Peter Keith Woodward

The growth of railway ground vibration problems — A review

Ground-borne noise and vibration from railway lines can cause human distress/annoyance, and also negatively affect real estate property values. Therefore this paper analyses a collection of technical ground-borne noise and vibration reports, detailing commercial vibration assessments undertaken at 1604 railway track sections, in 9 countries across the world. A wide range of rail projects are considered including light rail, tram lines, underground/tunnelled lines, freight, conventional rail and high speed rail. It documents the rise in ground-borne vibration problems and trends in the prediction industry, with the aim of informing the current research area. Firstly, the reports are analysed chronologically and it is found that railway vibration is a growing global concern, and as such, assessments have become more prevalent. International assessment metrics are benchmarked and it is found that velocity decibels (VdB), vibration dose value (VDV) and peak particle velocity (PPV) are the most commonly used methods of assessment. Furthermore, to predict vibration levels, the physical measurement of frequency transfer functions is preferential to numerical modelling. Results from the reports show that ground vibration limits are exceeded in 44% of assessments, and that ground-borne noise limits are exceeded in 31%. Moreover, mitigation measures were required on approximately 50% of projects, revealing that ground-borne noise and vibration is a widespread railroad engineering challenge. To solve these problems, the most commonly used abatement strategy is a modification of the railtrack structure (active mitigation), rather than the implementation of a more passive solution in the far-field.

Influence of viscous damping in the dynamic analysis of an earth dam using simple constitutive models

Abstract The results of dynamic non-linear two-dimensional finite element analyses of the Long Valley Dam in the Mammoth Lake area of California subjected to a real measured earthquake are presented. A simple elastic-perfectly plastic constitutive soil model is used to describe the stress-strain response of the soil and Rayleigh damping (i.e. viscous damping) is applied to account for the lack of hysteretic damping. The effect of the initial stress condition and the Rayleigh damping ratio are discussed, and the results of the analysis are compared to the measured response of the dam and to results presented by previous researchers. Good agreement is obtained in the up/downstream direction, but as experienced by previous researchers, the correct vertical frequency range is not achieved. The limitations of using viscous damping combined with simple constitutive models when studying the dynamic behaviour of real earth dams are shown.

Application of in situ polyurethane geocomposite beams to improve the passive shoulder resistance of railway track

Recent research has highlighted the effect of the individual contributions of the crib, shoulder, and base resistance to the lateral behaviour of a typical railway sleeper under loading. The contribution of the shoulder ballast has been seen to provide around 30 per cent of the lateral resistance for an unloaded sleeper. The addition of extra ballast in the shoulder area provides a very limited increase in lateral sleeper resistance. It is common in areas of high lateral loading, such as switch and crossings, to provide sleeper end plates to improve the passive resistance of the track. Sleeper end plates have, however, many disadvantages, not least is the need to disturb the ballast in order to facilitate their installation. The application of polyurethane reinforcement of the ballast shoulder to rapidly form an in situ GeoComposite shoulder beam (geobeam) has many advantages over end plates, including the ability of the lateral beam to be installed directly after the track geometry has been corrected; the lateral track geometry can then be ‘captured’ at installation. The beam can also be formed while the trains are still running. In this article the application of lateral GeoComposite side beams to improve the passive resistance of the shoulders is illustrated through analytical and numerical analysis. The application of the technique to actual problem sites is also presented and the performance of the technique at the Harford bridge transition site discussed.

Maintaining absolute clearances in ballasted railway tracks using in situ three-dimensional polyurethane GeoComposites

Maintaining track clearances in ballasted railway tracks are a critical issue for the safety and operational performance of the railway environment. In general, railway standards aredefined with respect to the minimum gauge clearance allowed between the dynamic swept envelope of the train vehicles and the fixed structure for a given vehicle speed. Absolute clearance of a line is categorized based on the clearance level, for example, in the UK, it is defined in terms of normal, reduced, or special reduced clearance. In special reduced clearance, the level of track fixity is defined as high fixity, medium fixity, and low fixity. In high track fixity, a concrete-slab track solution must be adopted; in medium track fixity, some form of ballast stabilization and/or reinforcement can be used. The principal requirement is that using a standard methodology, the clearances should always be greater than zero; the clearance representing the margin for unknown events. In this article, an in situ three-dimensional (3D) polyurethane ballast reinforcement technique is used to provide a very robust level of track fixity. The performance of the reinforcement technique is shown through experimental tests using a 200 ton capacity cyclic compression machine. The experimental tests are used to show the performance of the technique for applications like railway tunnels and station platforms where clearances issues are paramount. The base and shoulder GeoComposite experimental tests are performed with the initial ballast poorly compacted thus representing a worse case on-site scenario. Based on the experimental results, a new track fixity category is proposed termed virtual high fixity. A case study showing the impact and site application of the 3D polyurethane reinforcement research to Grovehill Tunnel UK is presented and reference is also made to another reinforced clearance issue site at Hoxton Station UK.

Earth pressure coefficients based on the Lade-Duncan failure criterion

Abstract The Mohr-Coulomb criterion has been extensively used to model the static and dynamic behaviour of retaining walls in both analytical and numerical studies, the main advantage being its simplicity. In the field of computational geomechanics, more sophisticated soil models have been proposed which take account of the intermediate principal stress σ 2 , giving rise to an increase in the equivalent friction angle when analysing plane strain problems. In this paper, a kinematic elasto-plastic soil model incorporating a Lade-Duncan failure criterion is used to calculate modified active and passive earth pressure coefficients for retaining walls. The results of the finite-element analysis are compared to an analytical study and found to be in good agreement once an approximation of the Lode angle at failure is made.

