The gabion and Terramesh reinforced soil wall are both made for an environmentally friendly solution.
Kathmandu’s dumping site of solid waste located in Gokarna, north east of Kathmandu was filled nearly to the maximum of its capacity by the year 2000. The northern hill slope of the dumping site, facing the road to Sankhu, started showing signs of erosion and traces of sliding. This phenomenon endangered the safety of the nearby population.
The sliding slope, measuring at a height of approximately 16m needed protection. A stream between the base of the slide and a nearby settlement had since long functioned as a buffer between the slide and the settlement. An old gabion retaining wall had previously been constructed at the base of the slide along the stream to function as toe wall and bank protection wall.
The potential removal of the old gabion wall became a critical issue. Among the available solutions, rigid structures like RCC and masonry walls had been deemed inappropriate due to the very high costs they would incur and the problematic construction feasibility (excavation depth for the foundation would further endanger the stability of the sliding slope). Also, these rigid structures are not ideal for use within these stream and river works where differential settlement is common.
The installation of new gabion retaining walls had been discussed previously but had not been actioned yet due to the problematic question of the required height. Ultimately it was decided that the most feasible solution, cost, and construction wise, would be a reinforced soil wall structure with a gabion facia; the Terramesh System.
Moreover, it was agreed that the existing gabion structure would be left undisturbed as it would work as an additional protection for the wall, mainly at its foundation.
A Terramesh system with four blocks (7m, 4m, 3m, and 2m) was designed and constructed. The minimum berm width between the blocks was 2m and greater to suit the purpose of slope stabilization and also to optimize the fill quantity.
The Terramesh system forms mechanically stabilized earth (MSE) structures with the appearance of a gabion wall. The gabion fascia unit has an integral steel wire double twist mesh geogrid ‘tail’ which extends horizontally into the backfill ro be reinforced. The soil backfill is spread over the wire mesh geogrid and well compacted. The provision of wire mesh as reinforcement sandwiched between well-compacted soil layers improves the performance of the soil, prevents the shear failure of the soil mass and the entire block works as a homogenous structure supporting the ground behind.
For structures of this height, the soilcreinforcement Terramesh System typically offers better value for money, than traditional gabion retaining walls as less gabion fill is required. That said, both types of structure integrate easily with the environment in a more natural way.
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