Patent Publication Number: US-6669404-B2

Title: Foundation drain system

Description:
TECHNICAL FIELD 
     The present invention deals with static underground structures that drain fluid or gas that is present at the exterior of a foundation or footing. More particularly, the field of the present invention involves the use of a porous medium that is either adjacent to the outside of a foundation or footing or part of a foundation or footing. 
     DEFINITIONS 
     The terms foundation and footing are used interchangeably herein to indicate a conventional structure (usually entirely underground) intended to be used to support vertical loads including floors and walls. Footings are customarily relatively wide, so as to maintain reasonable pressures on the underlining ground. 
     The term mat (or drainage mat) is used herein as equivalent to an alternate type of subsoil drain pipe (conduit) that is formed of a biodegradable resistant plastic back with a dimpled core that is faced with a biodegradable resistant filter fabric that is porous to water, but not soil particles. Such conduits are made by manufactures including JDR Enterprises; Alpharetta, Ga. under trade names that include “J-DRain” and by American Wick Drain Corporation; Monroe, N.C. under trade names that include “AKWADRAIN.” It is conventional to refer to the filter fabric as a geotextile and to form the filter fabric by techniques that include perforation of a film of biodegradable resistant plastic. It is known to make the filter fabric from plastics that include polypropylene, and to make the back and core from plastics that include polystyrene and polyvinyl chloride. U.S. Pat. Nos. 4,572,700, 4,923,331, and 4,943,185 include descriptions of conduits of the type encompassed by the term mat as used herein, and those patents are incorporated herein by reference. It is known to wrap filter fabric all of the way around the mat. 
     BACKGROUND 
     The Problems to be Solved 
     The major problem to be solved is the reduction of, or the elimination of, the detrimental effects of ground water in the vicinity of footings. Solutions to this major problem lower the water level in the vicinity of the footings. 
     In most locations, underground structures, such as footings, are subject to hydrostatic pressure from ground water. (Surface water will cause pressures when flooding is present.) A high water level outside of a footing causes an unbalanced pressure acting sideways against the footing. If the water level gets high enough, an unbalanced pressure acting sideways can be exerted on the wall supported by the footing. Footings and supported walls are not usually designed for such pressures, and eventually water will seep into the building through the almost inevitable cracks or joints. While coatings on the outside can reduce the water intrusion, it is usually not economical in residential buildings to design the footings and walls safely to withstand hydrostatically produced side pressures. 
     The traditional way to relieve hydrostatic pressure is to install a drain around, and close to, the footing. Various materials capable of communicating water are used to form the drains including perforated drain pipe (tile) under and adjacent to a layer of aggregate (such as small stones) that serves to reduce the rate of infiltration of the finer soil, which tends to clog the pipe&#39;s perforations. 
     The traditional practice is to cast the footing with concrete placed between form walls. A trench or hole wider than the eventual footing is dug around the perimeter of the site. Within the trench a form is constructed of an opposing pair of flat, abutting, vertical panels, or boards, made of wood, plastic, metal, or the like, so as to form a continuous channel to receive concrete. The opposing panels are spaced apart (usually by a constant distance) with their flat insides facing the channel and their outsides braced with stakes or the like. To communicate water from outside of the eventual footing to a sump, or the like, that is inside of the footings, sections of four inch pipe are placed on the bottom inside of the form, from one side of the form to the opposite side of the form, about every 25 feet (or as required by code). These periodically placed sections of pipe need to be protected from the ingress of concrete while the concrete is soft and will serve as through-conduits when the forms are removed. Concrete slurry is poured within the channel, leveled, and allowed to cure. After the concrete has cured, the forms are removed, drain pipe and aggregate (as aforementioned) are placed just outside of the footing, connection of the drain pipe to a sump (or the like) is effected (often through the aforementioned through-conduits), and the trench is backfilled. Placing drain pipe and aggregate often must be preceded by a labor intensive clearing of accumulated debris from the trench and the providing of an appropriate bed for the drain pipe. The traditional practice has evolved to include placing a fabric sock around the perforated drain pipe. The sock serves as a sieve to attenuate the ingress of soil particles into the perforated drain pipe while readily passing water. The traditional method just described may fairly be described as conventional. 
     Effecting a sound, long-lasting system of drainage using the described, conventional system requires significant workmanship. Opportunities for drain pipe to become dislodged or crushed are inherent in the traditional method described. The objectives of the present invention include overcoming the problems of the traditional method and its resultant system. As will be seen, the present invention may be carried out with workmen of little skill, and the system is inherently robust and resistant to damage. 
     In recent years, another method to relieve part of the hydrostatic pressure has found some favor. Herein, this method is called the horseshoe method. The horseshoe method begins after a foundation (including a set of through-conduits) and the wall the foundation supports have been constructed. Using an adhesive, or some other form of attachment, a mat is attached near the junction of the footing and the wall the footing supports after the wall and footing have been formed. The mat so placed must be periodically connected to a conduit or pipe extending away from the footing. That pipe (called a horseshoe conduit because of its appearance) connects to the mat and then curves down to connect to one of the aforementioned through-conduits. A horseshoe conduit is easily damaged during backfilling and operations near a horseshoe conduit. A horseshoe conduit is associated with each through-conduit and each horseshoe conduit must be water tight. 
     In addition to the susceptibility of damage to the horseshoe conduits during construction, the technique of using a mat near the junction of the footing and the wall the footing supports has additional issues. Since ground water is only removed from near the top of the footing, hydrostatic pressure on the footing (and on each horseshoe conduit) has not been significantly reduced. Damage to the footing could result and any breach of a horseshoe conduit (which are under pressure) will include damaging ingress of soil into the drainage system. 
     Whether the traditional method or the horseshoe method is used to effect a drainage system, such drains&#39; through-conduits are connected to a sump, or the equivalent, so that gravity, or a pump, tends to take water away from the footing. The present invention includes a novel way to solve the stated major problem of the reduction of, or the elimination of, the detrimental effects of ground water in the vicinity of footings. 
     The Efforts of Others 
     Improvements to the old traditional technique of foundation drainage described previously have long been sought. U.S. Pat. No. 3,613,323 to Hreha shows an early use of a perforated conduit (duct) placed on the outside of, and part of, a footing&#39;s form. A similar incorporation of a perforated conduit into the outside of a foundation&#39;s form is found in U.S. Pat. No. 5,120,162 to Parker, U.S. Pat. No. 5,399,050 to Jacobus, and U.S. Pat. No. 5,406,785 to Baum. In addition to the presence of a perforated conduit attached to, and on the outside of, a form wall, these devices include an expectation of at least the outside form wall and its conduit being permanent. Advantageously, at least one of the form walls does not have to be removed after concrete sets. Disadvantageously, while there might be a labor savings from not having to remove the permanent form wall, the permanent form wall is expected to be rather complex and expensive to manufacture, and to involve additional labor and expense to erect as compared to the old technique. The resulting drainage conduit will be in front of the resulting foundation and thus subject to all of the hazards attendant to the drainage tile of the older systems of drainage. A net advantage to these systems is not apparent and these systems have not found much favor in the marketplace. 
     A need remains for a foundation drainage system that minimizes the total capital and labor cost attendant to the total implementation of the drainage system, while producing a system that is inherently long lasting and likely not to be damaged by the hazards attendant to construction. The objectives of the present invention include satisfying these, and other, needs. 
     SUMMARY OF THE INVENTION 
     The present invention is a novel process of using mostly existing materials to effect an efficient and relatively inexpensive footing drainage system, and the apparatus that results from the use of that process. The process starts after the form for a footing is erected. 
     A mat (as previously described) is placed vertically inside of the empty form and with the mat&#39;s porous side against the inside of the outside wall of the form. The mat is extended horizontally along the entire length of the inside of the form being periodically spliced with suitable tape, or an equivalent. The bottom edge of the mat rests on the bottom of the form. Should drainage wish to be effected on the inside of a footing, a similar band of mat may be placed against the inside of the inside wall of the form. 
     Periodically, a T makes a fluid connection between the mat and a through-conduit that extends across the form to an attachment on the opposite form wall. When the form is removed after concrete is poured and cured, the T and through-conduit effect the way for water in the mat to pass to a sump, or the like, that is within the foundation. 
     Concrete is poured between the form walls and the concrete is leveled. With a small amount of care, it is easy to ensure that while pouring the concrete the concrete presses the mat against a form wall and that no concrete is between the mat and a form wall. The concrete level (height) is expected to be above (taller than) the mat and thus when the concrete cures a protective eyebrow of concrete will be formed above the mat. The presence of an eyebrow of concrete impedes causing damage to the mat after the forms are removed. A person working within the trench after the form is removed cannot step on the mat. The mat is also protected from backfilling of the trench, which takes place after the forms have been removed. 
     When the concrete has cured, the forms are removed. A conventional drainage system is connected to the now exposed openings to through-conduits (openings appear on the inside of the footing), and, when the trench adjacent to the now exposed fabric side of the mat (the fabric side of the mat appears on the outside of the footing and is essentially flush with the outside face of the footing) is cleared, one may place aggregate fill adjacent to the fabric. However, it has been found that the present invention functions satisfactorily, and preferably, without aggregate fill adjacent to the mat. The remainder of the trench is then backfilled and work progresses to the construction of structures to be supported by the well-drained footing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 : Perspective view of the inside and outside of a footing form, prior to the pouring of concrete, showing the invention in place. 
     FIG.  2 : Cross section through the form shown on FIG. 1 showing a side view of the invention. 
     FIG.  3 : Top view of the footing form prior to pouring of concrete. 
     FIG.  4 : Cross section in the same location as the cross section of FIG. 2 after the footing, and the wall and floor the footing supports, is finished. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention includes a method to make an improved foundation drainage system and the improved drainage system itself. While the preferred embodiment of the present invention involves water drainage away from a foundation or footing, it will be apparent that the present invention is applicable to any structure that is cast with concrete, or the like, where at least one form wall is used and where it is desirable to drain away water present adjacent to the structure. 
     The kernel of the method of the present invention involves the placement, within forms for receiving concrete, of a relatively long material (mat) that is capable of importing water through the material&#39;s sides while communicating water longitudinally. The present invention advantageously uses a mat manufactured by several companies that is equivalent to mats previously described. Because of familiarity with the soil drain mat made by American Wick Drain Corporation; Monroe, N.C., that company&#39;s AKWADRAIN™ prefabricated soil strip drain material is the preferred mat to be used with the present invention. It is apparent that the present invention includes, and can be used with, other materials having the properties that include being able to receive water through the material&#39;s sides, capable of communicating water longitudinally, and capable of being placed adjacent to a footing form wall prior to the pouring of concrete into the form. Water is the more important fluid to be appropriately dealt with by the present invention. However, it is apparent that the communication of other fluids is inherent as is the communication of gases including radon. 
     The preferred embodiment of the present invention may be seen even without words on FIGS. 1 through 4. On FIG. 1 one sees that mat  10  is placed along the bottom of the inside of outside-form-wall  40  with the porous face of mat  10  facing outward. Periodically, a T  20  is placed in fluid communication with mat  10  so as to be able to receive whatever fluid is within mat  10 . T  20  is attached to through-conduit  30  that extends across the form to flange  32 . Flange  32  is attached around its perimeter to the inside of inside-form-wall  42  with nails, or the like, so that concrete is not able to enter through-conduit  30 . Thus, an assembly is formed by mat  10 , T  20 , through-conduit  30 , and flange  32 . FIG. 2 shows a cross section through the assembly. The top view of FIG. 3 makes clear that mat  10  extends the entire length of the footing form. 
     To effect communication of water collected by mat  10  to a sump, or the like, aforementioned assemblies are spaced about 25 feet apart (or as required by applicable codes) along the form. The figures show only one such assembly. 
     Preferably, mat  10  is an AKWADRAIN™ soil strip drain made by American Wick Drain Corporation with a nominal thickness of one inch and a nominal height of six inches. The preferred mat  10  is available in one hundred foot lengths and thus only a few splices between lengths are needed on a residential foundation. Preferably those splices, not shown on the figures, are made by butting the ends of the mat  10  together and then wrapping with an appropriate tape having a contrasting color (such as white) so that the splices may easily be seen when looking down into the resulting footing from the ground surface. 
     Preferably, T  20  is adapted from a T manufactured by American Wick Drain Corporation and originally intended to be connected to a mat so as to extend away from the fabric side of the mat. Similar Ts suitable for use with the present invention are made by others and such Ts are readably fabricated. 
     Preferably, through-conduit  30  and its flange  32  are adapted from a conduit made by Carlton Industries of Flint, Mich. U.S. Pat. No. 5,643,311, incorporated herein by reference, shows the preferred conduit prior to adaptation on FIGS. 3 and 4. The adaptation includes replacing a flange on one end of the conduit of the &#39;311 patent with T  20 . The present invention is not limited to the use of only the preferred through-conduit. 
