Patent ID: 7473053

Claim:
In an injection molded thermoplastic arch shape cross section corrugated chamber, useful for receiving and discharging water beneath the surface of the earth; wherein the chamber has an arch top and opposing sides disposed on either side of a lengthwise vertical centerplane, running upwardly to the arch top; wherein the chamber has a multiplicity of alternating peak corrugations separated by valleys, wherein each of said peak corrugations and valleys has a length which runs transverse to the chamber length and up a first side of the chamber, across the arch top of the chamber, and down the opposing side of the chamber; wherein each peak corrugation comprises a pair of opposing-side webs, one of which webs runs to a valley running on along one lengthwise side of the peak corrugation, and the other of which webs runs to a valley running along the opposing lengthwise side of the peak corrugation; wherein the webs of said pair are angled relative to each other and thereby have an associated Peak Web Angle therebetween; the improvement which comprises: at least one peak corrugation having at least one segment of peak corrugation length characterized by (a) a Peak Web Angle which is substantially greater than the Peak Web Angles which characterize portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment; and, (b) web thicknesses which are substantially greater than the thicknesses of the webs of portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment.