Design of sewer pipes
Design of sewer pipes
(OP)
Greeting
I want to design sewer network and when i reading about design criteria i found two , one for minimum slope and other for minimum velocity and both of them theoretically in one relation actually what's the control ( slope or velocity),mean
if get the minimum velocity but less than the minimum slope is that acceptable or not
thanks
I want to design sewer network and when i reading about design criteria i found two , one for minimum slope and other for minimum velocity and both of them theoretically in one relation actually what's the control ( slope or velocity),mean
if get the minimum velocity but less than the minimum slope is that acceptable or not
thanks





RE: Design of sewer pipes
RE: Design of sewer pipes
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Design of sewer pipes
Whether you are expressing the sewer design criteria as the minimum velocity in terms of ft/sec or in slope of the sewer, you are essentially setting the same minimum design criteria.
Here are a few examples:
Gravity sewers shall be designed for a minimum velocity of three fps that exists at the time the pipe is placed into service. City Engineer approval must be obtained to use lower design velocities, except in the extreme upper reaches of the system with few connections. In these cases, 8-inch diameter minimum pipe size and 0.0044 ft/ft minimum slope will govern except for the last upstream reach to a terminal maintenance hole where 0.0060 ft/ft minimum slope will govern.
Sewer Pipe Design • Sewer pipes shall be designed for minimum velocity of 2 feet per second.
• The minimum pipe size for sanitary sewer is 8" inside diameter.
• If a flatter slope is proposed, the pipe shall be designed to prevent settlement of solids in the pipe.
3. Slope -
a. All sewers shall be so designed and constructed to give mean velocities, when flowing full, of not less than 2.0 feet per second, based on Manning's formula using an "n" value of 0.013. Based on an "n" value of 0.013, the following are the minimum slopes which should be provided; however, slopes greater than these are desirable:
Sewer Minimum Slope
Ft/100 feet
4 inch 1.05
6 inch 0.60
8 inch 0.40
10 inch 0.28
12 inch 0.22
14 inch 0.17
15 inch 0.15
16 inch 0.14
18 inch 0.12
21 inch 0.10
24 inch 0.08
27 inch 0.067
30 inch 0.058
36 inch 0.046
http://denr.sd.gov/documents/designnumber.pdf
RE: Design of sewer pipes
another question the velocity will be checked for actual loads or load multiply by peaking factor ( i use multiplied by P.F)
RE: Design of sewer pipes
Peak Hourly Flow is the ratio of peak diurnal flow to daily average flow. The ratio is determined from Fair & Geyer's chart "Ratio of Peak Hourly Flow to Design Average Flow".