The Northeast Frontier (NF) Railway is the operator of railway services in the entire north-east of India.
This area is characterised by exceptional beauty and at the same time by some of the most arduous terrain, which makes any expansion of the network complex and expensive.
With a view to improve passenger amenities, NFR decided to construct a new railway line from Dudhnoi to Mendipathar to connect the Garo Hills in Meghalaya with Assam and the rest of the country. This new line passes through very complex terrain and the new railway track is laid in cutting at a number of locations. To minimise excavation, the side slopes of the cuttings are almost vertical and there is a residual risk of rockfalls onto the track.
A rockfall protection solution was required to minimise the risk of rockfalls disrupting the train operations. Compounding the solution was the limited availability of space between the wall of the cutting and the train envelope.
Traditional rockfall mitigation solutions using drapery meshes function by controlling the falling rocks behind a containment curtain of drapery mesh. Periodically, the collected rock debris is emptied under maintenance. However, in this instance there was insufficient space between the cutting and the railway to collect rock debris. Therefore, a much stiffer mesh system was required. The mesh needed not only high tensile strength, but most importantly stiffness, so it would exhibit minimal deflection under load.
Accordingly, Maccaferri proposed High Energy Absorption panels (HEA Panels) and Steelgrid® MO meshes depending on the geology encountered. These were secured to the rock slope with top, bottom and intermediate anchors on the face.
HEA Panels are the stiffest and highest strength meshes in Maccaferri’s rockfall mitigation range. They are engineered from a single high tensile steel wire cable, laid into a grid configuration with a patented knot connection at each crossing point. This provides the HEA Panel with 25% higher junction strength than traditional steel cable net panels with clipped node connections.
Furthermore, this junction makes the panel far better at resisting puncture from bursting forces and tearing under extreme loads. This makes the HEA Panel ideal for demanding applications and is also used with soil nails or anchors where efficiency of load transfer is important to minimise deflection.
Where deflections were less critical, Steelgrid® MO was specified. This is a composite of double twist steel wire woven mesh, which is interwoven with high tensile steel cables. The 8mm steel cables are inserted longitudinally at intervals, enhancing the tensile strength and punch resistance of the traditional double twist woven mesh.
Supplied in rolled format, Steelgrid® is available in a range of strengths and stiffnesses, enabling the optimisation of the solution for the geological conditions encountered.
Top and bottom rope anchors were installed first. Then mid-slope anchors inserted to target specific geology.
Thereafter, the meshes were unrolled and secured to the slope.
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