Case Studies

Construction of landfill embankmentbyusing Techgrid Geogrid TGU (PVA & PA coated)

TechFab (India) Industries Ltd.
Kolkata, West Bengal.

Dhapa has been historically used for waste dumping for many decades. With the gradual development of the city towards the east, the garbage dumping has moved away further eastwards and the old dumping areas nearer to the main city are now used for farming.

The current “dumping area” is spread over about 35 hectares. It consists of two unlined dumpsites, spaced~ 500m apart – one closed dump of area ~ 12.14 ha and one active dump of area ~ 23 ha.

Establishment of a new and controlled landfill dump is planned in the area. Both the closed and the active dumpsite are unlined and without any environmental protection or mediation facilities. The closed dump site bearing of area of approximately 12.14 ha is the project site.

Scientificclosure & containment of Old MSW dump at Dhapa; Salt Lake Kolkata using Geosynthetics products.

Keywords

    Techgrid TGU 35 (PVA and PA coating); Geonet and Drainage composite.

Problem Description

  • Defining alignment of periphery as well as datum level of dump was another challenging task due to steep slope in some of the portion which spread beyond boundary line, horizontal shifting was not possible.
  • Profiling: excavation, shifting, filling, &compaction of existing waste in shape as per design were difficult to manage the pace of construction due   monsoon & high moisture content inthe naturally settled waste as well as natural openings for leachate flow.
  • Space constraint for movement of machinery and management of space to accommodate more waste in the same foot print area.
  • Handling of & shifting of existing waste due to high moisture content and opening of natural leachate flow.
  • Mass balancing of earthwork was difficult taking into account possibility of uneven primary settlement due to unanticipated compaction from heavy vehicular movement, settlement during monsoon as well as continuous settlement due to emission of gas.
  • Volume of soil layer was of gigantic proportions (about 1.5 lakh Cu.m) to procure, shifting up to 35m height on steep road, and achieving the desired level of compaction on slope was the most difficult task of the project.  Approximately 15000 truck load of soil transported from various location during night hours to avoid traffic congestion in city.
  • Availability ofspace for construction of new scientific landfills and storage of geogrids and liners which affected the procurement schedule.

Solution Proposed

Unlike any new landfill ,  management of  existing waste would require a detailed study of various  aspects including  design of slopes to accommodate more waste in the provided foot print  area; stability of base and embankment slopes ; ease of construction ; health & safety of  workman  etc.

In this case, embankment was constructed on weak foundation; there was possibility of uneven primary settlement. So, it was necessary to construct stable soil embankment, it was proposed to use Techgrid TGU Geogrid (PVA & Pa Coated) reinforcement &Geonet

  • Geogrid Wrap around system was used for raisning of embankment of the dump site from existing +25.0 m RL up to approximately +35.0 m RL in order to protect embankment from land slide and creating cell pockets to accommodate existing waste
  • Steeper slope building with use of  geonet
  • Existing soil lying should be reshaped, slope was steep 1V:2.5H and there was no scope for horizontal shifting so it need be reinforced with Geogrid on the Slope.

Execution On Site

Laying of Geogrid  –

  • The Geogrid was laid with the longitudinal direction parallel to the direction of the principal stress (perpendicular to the top of the slopes).
  • The Geogrid was installed in intervals of maximum 0.70 m.  Geogrid was anchored with wrap around in outer section with an overlap of minimum 5.0 m and with a horizontal (anchoring) length on the waste of minimum 10.0 m. 
  • Re-disposal of excavated waste on laid Geogrid was in two layers with the first layer between 0.4-0.5 m and the second layer between 0.2-0.3 m. 
  • After disposal and compaction of waste layers the Geogrid was wrapped around the margin of the waste and the next Geogrid was overlaid. 
  • Installation of Geogrid was following the manufacturer’s guidelines with the wrap around methodology

Jointing of Geogrid –

  • No joint in the longitude direction was accepted.  Geogrid was connected by simple overlapping in perpendicular direction to the role.  Overlapping was minimum 0.10 m.

Connections to structure –

  • Geogrid was cut in shape as required and with maximum distance between the penetrating structure and the Geocomposite at 0.25 m.  At the toe of the slope the Geogrid was installed on top of the erosion stone layer. The Geogrid had at minimum 0.5 m overlap in directly connection with the top of the stone layer.

CONCLUSIONS

The closure and containment of old waste was achieved scientifically with the aid of Geosynthetics products to get final height of 35m; 10 m higher than old unscientifically disposal. Further the new facility would have managed waste in a more efficient way to save almost 1.5 ha of land. This is important achievement & would have been possible due to steeper construction of slope by using Geogrid and other geosynthetics material.

Project was successfully completed by the contractor as per requirement of contract document.Over a period of few months a lush green turf was being formed on the outer face the slope. There is no way to understand that underneath the expansive gardens lie the garbage hills of the city for years.

This project made into many news channels

Stinking Dhapa dump to turn tourist destination by 2020

https://timesofindia.indiatimes.com/city/kolkata/stinking-dhapa-dump-to-turn-tourist-destination-by-2020/articleshow/59888917.cms

Eastern India’s Largest Garbage Dump Goes Green

https://www.msn.com/en-in/news/good-news/eastern-indias-largest-garbage-dump-goes-green/ar-BBXVrNv?li=AAggbRN

KMC converts Dhapa, largest open garbage dump-yard into a green plateau

https://www.getbengal.com/details/kmc-converts-dhapa-largest-open-garbage-dump-yard-into-a-green-plateau

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