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When our client required an expansion for a major municipal solid waste landfill site, Earth Tech provided the design, permitting and construction through a unique approach that utilized a flexible reinforced earth wall. The use of a flexible reinforced earth wall allowed the landfill to expand vertically, significantly increasing its capacity and extending the life of the landfill, without using a lot of land. This wall is approximately 1,300 feet in length and 45 feet high. It utilizes soil reinforcement made of a plastic grid and has natural grass growth on an almost vertical wall.
The reinforced wall was constructed with approximately 500,000 tons of structural fill material hauled from a nearby borrow area. The reinforcement was installed at a specified spacing determined by the slope stability analysis. The slope stability analysis determined adequate factors of safety for the vertical wall face.
This project consisted of several challenges during construction that were addressed by the Earth Tech. Some of the challenges included:
- The reinforced berm was constructed with two specified types of structural fill soil. The structural fill soil for the geogrid reinforcement zone of the wall was specified as a more free draining material to prevent buildup of water pressures in the wall. The construction quality control performed by Earth Tech required that the engineers closely monitor and test the placement of both types of structural fill.
- Organic dredge material was encountered in an area where the wall foundation soils were being placed. The contractor was instructed to remove the organic soils and replace the material with suitable structural fill materials for the wall foundation. This eliminated any concerns about portion of the wall sinking.
The flexible reinforced earth berm was designed to have a 0.5 horizontal to 1.0 vertical slope rather than the standard berm design of 3 horizontal to 1 vertical slope. This allowed Earth Tech to design a larger landfill expansion area for waste disposal. The increased landfill area will result in additional landfill capacity and an extended life expectancy for the landfill expansion. This will also result in substantial added revenue for the client.
Earth Tech has used this design for nine other solid waste landfill expansions. This technology is also being used in other areas to replace concrete or block retaining walls in stream crossings and in other applications to stabilize weak soil conditions.
