cofferdam systems

huangyhg

cofferdam systems?
i am putting together a cost estimate for a bridge. the bridge is to be constructed in a remote northern location (northern saskatchewan, near the nwt border, in canada). the bridge is to cross a river with a bedrock bottom. i am wondering what alternatives i have for the bridge pier construction. seeing as how the bottom of the river is bedrock, driven sheet piles are out of the question, as is the use of an earth type cofferdam. the width of the river is insufficient to allow an earth cofferdam without completely ubstructing the flow of the river. as well, an impermeable type fill material is unavailable due to isolation of the construction site.
the river is approximately 2.5 m (8.2') deep.
what cofferdam systems exist that would be suitable for this type of application?
thank you for any help you may be able to provide.
civil77 - i grew up in a bridge building family. while in high school, i had to opportunity be witness (up close) a project that may have had conditions similar to yours (bedrock bottom - but i think there was a some overburden).
the contractor constucted a traditional braced rectangular cofferdam (about 25 feet deep), but did not pump it. then he constructed another braced, concentric, rectangular, closed sheet pile wall around the cofferdam. as i re  
you can use fabriform concrete bags to seal up the bottom of the  prefabricated cofferdam. we recently supplied them to seal the bottom of a cofferdam at rabbit lake dam ontario.,for ontario hydro.they are placed at the bottom of the steel or concrete cofferdam and will pump up to fill all the voids in the rock bottom and seal the base of the cofferdam allowing you to pump.you dont need any bottom prep or formwork and are good for currents of 5 m/sec . dave ritchie . intrusion prepakt.
i really like slideruleera's post but also note that you can drive sheet pile in rock to a certain extent by drilling/coring ahead of the driving.  yes this is costly, but it has been shown to work.
regards,
qshake
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