Colin C. Ferguson

Calculation of Low-Frequency Ground Vibrations from Railway Trains

Understanding physical mechanisms of railway-induced groundvibrations is an essential prerequisite for reducing their impact on the built environment. In this paper the theory of generation of low-frequencygroundvibrations by moving trains in the framework of the quasi-static wheel pressure effect is developed using the Greens function formalism. Mechanical properties of the rail track and parameters of train and soil (including contact nonlinearity of the track-soil system) are taken into account in a theoretical model that considers generation of elastic waves by each sleeper of the track subjected to the action of all wheel axles. The analytical expressions have been derived and the numerical calculations have been carried out for the vibration spectra generated by trains. It is shown that these spectra depend strongly on the mechanical properties of soil, on the axle loads of the carriages and on the geometrical parameters of the track and train. Some practical methods are suggested to modify the spectra of railway-induced groundvibrations and to decrease their level in the chosen frequency intervals.

Contamination of indoor air by toxic soil vapours: the effects of subfloor ventilation and other protective measures

A steady-state analytical model is derived for estimating the concentration of vapour-phase contaminants in indoor air in houses with subfloor voids, given the contaminant concentration in bulk soil. The model includes the key mechanisms of transport and dispersion—contaminant partitioning into the soil-vapour phase, molecular diffusion, suction flow, stack effect, and ventilation, including contaminant transport by ventilation flow between subfloor void and living space. Using the model, different construction styles are examined from the point of view of their resistance to ingress of soil gases. Model results indicate that indoor air concentration depends strongly on wind velocity and on geometrical parameters of void and living space. Worked examples for houses of different construction styles illustrate the effects of wind velocity and house parameters on the concentration of benzene in soil that would give rise to its maximum permissible concentration in indoor air. Brief consideration is also given to concrete raft foundations and clean cover systems.

Contamination of indoor air by toxic soil vapours: a screening risk assessment model

Abstract A simple steady-state model is derived for estimating the concentration of vapour-phase contaminants in indoor air, given the contaminant concentration in the soil. The model includes the key mechanisms of transport and dispersion—contaminant partitioning into the soil-vapour phase, molecular diffusion, suction flow, and ventilation rate. It is shown that indoor air concentrations are largely controlled by two variables: soil permeability, and the half-life for contaminant removal from soil. A worked example shows the effect of these two variables on the concentration of benzene in soil that would give rise to a concentration of benzene in indoor air of 5 ppb (the recently proposed U.K. Air Quality Standard).

SOIL GUIDELINE VALUES IN THE UK: NEW RISK-BASED APPROACH

At present the UK uses a range of “trigger values” for certain contaminants and site end uses, together with other environmental criteria, to judge a site and the proposed remediation strategy.

Sampling Strategy Guidelines for Contaminated Land

Properly formulated spatial sampling designs are an important aspect of any contaminated site investigation. This paper reviews the design principles for effective spatial sampling. The number of sampling points needed to achieve a given probability of success in locating a hot-spot (critically contaminated area) depends on the sampling pattern chosen and the hot-spot size and shape. A new sampling pattern has been devised to provide near-optimum search efficiency when hot-spot shape and orientation are unknown. Specific guidance on sampling density is compared with that published in the Dutch Draft Standard.

UK Action (OR Intervention) Values for Contaminants in Soil for Protection of Human Health

In recent years the UK Department of the Environment has developed a framework for contaminated land risk assessment, including the derivation of new guideline (trigger) values (Ferguson & Denner 1994). These are an important component in an integrated procedure for site-specific risk assessment which combines consistency of approach with flexibility to ensure that local circumstances are taken into account.

Generation of surface acoustic waves by moving trains

The theory of generation of ground surface acoustic waves by trains is developed using the Greens function formalism. Mechanical properties of the rail track and parameters of train and soil (including contact nonlinearity of track-soil system) are taken into account. Its shown that generated ground vibration spectra depend strongly on the geometrical parameters of track and train, on the mechanical properties of soil, and on the axle loads of the carriages. Simple practical methods are suggested to modify, the spectra of railway-generated surface elastic waves and to reduce their level at chosen frequency bands

Predicting Trace Metal Uptake by Vegetables Grown in Contaminated Soils

Root uptake of trace metals from soil depends on the fraction of the total trace metal content that is accessible to plant roots and the ability of the plant to transfer the metal across the soil-root interface. Trace metal bioavailability is determined by the chemical form of the metal and its location in the soil. The complexity of trace metal behaviour in soils, and of the processes involved in root uptake, translocation and transformation, means that there is seldom a close or consistent relationship between total trace metal content in a soil and plant uptake. Interpretation is further complicated by large differences in the ability of different plant species (and even cultivars) to take up various trace metals from particular soils, and by variations in metal content as a function of growth stage and plant part.