3. Providing a biaxial goegrid reinforcement (5 m width) below the ballast:

Techgrid TGB-40, a knitted and PVC coated biaxial geogrid with a tensile strength of 40 kN/m in both machine and cross machine directions, aperture dimensions of 25x25mm and roll width of 5m, manufactured by Techfab India at its state-of-the-art plant in Silvassa, Union Territory of Dadra & Nagar Haveli was proposed for this purpose. The geogrid is manufactured from superior grades of high tenacity, high molecular weight and low carboxyl end group polyester yams which are formed into a grid structure using a highly sophisticated warp-knitting process and is then precision coated with a specially formulated PVC plastisol to produce a strong, flexible, tough, dimensionally stable and durable geogrid.

A layer of Techgrid biaxial geogrids installed below the ballast constraints and confines the ballast particles reducing the lateral and vertical movement of ballast and enhances the strength and stiffness of the ballast. Reinforcement of the ballast results in a marked improvement of the track performance through several mechanisms:

• Substantial reduction in the Iateral spreading of ballast and penetration, of the ballast into the sub grade and associated track settlements.
• Reduction in sub grade attrition and wear and tear of ballast
• Reduction in vertical stresses on the sub grade because of better load distribution by the reinforced ballast with enhanced strength and stiffness.
• Lower shear stresses on the sub grade with consequent increase in bearing capacity.
  
  

4. Placing cleaned ballast over the geogrrid and restore the track to the desired geometry.

Execution

The work was executed by Techfab India under the overall supervision of the Permanent Way Inspector. Because of the remoteness of the location und the small quantum of work, the work was carried out manually. The blocks allocated allowed completion of about 10 to 12 m of track each day. The rehabilitation work involved the following steps:

• Removal of the ballast and preparation of the exposed sub grade by dressing to ensure a cross-fall of 1 in 30 and ramming with wooden tampers (photo 4).

• Spreading of a thin layer of sand (about 50 mm thick) on the prepared sub grade to cover any ballast particle projecting from the sub grade (photo 5).