Reinforcement in railway earth structures refers to the installation of geogrids and geocomposites in the formation, embankments and slopes of a railway line. It increases bearing capacity, limits differential settlement and ensures the stability of the earth structure. Soft subgrades, cyclic train loading and fines migrating into the ballast are the main challenges. Naue covers each reinforcement function with DB HPQ-qualified products: Combigrid® for reinforcement with separation and filtration, biaxial Secugrid® for base course reinforcement, and uniaxial Secugrid® and Secugrid® HS for structurally designed embankments, slopes and load transfer platforms.
Naue reinforcement elements are used wherever railway formations and earth structures must carry high loads on soft ground or remain stable on a small footprint.
Reinforced formations on weak or cohesive soils for new rail corridors.
Load transfer platforms that carry embankment loads to the pile heads.
Steep reinforced-soil structures beside the track on a small footprint.
Reinforced fill at bridge abutments to reduce differential settlement.
Upgrading existing formations with reinforcement instead of full subgrade replacement.
The right reinforcement element depends on the subgrade, the loads, the need for separation and filtration, and whether the structure must be verified by calculation. DBS 918 039 assigns each of these functions its own application case.
Railway formations and earth structures carry construction traffic first and cyclic train loading afterwards. Secugrid® geogrids, which also form the reinforcement in Combigrid®, are made from stretched, monolithic flat bars with welded junctions. They pick up load at low strain, interlock immediately with the granular fill and resist.
Practical advantages for site teams:
Step-by-step installation sequence:
DBS 918 039 distinguishes reinforcement functions by application case. Two questions decide the choice: must fines migration from the subgrade be prevented, and must the earth structure be verified by calculation?
Key principle: Reinforcement increases bearing capacity and stability. Separation and filtration keep the formation clean. On fine-grained subgrades both functions are needed - and a site-combined geogrid with a separate nonwoven does not meet application case 3.5.
Technical benefit: reinforcement, separation and filtration in one factory-made layer.
Technical benefit: immediate interlock with the sub-ballast aggregate.
Technical benefit: long-term design strength based on creep tests to EN ISO 13431.
The table maps typical railway applications to the Naue product and the DB application case.
Note: For project-specific product selection and the stability calculation, contact the Naue Engineering & Design Department (EDD).
| Application | Naue product | Function | DB HPQ |
|---|---|---|---|
| Formation on fine-grained or soft subgrade | Combigrid® 40/40 Q1 GRK 4 DB; Combigrid® 60/60 Q1 GRK 4 DB for higher loads | Reinforcement + separation + filtration | 3.5 |
| Toe drainage trench | Secutex® 151 GRK 3 | Filtration of the collected water | 3.3 |
| Base course reinforcement (no design calculation) | Secugrid® 40/40 Q1, Secugrid® 60/60 Q1, Secugrid® 80/80 Q1, Secugrid® 40/40 Q6 | Higher bearing capacity, thinner base course | 3.6 |
| Reinforced slopes and noise barriers | Secugrid® 40/40 Q6, Secugrid® 80/80 Q6 and R6 | Stability of slope or wall, designed by calculation | 3.7 / 3.8 |
| Embankments on soft soil | Secugrid® R6 / Secugrid® HS | Stability during construction and in the final state | 3.8 |
| Load transfer platforms over piles | Secugrid® R6 / Secugrid® HS | Transfers embankment loads to the pile heads | 3.8 |
| Bridging of sinkholes and voids | Secugrid® R6 / Secugrid® HS | Limits surface deformation above voids | 3.8 |
These benefits come directly from how the Naue products work in this solution, and what they mean in practice for your project.
DB HPQ for every reinforcement function
Combigrid® (case 3.5), biaxial Secugrid® (cases 3.6 and 3.7), uniaxial Secugrid® R6 / HS (case 3.8) and Secutex® 151 GRK 3 (case 3.3) come from one manufacturer. This removes approval uncertainty at tender and construction stage.
Thinner layers, less aggregate
Layer thickness reductions of typically 20-50 % compared with unreinforced sections are achievable, depending on the project. In many cases, soil replacement can be avoided.
