ETL 1110-1-162
30 Sep 01
Geomembrane or other geosynthetic failure because of tensile stresses.
Cover penetration connection (e.g., gas vent pipe boots) failures because of the development of
stress concentrations.
Internal drainage layer and surface drainage disruption because of changes in design slopes.
Leachate or gas collection system disruptions because of changes in design slopes.
Surface water ponding.
(3) Design Criteria.
(a) Waste Settlement Analysis. Mechanical settlement, caused by the placement of the
landfill cover, occurs rapidly and is typically complete in several weeks. Mechanical settlement is a
function of the compressibility of the waste and is related to its void ratio. The combination of
mechanical secondary compression, physicalchemical action, and biochemical decay causes settlement
to continue with time. The method of settlement analysis typically used for landfills is presented by
Sowers (1973). EPA/600/52-87/025 and EPA/600/2-85/035 provide additional technical information
on the settlement of landfill covers. Settlement of a landfill should be determined across several sections
that are considered representative of it to determine if adverse impacts are expected as a result of
settlement.
A method for determining the stresses in geosynthetic fabrics resulting from differential settlement is
presented in EPA/625/4-91/025, Design and Construction of RCRA/CERCLA Final Covers.
(b) Foundation Settlement Analysis. If the foundation material under the waste fill is
composed of fine-grained soils, such as soft clays, foundation consolidation will contribute to the overall
settlement of the final cover. Traditional settlement analyses, based upon site-specific soil characteristics
and loading conditions, should be used to estimate foundation settlement. EM 1110-1-1904 provides
detailed information on how to do settlement analyses.
(c) Settlement Design Considerations. Prior to the placement of random fill material, the
landfill surface must be cleared of vegetation and can be proof-rolled to reduce settlement. Compaction
equipment weighing 18,000 to 45,000 kg (40,000 to 100,000 lb) is often used for proof rolling. The
initial 8 to 12 passes of this equipment has the greatest effect. It should be noted that this compaction
effort will affect only the upper few feet of waste, and resilient materials, such as old tires, will not
densify under any amount of rolling. When settlement of either the waste fill or the foundation is
expected to be excessive, preloading (or dewatering) can be used to minimize post-construction
settlement. After preloading is complete, the surcharge fill can be reshaped as the random fill layer.
b. Stability Analysis.
B-25
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