Sheet Piled Shaft Below Water With Pipe Penetration

[FinnB]

I am working on a project were we have to make a new connection to a pipe 16.5 feet below ground level. The pipe is beside a river with the underlying ground consisting of a free draining gravel.

The plan is to sink a shaft 15ft by 15 ft on plan using sheet piles and excavate down to the pipe and then dewater the shaft. The shaft will then provide a dry environment to allow the new pipe connection to be made.

The problem is the proximity of the river and the free draining gravel. Using pumping to lower the ground water level will be difficult to achieve from previous experience of the location. This is made more difficult as one sheet pile will have to stop above the level of the existing pipe where it penetrates into the shaft allowing water to freely enter the shaft.

Does anybody have any experience of solving the problem of how to block the water that will enter the shaft around the existing pipe?

I thought about pouring concrete around the existing pipe at the location it penetrates into the shaft. I think there may be a problem with pouring concrete against gravel when there is water freely flowing through it and into the shaft.

 

[charnott]

No experience but what just thinking about the issue. A targeted grouting scheme from the surface around the existing pipe location/shaft interface could significantly reduce flows in that area once you excavated out the shaft and approach it side on?

As with any grouting scheme however the proof of the pudding is in the eating...........tricky.

If your not a bidding contractor and are in a client side role why not meet with potential bidders to discuss constructability ahead of time to help develop your concepts for creation of tender documents?

 

[oldestguy]

On a similar job the site was protected from river water by first excavating a trench between the river and the job site. That trench was then filled with local clay. It cut down the flow to something manageable. However, since that date I have also worked with landfills where the contaminated site was feeding contaminate ground water else where. There a sealing was done by working bentonite slurry into the trench excavation soil as the trench progressed. Contact a contractor experienced with these cut-off trenches for advice. Other times the sediment on the bottom of a nearby lake suitably kept flow to the excavation way down.