, from individual root-soil interaction through to full soil-profile or slope scale.

Installation and performance of horizontal wells for dewatering at municipal solid waste landfills in China.

Vertical wells are conventionally used to lower leachate levels or pressures in municipal solid waste (MSW) landfills. However, they are not always efficient or even effective, and in some circumstances retro-fitted horizontal wells represent a potential alternative. However, horizontal wells can be difficult to install and there is a lack of data on their performance.

Experimental study of the intrinsic permeability of municipal solid waste.

Changing patterns of municipal solid waste (MSW) management, for example sorting for recycling and mechanical-biological treatment (MBT), will change the nature of the residual material going to landfill and in particular its intrinsic permeability. This is an important parameter, not least because of its influence on gas and leachate flows and the ramifications for gas and leachate management. This paper reports the results of laboratory permeability tests on specimens of MSW recovered from boreholes drilled in a Chinese landfill, under both liquid and gas flow.

Automated processing of railway track deflection signals obtained from velocity and acceleration measurements.

Measurements of low-frequency vibration are increasingly being used to assess the condition and performance of railway tracks. Displacements used to characterise the track movement under train loads are commonly obtained from velocity or acceleration signals. Artefacts from signal processing, which lead to a shift in the datum associated with the at-rest position, as well as variability between successive wheels, mean that interpreting measurements is non-trivial.

Behaviour of under sleeper pads at switches and crossings - Field measurements.

Major growth in rail traffic in many parts of the world in recent years has brought railway networks close to capacity and restricted the time available for track access to carry out maintenance work without costly temporary route closures. There are, therefore, significant benefits in designing or modifying ballasted track systems to reduce maintenance and associated access requirements. Under sleeper pads (USPs) offer the potential to extend ballasted track system life and to extend the intervals between routine maintenance.

A systems framework for national assessment of climate risks to infrastructure.

Extreme weather causes substantial adverse socio-economic impacts by damaging and disrupting the infrastructure services that underpin modern society. Globally, $2.5tn a year is spent on infrastructure which is typically designed to last decades, over which period projected changes in the climate will modify infrastructure performance.

Functional relationships for the estimation of van Genuchten parameter values in landfill processes models.

Numerical models of landfill processes need to be able to estimate the capillary pressure and relative permeability of waste as a function of moisture content using analytical equations such as the van Genuchten equations. The paper identifies the range of van Genuchten parameter values for use in models and proposes a formulaic relationship between these parameter values and saturated moisture content. The concept of porous material, its behaviour under unsaturated conditions and Mualem's integral transform equation that estimates relative permeability from capillary pressure are reviewed.

Biodegradation and flushing of MBT wastes.

Mechanical-biological treatment (MBT) processes are increasingly being adopted as a means of diverting biodegradable municipal waste (BMW) from landfill, for example to comply with the EU Landfill Directive. However, there is considerable uncertainty concerning the residual pollution potential of such wastes. This paper presents the results of laboratory experiments on two different MBT waste residues, carried out to investigate the remaining potential for the generation of greenhouse gases and the flushing of contaminants from these materials when landfilled.

Quantifying the effect of settlement and gas on solute flow and transport through treated municipal solid waste.

The effect of degradation and settlement on transport properties of mechanically and biologically treated (MBT) waste was examined by applying three different tracers to two waste columns (~0.5 m diameter) in a series of closed-loop experiments. One column was allowed to biodegrade and the other was bio-suppressed.

Behavior of an MBT waste in monotonic triaxial shear tests.

Legislation in some parts of the world now requires municipal solid waste (MSW) to be processed prior to landfilling to reduce its biodegradability and hence its polluting potential through leachate and fugitive emission of greenhouse gases. This pre-processing may be achieved through what is generically termed mechanical-biological-treatment (MBT). One of the major concerns relating to MBT wastes is that the strength of the material may be less than for raw MSW, owing to the removal of sheet, stick and string-like reinforcing elements during processing.

Clogging of landfill tyre and aggregate drainage layers by methanogenic leachate and implications for practice.

This paper reports the results of pilot scale tests carried out to investigate the clogging of shredded and baled tyres in comparison with aggregates when percolated by leachates representative of those generated by methanogenic stage landfills. Realistic lifetime loading rates of methanogenic leachate were applied, and clogging was not generally apparent in any of the drainage media studied. This is in apparent contrast to many other studies that have demonstrated the susceptibility of all forms of drainage media to biological and chemical clogging when percolated with high strength organic and calcium rich leachates.

Investigations into the landfill behaviour of pretreated wastes.

Mechanical-biological treatment of municipal solid waste has become popular throughout the UK and other parts of Europe to enable compliance with the Landfill Directive. Pretreatment will have a major influence on the degradation and settlement characteristics of the waste in landfills owing to the changes in the composition and properties of the wastes. This paper presents and compares the results of long term landfill behaviour of the UK and German MBT wastes pretreated to different standards.

Characterisation of the recalcitrant organic compounds in leachates formed during the anaerobic biodegradation of waste.

