INSPECTION PIT HATCH Russian patent published in 2006 - IPC E02D29/14 

FIELD: road building, particularly covers for manholes or the like.

SUBSTANCE: hatch comprises support ring with annular groove and reinforced lid with through orifices and lower part converging downwards. Upper lid part also converges downwards. Angle between side surface of upper lid part and vertical line is from 5° to 10°, angle between side surface of lower lid part and vertical line is equal to 25°-30°. Upper and lower lid part height ratio is 1:5 - 1:3. Two through orifices have elliptical cross-sections and are provided with steel pipes closely fitted in the orifices. The orifices are diametrically symmetric about lid center and are located from both sides of the center. Orifice ellipse axes ratio is from 2:3-2.5:3.5 and larger orifice ellipse axis has length equal to 1/15-1/20 of lid diameter. The lid and support ring are formed of high-strength concrete.

EFFECT: increased reliability.

2 dwg