Maximum

Depth Calculation

Assembly

A final manhole test was completed recently by HGE Inc. This document will summarize the results and the conclusion that may be drawn from them. The goal of testing was to establish a maximum depth for Rhino Polyethylene manholes in terms of radial earth pressures including groundwater effects. This was accomplished by applying a vacuum to the interior of the manhole until failure, and converting the vacuum measured to an equivalent depth. Vacuum, in inches of Mercury (inHg), was converted to pounds per square foot (psf). In turn, psf values were used to back calculate a maximum depth using equation No. 5 of ASTM F-1759-97 (Standard Practice for Design of High-Density Polyethylene (HDPE) Manholes for Subsurface Applications).

We have just completed a successful test where the standard manhole riser and short base were subjected to gradually increasing vacuum pressures until failure occurred by breaking of the seal at 23 inches of vacuum. It was concluded that the manhole was still structurally sound at a vacuum pressure of 20 inHg and the corresponding manhole depth was 16 feet.

An improved manhole riser and base were constructed by adding stiffening ribs to the riser and thickening the walls of the base by about 20%. This new riser and base were subjected to the maximum vacuum the pump could produce (23 inHg). A vacuum pressure of 23 inHg corresponds to a manhole depth of 18.5 feet. When the vacuum could no longer be increased, the pump was stopped, valves were closed to observe any additional deflection or any loss of vacuum. After 20 minutes, no additional deflection could be seen, and none of the vacuum was lost.

Be sure to download Rhino Manhole Max Depth Specifications for complete details, and more information.

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