Coffer dam dewatering design 4

[imad123]

I am designing the pumps for dewatering the flow coming from
the groung rock pores. I have the permebaility value of rock samples also. Can you help me how I will find the value of inflow from ground and how may pumps will need.
How much water will need to pump during construction.

I am middle of things, need help or refrence of any book.

Thanks

 

[dicksewerrat]

Permeability times area exposed times time exposed. convert to gpm. Don't forget the are of the bottom of the hole. compare to the pumps you have.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[SlideRuleEra]

Your calculations are a good start, but will give you the MINIMUM expected inflow. Other sources such as voids in the rock, flow at the boundary layer of the sheeting and thru the sheeting interlock could make inflow much higher. Be sure to allow space for additional or larger pumps to be installed.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[DRC1]

If your cofferdam is in soil, you need to construct a flow net as permiability will be a function of bothe the driving head and the depth of sheet penetration. This is covered in the US Steel Sheetpiling handbook on sliderulera's website. If your cofferdam is on rock and you are excavating to the rock, you will need to pour a tremmie to seal the dam. If the rock is fairly flat with suffient overburden on the outside and inside, you may want to try pumping, but be prepared to pour a seal.
Once the seal is poured, pumping need only compensate for seepage at interlocks.

 

[BigH]

If on soil, he might not have sheeting. On one that we had in northern Sumatra, - river gravel and a big river - we just made a dike and excavated - had to have 7 really big pumps to pump out the water intially - along with inside perimeter ditches. Later, 2 to 3 pumps were enough. Short term; enought to put in a river weir for irrigation.