Terre Armée India’s Engineering and Sustainable Technology Builds The World’s Tallest Reinforced Earth® Structure

Tindaria

In September 2011, Tindharia (26°51’16.10″N and 88°20’13.61″E), a picturesque town located on the Siliguri-Darjeeling highway, NH-110 (previously NH-55) in West Bengal, India experienced massive landslide following an earthquake and heavy rainfall. The landslide significantly affected three locations – S1 (Height 34.9m), S2 (Height 102.8m) and S3 (Height 38.7m) – resulting in the collapse of a section of roadway on the valley side of the mountain. Part of the Darjeeling Himalayan Railway (DHR), a UNESCO World Heritage Site that runs through Tindharia, was also cut-off due to this landslide. There was severe socio-economic impact on the residents along the NH-110 (previously NH-55) due to stoppage of vehicular movements and shortage of key supplies.

The Ministry of Road Transport & Highways, Government of India in collaboration with the Public Works Department (N.H. Circle-III), West Bengal took initiative to restore the landslide location and the historic road. Terre Armée India (Reinforced Earth India Pvt. Ltd.) was selected as the technology provider in this project. Terre Armée India designed a permanent and sustainable solution for restoration of this landslide. This complex engineering project required a mix of various innovative techniques to be considered in design and construction phase.

Tindharia Case Study

HIGHLIGHTS

  1. A challenging landslide protection and road widening project was successfully completed on NH-110 (previously NH-55) near Darjeeling in West Bengal, India.
  2. Innovative TerraLink® technology was used by Terre Armée India to build this engineering marvel with limited available space at base (2m to 5m), using high adherence GeoStrap® directly and mechanically connected with GeoTrel® facing with TerraNail® and further strengthened using pre-stressed FreyssiAnchor® (completely re-stressable cable ground anchors) in this project to stitch the new construction with the existing hill profile.
  3. The mechanical connection system adopted for this project as per codal provisions was an essential requirement to ensure transfer of loads between facing,  soil reinforcement and anchors/nails in high seismic zones and for the overall stability and greater performance of the reinforced filled structure.
  4. Highly compressible and durable (with heavy galvanisation of 500 gsm) fusion welded steel grid mesh (made of minimum 8mm diameter bars) was used to withstand higher deformations to meet any internal settlements.
  5. Safety and quality were top priorities for the project. Terre Armée India adopted the safest construction method for this unique project.
  6. Reduction of backfill quantity (up to 10x) led to cost optimisation and minimised environmental impact.
  7. The improvement of surface and sub-surface drainage systems ensured the structure’s long-term performance.
  8. The structure has performed well under seismic load when recently subjected to an Earthquake of 5.1 magnitude.

Very limited space was available at the base of the valley for constructing such tall retaining structures using traditional method. Innovative idea was “need of the hour” to suit the requirement of stabilising the existing unstable slope and to widen the road. This prompted Terre Armée India to use their innovative TerraLink® technology (shored or composite Reinforced Earth® structure). TerraLink® was designed after conducting a detailed global as well as compound stability check and finite element modelling of the collapsed slope to provide a robust and engineered structure, which can withstand differential settlement and impact from dynamic loads. The use of mechanical connection system between the soil reinforcement and soil nails ensures greater stability of the shored Reinforced Earth® structure and superior performance under extreme loading conditions. TerraLink® also optimized the cut and fill volume in this project. Internal and external drainage was also improved to channelize the run-off in the area.

The S2 Structure, which stands supreme at 102.8 meters, makes Project Tindharia the world’s tallest Reinforced Earth® structure and an acme of tall, steep slope soil reinforcement engineering. The innovative and sustainable TerraLink® solution used in this project has resulted in the widening of existing roadway, slope stabilisation, drainage improvement and rehabilitation of the massive landslide at Tindharia.

This project’s landmark success will surely instil greater confidence amongst the Engineering Fraternity in India as well as in various parts of the world and encourage them to take up more complex and challenging civil engineering projects like this in the future.

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