Meysam Banimahd

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.

Scour Around a Subsea Structure with Mudmat: Comparison of Field Data with Laboratory Data

This paper presents comprehensive field measurements around a subsea structure with a mudmat. Surveys are reported at two different times following installation, together with soil classification data for the seabed sediment and measurements of near seabed metocean currents. The field data is compared with scour predictions based on model scale experiments of a 3D printed replica structure subjected to a near bed velocity time series that mimics the field conditions. Comparisons indicate that predictions based on the experimental data agree well with respect to the extent and rate of scour, but only if site specific metocean conditions and soil properties are used together with the actual structural geometry. The experiments also indicate the role that a mudmat foundation can play in providing some inherent scour protection to the superstructure it supports.