Temperature effects on suction measurement using the filter paper technique

This paper presents the results of an experimental study of thermal effects on filter paper calibration curves used to obtain the soil suction. When the temperature is significantly different from ambient values, it is essential to consider the influence of temperature on the filter paper calibration curves to obtain a reliable soil suction measurement. The calibration curve of Whatman No. 42 filter paper was determined at 10°C, 25°C, and 50°C using the vapor equilibrium technique with sodium chloride solutions at different concentrations and the axis translation technique. The experimental results showed a major influence of temperature on the filter paper calibration curves. Using the obtained experimental data a calibration equation was proposed, taking into account the effect of temperature. The obtained calibration curves were then used to determine the soil water retention curve of kaolin clay, which showed lower retention capacity at higher temperatures.

Discussion of "measurements of suction versus water content for bentonite-sand mixtures"

The authors have presented a very interesting research paper on the comparison of various techniques for suction measurements of a compacted bentonite–sand mixture. One of the important techniques discussed in the paper is the filter paper method, and the authors used the filter paper calibration equations presented by Agus (2005). Different aspects of using the calibration equations proposed by the authors are examined and discussed here in light of previously published data and our laboratory test results. According to Agus (2005), the calibration curves for the Whatman No. 42 filter paper were obtained using the pressure plate technique for suctions less than 1500 kPa and using a desiccator (vapour equilibrium technique) for suctions higher than 2000 kPa. To determine what the authors called the ‘‘matric suction calibration curve’’ (eq. [2]), a filter paper was been placed directly over a ceramic disc in a pressure plate during matric suction equalization, and a dead weight was placed on top of the filter paper to maintain good contact between the filter paper and the ceramic disc. An equilibration period of 3 weeks was adopted for this calibration test. The noncontact filter paper calibration data (eq. [1]) was obtained using different concentrations of NaCl solutions, and a 5 week equilibration time was adopted for this technique. The authors performed the calibration test for two different sizes of filter paper: a standard-sized (55 mm diameter) and a small-sized (25 mm diameter) filter paper. Figure D1 presents the calibration curves for the Whatman No. 42 filter paper obtained by Fawcett and CollisGeorge (1967) at 22 8C, Chandler and Gutierrez (1986) at 21 8C, Chandler et al. (1992) at 21 8C, Leong et al. (2002) at 25 8C, the proposed calibration curves by Agus (2005) at 22 8C, and also the writers’ experimental data at 25 8C. The difference in the filter paper calibration curves may be due to factors such as equilibration time, temperature, and the use of different batches of filter paper as indicated by Marinho and Oliveira (2005). Using eq. 1 proposed by Agus (2005) for suctions less than 2000 kPa can cause significantly misleading results as the equation is based on experimental data by Agus (2005) for suctions greater than 4000 kPa. The proposed calibration curve for suctions less than 2000 kPa strongly disagrees with the calibration curves found in literature and also shows a very small sensitivity of suction in relation to filter paper water content (see Fig. D1). Although the authors reported the use of the proposed calibration curve only for suctions greater than 2000 kPa, it seems the proposed calibration curve has been used for total suction measurements lower than 2000 kPa, as data presented on Figs. 4a, 4b, and 5a (in the paper under discussion), which is not applicable. The writers obtained the filter paper (Whatman 42) calibration curve using two procedures. One was via vapour equilibrium using sodium chloride solutions at different concentrations, for suctions higher than 300 kPa.3 The calibration was performed in a temperature-controlled chamber, which maintained the desired temperature to ±0.1 8C. The other procedure used the pressure plate with the filter paper to be calibrated placed between two soil samples. The filter paper was protected by two larger-size filter papers. The arrangement of the soil samples and the filter papers was subsequently placed on a fully saturated high air-entry value ceramic disc in the pressure plate. An equilibration period of 2 weeks was adopted for both calibration procedures. The results obtained from the two procedures are shown in Fig. D1. From the results it can be observed that the data from the vapour equilibrium method for inducing suction agree with the calibration equation proposed by the authors only for suctions higher than approximately 5000 kPa. The data presented by the writers agree well with the data presented by the authors, when compared with the calibration curve represented by eq. [2], regardless of the method used for generating the suction (i.e., vapour flow or capillary flow). Therefore it can be concluded that a 2 week equilibration time is sufficient for a capillary flow of any level and for a vapour flow higher than 500 kPa. From Fig. D1 it can be observed that the last two points obtained using the vapour flow method (suction lower than 500 kPa) require a longer time to reach equilibrium. This is in agreement with Received 24 September 2010. Accepted 26 November 2010. Published on the NRC Research Press Web site at cgj.nrc.ca on 1 February 2011.

Advanced Numerical Modelling of Granular Soils

This chapter initially presents a brief review of the different types of constitutive soil models used in geomechanics and illustrates the implementation of a typical isotropic model. The constitutive behaviour of a double-hardening isotropic model is also highlighted as part of this review. The majority of the chapter is however concerned with the description and implementation of a multi-surface kinematic elastoplastic constitutive soil model into a finite element program. The calibration of the model to a particular sand under monotonic and cyclic loading and the results of typical boundary values problems under monotonic and dynamic loading are presented. The ability of the model to simulate earthquake induced liquefaction, through work published from the VELACS project, is also shown.