Gabriela Medero

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.

Traditional cob wall: response to flooding

Purpose – The influence of flood conditions upon traditional cob construction is little understood. This paper aims to investigate the ability of cob materials to resist flood situations and documents basic failure mechanisms. This work also seeks to investigate the wettability characteristics of cob materials utilising environmental scanning electron microscopy.Design/methodology/approach – This paper takes the form of a literature review and case study underpinning laboratory experiments.Findings – Cob walls that are suitably compacted, straw reinforced and are composed and manufactured of the correct materials appear to have the ability to resist total failure when subjected to initial flood conditions, however, the duration to which these structures will remain intact has still to be ascertained, and testing is ongoing. A correlation appears to exist between the rate of cob materials compaction and the duration to which the structural integrity of the walls was retained when the samples were submerge...

Determination of the soil water retention curve with tensiometers

An alternative technique for the determination of the soil water retention curve has recently been proposed whereby a tensiometer is used to measure soil suction and a balance to record the water content variations. The soil water retention curve is obtained by drying the soil either continuously or by stages (i.e. each drying stage is followed by an equalization period). Initial results from tests on compacted soil suggest that the relatively fast evaporation rate during continuous drying affects the water retention curve whereas the stage drying procedure provides more accurate results. Factors such as sample geometry and tensiometer position (relative to the sample) are also likely to affect the response obtained during continuous drying. These are the object of future investigation.

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.

Factors Influencing Water Retention Characteristics of Granular Materials

Numerous theoretical and experimental attempts have been made to study the influence of moisture on the behaviour of granular materials and to correlate the measured behaviour to the physical properties of the material whilst recognising the effect of its constituent particle properties. At present there seems to be no clear understanding on how these factors individually and collectively influence the unsaturated behaviour. One common approach has been to compare different materials on the basis of particle size and plasticity characteristics but ignore other factors controlling the inter-particle forces such as particle shape, particle interstices and asperities and physico-chemical phenomena. This paper describes an attempt to investigate the effect of particle size on the drying and wetting water retention characteristics for spherical glass beads. Distilled water and spherical glass beads were chosen to provide simple and well defined wet granular assemblies where the observed response can be attributed to purely glass-glass and glass-water interaction without the presence of other complex inter-particle interactions often present in unsaturated soils. The water retention curves were established for 0.09-0.15mm and 0.25-0.50mm particle sizes of similar-material glass beads. The results show that particle-water interaction alone can produce the hysteretic water retention characteristics with particle size significantly affecting the air- and water-entry values and also the wetting maximum water content. In addition, features of the water retention curve often observed in soils were well captured with glass beads.

Water Retention Characteristics of Non-plastic Granular Materials

This paper presents experimentally determined water retention curve (WRC) for glass beads. Due to its usefulness in the determination of other unsaturated properties of particulate media, WRC has become pivotal to the implementation of the mechanics of unsaturated soil and other particulate materials. In the work reported herein tests were carried out on spherical glass beads using a pressure plate. Digital microscopic images were also taken at different matric suctions to observe water bridges between the particles as the sample dried out. Results indicate a marked difference, called the hysteresis, between the primary drying and wetting paths of the water retention curve. Within the pendular bridges zone, however, the hysteresis disappeared. It is also shown that as matric suction increases water menisci and distribution of water changes.