A manhole is a box that is installed, of necessity, at a point where the trunk changes direc-tion, gradient, or both. One of these openings is often called a manhole, regardless of where it is located. Distances between manholes are normally 300 feet, but this distance may be extended to a maximum of 500 feet when specified. The access opening for a manhole, curb inlet, or junction box consists of the cover and a supporting metal frame. A frame for a circular cover is shown in figure 10-2.
Some covers are rectangular.
The frame usually rests on one or more courses of adjusting blocks so that the rim elevation of the cover can be varied slightly to fit the surface grade elevation by varying the vertical dimensions, or the number of courses, of the adjusting blocks. A junction box is similar to a manhole but is installed, of necessity, at a point where two or more trunk lines converge. The bottom consists of a formed slab, sloped in the Figure 10-2. Frame for an access opening. Integrated Publishing's Official Web Page Click here for a current index of everything on this web site.