Drainage systems are often installed to prevent water from accumulating in the soil near foundations of buildings. This water, acting under hydrostatic pressure, is forced through small gaps in the foundation wall and enters the building.
A common method to prevent this is to place an approximately horizontal drain external to and near the base of a foundation wall to channel water away from the foundation and thus relieve the hydrostatic pressure and consequent leakage.
This method reduces the hydrostatic pressure in the soil near the horizontal drain. It does not provide effective protection from water which permeates the soil from above, however, since this water percolates downward from the surface of the ground to the bottom of the foundation before it enters the drainage system. While percolating downward, this surface water saturates the soil and applies hydrostatic pressure on the upper foundation walls before it reaches the drainage system at the bottom of the foundation.
Another method for preventing foundation leaks is to coat the outer surface of the foundation with a sealant that prevents water in the saturated soil from forcing its way into the building. These sealants are fragile and are often damaged when installed or degrade after installation.
Drainage systems have been devised providing a sheet-like barrier covering the buried outer face of a foundation wall. Typical sheet systems are disclosed in U.S. Pat. Nos. 4,840,515, 3,965,686, 4,810,573, and 4,733,989.
Such sheet systems typically have interior voids between an inner sheet and a permeable outer sheet allowing water to leave the soil, pass into the voids, and flow by gravity downward into the horizontal drainage tube. Such systems are difficult and expensive to install, as the entire subterranean foundation wall is typically covered from near the surface of the ground to the horizontal drainage tube.
Other drainage systems (such as U.S. Pat. Nos. 4,930,272 and 4,869,032, below) channel water from between the walls of a foundation into a horizontal drain located inside the building and underneath a basement slab. For example, DiCello, U.S. Pat. No. 4,538,386, describes a drainage system comprised of horizontal drain pipes laid both outside the foundation wall and inside (within the foundation boundaries) the foundation walls, The internal drain pipes connect to the interior of a foundation wall and allow water to drain therefrom.
Many other devices are known in the art for soil drainage in general. For example, Delattre, U.S. Pat. No. 4,246,305, describes an extruded multichannel porous drainage strip for placing in water filled soil. There are also devices for forming a solid wall of backfilled material around a foundation, thus providing a porous path for downward water percolation. Minor et al., U.S. Pat. No. 5,017,042, describe a biodegradable accordion-like container for holding a layer of such coarse drainage material vertically against a foundation wall while the gap between the foundation and the excavation is backfilled.