Tying a forced main into a sanitary line via a manhole

[fugacity19]

I am installing a new forced main (10" polyethylene) of a water treatment's facility, which will tie into the municipality's 24" sanitary sewer line. The suggested tie in point is at precast concrete manhole. The manhole is 20 feet deep.

The municipality's water authority is worried that the forced main line who jet water to quickly into the manhole and wear away at its integrity. I am designing the pipe such that the discharge velocity of the fluid will be less than 5 ft/sec.

How could I make the tie in to this manhole? Does anyone know of any available detail drawings viewable on the web?

Any help would be appreciated.

 

[civilperson]

Use a variety of a drop manhole. Bring the 10" main to the MH at a elevation 5-8' below grade and then turn down when adjacent to the MH with a tee or wye. Continue the vertical portion of the tee up and then turn through the wall and turn back down.
Extend the downward portion of the tee/wye down. When at the invert elevation turn again horizontal and enter the wall of the manhole and continue through the MH into the shaped invert/outlet pipe, (assuming larger diameter like 18").

 

[francesca]

Is the discharge point the control point/highest point on the forcemain? Is there more than one pump on the forcemain meaning you'll have different discharge conditions depending on which pumps are pumping and which are off?

If the discharge point is the control point, then every foot above the manhole invert is more head you'll have to pump and over the lifetime of the installation, it will cost more in electricity, etc. to pump the extra 10'-15' of head than it will to install the forcemain at the bottom of the manhole.

If the discharge point is not the control point, then you have gravity flow into the manhole and can design accordingly.

 

[bimr]

We are using two manholes. The first manhole is for the discharge of the force main. The second manhole is gravity fed from the first manhole. The second manhole is also a drop manhole. Ideally, the entering force main and the exiting sewer should both be flowing in the same direction.