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Poor seal between tremie seal and NZ sheet pile cofferdam

Poor seal between tremie seal and NZ sheet pile cofferdam

Poor seal between tremie seal and NZ sheet pile cofferdam

Hey all, I have a perplexing problem.

I am administering the construction of a structure which has numerous underwater cofferdams for footings. Each cofferdam is driven to a depth of about 65ft on two sides but then as a temporary cofferdam driven for the "continuous sides" (the cofferdams progress linearly along the alignment and share longitudinal bulkheads). The excavation is about 19' under water table with 8 or 9 feet of concrete. The problem is, the tremie seal pours have gone quite well in terms of QA/QC and the "long" sides of the cofferdam have had quite good seals but the temporary bulkheads in the longitudinal direction have been consistently presenting leaks that require days upon days of urethane grout sealing. Are there any recommendations from the gallery for means and methods that might help create a strong bond between the tremie concrete and the temporary bulkheads?

RE: Poor seal between tremie seal and NZ sheet pile cofferdam

You really should show a sketch to clarify all elevations. How far down have you dewatered so far? Did you dewater to the top of the tremie yet? It seems to me that your 8' - 9' tremie seal is probably too thin for your water head. Is it 19' to the top of the tremie or to the bottom? Do you have 19' of unbalanced water pressure on the bottom of the tremie or do you have 19' to the top plus 8' or 9' feet more (28' total) acting on the bottom of the tremie? Calculate the unbalance head on the bottom off the full weight tremie concrete. Compare that to the weight of the full weight of the concrete tremie. Do you have enough concrete weight plus a reasonable safety factor to prevent the tremie from heaving?

Other thoughts: Are you counting on the SSP to provide some uplift resistance? Are the sheets clean enough to assure that the concrete is poured fully against the SSP without clumps of soil where the water could blow through? How far below the bottom of the tremie do the SSP extend? Did you do a flow net analysis or just multiply the head by 62.4? If your sheets are driven to 65 feet deep, do you really need a tremie pour?


RE: Poor seal between tremie seal and NZ sheet pile cofferdam

What comes to mind, is to clean the temporary steel sheet pile before it is driven. Probably quick sandblasting will help. Temporary sheet pile (all of a Contractor's temporary steel, for that matter) usually has a "hard" life... stored outside (corrosion), build up of dirt, concrete, etc. from being used many times with no attention to its condition.

Edit: PEinc - Sorry, did not see your post.

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