The present invention is an improvement on arch shaped leaching system conduits of the type described in U.S. Pat. No. 4,759,661, issued on Jul. 26, 1988 to James M. Nichols (the inventor herein) and Randall C. May, the disclosure of which is hereby incorporated by reference. The patented unit is characterized by a special sidewall construction which enables a conduit to be buried directly in the earth, providing a functionality equal to traditional perforated pipe and gravel installations, but with the avoidance of the cost and bother of surrounding gravel. The unit has enjoyed significant commercial success since its introduction to the public.
As the foregoing patent shows, the leaching system conduits are intended to be buried in the earth where they may receive liquids for dispersion. For instance, they can receive the effluent from a septic tank. Typically, the units by design are connected serially to each other by a shiplap joint, to achieve the desired subterranean dispersion area. Typically, the liquid being dispersed is introducted into the first end of an arch conduit series by a circular sewer pipe. Sometimes, spaced apart series of units are interconnected by circular sewer pipe.
For economic reasons, the units are made identical. Thus each has provision for a circular sewer pipe connection, an overlapping shiplap end and a corresponding overlapped shiplap end. End closures, essentially fitted plates, are used to make conduits with blind, or terminal, ends.
One of the desired features of the conduit is its ability to support heavy vertical loads, such as are applied by heavy motor vehicles passing across the surface of the earth within which the units are buried. To achieve this economically, the arch shaped conduit is typically made of a strong molded plastic and has special tapered corrugations along its length as shown in the patent.
The corrugations are special in that they enable nesting of the units, while still enabling the structural and liquid dispersal functions of the unit. At each opposing end of the unit there are valleys of approximately identical configuration which enable shiplap joint connection to similar units. Because of the structural discontinuity inherent at the shiplap joint the structure is somewhat weaker than desired despite the adjacent corrugations.
Another contribution to weakness at the joint region involves the provision for connection of the circular sewer pipe. The pipe is desirably connected to a unit at the uppermost elevation, i.e., the elevation of a peak of the corrugation. As shown in the patent, this necessitates a raised essentially sub-arch portion running transverse to the valley length at each end. When units are mated one to the other, the sub-arch shapes mate in shiplap fashion as do the main arch shapes of the ends. But, while the prior art configuration is effective in allowing the proper introduction of liquids into the arch, there is a weakening interruption of the web connecting the end valley with the peak of the adjacent corrugation.
Consequently, there is a tendency in the prior art unit for unwanted deflection of the joint region under severe loads. Because of the need to nest the units for economic shipping it is not feasible to build consequential internal stiffening. There has been a need for improvements in the construction which are both effective and suitable for economic construction.
Others have made somewhat similar arch shape units, in the past and presently. But these units have either been characterized by open ends, without particular closure, without shiplap, or with permanently closed ends where the inlet pipe enters relatively low down from the peak. Consequently, the problems described above have not been resolved heretofore.