PREFABRICATED FOUNDATION AND SOIL DRAINAGE SYSTEMS

These field-constructed foundation drainage systems are obviously very difficult to build properly and often perform poorly over time due to infiltration into the drainage piping by silt, sand, and soil that will eventually clog the entire system. Manufacturers have responded by developing “idiot-proof” systems to replace these now-antiquated field constructed systems. These prefabricated systems are relatively inexpensive and make them completely reasonable for use as additional water control for practically any construction project including residential, multifamily, commercial, and civil structures. These systems add superior protection for minor costs to any project. For example, concrete slabs without reinforcing can withstand hydrostatic pressure equal to approximately 2.5 times the slab’s thickness. In practically every structural design, it becomes much more economical to add under-slab drainage than to increase the thickness of the slab.

Prefabricated plastic soil drainage systems are available from a number of manufacturers. These products are manufactured in a variety of plastic composite formulations including polypropylene, polystyrene, and polyethylene. Figure 2.2 pictures a typical manufactured drainage product. The systems combine specially designed drainage cores covered with geotextile fabric in prepackaged form that eliminates all field construction activities except trenching and backfilling operations.

FIGURE 2.2 Typical foundation premanufac-
tured drainage system with geotextile attached.

The systems are idiot-proof in that the product is merely laid into the area designated for a drainage field. Only appropriate sloping of the trench to collection points is required. Figure 2.3 presents a simplified isometric detail of a drainage system installation. The product is puncture- resistive to protect its performance during backfill. Manufacturers also provide ample accessories (including termination and transition detailing) to complete the installation. Figures 2.4 and 2.5 show available accessories including a tee connection to join one branch of a drainage to another, and an outlet connection for collection of water that terminates at a drain box or culvert.

FIGURE 2.3 Isometric detail of drainage system.
(Courtesy of American Wick Drain Corporation)

FIGURE 2.4 “T” connector for drainage system.
(Courtesy of American Wick Drain Corporation)

FIGURE 2.5 Outlet connection for drainage sys-
tem. (Courtesy of American Wick Drain
Corporation)

Materials are available in a variety of widths (up to 36 in) and lengths provided in rolls of up to 500 ft long. The product should be puncture-resistant with some elongation capability for movement after installation, and be resistant to the natural or human-made elements to be found within the intended service area.

Prefabricated Foundation Drainage System Installation The product can be laid into preexisting trenches available from foundation construction or trenches constructed specifically for the drainage field. The width of the trench is typically 2–6 in wide. The depth of the trench is determined...