Civil Engineering - Waste Water Engineering - Discussion


If the diameter of sewer is 225 mm, the gradient required for generating self cleansing velocity, is

[A]. 1 in 60
[B]. 1 in 100
[C]. 1 in 120
[D]. none of these.

Answer: Option C


No answer description available for this question.

Sandip Ghosh said: (Dec 9, 2014)  
But actually 1 in 105 for a velocity of 0.9m/s & 1 in 150 for a velocity of 0.75m/s.

Aman Gautam said: (Dec 10, 2014)  

Greater is the gradient, greater is the velocity. Thus your point is wrong and as for 225 mm diameter, velocity should be 1 m/s. So it would require the highest gradient.

Manohar said: (Jul 9, 2015)  
Yes, the gradient, 1 in 105 is greater than 1 in 150.

Ganesh said: (Oct 29, 2015)  
Which formula is used here to calculate self cleansing formula?

Akash said: (Dec 26, 2015)  
V-under root (8 beta under f multiply by (specific gravity of solids- 1)*g*diameter of solids). Find v and using manning or any other formula find slope. But data is not sufficient.

Narayan said: (Jan 17, 2016)  
Velocity of the sewer is 0.9 to 0.75 m^3/s.

So assume velocity of sewer V = 0.9 m/s.

And using the manning's formula:

V = R^2/3*s^1/2/n but the wastage flow is not specify.

Ritesh Dev Singh said: (Dec 20, 2016)  
By Shield's Theory,

Self - cleansing velocity (Vs),
Vs= √ {8kgd'(G-1)}÷f], where,
k= (1-n)sin θ.

Vaibhav Gupta said: (May 9, 2017)  
Explain the expression for self-cleaning velocity.

Marwa said: (Jun 21, 2017)  
Which formula is used?

Please help me?

Himajwala said: (Aug 21, 2017)  
I didn't understand which formula was used. Can anyone help me?

Sanjay said: (Sep 9, 2017)  
Self cleaning velocity is 0.75 m/s to 0.9 m/s.
So 100/120 =0.83.
100/60 =1.66.
100/100 =1.
So right answer is 1 in 120.

Dheeraj Singh said: (Sep 16, 2017)  
The slope of sewer should be designed for min permissible velocity at min flow but in this case, a material made of sewer not given so can't be calculated if I assume brick-lined sewer then calculate slope by given velocity trial and error velocity (1to2.5).

Gubendhiran said: (Jan 13, 2018)  
Using Manning's formula.

For circular sewer R=D/4=0.225/4=0.05625m.
Vs=ranges from 0.45 to 0.8 m/s from S.K.GARG EEN Vol IIT.
Take Max for design Vs=0.8 m/s.
n=Manning's constant=0.015.
So we can option 'C'.

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