A clean formation
The nonwoven integrated in Combigrid® prevents fines from migrating from the subgrade into the sub-ballast and ballast, a main cause of track geometry loss on soft subgrades.
Stability verified by calculation
Secugrid® structures are dimensioned to EBGEO or BS 8006-1. The long-term design strength is based on creep tests to EN ISO 13431 and project-specific reduction factors.
Reinforcement in railway earth structures describes the installation of geogrids or geocomposites in the formation, base course, embankments and slopes of a railway line. It increases bearing capacity, limits differential settlement and ensures the stability of the earth structure. Typical triggers are subgrades with a CBR below 3%, strict deformation limits, steep slopes and embankments on soft soil or piles.
Case 3.5 covers reinforcement with additional separation and filtration (Combigrid® 40/40 Q1 GRK 4 DB). Case 3.6 covers base course reinforcement without design calculation (biaxial Secugrid®). Cases 3.7 and 3.8 cover reinforcement elements in earth structures designed by calculation, with biaxial and uniaxial Secugrid® respectively. Case 3.3 covers filter elements in drainage installations such as the toe trench (Secutex® 151 GRK 3).
Use Combigrid® where the subgrade is fine-grained, cohesive or soft and fines could migrate into the sub-ballast. Combigrid® 40/40 Q1 GRK 4 DB provides reinforcement, separation and filtration in one product; a site-combined geogrid and separate nonwoven does not meet application case 3.5. Use biaxial Secugrid® where only the base course needs reinforcement.
Biaxial Secugrid® 40/40 Q6 and Secugrid® 80/80 Q6 are used where forces act in two directions, for example in reinforced slopes. Uniaxial Secugrid® grades from 80/20 R6 to Secugrid® 400/40 R6 and Secugrid® HS, with tensile strengths of more than 400 kN/m up to 1,200 kN/m, carry high forces in one direction in embankments on soft soil, load transfer platforms over piles and when bridging voids.
A load transfer platform is a reinforced granular layer placed over a pile grid. Layers of uniaxial Secugrid® R6 or Secugrid® HS span between the piles and carry the embankment load to the pile heads, which limits differential settlement at the surface. A rigid pile cap slab is often not required. Design follows EBGEO and BS 8006-1.
Layer thickness reductions of typically 20-50 % compared with unreinforced sections are achievable, and in many cases soil replacement can be avoided. Actual savings depend on the subgrade, the loads and the design.
On DB projects, DBS 918 039 (HPQ for each application case) and RIL 836 apply. Design follows EBGEO and BS 8006-1. Tensile strength is tested to EN ISO 10319 and creep to EN ISO 13431, which together form the basis of the long-term design strength. For filter nonwovens, the characteristic opening size is determined to EN ISO 12956.
The long-term design strength (LTDS) is derived from the characteristic short-term tensile strength (EN ISO 10319), reduced by factors for creep (EN ISO 13431), installation damage and environmental effects, in accordance with EBGEO or BS 8006-1. Documented installation damage reduction factors for Secugrid® range from 1.10 to 1.46, depending on the fill material.
For the polypropylene Q1 grades of Secugrid® and Combigrid®, the Declaration of Performance (Annex B) states a durability of at least 100 years in natural soils with a pH of 4 to 9 and soil temperatures below 25 °C. For polyester grades, the creep behaviour is tested to EN ISO 13431 and enters the long-term design strength.
Geosynthetic reinforcement in railway earth structures is designed in accordance with DB AG standards and recognised design codes. The Naue Engineering & Design Department (EDD) supports project-specific dimensioning and stability calculations:
Naue Combigrid® is a geogrid with integrated nonwoven geotextile that combines stabilisation, reinforcement, separation and filtration in a single installation step.
Naue Secugrid® geogrid stabilises and reinforces roads, embankments, working platforms, slopes and walls.
Naue Secugrid® HS is a high strength geogrid for soil reinforcement in embankments and load transfer platforms on soft soils.
Naue Secutex® is a mechanically bonded nonwoven geotextile for separation, filtration and protection for the use in roads, railways, environmental and hydraulic engineering projects.
