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Water volume and extraction within a sheet pile cofferdam

Water volume and extraction within a sheet pile cofferdam

Water volume and extraction within a sheet pile cofferdam

(OP)
I've been asked to prepare some preliminary research and method statements for the sump pumping of water within a cofferdam for the construction of a new under ground car park.

The dig will be around 5m deep to underside of our raft slab from previous well tests we hit water table between 2.5-3m of the 5m dig and the ground consists of a mixture of sand and balast until 3.5-4m where it is blue clay (no water rises from clay)

I'm being asked to spec a sump pit within the cofferdam to extract water prior to the excavation and im being asked the following:

How many pumps will I need.
How much water will they extract per hour.
How much water will be extracted in total
How long will it all take on the assumption of 24hour pumping

My main priority is working out how much water is in cofferdam to extract, any help would be appreciated

RE: Water volume and extraction within a sheet pile cofferdam

People don't always ask the right questions.  I'd ask what toe penetration is needed to prevent bottom heave and the formation of mud from an otherwise stiff clay.

You can model this as a fully-penetrating well. The well radius being determined by taking the area of the dig and calculating the radius that would create the same area.

Here's a good resource for well equations:

http://www.army.mil/usapa/eng/DR_pubs/dr_a/pdf/tm5_818_5.pdf

f-d

¡papá gordo ain't no madre flaca!

RE: Water volume and extraction within a sheet pile cofferdam

number of pumps, pumping rate and time to pump it all is up to you. total volume pumped - calculate the amount of water in the sand layer and then your assumption of how much water will seep under the cofferdam - all assuming no rain and no leaks.

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