39    GEOSYNTHETICS FOR USE IN WASTE FACILITIES
John A. Bove, Geotechnical Engineer
George R. Koerner, Geotechnical Engineering Manager
S & ME, Inc.,
Fairfield, Ohio 45014
INTRODUCTION
Geosynthetics are man-made synthetics used in the improvement of soil and rock. The word
"Geosynthetics" is a generic term which collectively describes geotextiles, geomembranes, geonets,
geogrids and geocomposites. Each of these terms is briefly defined below:'
Geotextiles a permeable textile material. Commonly called filter fabrics. In waste
facilities Geotextiles can function as filters, separators, lateral drains or
provide reinforcement in ramp structures.
Geomembranes are very low permeability liners or barriers used to control fluid migration.
Geonets are polymeric materials in the form of extruded nets. These nonde-
formed nets are used as drainage cores to transmit large quantities of
fluid in both leacheate collection and leak detection systems.
Geogrids like geonets, these materials have a netlike configuration. However,
their primary function is reinforcement. Hence, they are either strain
hardened sheet materials or scrim reinforced to increase their tensile
properties.
Geocomposites consist of various combinations of the aforementioned materials. They
function due to the synergistic nature of their component parts.
The growth and development of geosynthetics has been phenomenal. Geosynthetics have become
common to the engineering community over the past decade, and at present represent a billion dollar
industry in the U.S. alone. The reasons for this tremendous growth are two fold. First, geosynthetics
are an economically viable alternative and can perform a wider range of tasks than conventional
construction materials. Secondly, the manufacturers of geosynthetics can "tailor" a product to suit
any application. In some cases, geosynthetics can remedy a situation which was impossible to solve by
conventional means.
As more potential geosynthetics applications are identified, it is the job of the design engineer to
isolate the required performance characteristics of the material and to write specifications to acquire
such a material. The method described above is known as design by function. It is commonly accepted
that there are five functions that a geosynthetic can serve. These five functions are separation,
filtration, drainage, reinforcement and moisture barrier. Depending on the application, the five
functions can occur as individual functions or in combination with one another. It is the goal of a
designer to prioritize the functions governing his project, and to design accordingly. The following is a
brief review of the various functions a geosynthetic can serve in a waste facility.'
Separation this function is to prevent the mixing of two dissimilar materials. A
geosynthetic is placed at the interface of two materials such as native
subgrade and a drainage stone. Hence the migration of fines into the
stone is reduced and the integrity of the stone is maintained.
Filtration filtration implies flow perpendicular to the plane of the material. In
short, this function is concerned with "permittivity"; the ease at which
fluid flows across the plane of the fabric. The geosynthetic must be
open enough to allow water to flow through it but "tight" enough to
insure the formation of an upstream soil filter.
Drainage geosynthetic can function as a drain. Drainage refers to in-plane flow.
The major consideration for this function is "transmissivity" (planar