Pulling a trench box?

[Dirt Dogg]

Here' s a question for the deep excavation experts. I will give you what I know and you fill in the rest. I am laying 8" PVC to a grain unloading pit for drainage.
The trench will start out at 4 ft and end up at 14 ft
300 ft will be 8-10 ft deep
150 ft at 10-14 ft
200lc komatsu
42" bucket
8x16 box
Now for the questions
I plan on benching to top off so I can use the 8ft box is this safe?
Do I cut the trench so the box fits loose or leave it a little snug?:beatsme
I've heard if you leave the box loose and the wall caves it will pinch the box and I will not be able to pull it is this true?:beatsme
Ive never needed to pull a box so what are the tricks that will help things go smooth? Any advice on this subject would be appreshiated:notworthy
Thanks, Scott

 

[digger242j]

I plan on benching to top off so I can use the 8ft box is this safe?

Take a look here. It's got pictures. Note that there needs to be 18" of box showing above the sloped or benched part of the trench.

Do I cut the trench so the box fits loose or leave it a little snug?
I've heard if you leave the box loose and the wall caves it will pinch the box and I will not be able to pull it is this true?

Been there, done that, and it's no fun. If one side of the trench collapses against the box, and there's enough space on the other side, it'll knock the box sideways, and maybe disturb your pipe, or lean it to the side so that it's impossible to reach into it with a bucket, or knock it out of line with the trench. It'll be harder to pull forward like that as well. Snug is better.

 

[mflah87]

you should be able to pull it, just try and stay tight to the box so your not stretched way out. Do you have a wide area you can bench or are you tight? What you could do is bench like a 4 ft area on each side, then dig down next to the trench box 18" to be safe and legal. Other than that you'd have to get another box which will be a pain in the neck.

 

[RonG]

That bucket might be too wide to be working inside of the trench box too.If you are bedding or covering the pipe with stone a narrow bucket will save you money if you happen to be buying the stone.A 200 size machine will not have much reach at those depths so you may need to use short pipe to make it work.I have had to cut pipe under those conditions to get the job done which wastes pipe unless you have a lot of ferncos.Ron G

 

[TRACKHOE71]

leave the box snug, if it shouls happen that the box becomes loose what ive doen in the past is put some material on the oppsite side of the way its leaning and beat it down a little bit with th bucket it should push it self back over to get ya straighten out. if you happen to over dig yourself for your yor cut, you can actullay cut yourself down a little more or cut a littel ramp in, that will bring you safely closer to the box, to be able to get your reach if need be, just keep in mind that if you do need to do that, just make sure that your bench is back far enough so that when you go to swing that the house of the machine doesnt swing into the dirt then youll have more problems.

 

[rino1494]

Digging 14ft deep with a 200 is tricky. You have to dig a little bit at a time and pull the box only 3 or 4 ft at a time. It takes some time to lay 1 piece of pipe. I've put sewer mains in that were 19ft deep with our 200. Just had to take about bench it down about 5 ft.

You want to keep the box tight and above the pipe. If you keep it loose it will sit on the bottom and when you pull the box, you risk pulling apart a joint. You need to slope back the trench above the box. Start 1ft below the top of the box and slope it at a 1:1 - 2:1 depending on the type of soil. If it is sand, you may have to go more.