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Strengthening the sub ballast layer

The static and dynamic loads acting on the main road bed of railways have a significant impact on all underlying layers. The roadbed is, in fact, the foundation of the superstructure. Violations in the design and in the geometry of the rail track leads to a reduction in the quality indicators of the structure as a whole and affects the safety of rail traffic. Therefore, improving the reliability of work in the new construction, as well as strengthening the existing exploited roadbed is the most important and responsible tasks.

The element of the subgrade, directly under the moving load’s force is the fundamental base. It is often subject to deformations in the form of ballast troughs, lodges, etc., accompanied by the dilution of clay soil with splash from under the sleepers or the extrusion of the masses of this soil onto the surface of the ballast prism. The solution to this problem can be divided into two parts: the separation of layers (ballast and road bed) to prevent their mixing and increasing the carrying capacity of the main site of the road bed - reinforcement. The biaxially oriented flat geogrid “Slavros ZhD-P” successfully copes with these tasks. Such geogrids have high tensile strength in both longitudinal and transverse directions, high abrasion resistance, UV resistance

The material is delivered in rolls of 4 m wide, which allows stacking it in a mechanized way under the ballast with the help of crushed stone cleaning machines during scheduled repairs to the superstructure. With new construction, the geogrid can be rolled out manually.

Necessary tasks can be accomplished due to the effect of the casting of individual ballast particles in the cells of the geogrid, since the cell size of the geogrid is less than the size of the crushed stone fraction. It creates a kind of reinforced plate, which has a much greater modulus of elasticity and better perceives the load from the rolling stock, redistributing it to the underlying layers with a decrease in the vertical stress in the rail sections. It also eliminates the indentation and mixing of the ballast with the subgrade.

When reinforcing, the Slavros Railway-P geogrid is placed on the surface of the additional sandy layer of the base (on the surface of the road bed in its absence) under the ballast layer. The subballast layer reinforced with geogrids provides a smooth change in stiffness, which is achieved by a different number of reinforcement layers throughout the transition section. The number of layers and characteristics of geogrids should be determined on the basis of specific geotechnical conditions and line load capacity.

The characteristic section of the roadbed is the approach to bridges, where due to the different rigidity of the groundwork and spans, a large dynamic effect in the form of subsidence appears. Geosynthetic materials that provide variable base stiffness when approaching bridges are used here. In these areas, gradually increase the thickness of the ballast layer at the approach to the bridge abutment, replacing the soil of the upper part of the embankment. To avoid deformations of the ballast, it is advisable to place between the layers of the geogrid "Slavros ZhD -P". When constructing a transition section with a length of at least 25 m and fitting 5-6 layers of the Slavros ZhD-P geogrid at the bridge abutment with a gradual decrease in the length of each layer with a step of 5 m along the length of the section, a smooth increase in the elastic modulus of the path is ensured.

The use of geogrid brand "Slavros ZhD -P" will allow to solve the following tasks:

  • reduce the cost of operating the railway;
  • reduce the frequency of scheduled maintenance;
  • reduce the load on the soil and increase the overall elastic modulus of the ballast layer;
  • reduce vibration effects on soils;
  • eliminate mixing of the contacting layers.