Re: OT--sewer colapse

Posted by Billy NY on December 28, 2016 at 16:56:10 from (74.76.4.60):

In Reply to: OT--sewer colapse posted by ohiojim on December 28, 2016 at 04:57:07:

The photo shows what has to be done to bench down, support the trench walls, ventilate etc.

I've worked on pipe crews when in the site work field while in my 20's and some gravity sewer piping we installed ranged from 20' to over 30' deep. Some were in fine sand with high water tables !

Open cut trenches at those depths call for mass excavation and all the rest, trench boxes, well points, large equipment.

One of the deeper ones had manhole inverts at 34' deep in sand with a water table to contend with. I have photos of that job. We benched down with a 350 L cat excavator, dewatered with well points, used trench boxes to support the side walls of the cut below the first bench. Backfilling was fun, a pair of D6D's on either side of the cut, pipe and manhole sections in the center. We ran 30 yard scrapers to bring fill back in there once there was enough cover. It's not often that the rim elevation of the manhole is way up over the rops of your dozer ! One old timer got fired for bumping the stack of manhole sections. The foreman said, if you hit any of those risers, just park the machine and leave the site, he was not joking. You do have to look behind you when backing up, if that was a person it would not be funny. The entire crew got a lecture on looking back when in reverse. Sure there is that mirror, but still.

I don't care for deep cut excavation so much, one job I was holding up a phone line with a rope, a huge section fractured off and I rode that down 17' into the cut and was hanging by one hand from that rope, waving at the excavator operator so he could see me before taking another bucket out of that hole. Fine sand conditions. Same job, when installing a lateral to the new convenience store,the foreman was checking grade in a 5' deep trench, while I was digging it. Progressing along, he left the rod further back in the trench, so he went to get it and on his return another section fractured off the side and pinned him against the opposite side of the cut, squeezing the air out of him. Thing was, you could dig to grade, unroll more copper line, further back it would collapse as time went by, so you had to stay ahead of it. A trench box was needed. I leaped out of the cab through the back window to get his head cleared so he could breath. Took me well over an hour to dig him out by hand! Boss man knew better having been part owner in a well established heavy & highway site contractor. He had miles of experience and I never understood why we were doing this 1000' foot of sewer main in sand with minimal equipment until things like the above started happening. We got it all done and sure enough the darned pipe settled upon camera inspection and he had to send another crew back to dig it up an fix it. I was on another job at that time thankfully!

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