Geology Reference
In-Depth Information
The geotechnical properties of embankment foundation materials are
determined by physical tests to assess the compressive and shear strengths,
bearing capacity, permeability, consolidation and cohesion, plasticity, and
moisture content of the potential foundation materials. In particular,
determining the permeability of the surficial materials that underlie the
impoundment is necessary for assessment of possible seepage from the pond;
this is especially important if a mine underlies the impoundment.
Geotechnical investigations also involve drilling in the “footprint” of the
embankment. Drilling programs are designed to penetrate the foundation
materials to an appropriate depth. Multiple holes are required along the
embankment footprint to establish homogeneity or variability of the foundation
materials throughout the structure. Materials recovered from the drill hole are
tested to establish strength, consolidation, and permeability characteristics.
Settlement of the embankment foundation is generally not a factor in
embankment design where the foundation is sound rock and the embankment
area has not been undermined. Although many embankments are constructed
from noncohesive materials and are not subject to cracking, some compacted
refuse materials exhibit brittle behavior and may crack as the foundation
material settles. Particular attention is given to the foundation of both starter
dams and embankments to avoid embankment cracking, which can be caused
by differential settlement between a compressible valley bottom and rock
abutments or outcrops.
In some cases, the geotechnical properties of the basin foundation
materials are also characterized. The basin area is not always drilled, but where
subsidence of below-drainage mine workings is a possibility, operators
sometimes drill and test as they do for the embankment foundation. Boreholes
in the basin area must be plugged to limit communication between the
impoundment and the underlying strata.
Finally, geotechnical characterization of the construction materials to be
used for the embankment is also a routine part of site evaluation. Most coal
operators utilize the coarse refuse generated by the coal preparation process to
construct the embankment. Using coarse refuse for embankment construction
solves the disposal issue for the coarse waste, which would otherwise have to be
disposed of elsewhere within the mine's permitted area. Coarse refuse is fairly
homogeneous in particle size and strength characteristics over time and is
therefore a comparatively predictable construction material for meeting the
engineering design specifications for embankment materials.
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