Test Pits May No Longer Be Viable Investigation Tool

[Ron]

To stop the use of observation (test) pits would be a disservice to the entire design and construction industry. As csd72 said, there are numerous safety guidelines to follow and if they are breached, disaster can result. So follow (most of) them. You can gain more information from test pits than you'll ever get from auger borings.

Cave-ins for test pits are common in the soils in my area. We have a high water table and generally sandy soils, but the best way to delineate old topsoil layers and other deleterious stratification in the upper few feet is with test pits.

Using reasonable care and precautions, it doesn't have to be either dangerous or prohibitively expensive. Sometimes all it takes is a larger hole to make it safe.

 

[Tatsu]

A senior engineer showed up on my site. He stepped in bucket of excavator and wend down into a pit (3-4m deep). I thought that the bucket might protect him from relatively smaller wall collpase but not from collapse of entire pit.

After watching many test pit wall collapses, I don't put anybody (including myself) in there. Force from collapsing pit is just massive. When I have to do some work in test pit, I make benches. I guess everybody does. I often end up making big pit though.

 

[Ussuri]

He stepped in bucket of excavator and wend down into a pit

In the bucket! I would say thats even worse. Not only going into the pit but using the excavator as a means of access is dangerous.

 

[darthsoilsguy2]

a side anecdote -

I remember a mason who's work i had to inspect. I would climb his scaffolding and look at the work on a daily basis.

he watched me one day and told me that it didn't matter about my pay, reputation, or bills... no job is worth losing your life. i told him that i wasn't doing anything different than his workers. he told me i was. he said his workers didn't think they were going to die doing this, and watching me climb the scaffolding he could tell that i thought i differently.

i'm not afraid of most scaffolding anymore... but there are sometimes that i'll look at it and say "i'm not getting on these bozos scaffolding today"

everything can kill you if you let it.

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i think the death of a coworker is punishment enough. i can't see engineering managers out there doing more for actual safety improvement due to this law. if this law is at play in influencing a company's safety, i'm imagining more pages on a health and saftey program.... i'm imagining more training sessions.... i'm imagining a safety officer being assigned who has the least field experience.... i'm imagining unrealistic safety protocols that don't apply if the sun is not ecclipsed while a rooster crows...and safety lost in a sea.

 

[ishvaaag]

Since men have every kind of machine it wouldn't be as difficult to produce a light one with some arm to lower with a light, hi-res cam and a jack and reaction feet to take the "undisturbed" material. Surely it also will produce more standard results than by hand. And once popularized, nothing that a mid geotech firm can't buy.

 

[ecanuck]

Years back, while managing a geotech office, I was responsible for a number of eng's and tech's doing pits. The rule is common sense - stay out if it is deep or liable to collapse. If sufficient data cannot be obtained then we would recommend borings to supplement the pits (although that would be rare).

Usually, if there are fine structures like sand seams in clay, the intact diggings will show them. Also a telephoto lens on a camera comes in handy.

One thing that has not been mentioned is backfilling. Believe it or not, some test pits are left open. Recently I almost fell into one with my farm tractor - left open years ago by the local transportation deparment doing aggregate sampling.

Our pits were backfilled before leaving the site.

My opinion is that I hope government will not enact carte blanche rules about this. As a rabid libertarian I say we have enought of them! :>)

 

[BigH]

http://www.nce.co.uk/5204043.article

 

[racookpe1978]

Why not make a sample grab device by attaching a 2-4 inch round, open-ended "cutter head" cylinder (like a post-hole digger) to a 8 or ten foot pole?

Stand at the top of the pit, run the sample grabber down into the pit towards the wall, cut a circular scoop of out the wall side, then pull it back out. You have the actual undisturbed sample, the known sample point and height/depth below round, and the known alignment of the layers and whatever "fossils" are in the muck.

 

[Patgeotech]

From my experience, after a close collapse encounter, I always preferred to take along 'an extra pair of eyes' when undertaking trial hole excavation as one could always possibly miss something in the trial hole and the extra eyes were useful for detection of buried services. I have seen many young geologists, technicians, geotechnical engineers that are placed onto a particular site and told that they have 30 trial holes to complete in 1.5 days - this puts added pressure on the fieldwork staff and she/he forgets the dangers associated with excavation work - the fact that the young geologist was in the trial hole while it was raining, is quite unbelieveable - all geologists/geotech engineers know that water is a trigger mechanism for soil movement - I cannot but wonder what he was instructed to do and whether he was under a strict timeline. It is a sad day when these sort of accidents occur and may/could of been avoided.

I personally profile/log my trial holes from the surface - easy and one becomes more efficient the more one does it. We are not allowed to get into a trial holes deeper than 1.0 metre. Anything deeper must be shored.