Trench Stabalization...

[Water-N-Mine]

I wondered if you guys couldn't help me. I run a JD 450 excavator part time at a local gravel mine. We are in the works of dewatering a new cell. The treches are about 12 foot deep in bad type C soil. But right at water level is sand so it will cave off even in two foot steps. I normally don't have a problem shelving back a pipe trench to keep it stable. But, this trench needs to stay open for 2 years. I have tried various ways of narrow stepping to wide stepping shoring but I just can't seem to do it without the sides breaking off.
Saturday I was on the mine by myself and had a hell of a time with it. The only thing that worked for me was to wide V cut the top 10 feet of trench. Ofcourse this wasn't what the Boss wanted and I got ripped for doing it. Last night he showed me what he wanted in the way of shelf shoring. So I attemped to step the trench back and as luck would have it the trench fell in fourty feet away. Is there anything in can do from an operator standpoint to prevent the trench from collapsing.
I am worry too many more of these screw ups may cost me my gig.. Anyone help me???

 

[dayexco]

you'll never keep type c open w/water at a 2:1. it's not your fault. as long as water is allowed to migrate into your excavation and erode the bottom of your excavation.....it's going to cave. you need to tell him to dewater

 

[digger242j]

Or, to quote Mr Scott, from Star Trek, "Ya can't change the laws o' physics, lad."

 

[Water-N-Mine]

I finally got the trench to stabalize last night and peobably saved my "yob".(local language here) :ban But I thought I would share how I went about it in case others may have the same problem in the future. The trench itself is 72" wide and I carried grade 4" below water level with a flat bucket. If I put my teeth into the floor it would cause the walls to undermine. The first bench is 48" wide on each side 12" up from the water level. The second is a bucket wide and 2' bench the third is a bucket wide and a 4 bench.This leaves a 4 feet of wall up to existing grade. The main thing I concentrated on was keeping that first and second level square and flat if the corners were disturbed it would have to be cut down again. Thanks for the insight....:drinkup