30 Sep 01
requirements for placement. At a minimum, one set of borrow assessment tests should be done for
each borrow source proposed. A set should consist of classification, moisturedensity (compaction),
(a) Classification Testing. Test pits or borings should be made in a grid pattern to char-
acterize each proposed borrow source. Small samples obtained from borings are excellent for index
property testing but often do not provide a very good indication of subtle stratigraphic changes in the
borrow area. Test pits excavated into the borrow soil with a backhoe or other excavation equipment
can expose a large cross section, providing a much better idea of the variability of soil than viewing small
soil samples obtained from borings. Soils should be grouped into "principal types" based on visual
classification by a qualified geologist or geotechnical engineer. Classification testing should be
performed on representative samples of each principal type or combination of materials. At a minimum,
one set of classification tests should be performed per 5000 m3 (6500 yd3) of proposed borrow.
Classification testing should consist of moisture content, liquid and plastic limits, and particle size
(b) Compaction Testing. One of the most important aspects of constructing a clay barrier
layer is proper remolding and compaction of the soil. The traditional method of specifying the
"acceptable zone" of moisture contents and densities has been based on achieving adequate strength
and limiting compressibility. This method is not ideal for clay layers designed to achieve low hydraulic
conductivities. EPA/600/R-93/182 provides detailed guidance on a satisfactory approach to developing
moisturedensity criteria for a clay barrier layer. The same general procedure may also be used for
soilbentonite mixtures. The procedure is outlined below:
For each soil type to be used in the clay barrier layer, prepare and compact samples with modified
(ASTM D 1557) and standard (ASTM D 698) compaction procedures to develop compaction
Based on compaction test results, specimens should be compacted to various densities and
permeated using the test procedure described in ASTM D 5084. Confining pressures and hydraulic
gradients used to perform this testing should be representative of landfill cover conditions.
An acceptable zone should be developed that encompasses the moisture contents and densities that
achieve the required permeability.
The acceptable zone should be modified on the basis of shear strength considerations, if applicable.
j. Barrier Layer--Geosynthetic Clay Liner.
(1) General. Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers