Abstract:
Tubular segments may be nestably interconnected, with the lower end of one tubular segment compressively inserted into the upper end of another tubular segment. A mat formed of such tubular members, and a fluid storage system formed of a plurality of such vertically stacked mats, are also disclosed.

Description:
The present invention generally relates to systems for subsurface fluid drainage and storage, and more particularly to a system and method for vertically stacking in a nested relation an apparatus especially suited for promoting, directing, and storing rain and irrigation water drainage on and/or below the land&#39;s surface. 
     Most of the subsurface fluid and drainage and storage systems known are variations on a fundamental concept of providing lateral drainage through one or more layers of sorted gravel or crushed rock. In the typical known system, a layer of gravel underlies the smaller-particle root zone beneath the upper surface of soil. Water passing through the root zone reaches the gravel layer, and then presumably flows laterally through the gravel layer to a perforated pipe or French drain for discharge into a nearby surface watercourse or into a storm sewer system. Known systems however, are vulnerable over time as the gravel settles into an ever more densely packed layer. As fine sand filters down and fills voids in the gravel, the gravel layer&#39;s fluid transmissivity is adversely affected. Additionally, gravel&#39;s tendency to settle reduces the desirability of placing pipes within a gravel layer, as severe settling and compaction may lead to pipe rupture. 
     U.S. Pat. Nos. 5,250,340; 5,102,048; 5,848,856; and 5,123,778, the entire disclosures of which are hereby incorporated by reference, disclose additional systems that generally relate to the drainage and storage of fluid. 
     SUMMARY OF THE INVENTION 
     A subsurface fluid drainage and storage system with high void storage volume that is placed in compression, instead of bending or tension, that provides for very high loading. The dranage and storage system preferably is comprised of one or more mats nestably stacked upon each other. Each mat comprises crush-resistant support members each possessing a substantially open receiving end located near the top of the support member, a substantially open compression fitting located near the bottom of the support member, a plurality of ribs extending longitudinally along the inner sidewall of the support member, and at least one peripheral wall opening extending upward longitudinally from the bottom of the compression fitting and terminating above the compression fitting. The support members are held in spaced relation to one another by interior struts such that the interior struts and the support members define a grid. An exterior strut, operatively connected to at least one support member extends along the perimeter of the grid to provide added support. The compression fitting allows the mats to be vertically stacked in a nested relation and thereby provides increased strength against lateral forces, relatively compact construction, larger storage volume, ease of transport, and ready installation. Additionally, the system may be encased by an impervious liner to allow the system to store water. 
     There has thus been outlined certain features of the invention in order that the detailed description that follows may be better understood. There are additional features of the invention that will be described which will form the subject matter of the claims appended. It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed are for the purpose of description and should not be regarded as limiting. As such those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of the invention; 
     FIG. 2 is a top view of the preferred embodiment of the invention shown in FIG. 1; 
     FIG. 3 is a perspective view of multiple embodiments of the invention shown in FIG. 1 in a stacked nested relation; 
     FIG. 4 is an illustration of a preferred form of the invention shown in FIG. 1 enclosed in a liner for subsurface disposition; 
     FIG. 5 is a cross section view of an interior strut in the embodiment shown in FIG. 1 taken along the line  5 — 5 ; 
     FIG. 6 is a cross section view of an exterior strut in the embodiment shown in FIG. 1 taken along the line  6 — 6 ; 
     FIG. 7 is a side view of one of the support members in the embodiment shown in FIG. 1; 
     FIG. 8 is a cross sectional downward view of the support member shown in FIG. 7, taken along the line  8 — 8 ; 
     FIG. 9 is a cross sectional downward view of the support member shown in FIG. 7, taken along the line  9 — 9 ; 
     FIG. 10 is a cross sectional downward view of the support member shown in FIG. 7, taken along the line  10 — 10 ; 
     FIG. 11 is a cross sectional downward view of the support member shown in FIG. 7, taken along the line  11 — 11 ; 
     FIG. 12 is a fragmental cross sectional view of the support member shown in FIG. 7; 
     FIG. 13 is a cross-sectional view of one of the tubular members shown in FIG. 1; 
     FIG. 14 is a zoom view of one of the fingers shown in FIG. 13; and 
     FIG. 15 is a longitudinal cross sectional view of the support member shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, like reference numerals designate corresponding structure throughout the views. 
     The present invention generally relates to a mat for subsurface fluid drainage and storage in which the mat is placed in compression and whereby a plurality of mats may be vertically, nestably stacked and thereby provide increased strength against lateral forces, relatively compact construction, larger storage volume, ease of transport, and ready installation. As a setting for the following discussion, the preferred form of the invention will be described for use in collecting and storing water, however, it will be readily appreciated that aspects of the invention will be conformable with other uses of collecting and storing liquids and even gases. 
     The improved system for subsurface fluid drainage and storage involves a comparatively simple and inexpensive gravity flow system which reduces the amount of time excess water spends in the soil. In the practice of a preferred embodiment of the invention, water percolates only about 30.0 to about 45.0 cm. vertically down through the root zone before entering a physical drainage structure and then being transported to a collector pipe. Known subsurface systems typically require water to travel a meter or more vertically and/or horizontally before encountering a drain pipe from which effective drainage may occur. 
     Referring to the drawings in more detail, there is illustrated in FIGS. 1 to  4  a preferred form of the invention that utilizes a mat A comprised of an array of support members  20  that each preferably possess a substantially open receiving end  21 , a substantially open compression fitting  22 , one or more stiffening ribs  24 , one or more support ribs  26 , and at least one peripheral wall opening  28 . Each support member  20  preferably comprises a thin-walled cylindrical column integrally molded from a semi-rigid thermoplastic material, and for best results, a high impact polypropylene or high density polyethylene plastic. Additionally, it should be noted that support members of other than cylindrical shape may be used, for instance, oval, hexagonal, rectangular, square, triangle, octagonal, or other cross-sectional may be utilized. 
     Referring now to FIGS. 7 and 12, The compression fitting  22  of a support member of an upper mat preferably is designed to be axially inserted into the receiving end  21  of a support member of a lower mat such that the support members may be stacked in a nested relationship. The compression fitting  22  is located near the bottom of the support member  20  and extends around the perimeter of the support member  20  and longitudinally upwards to preselected distance, preferably about one to one and one-half centimeters, however, for best results the compression fitting  22  should not extend longitudinally higher than the peripheral wall opening  28 . Additionally, the compression fitting  22  possesses a smaller outside perimeter than the receiving end  21  and preferably possesses a beveled edge to allow the support member  20  to be stacked in a vertical nested relation. A plurality of eight equal angular spaced fingers  40 , help align the compression fitting  22  during its insertion with the receiving end  21  of a lower support member, extend below the compression fitting  22  and are preferably beveled to allow the compression fitting  22  to be easily axially inserted into the receiving end  21  of another support member  20 , as is illustrated in FIG.  3 . 
     Referring now to FIG. 13, which is a longitudinal cross-sectional view of one of the support members  20 , four equally angular spaced support ribs  26  are longitudinally disposed on the interior side of the support member  20  and extend longitudinally from approximately the receiving end  21  to approximately the top of an associated peripheral wall opening  28 . For best results, the support rib  26  should be located on the interior wall at approximately the same position as where the struts, either internal or external, terminate on the outside wall of the support member  20 . The support ribs  26 , may in fact be operatively connected or integrally formed with the internal  32  or external struts  34 . Additionally, as best shown in FIG. 13 the support rib  26  widens gradually from the top of the support member  20 , however, this illustration is not intended to limit the size and shape of the support rib  26 . FIG. 13 also shows eight stiffening ribs  24  which begin below the receiving end  21  and extend past the compression fitting  22 , terminating with a corresponding finger  40 . Preferably, the upper end of the stiffening ribs  24  is recessed from the receiving end  21  a distance approximately equal to, or at least as high as, the height of the compression fitting  22 . Such dimension will allow the compression fitting to be totally insertable into the receiving end, prevent the compression fitting from being inserted too deeply, allow the stacked mats to be in nested relation, and aid in the formation of a rigid, stable structure. 
     The stiffening ribs  24  are double in thickness below a point approximately even with the upper end of the peripheral wall openings  28 . It should be noted that the stiffening ribs  24  are not required to double in size, and this dimension is not intended to limit the invention. Each stiffening rib  24  terminates in a corresponding finger  40  that is preferably beveled to allow for ease in axially inserting the compression fitting  22  into the receiving end  21  of another support member. The fingers  40  extend below the compression fitting  22 , and once axially inserted, aid in preventing the support member  20  from rotating with respect to mated support member. Additionally, four equal angularly spaced peripheral wall openings  28  in the compression fitting  22  cooperates with the four corresponding support ribs  26  of the lower support member to help prevent the matrix from rotating. Preferably, the support member  20  will possess four peripheral wall openings  28 , that roughly divide the compression fitting  22  into four quadrants. Each quadrant preferably has two stiffening ribs  24  extending down and terminating into fingers  40  that extend below the compression fitting  22  and the support member  20 . Preferably, the fingers  40  in each quadrant oppose each other as shown in FIG.  13 . 
