The top and bottom elevations of sewer pipes are critical pieces of information for the design of sewer systems and the pipes that connect to them. Pipes are placed so that flow is continually moving downhill. Construction around pipes is regulated to ensure that the flow is uninterrupted and protect pipes from damage.
Sewer Pipes and Construction
Urban development depends on sewer pipe installations for the health and safety of residents. Standards exist for minimum clearance horizontally and vertically from sewer pipes during the construction of a building. The standards ensure that the function of the sewer pipe won't be impeded and that access will be clear for maintenance and repair activities. Familiarity with the terminology is helpful when executing construction activities that involve connecting residential services to municipal lines or building structures near them.
Gravity keeps water and other liquids flowing in pipes by way of sloped ground. The rise of sewer pipes is the vertical height the pipe reaches from a fixed low point on the slope to a high point over a horizontal distance, or the run. The slope angle determines the velocity of the flow -- water flows more quickly down a steeper slope. Minimum slopes are set according to the size of the pipe and expressed as percentages.
The invert level, or elevation, is the lowest point of the pipe on the inside of the pipe, indicated as IL on drawings. The ground below the bottom of the pipe may be somewhat lower than the invert, depending on the thickness of the pipe. When the diameter of the pipe and the thickness of the pipe wall level is subtracted from the elevation at the crown, or top, of the pipe, the result is the invert level.
Building officials often require detailed information about how sewer and water connections for development connect to municipal mains. Invert elevations for the pipes must be submitted as part of the design, and a uniform grade for the rise of the pipe will be specified. Manhole rim elevations and the invert elevation for the pipe that the manhole accesses are located on the plan so that the depth of the pipe can be found.