Sand-gravel mixtures

Various sand-gravel layers are specified for use in railways which should protect the bordering soil from damaging deformations and frost. These protective layers have different tasks to perform:[1]

  • load-sharing effect
  • frost protection
  • separator and filter layer
  • dissipation of the rain water as seepage and through the drainage layer

Depending on your primary task protective layers can be divided into the following subgroups:[2]

Formation protective layer

The formation protective layer serves as a classic track-bed layer, functions as a separator and filter and protects the subsoil from possible frost effects.

Frost protection layer

Frost protection layers protect from frost penetration and are often used in combination with formation protective layers.

Protective layers with additional measures

Attempts were made repeatedly to improve the properties of protective layers by additional measures. This includes the use of geotextiles, the sealing in water protection areas as well as the treatment of the material with binders.

Through the use of heavy track components (concrete sleepers) and the increase in load, the load carrying capacity and the dynamic stability of the subsoil has gained importance. It is therefore common on main lines, in the course of a track renewal (relaying) of a section of line to carry out a detailed check of the subsoil condition. Experience in the maintenance history of the plant should, in any case, be taken into account.[3]

When installing protective layers, it is important to ensure that they cover the full width of the railway axis up to the edge of the formation under sufficient consolidation. From the edge of the formation, the protectivelayer should be flattened up to the railway ditch at the angle of the embankment. Special attention should be paid to the connection between the formation protectivelayer and side ditch or drainage facilities of any kind.

In general, the thickness of the protective layer is determined by the safety against frost and the maximum allowable deformation of the ballasted track systems (depending on the route class). The thickness can be reduced by the use of geosynthetics, and thus the necessary material and logistics requirements reduced.  

The logistical effort, time and financial cost of installing a supporting layer is significant. The cost for one metre amounts to EUR 300 to 800, which can only be justified economically by considering the entire life cycle.[2] [4]

Protective layer with a flat surface to the adjacent side path
Protective layer with a flat surface to the adjacent side path
© Plasser & Theurer

You can find suitable specialist literature to the topic here:

Railway Transformation

Railway Ground Engineering

The second edition of Railway Ground Engineering has been completely reworked and extended. It provides comprehensive information on the essential relationships and dependencies between superstructure, substructure and subsoil subjected to the effects of the rail System.

This manual is intended to be a practical reference book for everyone involved in the planning, design and construction of earthworks and other geotechnical structures, as well as a manual for low track maintenance . With the comprehensive presentation of the new partial safety concept in geotechnics, it is also a valuable aid for students and teachers at universities and technical Colleges.

Best Practice in Track Maintenance, Vol 1 - Infrastructure Management

Infrastructure Management Volume 1 looks at aspects of infrastructure management with particular reference to the single European railway area. Based on best-practice examples from Central Europe, measures for the targeted retrofitting and improvement of the infrastructure maintenance of the existing network are presented. In many cases, infrastructure operators are faced with a generational change, which accelerates the process. Modern information and communication technology can simplify the comprehension and presentation of complex contexts. Modified approaches to asset management and life-cycle management enable implementation of the "transparent permanent way" or the "railway 4.0".

  1. [1] Lieberenz, K.; Piereder, F.: Entwicklung von Schutzschichten mit Geokunststoffen. Eisenbahningenieur Kalender 2013, S. 252–270.
  2. [2] Fischer, R.; Göbel, C.; Lieberenz, K. et al.: Handbuch Erdbauwerke der Bahnen. Planung, Bemessung, Ausführung, Instandhaltung. Eurailpress in DVV Media Group, Hamburg, 2013.
  3. [3] Hansmann, F.: Großmaschineneinsätze bei Untergründen mit geringer Tragfähigkeit, Sonderheft Geotechnik. Der Eisenbahningenieur 2016, Heft 6, S. 13–16.
  4. [4] Hansmann, F.: Großmaschineneinsätze bei Untergründen mit geringer Tragfähigkeit, Sonderheft Geotechnik. Der Eisenbahningenieur 2016, Heft 6, S. 13–16.