     Referring now to FIGS. 1 and 12, preferably the compression fitting  22  possesses the same inside perimeter as the support member  20  and the receiving end  21 . However, the outside perimeter of the compression fitting  22  is smaller than the outside perimeter of the receiving end  21 , whereby a shelf  30  is created that will aid in stabilizing the support member  20  when vertically stacked. Please note that FIG.  12 , as shown, has inverted the illustration such that the compression fitting  22  appears towards the top of the drawing. In another preferred embodiment, the outside perimeter of the compression fitting  22  will approximately equal the outside perimeter of the support member  20  at the top of the compression fitting  22 , but will taper inwardly towards the bottom of the compression fitting  22  such that the outside perimeter at the bottom of the compression fitting  22  is smaller then the outside perimeter at the top of the compression fitting  22 . The peripheral wall openings  28 , allow water to flow through the support members in two perpendicular directions, laterally through each support member while the open interior of the support members and the spacing of the support members allows water to flow vertically through and between the support members and laterally between the support members. 
     Referring back to FIGS. 1 and 2, there is shown a plurality of support members  20  disposed in a uniform rectangular array defined by a plurality of perpendicular rows and columns defining the mat A. Internal struts  32  operatively connected or preferably integrally molded to the support members  20  provide added strength to resist external and/or lateral soil and water pressure. For best results the internal struts  32  should be T-shaped beams, as shown in FIG.  5 . An external strut  34  is operatively connected or preferably integrally molded with a support member  20  located at the corner of mat A. As illustrated, the external strut  34  extends along one perimeter side of mat A, and is connected to support members  20  located at the corners of mat A. The external strut  34  may either be connected to mat A at the corner support members  20 , may be operatively connected or integrally molded directly to the outside wall of each support member  20  located on that perimeter side, or for best results, the external strut  34  should be operatively connected or integrally molded to every support member  20  along the perimeter side by an internal strut  32  that extends outward from each support member  20 , as shown in FIG.  1 . For best results the external strut should be an L-shaped beam, as shown in FIG.  6 . 
     The peripheral wall opening  28  extends longitudinally upward from the bottom of the compression fitting  22  to a point approximately equal to or above the compression fitting  22 . Preferably, there are four openings disposed at ninety degree angular intervals positioned under a corresponding support rib  26 . The sides of each peripheral wall opening  28  preferably extend longitudinally and parallel to each other, with the upper end of each peripheral wall opening  28  being preferably rounded or actuated. The peripheral wall openings  28  divide the compression fitting  22  into four quadrants, whereby each peripheral wall opening  28  is separated from another peripheral wall opening  28  by two stiffening ribs  24 . The stiffening ribs  24  and the support ribs  26  provide strength and rigidity to the support member  20 , extend longitudinally along the inner sidewall of each support member  20 , and are operatively connected or preferably integrally molded to the support member  20 . Preferably, eight stiffening ribs  24  and four support ribs  26  extend along the inner sidewall of the support member  20 . As illustrated in FIGS. 8 and 9, the support ribs  26  are disposed at ninety degree angular intervals. The stiffening ribs  24  are preferably disposed between support ribs  26  such that there is a thirty degree angular interval between each stiffening rib  24  and between a stiffening rib  24  and a support rib  26 . Both the stiffening rib  24  and the support rib  26  are preferably frustoconical in shape. 
     FIG. 3 illustrates a plurality of mats in stacked, nested relation. For reference these mats are labeled mat A, mat B, mat C, and mat D. Each mat is preferably substantially identical to each other mat and is constructed according to the principles outlined above. As has been illustrated, the substantially open receiving end  21 , is adapted to receive the compression fitting  22  of the support member directly above. For example, the compression fittings of mat B are axially inserted into the substantially open receiving end support member of mat A. It should be noted that only four mats are illustrated in stacked, nested relation for the purposes of illustration, not limitation. 
     Referring now to FIG. 4, one or more sheet layers  42  may be secured to or placed over the face of the stacked, nested mats. For example, one or more layers  42  may be sealingly wrapped over the sides, bottom, and top of the stacked mats to allow the mats to be used to store fluids. Preferably, the sheet layers  42  are geotextile materials and/or geomembranes, and or skeletal layers in accordance with the disclosure of U.S. Pat. No. 4,896,993, which is hereby incorporated by reference although the layers  42  may be liquid or gas impermeable. A sheet layer  42  may be applied to the bottom surface of the mat A, and the upper ends of the support members  20  inserted downwardly into a ground surface for purposes for erosion control. The upper sheet layer would then provide a stabilized surface for vehicles or pedestrian traffic or establishment and/or protection of vegetation. The mats also provide additional support for the layer  42  because the internal and external struts provide additional supporting contact points. One or more drain pipes  38  may also be used to control the in flux or evacuation of water from the structure. This construction results in the formation of voids within and passages between the support members, and also in the exclusion of particulate material from the integral structure between the mats. It is contemplated that this embodiment would be utilized in construction applications to form drainage passages, or storage containers. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.