Listen to the information twice and answer the questions (1-5)

1) What is the main function of sub-ballast?

2) What are the other purposes of sub-ballast?

3) The grading of sub-ballast needs special laboratory testing, doesn’t it?

4) Is capping or sub-ballast much more easily compacted?

5) What cases does sub-ballast provide a better solution than capping in?

VII

Read the article and write your annotation to it

Demands on subgrade drive GPR development

James P Hyslip PhD PE

Vice-President Engineering, Optram Inc.

THE CONDITION of track substructure has a profound influence on track performance. Ensuring that it is in good condition and keeping it that way is essential on high tonnage lines, although determining precisely what that condition is may not be straightforward. The advent of tools such as ground-penetrating radar will make this process easier, and pioneering work with GPR has been carried out in North America.

The application of GPR in the railway industry can be separated into three categories: site-specific investigations, maintenance planning and monitoring.

In the first area, GPR provides a means to obtain a visual image of the substructure along a section of track with particular chronic problems. Along with railway geo-technology, this can be used to determine the root cause of the problem, the precise sections needing repair and cost-effective treatment.

In the second area of application, GPR provides the ability to survey many kilometers of track and provide a relative measure of maintenance priority using performance indices. Finally, GPR can be used to monitor chronic sites regularly and to observe the effectiveness of remedial treatment.

Tests on more than 200 km of track have demonstrated that GPR assessment can be used to produce quantitative indices for use in managing track maintenance. A prototype system consisting of three sets of 1 GHz air-launched horn antennae mounted on a road-rail vehicle is already surveying below the track at both sleeper ends and along the track centre line, while specifications are being drawn-up for a new generation of GPR to be fitted on purpose-built recording cars operating at up to 100 km/h.

https://www.railwaygazette.com;

VIII