LANDFILLING METHODS AND OPERATIONS

The methods used for landfilling dry areas are classified into area, trench and depression.

1) AREA METHOD

Area method is used when the land is not suitable for the excavation of trench where solid waste is placed. In this method the waste is unloaded and spread in the long narrow strips in layers that vary in depth from 16 to 30 in. Each layer is compacted in day's operation until its height reaches the 6 to 10 ft. At the end of each day's operation 6 to 12 in layer of cover material is placed over the completed fill. The cover material is hauled from the nearest borrow pit or adjacent land from trucks or earth moving equipment. 

The filling operation is started by building an earthen lavee against which wastes are hauled and compacted. The length of unloading area is based on site conditions and size of operation. The width of compacted waste varies from 8 to 20 ft depending on the terrain. A complete lift having cover material is called a cell. Successive lifts are placed on top of one another until the final grade is reached that is called ultimate development plan. The length of unloading area used every day should be such that final height of fill is achieved at the end of days operation.

2)TRENCH METHOD

The trench method is used when there is enough amount of cover material available at the site and the water table is near the surface. The solid waste is placed in trenches that vary in length from 100 to 400 ft, depth from 3 to 6 ft and width from 15 to 25 ft. In the beginning of the process some part of trench is dug and waste is piled to form an embankment behind the first trench. Wastes are placed there and thin layers of 18 to 24 in are made and compacted. This process continued until the required height is achieved. The length of trench should be such that at the end of days operation final height is achieved. The cover material is gained from the excavation of nearest trench or continuing the trench that is being filling.

3) DEPRESSION METHOD

In the areas where artificial or natural depressions are present, they can be used for landfilling operations. Canyons, Ravines, quarries and dry borrow pits all can be used for this. The technique of placing and compacting the waste depends upon the geometry of the site, properties of cover material, hydrology and geology of site and access to the site. 

In canyon the floor is flat and the first filling is done here by the method of trench. After this the filling is done at the head end of canyon than at the mouth of canyon. This avoids the water accumulation behind the landfill. Wastes are deposited at canyon floor and pushed against canyon face at the slope of 2 to 1 . High compaction is achieved. The compacted density achieved as high as 1,200 Ib/yd3 was seen. 

4) CONVENTIONAL METHODS FOR WET AREAS

Swamps, marshes, tidal areas, ponds and quarries are wet areaas that could be used for landfilling. Due to the problems of odor and ground water contamination the design of landfill in wet areas is a serious concern. 

To bear mudwaves and to enhance structure stability dikes are used to divide the cells or lagoons by riprap trees, lumber demolition waste,, tree limbs and other relevant materials with clean fill material. Sometimes to avoid the malodorous lechate movement and gases in lagoons, the clay and wood sheet piling or leightweight interlocking steel are used. 

The problems could also be ressolved by first draining the site and then lining the bottom with clay liner and other sealants.