The challenge
Tunnel T-48 is on the Katra-Banihal section of the Udhampur-Srinagar-Baramulla Rail Link (USBRL), a 272 km line joining the Kashmir Valley to the Indian Railways network through the Himalayas. It is described as the third longest railway tunnel in India, about 6.3 miles long. It carries a single track in a main tunnel of about 40 m², with a parallel escape tunnel of 18.4 m². Most of it was excavated by mechanical breaking and drill and blast. Support is a dual lining: an initial shotcrete lining and a final cast-in-place concrete or shotcrete layer. Tests on drilled cores showed that some sections did not reach the required compressive strength, water penetration, permeability, density and porosity values. Extra shotcrete reinforcement or an inner lining was needed.
The DCP solution
Transrail Lighting Limited needed admixtures for the wet shotcrete. Liquid alkali-free accelerators were proposed because they cut setting time, give early strength, lower dust and rebound, and are safer for applicators than alkaline accelerators. DCP supplied Proset AF, an alkali-free liquid accelerator for wet-mix sprayed concrete. It improved bond and resistance to sagging, increased the thickness that can be sprayed in one pass and reduced rebound and dust. DCP also supplied Supaflo PC300, a polycarboxylate ether high range water reducer, to give better flow, cohesion and strength at a lower water to cement ratio.
DCP products used
How it was applied
- Run spray trials to set the Proset AF dose by setting time, strength and dispersion.
- Batch the wet-mix shotcrete with Supaflo PC300 at the dose set by DCP's R&D centre.
- Add Proset AF at the nozzle and spray the lining.
The result
Supaflo PC300 was approved at the doses DCP proposed, and good quality shotcrete was achieved without extra water, superplasticiser or retarder.
