How to Brace a Hole in Vertical Secant Pier Shaft

[dcarr82775]

I have a 28ft diameter temporary access shaft that is to be constructed using secant piers. No ring beam at the top. Down about 26-ft they need to cut a 11-ft diameter hole in the piers to jack a pipe. Theoretically it is a ring, and for most of the ring I am ok with assuming it acts as one. However, where the hole is cut for the pipe I want to provide something to keep the piers from acting like marbles and rolling with respect to each other. Really just to provide some resistance to the piers rolling into the shaft if that makes sense. I was thinking of using a rolled tube or channel shape designed per the AISC column bracing requirements.

Sound like a reasonable approach? I am open to other approaches.

 

[thaidavid40]

Sounds a reasonable approach to me - similar to internal rings and wales in circular cofferdams.

Thaidavid

 

[BUGGAR]

We did similar when we excavated a shaft for a tunnel. We were using stamped steel liner plates for the shaft with a ring beam (rolled H sections) above and below the tunnel opening as you are planning. We then used tunnel ring beams and miscellaneous strut bracing (huge amounts of bracing because that's what you do underground) to form a portal to launch our horizontal tunnel through the shaft wall. The tunnel was also liner plate and ring beam construction.

 

[dcarr82775]

Thanks