Geosynthetic Railways

CG Geotextiles have been successfully used for more than 11 years in the construction of permanent way. Their primary use is as a filter separator layer situated between the ballast and the sub-ballast.

Where the subgrade consists of coarse soils e.g. sands and gravels, the geotextile acts as a separator between the subgrade and the ballast. The subgrade, under the effect of pressure and vibration from trains passing overhead, is prevented from working its way up into the large voids between the rail ballast stones and conversely, the ballast stones are prevented from working their way down into the soil subgrade. Without a geotextile in place, progressive settlement of the track could occur resulting in loss of track alignment and increased maintenance requirements. The pores in the geotextile are small enough to block the passage of fine sand and very coarse silt but large enough to allow the transmission of groundwater for pore water pressure relief.

Water is often present at the interface below rail ballast and subgrade because rainwater is free to percolate down through the ballast to subgrade level.

Silts and clays tend to disintegrate in water when aided by the vibration from trains and abrasion from ballast.

Under the pressure and deflection created by a train passing overhead the resultant slurry can be ‘pumped’ up into the ballast through any geotextile.

This results in progressive settlement of the track structure due to ground loss into the ballast. In addition the ballast is increasingly contaminated by the slurry and thus performs its functions less well. If unchecked, ‘pumping’ leads to very substantial maintenance requirements.

A solution to this problem is to place a layer of suitably graded ‘blanketing sand’ directly onto the silt clay or mudstone subgrade. This acts as a fine soil filter and is well proven in preventing the ‘pumping’ of fine soils. The geotextile is placed on top of the sand blanket to maintain separation between the sand and ballast and retain the integrity of the filter system.

• Steepened Embankments

• Dams and Flood Defense Bunds

• Retention Bunds

• Green Walls

• Culvert Head Walls

• Sound Barriers.

Geosynthetic, you can trust.