ETL 1110-1-162
30 Sep 01
should be used for static conditions. This value may need to be increased in seismically active areas. If
possible, friction testing should be conducted during design using site-specific materials and anticipated
field conditions. Where this is not possible, frictional resistance values should be selected for design
calculations on the basis of tests performed by others under conditions that are similar to those
anticipated in the field.
(c) Waste Fill Mass and Foundation Stability. After the slopes are preliminarily selected,
the overall stability of the waste fill mass and foundation needs to be analyzed. As noted previously, the
geotechnical characteristics of waste materials are extremely difficult to determine. The mechanical
behavior of municipal refuse is typically expressed in terms of an apparent friction angle and a cohesion
intercept. These parameters are back-calculated from actual cases of failure or cases where large
deformations in refuse have occurred. They can also be conservatively estimated by observing existing
refuse slopes and then back-calculating to determine the strength parameters, assuming a factor of
safety of 1.0. It should be noted that waste mass materials could be highly variable. The text entitled
Geotechnical Practice for Waste Disposal (Daniel 1993) provides estimates of waste strength
parameters. Additional information on properties of waste fill materials can be found in ASTM STP
1070 (Morris and Woods 1994). Strength parameters used for the foundation soils are usually
determined through field sampling and laboratory testing. Seismic considerations should also be
addressed where applicable. The computer program UTEXAS (current version) may be used to
perform stability analyses for landfills. Edris and Wright (1992) provide information on the use of
UTEXAS.
(d) Waste Fill Mass and Foundation Factor of Safety. Recommendations for minimum
factors of safety for slope stability analyses can be found in the document entitled Guide to Technical
Resources for the Design of Land Disposal Facilities (EPA/625/6-88/018). If the designer is
confident of strength parameters, a safety factor of 1.25 is recommended where there is no imminent
danger to human life or to the environment if the slope fails. The safety factor should be increased to
1.5 when strength values are uncertain. When there is imminent danger to human life or if there would
be a major environmental impact if the slope failed, the minimum factor of safety should be 1.5 or
greater.
(e) Other Stability Issues. In addition to the items presented above, there are a number of
other factors that may need to be considered during design. These include the effects of surface water,
leachate seepage forces, desiccation cracking, seismic conditions, freezethaw effects, construction
equipment loadings, and long-term stress relaxation of reinforcement geosynthetics.
c. Test Fills.
(1) General. A test fill is sometimes constructed before the full-scale landfill cover for the
following reasons:
To evaluate cover stability.
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