     After mat  10  has been placed within the footing form and connected to sets of T  20  and through-conduit  30  in the manner described, concrete is poured between outside-form-wall  40  and inside-form-wall  42 . Flange  32  anchors one end of through-conduit  30 . The stiffness of through-conduit  30 , and gravity, serve to keep the assembly in place. Only slight care needs to be exercised while pouring concrete to ensure that the concrete exerts pressure against the back of mat  10  so as to press the fabric face of mat  10  against the inside of outside-form-wall  40  without allowing any concrete to appear between the fabric face of mat  10  and the inside of outside-form-wall  40 . The depth of concrete is expected to be greater than the height of mat  10  so that concrete will be above all of the assembly. 
     After concrete is poured between outside-form-wall  40  and inside-form-wall  42  to an appropriate depth that is greater than the height of mat  10 , the concrete is allowed to cure. When the concrete is reasonably cured, the form is removed. Outside-form-wall  40  and inside-form-wall  42  are removed leaving a concrete footing with mat  10  at its outside base prepared to receive water present on the outside of the footing and to communicate the water so received through the footing using a set of Ts  20  and associated through-conduits  30  to the inside of the footing. Inside of the footing, an inside drain  34  is attached to the now open through-conduit  30 . Inside drain  34  communicates in a conventional manner to a sump, or the like. Optionally, as shown on FIG. 4, aggregate  56  is placed against mat  10  so as to facilitate filtering, and the outside of the footing trench is backfilled with fill  50 . It has been found that the practice of this invention does not require aggregate  56  being placed against mat  10  prior to backfilling, and that lack of a need to use aggregate  56  is a feature of the present invention. The preferred way of practicing the present invention is not to use aggregate. One may now proceed to use the footing to receive floor  64  or wall  70 . FIG. 4 shows a cross section through a finished concrete footing  60 . Note the protective eyebrow  62  of concrete that is above mat  10 . Eyebrow  62  is desirable. However, it is known to have mat  10  cover all of the face of the footing rather than the preferred recessing of mat  10  into part of the face of the footing. 
     The present invention includes a method of providing fluid drainage for a concrete footing  60  that is cast by placing concrete between an outside-form-wall  40  and an inside-form-wall  42 , including, after the form walls are erected, the steps of: placing a drainage mat  10 , having a face and a back, against the inside of the outside-form-wall  40  extending along the length of the outside-form-wall  40 ; attaching the proximate end of at least one through-conduit (such as through-conduit  30 ) in fluid communication with the drainage mat  10  and extending the distal end of the through-conduit to be flush with the inside of the inside-form-wall  42 ; placing concrete between the outside-form-wall  40  and the inside-form-wall  42 ; allowing concrete reasonably to cure, which produces a foundation  60 ; removing the outside-form-wall  40  and the inside-form-wall  42 ; attaching conventional means for drainage (such as inside drain  34 ) to the exposed distal end of at least one through-conduit; and backfilling the foundation. 
     The foundation drainage system produced by the method of the present invention includes a drainage mat  10  essentially flush with the outside of the foundation, and at least one through-conduit (such as through-conduit  30 ) in fluid communication with drainage mat  10  and extending through the concrete footing  60  to communicate with conventional means for drainage (such as inside drain  34 ). 
     The foundation drainage system produced by the method of the present invention may also be described with reference to the essentially flat surface of the outward-looking face of concrete footing  60  even when the essentially flat surface of the outward-looking face of concrete footing  60  is not vertical. In such a case, the drainage mat  10  may be described as being recessed into part of the outward-looking-face of the foundation  60  such that the mat&#39;s outward-looking-face does not extend significantly outward of the essentially flat surface of the outward-looking-face of the foundation, and such that at least one through-conduit (such as through-conduit  30 ) is in fluid communication with drainage mat  10  and extending through the foundation  60  to communicate with conventional means for drainage (such as inside drain  34 ). 
     Preferably the method and system include: the use of a drainage mat that is capable of importing fluid through the mat&#39;s face while communicating fluid longitudinally or a drainage mat that has a biodegradable resistant back with dimpled core and a face of biodegradable resistant filter fabric that is porous to water, but not soil particles; and placing concrete to a height greater than that of the drainage mat so as to produce eyebrow  62 . 
     Preferably the system includes the drainage mat  10  being surmounted with part of the foundation&#39;s concrete, and the drainage mat  10  being recessed into part of the outward-looking-face of the foundation between the bottom of the foundation  52  and the top of the foundation. 
     It will be apparent to one skilled in the art that variations of the disclosed invention are possible without departing from the essence of the invention. Alternates to the preferred mat  10  are ubiquitous. Alternate ways to implement the function of the preferred T  20  and through-conduit  30  may be developed with little experimentation. Such modifications and equivalents are within the ambit of the present invention.