Explorative backhoe trenches and personal safety 1

[Mccoy]

Hi,
browsing the past threads (I thing the slope eng forum) I came across a discussion on backhoe trenches used to investigate the fine details of (superficial) stratigraphic sequence. In my country (Italy) that's a pretty common way to proceed. I've got some serious doubts though upon the safety of this practice, supported by past experience and recounts; specifically, I've seen quite a few backhoe trenches, of various depth, collapse (entirely or partially) in a time ranging from one to 5-6 seconds.
Moreover, there was a local professor of geology who worked a lot with explorative trenches. Probably he was aware of the hazard, because often he had other geologists gone inside the trench and collect litho-stratigraphic info. One day he was surprised by a sudden wedge failure while standing on the trench edge, and was dragged down and buried alive.
Now they organize lectures to his memory.
Believe me, I too would love to get my hands dirty as much as possible but when approaching those trenches I'll just have a look from above, keep my hands clean and walk away safe and sound!
My question is: do you guys follow any safety rules when descending into trenches? Do you routinely use protections or devices of sorts? How do you assess the stability of a trench and be so sure about it to potentially endanger your life ?

 

[gandersen]

Mccoy:

In the U.S. there are safety requirements because of the potential for failures in open trenches. OSHA (Occupational Safety and Health Adminstration) has published guidelines based on soil type and depth of excavations. Trench boxes are most commonly used for support. You should browse the OHSA website and download the appropriate information.

Glen

 

[BigH]

Sure I do {blush] - seriously, I've gone down into many test pit trenches when I probably shouldn't have - but I saw no cracking behind the crests, it was only a short time after opening (less than 5 minutes), I used my judgment due to the type of ground, and my pits were typically less than 3m deep (small backhoe - not excavator) etc. gandersen indicates the basic safety requirements for him - there is a lot of material on the web - I did a major browse a few months back on this topic. Generally for 4 to 5 ft (1.2 to 1.5m) the sides can be cut vertically - after that, in general, cut the sides back 1:1. Now did I always do that? . . . If I was nervous, I got the backhoe operator to gently pick up some "blocks" of the material I wanted, then took my sample from them after "cleaning" them off.

 

[Focht3]

It is a valid concern. In my practice, the trenches don't have vertical walls. If they are deeper than 5 feet, we 'bench' the excavation to reduce the risk -

After all, Safety First!



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[Mccoy]

Gandersen,
I'm aware of the OSHA regulations (similar ones are enforced in Italy) but I'm not aware of any field engineer or geologist using shields, boxes or cages for trench exploration. Some of these contraptions would cover the trench walls and the valuable lithologic/stratigraphic details displayed, others are downright unconvenient and time-consuming for such a supposedly expeditious recognition. Only time I read they were extensively used was in some huge dam project in Canada, people used steel cages going down explorative shafts (drilled thru rock. mainly).
Benching the excavation appears sensible, only I reckon it makes the soil structures less evident.

 

[BigH]

One aspect to remember in small exploration pits is that the size is small and there is always some 3-D effects. But Focht3 has it right - if in any doubt - be safe.

 

[jheidt2543]

In the US, doesn't OSHA require a ladder in the pit if the depth is over 5'?

I admire BigH's honesty and must admit I've been in some trenches and confined spaces without safety equipment too. But, just because I was lucky enough to survive my younger stupid days, doesn't make it right, it just makes me lucky. I've since learned that working safely may take a little longer, I at least get to finish the day!