Pressure / Force Calculations in Gravity Storm Systems

[cher122976]

I have a 24" RCP gravity storm system with max 8% slopes and 18 fps velocities. I am trying to calculate the water pressure / force at each 90 degree manhole junction in order to determine if the forces will cause any lateral movement in the manhole. Anyone have any ideas on how to do perform these calculations?

 

[Takazviona]

Normally I would put a drop at the manhole to reduce as much velocity as possible. From the manhole the velocity will be assumed to be zero. The down stream pipe will be considered as a pipe with a submerged inlet.

If you don’t put a drop use the principal of conservation of momentum to calculate the forces. You can calculate the pressures from the Bernouli equations. Pressure X Area = Force. Do not forget to use the angle since the forces have an x and y components.

 

[WL123]

I've also used drop manholes when there is a lot of flow at a steep slope. I have used oversized manholes and placed the inlet pipe offset from center of manhole to let the stormwater swirl around and drop to disapate the energy, rather than let it slam into the opposite side.

 

[WL123]

I've also used drop manholes when there is a lot of flow at a steep slope. I have used oversized manholes and placed the inlet pipe offset from center of manhole to let the stormwater swirl around and drop to dissipate the energy, rather than let it slam into the opposite side.