30 Sep 01
100 m (300 ft).
(3) Bedding Materials and Pipe Perforations. The design of bedding materials and drainage
media must include an evaluation of the criteria outlined in Paragraph B-3e, Filter Layer-- Granular
Materials. EM 1110-2-1901 provides guidance on sizing perforations for preventing infiltration of
material into the perforated pipe:
50% size of filter material ≥ 1.0 (holes) or ≥1.2 (slots)
hole diameter or slot width
(4) Pipe Considerations. Perforated polyvinyl chloride (PVC) pipe, smooth-walled high-
density polyethylene (HDPE) pipe, or corrugated HDPE pipe may be used to construct a drainage
collection system. The most common are corrugated HDPE pipe systems. These materials are easy to
install in the field, flexible enough to withstand minor settlements, and are relatively inexpensive.
(a) PVC Pipe. PVC pipes are often supplied in 6.1-m (20-ft) lengths and are joined via
couplings or with bell and spigot ends. The basic resin should be as defined in ASTM D-1755. For
PVC specified as Schedule 40, 80, and 120, reference ASTM D-1785. For pipe specified by the
standard dimension ratio (SDR), the appropriate specification is ASTM D-2241.
(b) HDPE Smooth-wall Pipe. HDPE smooth-wall pipes are generally supplied in 6.1-m
(20-ft) lengths and are joined using butt-end fusion. Other joining methods are also available. The
HDPE material consists of 9798% resin, with approximately 2% carbon black and minor other
(c) HDPE Corrugated Pipe. This pipe is available in several forms, each design being
supplier-specific. The pipe may be perforated or slotted, the inside may be smooth lined or not, and
various connections and fittings are available as well. HDPE corrugated pipe is the one most commonly
used for cover drains. AASHTO M 252 and M 294 provide detailed design information for corrugated
h. Barrier Layer--Geomembrane.
(1) General. The objective of the barrier layer is to minimize percolation of precipitation into
underlying waste materials. Geomembranes are thin sheets of flexible, relatively impervious polymeric
materials, whose primary function is to act as a barrier to liquids and vapors. The polymeric materials
are manufactured into sheets and transported to the job site, where they are placed and seamed.
(2) Design Criteria. Common types of geomembranes currently being used for landfill covers
are PVC and polyethylene, with polyethylene being the most frequently used geomembrane on Corps of
Engineers projects. A minimum thickness of 1.0 mm (40 mils) is recommended for cover