This study investigates the use of UV absorption and fluorescence spectroscopy to assess the early development of recalcitrant organic compounds in leachates formed during the anaerobic biodegradation of municipal solid waste. Biochemical methane potential tests were carried out on fresh waste (FW) and composted waste (CW) over a period of 150 days and leachates produced from the degradation of two wastes were analysed for humic-like (H-L) and fulvic-like (F-L) structures by UV spectroscopy and fluorescence excitation-emission-matrix analyses. During anaerobic biodegradation, the synthesis and utilization of H-L and F-L structures in the leachates over time was indicative of the generation of the recalcitrant organic compounds.

Leachate recirculation in a landfill: some insights obtained from the development of a simple 1-D model.

The re-introduction of leachate back into the waste can play an important part in landfill management. It can encourage biodegradation by raising the water content and transporting bacteria, nutrients and waste products. It also enables leachate to be stored within the body of the landfill, for example to help minimise temporal variations in the load on a leachate treatment plant.

Modelling the compression behaviour of landfilled domestic waste.

This paper discusses the mechanisms involved in the compression of domestic waste, and how the resulting compression behaviour may be modelled. Reference is made to experimental data illustrating the effect of gas content and pore water pressure on bulk density and drainable porosity, and a theoretical model able to reproduce some but not all features of the data is presented.

Mechanical aspects of rabbit fecal dehydration.

The hydrostatic pressure required to reduce the water content of rabbit feces in an odometer from greater than 80 to less than 65% was approximately 5 atm. This pressure was unaffected by raising the temperature from 20 to 37 degrees C. It became progressively more difficult to dehydrate feces as consolidation occurred, as is evident from the significant (P less than 0.

Browning reaction systems as sources of mutagens and antimutagens.

Heated food systems contain hundreds of chemical compounds, some being mutagenic and others being antimutagenic. Studies have indicated that foods exposed to drying, frying, roasting, baking, and broiling conditions possess net mutagenic activity as assessed by the Ames/Salmonella/microsome mutagenicity test and the chromosome aberration assay with Chinese hamster ovary (CHO) cells. With the above-mentioned heat treatment of food, nonenzymic browning reactions are generally proceeding at rapid rates and are involved in the development of mutagens.

Induction of mitotic gene conversion by browning reaction products and its modulation by naturally occurring agents.

Mitotic gene conversion in the D7 strain of Saccharomyces cerevisiae was significantly enhanced by exposure to non-enzymatic browning reaction products. These products were formed during the heating of sugar (caramelization reaction) or sugar-amino acid mixtures (Maillard reaction) at temperatures normally used during the cooking of food. Several modulating factors of this convertogenic activity were identified.

Clastogenic activity of bile acids and organic acid fractions of human feces.

Chloroform extracts of fecal material from 4 subjects on normal mixed western diets were fractionated to obtain an acid fraction and a hexane extract containing neutrals and bases. The acid fraction from at least 2 of the donors induced an elevated frequency of chromosomal aberrations and exchanges in Chinese hamster ovary (CHO) cells. Since acid steroids are expected to be present in the acid fraction, 5 bile acids were assayed for clastogenic activity in CHO cells.

Antimutagenic activity of browning reaction products.

The Salmonella typhimurium assay was used to determine the antimutagenic effect of products of 2 non-enzymatic browning reactions obtained by heating a lysine-fructose mixture at 121 degrees C for 1 h and by carmelizing D-sucrose at 180 degrees C for 1.5 h. The antimutagenic effect was tested by exposing strain TA1535 in suspension to N-methyl-N' -nitro-N-Nitrosoguanidine (MNNG) in the presence of the browning reaction products.

The action of transition metals on the genotoxicity of simple phenols, phenolic acids and cinnamic acids.

Simple phenols (catechol, 4-methyl catechol, resorcinol, phloroglucinol and pyrogallol), phenolic acids (p-hydroxybenzoic acid, protocatechuic acid, vanillic acid, gallic acid, syringic acid and salicylic acid), a phenylacetic acid (3,4-dihydroxyphenylacetic acid) and eugenol were assayed for clastogenic activity in Chinese hamster ovary (CHO) cells with and without the addition of a n S9 mixture, Cu2+ (10-4M) and Mn2+ (10-4M). All dihydroxylated and trihydroxylated phenolics induced chromatid breaks and exchanges. The introduction of a methyl group seems to reduce the clastogenic capacity.

A comparative genotoxicity study of chlorogenic acid (3-0-caffeoylquinic acid).

Chlorogenic acid, a compound which occurs naturally in many food items, was assayed for genotoxic activity in 3 different test systems: reverse mutations in the preincubation test with Salmonella typhimurium, gene conversion with Saccharomyces cerevisiae strain D7, and chromosome aberrations in Chinese hamster ovary (CHO) cells. Chlorogenic acid was directly convertogenic and clastogenic, but lacked a mutagenic capacity in the Salmonella bioassay. The transition metal Mn2+ enhanced the clastogenic and convertogenic activity of chlorogenic acid.

Clastogenicity of furans found in food.

Cultured Chinese hamster ovary (CHO) cells were exposed for 3 h to furan and 6 furan derivatives (furfural, furfuryl alcohol, 5-methyl furfural, 2-methyl furan, 2,5-dimethyl furan and 2-furyl methyl ketone). Each of the 6 furan derivatives induced a relatively high frequency of chromatid breaks and chromatid exchanges in the absence of a liver microsomal activation preparation. The response of the furans to the addition of an S9 mixture differed.