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cell separation prevents continuous burn-through if combustion occurs

Source: Data from G. Tchobanoglous, H. Theissen, and S. Vigil, 1993, Integrated solid waste management: Engineering principles and management issues (New York: McGraw-Hill).

Source: Data from G. Tchobanoglous, H. Theissen, and S. Vigil, 1993, Integrated solid waste management: Engineering principles and management issues (New York: McGraw-Hill).

phase is filled so that it is ready to receive waste as soon as the current phase is filled. The liners and leachate collection systems of adjacent phases are usually tied together.

The size of landfill phases depends on the rate at which waste is deposited in the landfill, local precipitation rates, state permitting practice, and site topography. At landfills receiving large amounts of waste per day, phase size can be chosen so that phase construction equipment is always in use. As soon as the construction of one phase ends, construction of the next phase begins. Smaller landfills cannot operate this way.

Figure 10.13.3 shows several points in a normal, excavated, landfill lifetime, simplified because the landfill has only one phase. Part (a) shows the landfill just before waste is deposited. The liner is installed at grades that cause leachate to flow toward leachate collection pipes. Groundwater monitoring wells are also installed. Part (b) shows the second waste lift of an operating landfill cell being created. Each lift consists of a layer of daily waste cells. Each daily cell consists of the waste deposited during a single operating day. Daily cells are separated by the cover soil applied at the end of each day. To keep the daily cover and litter to a minimum, operators should keep the working face as small as possible.

Temporary roads on the landfill allow truck traffic easy access to the working face of the landfill. During wet weather, use of a special easy access area for waste disposal may be necessary.

Part (c) of Figure 10.13.3 shows the completed landfill. Five lifts are created, the final cover is installed, vegetation is established, and gas collection wells are installed.

Landfill excavations have sloping bottoms and sides. Excavated side slopes are generally not more than a ratio of 1:1. Their stability must be checked, typically with rotational or sliding-block methods. Bottom slopes are generally 1 to 5%. However, when landfills are built on sloping terrain, bottom slopes can be steeper, requiring stability analysis as well. Operators must also check the stability of the synthetic liner on steeper slopes to ensure that it does not slip or tear. This analysis is based on the friction force between the liner and the material just below the liner. Planners should estimate the bearing capacity of the soil below the landfill and future settlement to ensure that problems associated with differential settling do not ensue after waste is deposited in the landfill. Finally, the pipes used in the leachate collection system must be able to bear the weight of the waste placed on top.

The side slopes of the top of the landfill are generally a ratio of 3:1 or 4:1. Large landfills have benches, or terraces, on the side slope to help reduce erosion by slowing down water as it flows down the sides. The central por-

Leachate

Leachate

FIG. 10.13.3 Development of a landfill: (a) excavation and installation of landfill liner, (b) placement of solid waste in landfill, (c) cutaway through completed landfill. (Adapted from G. Tchobanoglous, H. Theissen, and S. Vigil, 1993, Integrated solid waste management: Engineering principles and management issues [New York: McGraw-Hill].)

FIG. 10.13.3 Development of a landfill: (a) excavation and installation of landfill liner, (b) placement of solid waste in landfill, (c) cutaway through completed landfill. (Adapted from G. Tchobanoglous, H. Theissen, and S. Vigil, 1993, Integrated solid waste management: Engineering principles and management issues [New York: McGraw-Hill].)

tion of the top of the landfill is relatively flat because height limitations keep landfills from being pointed cones. However, a slight slope (3 to 6%) is maintained to encourage run-off.

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